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One of the greatest mysteries in science is why there is only one species of humans in the world today. These past human species are modern humans’ older ancestors. Now, researchers believe that they know why our ancestors disappeared. Since they could not adapt to climate change the past human species became extinct, unlike Homo sapiens .
Past Human Species Who Shared the Planet
For millennia there was more than one human species roaming the earth. Indeed, they often interbred with each other, and for this reason modern humans have genes of long-extinct past human species. A group of Italian researchers decided to examine why our ancestors vanished from the face of the earth and why we were the only ones to survive.
The researchers wrote in One Earth that ‘At least six different Homo species populated the World during the latest Pliocene to the Pleistocene.’ They focused on why Homo habilis, Homo ergaster, Homo erectus, Homo heidelbergensis, and Homo neanderthalensis , all went extinct. These species of homo disappeared, the authors of the study are quoted in Science Daily as saying, “despite technological innovations including the use of fire and refined stone tools and the formation of complex social networks.”
Stone tools and simple clothing weren’t enough to save past human species. ( ExQuisine /Adobe Stock)
Recreating the Prehistoric Climate
The Italian researchers hypothesized that climate change played a key role in the demise of species such as the Neanderthals. All of them had a climatic niche, that is a climate that they had adapted to successfully. H. sapiens were included in the study to determine why they survived, unlike their relatives. Researchers examined an extensive fossil database spanning over a million years. They developed a climate emulator to create a model of past climates and how they changed over 5 million years.
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Climate Change and the Extinction of Past Human Species
Using factor analysis, the experts were able to calculate how the changes in temperature and rainfall impacted the climate niche of each species . For three species, H. heidelbergensis, H. erectus, and H. neanderthalensis , they found that ‘their climatic niche widths shrunk suddenly just before they vanished,’ reports One Earth .
This means that the climate changed, making their environment challenging and they could not adapt to the new environment. This contributed greatly to their extinction. In the case of the Neanderthals, this was “made even worse by competition with H. sapiens,” according to Dr. Pasquale Raia of Naples University.
Neanderthals had to compete with Homo sapiens too. ( ginettigino /Adobe Stock)
The data from the climatic simulator offers strong evidence that the three extinct species of Homo were not able to cope with rising or cooling temperatures. Raia is quoted by Science Daily as saying that “We were surprised by the regularity of the effect of climate change.”
While there is evidence, based on the geographical distribution of remains, that the archaic humans tried to move to more favorable climates they were not able to adjust to the new conditions. Dr. Raia is quoted by The Independent as saying that:
“It was crystal clear, for the extinct species and them only, that climatic conditions were just too extreme just before extinction and only in that particular moment.”
Why Modern Humans Survived
In One Earth the study’s authors wrote that ‘Our results show striking differences in vulnerability between H. sapiens and the significantly more vulnerable extinct species .’ It appears that our Homo sapiens ancestors were less vulnerable to environmental changes. They had a much wider climatic niche, that is to say, that they could endure and adapt to changing temperatures and environmental conditions. Their cognitive abilities and technologies, such as fire , meant that they could ‘mitigate the effects of climate change on their survival by effectively manipulating their own microclimates or moving rapidly to settle under better conditions’ states One Earth .
However, the study noted that climate change also often had a profound impact on H. sapiens and could again in the future. At a time of rapid climate change the results of the study on early humans’ extinctions are truly relevant. Raia is quoted by The Independent as saying that “It is worrisome to discover that our ancestors, which were no less impressive in terms of mental power as compared to any other species on Earth, could not resist climate change.”
A Thunderous Warning Message
Unlike in the past, the current changes in the climate are almost certainly linked to human activities. The Independent quotes Dr. Raia as stating that “I personally take this as a thunderous warning message.” The research shows that modern humans are as vulnerable as our ancient extinct relatives, such as the Neanderthals, to climate change . We too may one day be as helpless as they were when their environment changed. Just because we successfully adapted in the past , that does not mean that we can in the future.
The planet is dying faster than we thought
A triple-threat of climate change, biodiversity loss and overpopulation is bearing down on Earth.
Humanity is barreling toward a "ghastly future" of mass extinctions, health crises and constant climate-induced disruptions to society — one that can only be prevented if world leaders start taking environmental threats seriously, scientists warn in a new paper published Jan. 13 in the journal Frontiers in Conservation Science.
In the paper, a team of 17 researchers based in the United States, Mexico and Australia describes three major crises facing life on Earth: climate disruption, biodiversity decline and human overconsumption and overpopulation. Citing more than 150 studies, the team argues that these three crises — which are poised only to escalate in the coming decades — put Earth in a more precarious position than most people realize, and could even jeopardize the human race.
The point of the new paper isn't to scold average citizens or warn that all is lost, the authors wrote — but rather, to plainly describe the threats facing our planet so that people (and hopefully political leaders) start taking them seriously and planning mitigating actions, before it's too late.
"Ours is not a call to surrender," the authors wrote in their paper. "We aim to provide leaders with a realistic 'cold shower' of the state of the planet that is essential for planning to avoid a ghastly future."
What will that future look like? For starters, the team writes, nature will be a lot lonelier. Since the start of agriculture 11,000 years ago, Earth has lost an estimated 50% of its terrestrial plants and roughly 20% of its animal biodiversity, the authors said, citing two studies, one from 2018 and the other from 2019. If current trends continue, as many as 1 million of Earth's 7 million to 10 million plant and animal species could face extinction in the near future, according to the new paper.
Such an enormous loss of biodiversity would also disrupt every major ecosystem on the planet, the team wrote, with fewer insects to pollinate plants, fewer plants to filter the air, water and soil, and fewer forests to protect human settlements from floods and other natural disasters, the team wrote.
Meanwhile, those same phenomena that cause natural disasters are all predicted to become stronger and more frequent due to global climate change. These disasters, coupled with climate-induced droughts and sea-level rise, could mean 1 billion people would become climate refugees by the year 2050, forcing mass migrations that further endanger human lives and disrupt society.
Overpopulation will not make anything easier.
"By 2050, the world population will likely grow to
9.9 billion, with growth projected by many to continue until well into the next century," the study authors wrote.
This booming growth will exacerbate societal problems like food insecurity, housing insecurity, joblessness, overcrowding and inequality. Larger populations also increase the chances of pandemics, the team wrote as humans encroach ever farther into wild spaces, the risk of uncovering deadly new zoonotic diseases — like SARS-CoV-2, the virus that causes COVID-19 — becomes ever greater, according to a study published in September 2020 in the journal World Development.
While we can see and feel the effects of global warming on a daily basis — like record-setting heat across the world and increasingly active hurricane seasons, for instance — the worst effects of these other crises could take decades to become apparent, the team wrote. That delay between cause and effect may be responsible for what the authors call an "utterly inadequate" effort to address these encroaching environmental threats.
"If most of the world's population truly understood and appreciated the magnitude of the crises we summarize here, and the inevitability of worsening conditions, one could logically expect positive changes in politics and policies to match the gravity of the existential threats," the team wrote. "But the opposite is unfolding."
The study of human extinction arose relatively recently in human history. Ancient Western philosophers such as Plato, Aristotle, and Lucretius wrote of the end of humankind only as part of a cycle of renewal. Later philosophers such as Al-Ghazali, William of Ockham, and Gerolamo Cardano expanded the study of logic and probability and began discussing abstract possible worlds, including a world without humans. The notion that species can go extinct gained scientific acceptance during the Age of Enlightenment in the 17th and 18th centuries, and by 1800, Georges Cuvier had identified 23 extinct prehistoric species. 
In the 19th century, human extinction became a popular topic in science (e.g., Thomas Robert Malthus's An Essay on the Principle of Population) and fiction (e.g., Mary Shelley's The Last Man). In 1863, a few years after Charles Darwin published On the Origin of Species, William King proposed that Neanderthals were an extinct species of the genus Homo. At the turn of the 20th century, Russian cosmism, a precursor to modern transhumanism, advocated avoiding humanity's extinction by colonizing space. 
The large scale destruction of World War I and the development of nuclear weapons at the end of World War II demonstrated that omnicide (human extinction caused by human actions) was not only possible, but plausible. In 1950, Leo Szilard suggested it was technologically feasible to build a cobalt bomb that could render the planet unlivable. Rachel Carson's 1962 Silent Spring raised awareness of environmental catastrophe. In 1983, Brandon Carter proposed the Doomsday argument, which used Bayesian probability to predict the total number of humans that will ever exist. By the beginning of the 21st century, the study of "existential risks" that threaten humankind became "a growing field of rigorous scientific inquiry". 
Many experts who study these issues estimate that the total chance of human extinction in the 21st century is between 1 and 20%. In 2008, an informal survey of experts on different global catastrophic risks at the Global Catastrophic Risk Conference at the University of Oxford suggested a 19% chance of human extinction by the year 2100. The conference report cautions that the results should be taken "with a grain of salt" the results were not meant to capture all large risks and did not include, for example, climate change, and the results likely reflect many cognitive biases of the conference participants. 
In his book The Precipice: Existential Risk and the Future of Humanity, Toby Ord gives his overall estimate at the likelihood of human extinction risk this century as 1 in 6.  
In a 2010 interview with The Australian, Australian scientist Frank Fenner predicted the extinction of the human race within a century, primarily as the result of human overpopulation, environmental degradation and climate change. 
- A common belief is that climate change could result in human extinction.  In November 2017, a statement by 15,364 scientists from 184 countries indicated that increasing levels of greenhouse gases from use of fossil fuels, human population growth, deforestation, and overuse of land for agricultural production, particularly by farming ruminants for meat consumption, are trending in ways that forecast an increase in human misery over coming decades.  An October 2017 report published in The Lancet stated that toxic air, water, soils, and workplaces were collectively responsible for nine million deaths worldwide in 2015, particularly from air pollution which was linked to deaths by increasing susceptibility to non-infectious diseases, such as heart disease, stroke, and lung cancer.  The report warned that the pollution crisis was exceeding "the envelope on the amount of pollution the Earth can carry" and "threatens the continuing survival of human societies".  Carl Sagan and others have raised the prospect of extreme runaway global warming turning Earth into an uninhabitable Venus-like planet. Some scholars argue that much of the world would become uninhabitable under severe global warming, but even these scholars do not tend to argue that it would lead to complete human extinction, according to Kelsey Piper of Vox. All the IPCC scenarios, including the most pessimistic ones, predict temperatures compatible with human survival. The question of human extinction under "unlikely" outlier models is not generally addressed by the scientific literature. Factcheck.org judges that climate change fails to pose an established 'existential risk', stating: "Scientists agree climate change does pose a threat to humans and ecosystems, but they do not envision that climate change will obliterate all people from the planet."  On a much longer time scale, natural shifts such as Milankovitch cycles (quaternary climatic oscillations) could create unknown climate variability and change. 
- A pandemic involving one or more viruses, prions, or antibiotic-resistant bacteria. Past pandemics include the 1918 Spanish flu outbreak estimated to have killed 3-5% of the global population, the 14th century Eurasian Black Death pandemic, and the various European viruses that decimated indigenous American populations. A deadly pandemic restricted to humans alone would be self-limiting as its mortality would reduce the density of its target population. A pathogen with a broad host range in multiple species, however, could eventually reach even isolated human populations,  U.S. officials assess that an engineered pathogen capable of "wiping out all of humanity", if left unchecked, is technically feasible and that the technical obstacles are "trivial". However, they are confident that in practice, countries would be able to "recognize and intervene effectively" to halt the spread of such a microbe and prevent human extinction. 
- Human activity has triggered an extinction event often referred to as the sixth "mass extinction",  which scientists consider a major threat to the continued existence of human civilization.  The 2019 Global Assessment Report on Biodiversity and Ecosystem Services, published by the United Nations' Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, asserts that roughly one million species of plants and animals face extinction from human impacts such as expanding land use for industrial agriculture and livestock rearing, along with overfishing.  A 1997 assessment states that over a third of Earth's land has been modified by humans, that atmospheric carbon dioxide has increased around 30 percent, that humans are the dominant source of nitrogen fixation, that humans control most of the Earth's accessible surface fresh water, and that species extinction rates may be over a hundred times faster than normal. 
- Overpopulation: The Global Footprint Network estimates that current activity uses resources twice as fast as they can be naturally replenished, and that growing human population and increased consumption pose the risk of resource depletion and a concomitant population crash.  Evidence suggests birth rates may be rising in the 21st century in the developed world.  Projections vary researcher Hans Rosling has projected population growth to start to plateau around 11 billion, and then to slowly grow or possibly even shrink thereafter.  A 2014 study published in Science asserts that the human population will grow to around 11 billion by 2100 and that growth will continue into the next century.  through a preference for fewer children.  If developing world demographics are assumed to become developed worlddemographics, and if the latter are extrapolated, some projections suggest an extinction before the year 3000. John A. Leslie estimates that if the reproduction rate drops to the German or Japanese level the extinction date will be 2400. [a] However, some models suggest the demographic transition may reverse itself due to evolutionary biology. 
- A supervolcaniceruption. 
Some scenarios involve extinction as a result of the effects or use of totally new technologies. Scenarios include:
-  and biological weapons, whether used in war or terrorism, could result in human extinction.  Some fear a hypothetical World War III could cause the annihilation of humankind, perhaps by a resulting nuclear winter as has been hypothesized by experts.  Noun and Chyba propose three categories of measures to reduce risks from biotechnology and natural pandemics: Regulation or prevention of potentially dangerous research, improved recognition of outbreaks and developing facilities to mitigate disease outbreaks (e.g. better and/or more widely distributed vaccines). 
- The creators of a superintelligent entity could inadvertently give it goals that lead it to annihilate the human race.  A survey of AI experts estimated that the chance of human-level machine learning having an "extremely bad (e.g., human extinction)" long-term effect on humanity is 5%. 
- Uncontrolled nanotechnology (grey goo) incidents resulting in the destruction of the Earth's ecosystem (ecophagy). Chris Phoenix and Treder classify catastrophic risks posed by nanotechnology into three categories: (1) From augmenting the development of other technologies such as AI and biotechnology. (2) By enabling mass-production of potentially dangerous products that cause risk dynamics (such as arms races) depending on how they are used. (3) From uncontrolled self-perpetuating processes with destructive effects. Several researchers say the bulk of risk from nanotechnology comes from the potential to lead to war, arms races and destructive global government. 
- Creation of a micro black hole on Earth during the course of a scientific experiment, or other unlikely scientific accidents in high-energy physics research, such as vacuum phase transition or strangelet incidents.  There were worries concerning the Large Hadron Collider at CERN as it is feared that collision of protons at near the speed of light will result in the creation of a black hole, but it has been pointed out that much more energetic collisions take place currently in Earth's atmosphere. 
- Some scenarios envision that humans could use genetic engineering or technological modifications to split into normal humans and a new species – posthumans.  Such a species could be fundamentally different from any previous life form on Earth, e.g. by merging humans with technological systems.  Such scenarios assess the risk that the "old" human species will be outcompeted and driven to extinction by the new, posthuman entity. 
- A geological or cosmological disaster such as an impact event of a near-Earth object (NEOs),  which serve as an absolute threat to the survival of living species.  A single extraterrestrial event (asteroid or comet impact)  can lead to widespread species extinctions. However, none of the large "dinosaur-killer" asteroids known to Spaceguard pose a near-term threat of collision with Earth.  , gamma-ray bursts, solar flares, and cosmic rays, if strong enough, could be lethal to humans on Earth. 
- The Earth will naturally become uninhabitable due to the Sun's stellar evolution, within about a billion years.  In around 1 billion years from now, the Sun's brightness may increase as a result of a shortage of hydrogen, and the heating of its outer layers may cause the Earth's oceans to evaporate, leaving only minor forms of life.  Well before this time, the level of carbon dioxide in the atmosphere will be too low to support plant life, destroying the foundation of the food chains.  See Future of the Earth.
Nick Bostrom, a philosopher at the University of Oxford known for his work on existential risk, argues that it would be "misguided" to assume that the probability of near-term extinction is less than 25% and that it will be "a tall order" for the human race to "get our precautions sufficiently right the first time", given that an existential risk provides no opportunity to learn from failure.   A little more optimistically, philosopher John Leslie assigns a 70% chance of humanity surviving the next five centuries, based partly on the controversial philosophical doomsday argument that Leslie champions. Leslie's argument is somewhat frequentist, based on the observation that human extinction has never observed, but requires subjective anthropic arguments.  Leslie also discusses the anthropic survivorship bias (which he calls an "observational selection" effect on page 139) and states that the a priori certainty of observing an "undisastrous past" could make it difficult to argue that we must be safe because nothing terrible has yet occurred. He quotes Holger Bech Nielsen's formulation: "We do not even know if there should exist some extremely dangerous decay of say the proton which caused eradication of the earth, because if it happens we would no longer be there to observe it and if it does not happen there is nothing to observe." 
Some scholars argue that certain scenarios such as global thermonuclear war would have difficulty eradicating every last settlement on Earth. Physicist Willard Wells points out that any credible extinction scenario would have to reach into a diverse set of areas, including the underground subways of major cities, the mountains of Tibet, the remotest islands of the South Pacific, and even to McMurdo Station in Antarctica, which has contingency plans and supplies for a long isolation.  In addition, elaborate bunkers exist for government leaders to occupy during a nuclear war.  The existence of nuclear submarines, which can stay hundreds of meters deep in the ocean for potentially years at a time, should also be considered. Any number of events could lead to a massive loss of human life but if the last few (see minimum viable population) most resilient humans are unlikely to also die off, then that particular human extinction scenario may not seem credible. 
Stephen Hawking advocated colonizing other planets within the solar system once technology progresses sufficiently, in order to improve the chance of human survival from planet-wide events such as global thermonuclear war.  
More economically, some scholars propose the establishment on Earth of one or more self-sufficient, remote, permanently occupied settlements specifically created for the purpose of surviving global disaster.   Economist Robin Hanson argues that a refuge permanently housing as few as 100 people would significantly improve the chances of human survival during a range of global catastrophes.  
Eliezer Yudkowsky theorizes that scope neglect plays a role in public perception of existential risks:  
Substantially larger numbers, such as 500 million deaths, and especially qualitatively different scenarios such as the extinction of the entire human species, seem to trigger a different mode of thinking. People who would never dream of hurting a child hear of an existential risk, and say, "Well, maybe the human species doesn't really deserve to survive".
All past predictions of human extinction have proven to be false. To some, this makes future warnings seem less credible. Nick Bostrom argues that the absence of human extinction in the past is weak evidence that there will be no human extinction in the future, due to survivor bias and other anthropic effects. 
Sociobiologist E. O. Wilson argued that: "The reason for this myopic fog, evolutionary biologists contend, is that it was actually advantageous during all but the last few millennia of the two million years of existence of the genus Homo. A premium was placed on close attention to the near future and early reproduction, and little else. Disasters of a magnitude that occur only once every few centuries were forgotten or transmuted into myth." 
There is evidence to suggest that collectively engaging with the emotional experiences that emerge during contemplating the vulnerability of the human species within the context of climate change allows for these experiences to be adaptive. When collective engaging with and processing emotional experiences is supportive, this can lead to growth in resilience, psychological flexibility, tolerance of emotional experiences, and community engagement. 
"Existential risks" are risks that threaten the entire future of humanity, whether by causing human extinction or by otherwise permanently crippling human progress.  Multiple scholars have argued based on the size of the "cosmic endowment" that because of the inconceivably large number of potential future lives that are at stake, even small reductions of existential risk have great value. Some of the arguments run as follows:
- wrote in 1983: "If we are required to calibrate extinction in numerical terms, I would be sure to include the number of people in future generations who would not be born. (By one calculation), the stakes are one million times greater for extinction than for the more modest nuclear wars that kill "only" hundreds of millions of people. There are many other possible measures of the potential loss – including culture and science, the evolutionary history of the planet, and the significance of the lives of all of our ancestors who contributed to the future of their descendants. Extinction is the undoing of the human enterprise." 
- Philosopher Derek Parfit in 1984 makes an anthropocentricutilitarian argument that, because all human lives have roughly equal intrinsic value no matter where in time or space they are born, the large number of lives potentially saved in the future should be multiplied by the percentage chance that an action will save them, yielding a large net benefit for even tiny reductions in existential risk. 
- Humanity has a 95% probability of being extinct in 7,800,000 years, according to J. Richard Gott's formulation of the controversial Doomsday argument, which argues that we have probably already lived through half the duration of human history.
- Philosopher Robert Adams in 1989 rejects Parfit's "impersonal" views, but speaks instead of a moral imperative for loyalty and commitment to "the future of humanity as a vast project. The aspiration for a better society – more just, more rewarding, and more peaceful. our interest in the lives of our children and grandchildren, and the hopes that they will be able, in turn, to have the lives of their children and grandchildren as projects." 
- Philosopher Nick Bostrom argues in 2013 that preference-satisfactionist, democratic, custodial, and intuitionist arguments all converge on the common-sense view that preventing existential risk is a high moral priority, even if the exact "degree of badness" of human extinction varies between these philosophies. 
Parfit argues that the size of the "cosmic endowment" can be calculated from the following argument: If Earth remains habitable for a billion more years and can sustainably support a population of more than a billion humans, then there is a potential for 10 16 (or 10,000,000,000,000,000) human lives of normal duration.  : 453–4 Bostrom goes further, stating that if the universe is empty, then the accessible universe can support at least 10 34 biological human life-years and, if some humans were uploaded onto computers, could even support the equivalent of 10 54 cybernetic human life-years. 
Some philosophers posit that human extinction would not be a bad thing, but a good thing. Antinatalist David Benatar argues that coming into existence is always a serious harm, and therefore it is better that people do not come into existence in the future.  Further, David Benatar, animal rights activist Steven Best, and anarchist Todd May, posit that human extinction would be a positive thing for the other organisms on the planet, and the planet itself, citing for example the omnicidal nature of human civilization.    The environmental view in favor of human extinction is shared by the members of Voluntary Human Extinction Movement who call for refraining from reproduction and allowing the human species to go peacefully extinct, thus stopping further environmental degradation. 
Psychologist Steven Pinker calls existential risk a "useless category" that can distract real threats such as climate change and nuclear war. In contrast, other researchers argue that both research and other initiatives relating to existential risk are underfunded. Nick Bostrom states that more research has been done on Star Trek, snowboarding, or dung beetles than on existential risks. Bostrom's comparisons have been criticized as "high-handed".   As of 2020, the Biological Weapons Convention organization has an annual budget of US$1.4 million. 
Although existential risks are less manageable by individuals than – for example – health risks, according to Ken Olum, Joshua Knobe, and Alexander Vilenkin, the possibility of human extinction does have practical implications. For instance, if the "universal" Doomsday argument is accepted it changes the most likely source of disasters, and hence the most efficient means of preventing them. They write: ". you should be more concerned that a large number of asteroids have not yet been detected than about the particular orbit of each one. You should not worry especially about the chance that some specific nearby star will become a supernova, but more about the chance that supernovas are more deadly to nearby life than we believe." 
Multiple organizations with the goal of helping prevent human extinction exist. Some examples are the Future of Humanity Institute, the Centre for the Study of Existential Risk, the Future of Life Institute, and the Machine Intelligence Research Institute.
At least one organization professes that its express purpose is to hasten complete human extinction and the end of the world: The Centre for Applied Eschatology. 
Jean-Baptiste Cousin de Grainville's 1805 Le dernier homme (The Last Man), which depicts human extinction due to infertility, is considered the first modern apocalyptic novel and credited with launching the genre.  Other notable early works include Mary Shelley's 1826 The Last Man, depicting human extinction caused by a pandemic, and Olaf Stapledon's 1937 Star Maker, "a comparative study of omnicide". 
Aliens: Advanced species might want to destroy humanity, scientist warnsLink copied
Scarlett Moffatt says that she was &lsquoabducted by aliens&rsquo
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Curiosity is the great motivator for scientists, but one expert believes it might be best if they fought their urges before contacting aliens. An advanced species of extraterrestrials could easily view humans as primitive or a nuisance and wipe us out accordingly, Jacco van Loon, astrophysicist and director of Keele Observatory at Keele University, warned.
Life on Earth is a newcomer in comparison to the age of the Universe.
The first signs of life on our planet appeared around 3.5 billion years ago, but the Universe has been around more than 10 billion years longer.
If life is not unique to Earth, it is extremely feasible that something came before us and would be much more advanced, assuming these aliens followed the same trajectory as life on Earth.
And judging by humanity's past, a more technologically advanced species often has no regard for civilisations not as advanced on the technological timescale, such as when Europeans encountered native Americans, and almost killed them off in order to conquer the New World.
Aliens: Advanced species might want to destroy humanity, scientist warns (Image: GETTY)
Aliens might be much more advanced than us (Image: GETTY)
Prof van Loon was answering a question on why aliens have yet to contact Earth when he said an advanced species could easily wipe us out.
He wrote in The Conversation: "[Aliens] may . be interested in our planet. Earth has perfect conditions for life.
"Aliens might need another home, if for some reason &ndash such as climate change, nuclear war or an enormous asteroid impact &ndash they had to leave their own planet.
"It&rsquos also possible that they would not be looking for friendship.
Scientists are trying to find aliens (Image: GETTY)
"There are plenty of examples from our history of times when humans have travelled somewhere on Earth and acted cruelly, killing or enslaving the people that lived there.
"Aliens settling on Earth might want us out of their way. There&rsquos another reason &ndash humans are predators who eat other lifeforms. Aliens might find us nutritious or tasty too."
However, Prof van Loon also said aliens just might not be interested in us, but that does not mean we might not find them in the near future.
He continued: "Some aliens might find us boring, hard to understand, too primitive to deserve their attention, or potentially bearing disease.
What is the Drake Equation? (Image: EXPRESS)
"Conversations across the vastness of space take many years, and travel much longer still.
"Some aliens might simply not be interested in life beyond their own world.
On the other hand, it may be that life such as ours is actually very common. With so many worlds and civilisations to choose from, we may simply not yet have caught their eye.
"If that is the case, we might soon detect alien life around nearby stars for ourselves."
Mass extinction could happen AGAIN as experts warn over repeat of ‘Great Dying’ that wiped out 96% of species
THE LARGEST extinction event in Earth's history was caused by global warming - and our planet may be in for another enormous wipeout, scientists warn.
Continued climate change could lead to a repeat of the Great Dying, which killed off 96% of life on Earth around 250 million years ago.
Long before the dawn of the dinosaurs, Earth was populated with plants and animals that were mostly obliterated after a series of massive volcanic eruptions in Siberia.
The mass extinction, triggered 252million years ago, essentially set life on our planet back to square one, and was followed by a period spanning millions of years in which life had to multiply and evolve once more.
Now researchers have shown that the Great Dying, which killed 96% of Earth's ocean creatures, was caused by global warming.
As volcanoes belched greenhouse gases into the atmosphere, Earth's oceans heated up, and its warming waters could no longer hold enough oxygen for life to survive.
Scientists at the University of Washington warned that man-made climate change could trigger a similar event within the next few hundred years.
"Under a business-as-usual emissions scenarios, by 2100 warming in the upper ocean will have approached 20 percent of warming in the late Permian, and by the year 2300 it will reach between 35 and 50 percent," said study author Justin Penn.
"This study highlights the potential for a mass extinction arising from a similar mechanism under anthropogenic climate change."
The Washington team ran computer models to simulate the effects of the Great Dying on Earth's ancient oceans.
They showed that sulphur and other greenhouse gases pumped into the atmosphere starved Earth's oceans of 80% of their oxygen.
How We Won the Hominid Wars, and All the Others Died Out
How did our species come to rule the planet? Rick Potts argues that environmental instability and disruption were decisive factors in the success of Homo sapiens : Alone among our primate tribe, we were able to cope with constant change and turn it to our advantage. Potts is director of the Smithsonian Institution’s Human Origins Program , curator of anthropology at the National Museum of Natural History in Washington, D.C., and curator of the David H. Koch Hall of Human Origins , which opened at that museum last year. He also leads excavations in the East African Rift Valley and codirects projects in China that compare early human behavior and environments in eastern Africa with those in eastern Asia. Here Potts explains the reasoning behind his controversial idea.
Why did our close relatives—from Neanderthals to their recently discovered cousins, the Denisovans , to the hobbit people of Indonesia —die out while we became a global success?
That is the million-dollar question. My view is that great variability in our ancestral environment was the big challenge of human evolution. The key was the ability to respond to those changes. We are probably the most adaptable mammal that has ever evolved on earth. Just look at all the places we can live and the way we seek out novel places to explore, such as space.
The classic view of human evolution doesn’t emphasize adaptability. It focuses more on the idea that we were inevitable: that famous march from ape to human. It’s a ladder of progress with simple organisms at the bottom and humans at the top. This idea of inevitability runs deep in our societal assumptions, probably because it’s comforting—a picture of a single, forward trajectory, ending in modern humans as the crown of creation.
But recently discovered fossils show an incredible diversity in the human family tree. That seems like the opposite of a ladder.
Right. The tremendous fossil discoveries of late have given us a lot more knowledge about the diversity of human experiments, and diversity is the theme that needs to be underlined. Yet in spite of the great variety in earlier human species, we are the only one that remains of a diverse family tree. That might seem to indicate something special about us, but in fact even we barely made it. Between 90,000 and 70,000 years ago, our own species almost bit the dust. Several genetic studies show a bottleneck back then, a time when the total number of Homo sapiens was tiny. So we, too, were an endangered species.
How did you come to see adaptability as the key to our ultimate evolutionary success?
I first got interested in this idea during my excavations in southern Kenya , where the changes in different layers of sediment, indicating different habitats at different times, were really obvious. Every layer suggested a change in vegetation as well as moisture, the kinds of other animals that were around, and the survival challenges faced by our ancient predecessors. I wondered if our lineage thrived precisely because our ancestors could adjust to those changes. I called this hypothesis variability selection —the idea that change itself was a selective pressure. Repeated, dramatic shifts in the environment challenged many species and may have actually selected for the features that have come to typify Homo sapiens , especially our ability to alter our immediate surroundings.
In the classic view, it was thought that we emerged on the savanna as conditions dried and cooled. We imagined our earliest ancestors in a backdrop of dry and grassy plains that basically forced the emergence of walking upright, tool use, and a larger brain, ultimately leading to language and culture and global success.
Now, it’s certainly true that there has been marked global cooling and drying over the last 70 million years. But during the period of human evolution [since the appearance of our first direct ancestors in Africa], there were actually very pronounced fluctuations between warm and cool, between moist and arid. One way you can tell is by looking at different oxygen isotopes in the fossilized skeletons of ocean microorganisms . A heavier isotope is present during cooler periods, and a lighter one in warmer periods. I plotted out the variability in million-year intervals and found that about 6 million years ago, that variability went off the charts and kept increasing. That struck me as really strange, because that’s the time when the human story begins. African environments showed especially strong shifts between arid and moist climates during the past 4 million years.
Our ancestors had to survive all these settings. I started to think, What if all that variability is not noise in the overall cooling and drying trend, but a very important test of the capacity of a creature to survive? This idea helps explain how we started out as a small, apelike, herbivorous species 6 million years ago in tropical Africa, and after a history of origin and extinction of species, what’s left today is us: a single species all over the planet with an astonishing array of abilities to adjust.
What are the cardinal features of adaptability that set us apart?
You can go back more than 3 million years to Australopithecus afarensis [the famous “Lucy” species], which over time maintained the ability to walk on two legs and to climb in trees. That’s a primal adaptable feature near the root of our evolutionary tree, and it allowed this species to make its way between areas of woodland and open savannas to find food.
Stone tools, which first emerged 2.6 million years ago, are another feature of our adaptability. When it comes to acquiring and processing food, a hammerstone is better than a big molar, and a knapped flint is sharper than a pointed canine. All manner of foods opened up to the genus Homo with stone tools.
The emergence of a large brain, with complex connectivity among neurons, suggests that the brain itself is an organ of adaptability. It allows us to take in information about the environment, organize, form social alliances, and raise the probability of survival in difficult times. You can see in the archaeological record that our early ancestors transported food from the place it was found to another place where members of the social group would meet. We modified the shapes of stones, we carried food, made fire and protective shelters, and we eventually began to cultivate crops and manipulate the environment in order to grow them. All of these small ways of altering the immediate surroundings strike me as reasonable adaptations to the instability of habitats.
If you are right, what killed off the Neanderthals? They had big brains too. They had stone tools, and they buried their dead, which means they had culture. They were also hardier and better adapted to cold than we are. So what did they lack?
That’s a question we’re exploring now. It’s important not to underestimate the Neanderthals. They endured for a long time in the comings and goings of ice ages.
Whenever glacial habitats invaded Europe and Asia, it appears that the Neanderthals moved south, into Iberia and the Italian peninsula, to take advantage of the warmer places. Overall, their bodies show evidence of cold adaptation. Yet during one cold period, when the Neanderthals retreated, populations of Homo sapiens began to infiltrate the cold regions. How could they do this, especially since these populations were dispersing from tropical Africa? The difference is that these early populations of our species had developed the ability to invent new tools, like sewing needles that were useful in producing warm, body-hugging clothing. Preserved beads and stones suggest that they, but not the Neanderthals, maintained social networks over vast areas. My guess is that in Africa, Homo sapiens evolved better ways of adjusting to the arid-moist fluctuations—the key to adaptability—than the Neanderthals did to the cold-warm fluctuations in their part of the world. There are a lot of scientists interested in testing these ideas with new fossil and archaeological evidence.
In the end, despite the adaptable features they inherited, the Neanderthals ended up as more habitat specialists than we did. Their options were more limited. As a result, our species ended up all over the world while theirs vanished.
Actually, my answer to “Are we it?” is to turn the assumption on its head. Considering that we are the only survivor of a diverse family tree —that is, an evolutionary tree characterized by lots of extinction—the notion that our twig is the final blossom of evolution is incredibly outdated. It’s incorrect no matter how ingrained it is in our thinking. Our amazing adaptability has allowed us to shape the environment to our own needs. This transformation has taken place in a remarkable period of climate stability, over the past 8,000 years or so. One deeply ironic result is that we have now narrowed our own options at a time when climate fluctuation appears to be increasing. Of an estimated 15,000 species of mammals and birds, fewer than 14 account for 90 percent of what we eat. Of more than 10,000 edible plants, three crops—wheat, rice, and corn—provide half the world’s calories. And through greenhouse gases released by burning fossil fuels, we’re pulling on the strings of the earth’s unstable climate.
By narrowing our options at a time of increasing instability, could we be inadvertently engineering our demise?
I see two possible scenarios for the future. We could change our current course and try to work carefully with the natural dynamics of the planet and the uncertainties of the environment, especially when it comes to our own inadvertent effects. Or we could continue shaping the earth in our own image, so to speak. We could theoretically, through engineering, create a membrane around the earth that controls temperature and rainfall, for instance. These two courses represent two very different views of the earth and our place on it. Whether the next chapter of the human story will be the last chapter may depend on the balance we strike between those two courses.
The Planet Has Seen Sudden Warming Before. It Wiped Out Almost Everything.
In some ways, the planet's worst mass extinction — 250 million years ago, at the end of the Permian Period — may parallel climate change today.
Some 252 million years ago, Earth almost died.
In the oceans, 96 percent of all species became extinct. It’s harder to determine how many terrestrial species vanished, but the loss was comparable.
This mass extinction, at the end of the Permian Period, was the worst in the planet’s history, and it happened over a few thousand years at most — the blink of a geological eye.
On Thursday, a team of scientists offered a detailed accounting of how marine life was wiped out during the Permian-Triassic mass extinction. Global warming robbed the oceans of oxygen, they say, putting many species under so much stress that they died off.
And we may be repeating the process, the scientists warn. If so, then climate change is “solidly in the category of a catastrophic extinction event,” said Curtis Deutsch, an earth scientist at the University of Washington and co-author of the new study, published in the journal Science.
Researchers have long known the general outlines of Permian-Triassic cataclysm. Just before the extinctions, volcanoes in what is now Siberia erupted on a tremendous scale. The magma and lava that they belched forth produced huge amounts of carbon dioxide.
Once in the atmosphere, the gas trapped heat. Researchers estimate that the surface of the ocean warmed by about 18 degrees Fahrenheit. Some researchers argue that the heat alone killed off many species.
Others believe that the warmth reduced oxygen in the ocean, asphyxiating the species living there. Rocks from the mass extinction appear to have formed when at least some of the ocean was lacking oxygen.
In previous research, Dr. Deutsch has explored how living animals adapt to temperature and oxygen levels in the seas. Animals with a fast metabolism need a lot of oxygen, for example, and so they can’t live in parts of the ocean where oxygen falls below a certain threshold.
Warm water makes the challenge even more difficult. Warmer water can’t hold as much dissolved oxygen as cold water. Even worse, warm water can also increase an animal’s metabolism, meaning it requires more oxygen just to stay alive.
Cod, for example, are not found below a latitude running roughly from New England to Spain. South of that line, warmth and low oxygen are just too great for the species.
Dr. Deutsch and Justin Penn, a graduate student, recreated the world at the end of the Permian Period with a large-scale computer simulation, complete with a heat-trapping atmosphere and a circulating ocean.
As the Siberian volcanoes flooded the virtual atmosphere with carbon dioxide, the atmosphere warmed. The ocean warmed, too — and according to the model, it began losing oxygen.
Some parts lost more than others. On the surface, for example, fresh oxygen was produced by photosynthetic algae. But as the ocean warmed, its circulatory currents also slowed, the model demonstrated.
Oxygen-poor water settled to the bottom of the oceans, and before long, the deep was gasping.
Rising temperatures and plunging oxygen must have made huge swaths of the oceans uninhabitable. Some species survived here and there. But most disappeared completely.
“Everything was losing a lot of habitat, creating the risk of extinction,” said Dr. Deutsch. “But the risk was actually higher in places that were cold. That was a bit surprising.”
You might expect that animals near the Equator would be at a greater risk, because the water was warm to begin with. But Dr. Deutsch’s model suggested a very different kind of apocalypse.
Animals in oxygen-rich cold water could not handle the sudden drop, while those in tropical waters were already adapted to poor oxygen. And the cold-water species could not find refuge elsewhere.
To test their simulation, the researchers teamed up with Jonathan Payne and Erik Sperling, paleontologists at Stanford University. They dug into a huge online database of fossils to chart the risks of extinction at different latitudes during the catastrophe.
When they were done with their analysis, they sent their graph to Seattle. Dr. Deutsch and Mr. Penn compared it to the prediction from their computer model.
They matched. “This was the most exciting moment of my scientific life,” said Dr. Deutsch.
Michael Benton, a paleontologist at the University of Bristol in England, who was not involved in the study, said that it resolved the roles of heat and oxygen as causes of the mass extinction. “This makes a clear case that, of course, the two are linked,” he said.
The new study offers an important warning to humans over the next few centuries.
The Siberian volcanoes ultimately delivered much more carbon dioxide into the atmosphere than we will ever emit by burning fossil fuels. But our annual rate of carbon emissions is actually higher.
The carbon we released over the past two centuries already has made the atmosphere warmer, and the ocean has absorbed much of that heat. And now, just as during the Permian-Triassic extinction, the ocean is losing oxygen. Over the past fifty years, oxygen levels have declined by 2 percent.
“The way the Earth system is responding now to the buildup of CO2 is in the exact same way that we’ve seen it respond in the past,” said Lee Kump, a geoscientist at Penn State University.
Just how much warmer the planet will get is up to us. It will take a tremendous international effort to keep the increase below about 4 degrees Fahrenheit.
If we proceed to use up all the fossil fuels on Earth, it could warm by as much as 17 degrees Fahrenheit by 2300.
As the ocean warms, its oxygen levels will continue to drop. If ancient history is any guide, the consequences for life — especially marine life in the cooler parts of the ocean — will be disastrous.
“Left unchecked, climate warming is putting our future on the same scale as some of the worst events in geological history,” Dr. Deutsch said.
Scientists are now detecting the first flashing warning lights on the Earth System dashboard, telling us humanity is already pushing beyond our world's safe operating space for multiple planetary boundaries and approaching tipping points.
"We have changed the planet so much that it is very likely that there will be significant impacts, and we're seeing those impacts in the last five years," Shaw said.
An example: melting of the Greenland and West Antarctic ice sheets has accelerated since the early 1990s, suggesting these colossal ice deposits may have now entered a new state of sustained and escalating retreat, after many centuries of stability. Contained within these now vulnerable ice sheets is enough water to raise the global sea level by more than 65 meters (213 feet).
Similarly, Arctic sea ice is retreating and scientists predict the region could be mostly ice-free in the summer as early as 2035 — with no certainty of what extreme changes this might bring.
Other early warning signs that we are approaching a climate change tipping point include increasingly frequent and severe droughts, heat waves, storms, and tropical cyclones.
"The number of climate-related natural disasters is climbing at an alarming rate, with significant economic and health impacts, especially for the most vulnerable," said Ana María Loboguerrero Rodríguez, head of Global Policy Research for the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS).
No one knows how much stress civilization can withstand before it starts to collapse.
Manaus, Brazil, with more than 2 million people, lies at the heart of the world’s largest rainforest, making it a good spot for tracking the forest’s pathogens—as well as a potential spillover point.
A black-and-white photograph in a second-floor foyer of Fiocruz Amazônia depicts one inspiration for this work: Brazil’s legendary doctor and disease sleuth, Carlos Chagas. Attired for an expedition in a white suit and knee-high boots, Chagas stands in a canoe surrounded by his oarsmen. In 1909, Chagas discovered the cause of the disease that now bears his name. Using a simple microscope, he identified the culprit as a protozoan (now called Trypanosoma cruzi) and showed that it is transmitted by the bite of triatomine bugs, often called kissing bugs. Chagas disease, whose symptoms range from fever to heart failure decades later, still kills hundreds of thousands of people a year in Latin America.
Naveca is doing similar detective work with the more sophisticated tools of modern genetics. One pathogen that concerns him is the little-studied Oropouche virus, which is spread primarily by a species of midge, Culicoides paraensis. Oropouche, which causes fever, headache, and joint pain, has sparked at least 30 outbreaks and sickened more than 500,000 people since it was first identified in 1955. Its range has gradually expanded to include Panama, six South American countries, and Trinidad and Tobago, where it first appeared. The midge itself, however, lives as far away as the northern United States, where it and related insects are called no-see-ums, suggesting the virus could spread beyond South America. The southern house mosquito (Culex quinquefasciatus), a carrier of West Nile and Saint Louis encephalitis viruses, can also transmit Oropouche, though not very efficiently, and its range throughout the tropics raises the possibility of Oropouche outbreaks in Africa, southeast Asia, and Australia.
RNA in a tube of monkey feces will be analyzed for signs of novel pathogens. Image by Dado Galdieri/Hilaea Media. Brazil.
Virologist Felipe Naveca compares RNA results from animal samples against known viral sequences. Image by Dado Galdieri/Hilaea Media. Brazil.
Biologist Paulo Bobrowiec works with a collection of bats at the Amazon Research Institute in Manaus, Brazil. Bat viruses have a history of crossing to humans. Image by Dado Galdieri/Hilaea Media. Brazil.
A veterinarian draws blood from a sedated pied tamarin in a Manaus, Brazil, park. Image by Dado Galdieri/Hilaea Media. Brazil.
A sloth gets a drink at a wildlife rescue center. Image by Dado Galdieri/Hilaea Media. Brazil.
Naveca and his colleagues hope to find out which animal or animals are the primary natural reservoirs for this virus. There are plenty of candidates: Oropouche has been identified in sloths, marmosets, finches, and several other birds and mammals. The team recently reported using the polymerase chain reaction to identify the virus’ genetic material in urine and saliva—as opposed to blood—which could make the hunt for its animal reservoir easier and aid diagnosis in patients.
Naveca is also worried about another little-studied virus that is rapidly expanding in South America: the Mayaro virus, which causes flulike symptoms, making it hard to distinguish from more common tropical diseases such as chikungunya and dengue fever. As with Oropouche, he’s hoping to pinpoint the virus’ natural reservoirs and investigate whether cases of it are going undiagnosed.
Mayaro is a likely candidate for the next large-scale outbreak of an animal virus in Brazil or beyond, Naveca and other scientists warn. Its primary vector, the mosquito Haemagogus janthinomys, is a forest dweller restricted to Central America and northern South America, but laboratory experiments show the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (A. albopictus)—two species widely distributed in tropical and subtropical areas—can also transmit the disease. A. aegypti is especially well adapted to breeding in cities.
Illegal construction encroaches on rainforest near Manaus, turning people and animals into intimate neighbors. Image by Dado Galdieri/Hilaea Media. Brazil.
To Naveca, the Zika virus is a case study in the value of tracking obscure pathogens. First identified in Africa in 1947, where it spilled over from monkeys, it circulated largely unnoticed and with few casualties for decades. Then, it caused an outbreak in Oceania in 2013 and, 18 months later, a massive epidemic in Latin America. Researchers suddenly discovered a disturbing consequence of the disease—microcephaly and other birth defects in infants born to infected mothers. “Zika was a virus that nobody was paying attention to until 10 years ago,” Naveca says. “We can fight better the enemies we know better.”
Naveca now hopes to carry on Chagas’s disease-hunting tradition with a deal he’s negotiating to procure a 25-meter, flat-bottomed boat that has been outfitted to be a floating laboratory. Preserving perishable human and animal samples at remote field sites has been a critical obstacle, and the vessel would bring the lab to the biological materials, rather than the other way around. Naveca hopes to join its maiden research voyage, possibly later this year, to remote Amazon villages, where he and colleagues plan to trap bats, rodents, primates, and insects, and bring a trove of specimens back to Fiocruz Amazônia.
In a fragment of Amazon rainforest within the city of Manaus, Brazil, parasitologist Aline Ramos holds samples of feces, bodily fluids, and tissue collected from pied tamarin monkeys. Image by Dado Galdieri/Hilaea Media. Brazil.
EVEN WITHIN MANAUS, there are lots of opportunities for fieldwork. When Science visited last year, Gordo had set up an improvised lab inside a classroom at Sumaúma State Park, a tiny patch of uncut rainforest in the middle of the city, wedged between a busy highway and an upscale mall. Using cages baited with ripe bananas, he and his assistants trapped nine pied tamarins and injected them with a sedative, then swabbed their oral and anal cavities, clipped locks of hair, and drew blood. Then they set the animals free.
It’s peculiar and sometimes dangerous work. Monkeys have bitten and sneezed on Gordo, and on this trip a syringe broke as he squeezed the plunger, spraying monkey blood on his face shield. He says his wife complains when he stashes monkey carcasses in their home fridge.
Manaus’s Yoda-faced pied tamarins live all over the city. Like North American squirrels and raccoons, they don’t respect property lines and make urban gardens their pantries and playgrounds. There’s no evidence so far that Manaus’s urban monkeys are a human health threat, and Gordo, worried about “unreasonable killings or deforestation,” is reluctant to discuss that possibility. But he and others are investigating whether monkeys carry parasites, such as the nematodes that cause filariasis, or viruses such as Zika and chikungunya.
For Gordo, an equal concern is spillback—infections passed from humans to wildlife. Zika, for example, appears to have traveled from humans back to wild monkeys during Brazil’s epidemic. Fears that the virus might harm wildlife rose when researchers showed that a pregnant monkey native to Brazil had a spontaneous abortion after it was exposed to Zika. The fetus had birth defects similar to those seen in humans.
So far, Gordo has not found the virus in Manaus’s monkeys, but they may be at risk: A study he co-authored last year found mosquitoes from two species thought to carry Zika, Haemagogus janthinomys and Sabethes chloropterus, in both monkey and human habitats in a forest reserve on the edge of the city. The pied tamarins are already critically endangered, found nowhere else but in and around Manaus. Their population is expected to decline by 80% within the next 16 years. A virus outbreak could push them over the edge.
Students wait to sample animals while veterinarian Alessandra Nava stores specimens in liquid nitrogen (right). Image by Dado Galdieri/Hilaea Media. Brazil.
Humans are at risk from spillback as well. In Europe and the United States, scientists worry about COVID-19 outbreaks on mink farms, for example, because such events give the virus more opportunities to evolve and jump back into people. Likewise, primate populations infected with Zika could reignite human outbreaks. This happened with yellow fever: Brought to South America centuries ago with the slave trade, the virus has been impossible to eliminate from Brazil because it established itself in wild monkey populations, which occasionally pass it back to people.
After trapping monkeys for a day in the Sumaúma park, Gordo went home and bottle-fed an infant pale-throated sloth only slightly larger than his cupped hands. A friend had found it untended on the ground in a forest fragment not far from his university office. Despite everything he’s learned about zoonotic diseases, Gordo said he was “not too worried.” The sloth pup looked healthy. But several weeks later it got sick and died, possibly from pneumonia.
NAVA BELIEVES the Fiocruz center’s work is only becoming more urgent with changing land use patterns in the Amazon. Deforestation has soared since Bolsonaro came to power in 2019—transforming habitat in ways that could make viral hosts and vectors more dangerous and increasing the likelihood of spillover.
In 2016, she and colleagues reported that 9% of bats in small clearings around settlements in Brazil’s coastal Atlantic Forest had active infections of one or more of 16 viruses, including coronaviruses and hantavirus. In less-disturbed forests nearby, fewer than half as many bats were infected, and with only six different viruses. The findings fit a widely debated hypothesis known as the dilution effect, which holds that in forests with greater biodiversity, mosquitoes and other vectors have more targets and end up biting animals not capable of incubating a given virus, thereby slowing its spread. Reducing biodiversity by clearing land can do the opposite, and it also pushes humans into closer proximity to wildlife. Bats are a particular concern, Nava says, because they often roost in buildings.
It all underscores the need to stop destroying rainforest, she says—although she acknowledges that Brazil’s policies are unlikely to change under Bolsonaro, who has nearly 2 years left in his term. In the meantime, Nava says, disease fighters must keep monitoring the jungle for dangerous diseases. “We have no power to reduce deforestation,” she says. But, she adds, “We have the power to search for new viruses.”
Are We Really Running Out of Time to Stop Climate Change?
Activists and politicians have been criticized from the right for saying we have only 12 years to stop climate change. Scientists say the situation is in some ways worse than that.
Are we running out of time to stop climate change? Nearly a year has passed since the Intergovernmental Panel on Climate Change (IPCC) warned that limiting global warming to the 1.5-degree Celsius (2.6 degrees Fahrenheit) mark by the end of the century — a goal set to stave off the worst impacts of climate change — "would require rapid, far-reaching and unprecedented changes in all aspects of society."
Some politicians and writers have thrown their hands up in the air and argued that it's too late, and that human civilization is simply not up to the task. Others, meanwhile, took the report as a call to arms, reframing one of its points as a political organizing message: We have only 12 years to stop climate change, and the clock is ticking. (A year later, we're down to 11.)
But the full picture is both more and less dire than a slogan can capture. We can't stop climate change — because it's already here, and it's already too late to reverse many of its catastrophic effects. What's true is that things are on track to get much worse over the course of this century, and that if we're going to stop those things from happening, society is going to have to start hitting some important deadlines fast. There's a big one coming 12 years after the IPCC report. Blowing through it won't immediately plunge society into a "Mad Max"-style dystopia, as some have suggested — perhaps tongue in cheek — but it will make sure everything keeps getting steadily worse, and it will make turning things around down the road that much harder.
Some scientists are nervous that overemphasizing the 2030 deadline might mislead the public about the nuances of climate change. But others pointed out to Live Science that activists have a task that's different from that of researchers — one that requires straightforward goals and clear, simple ideas.
The IPCC report, which the U.N. climate science body released Oct. 8, 2018, revealed that the best path to limiting warming to an increase of 1.5 C by 2100 involves cutting net human carbon dioxide (CO2) emissions 45% by 2030 (12 years after the report was published) and then cutting emissions further to net zero by 2050. It was far from the first dire warning that the agency had issued. But this one seemed to take root in the public discourse around climate change, possibly because of how news stories summarized the report. An Oct. 8, 2018, headline in The Guardian read, "We have 12 years to limit climate change catastrophe, warns UN." Vox headlined its article "Report: we have just 12 years to limit devastating global warming." Smithsonian.com wrote, "The World Was Just Issued 12-Year Ultimatum On Climate Change."
In an interview with writer Ta-Nehisi Coates three months later, on Jan. 21, Rep. Alexandria Ocasio-Cortez, D.-N.Y., spelled out how the report's conclusions had entered the zeitgeist:
"Millennials and Gen Z and all these folks that come after us are looking up, and we're like, 'The world is going to end in 12 years if we don't address climate change, and your biggest issue is how are we gonna pay for it?'"
Here's the thing: Scientists never said the world was going to end in 12 years if we don't stop climate change. Even researchers known for ringing the alarm bells on climate change are far more likely to speak in terms of decimal places and nonlinear effects than to talk about the end of civilization as we know.
Prominent activists rarely bring up doomsday, either. Messages from the Global Climate Strike organizers and the U.S.-based Sunrise Movement focus on long-term climate shifts, not an impending, sudden disaster. Still, the 12-year deadline looms large in the culture.
"It has achieved an absoluteness in its role in societal dialogue that's not in line with scientific fact," said Katharine Mach, a climate scientist at the University of Miami and one of several lead authors of the IPCC report.
"The world will not end if we pass 1.5 degrees Celsius of warming above preindustrial levels," Mach said.
And failing to hit a 45% reduction target won't lead to 1.5 C of warming by 2030, as Lini Wollenberg, a University of Vermont climate researcher and leader of the CGIAR Research Program on Climate Change, Agriculture and Food Security, told Live Science. It does, however, increase the chances of hitting 1.5 degrees C by 2100 and experiencing many more climate catastrophes on our way through the 21st century, Wollenberg said.
The issue is that any program set up to mitigate warming will have two basic components: short-term cuts to emissions and longer-term efforts to pull carbon out of the atmosphere. (This doesn't necessarily mean giant, futuristic CO2-sucking machines, but may mean things like growing forests.)
"Some people — I'm hazarding industry and those focused on maintaining a growth-focused economy — would argue that we don't want to sacrifice things in the short term, and that society will figure out the technology to deal with it later," Wollenberg said.
But every year of delay on cutting greenhouse gas emissions means that carbon-capture efforts down the road will have to be even more fantastical and dramatic (including heavy reliance on carbon-capture technologies that may never work). And each year in which we do nothing, the world will cross more climate tipping points that will be difficult to undo, Wollenberg said.
The year 2030 has been bouncing around climate-policy documents for a while, Wollenberg said. (It also turned up in the Paris Agreement, for example, as did the goal of net zero by 2050.) Researchers saw that target as part of a reasonable time frame for drawing down emissions without it resulting in unbearable economic costs or having humanity rely too heavily on future carbon-capture efforts, she said.
"It could have been 2020, 2012 or 2016," Wollenberg said, adding that 2030 "used to seem a lot further away."
The 1.5 C target was picked for similar reasons — an effort to balance what's possible against what's necessary. But, similar to the 12-year time frame, 1.5 degrees is a target set by scientists, not an immutable scientific fact.
"We know that the risks go up [as temperature rises]. We're already experiencing widespread impacts of the changing climate," Mach said, pointing to the ongoing consequences of 2019's 1 C (1.8 F) of warming above preindustrial levels. "It will be greater at 1.5 degrees of warming, and may go up from there in some very substantial ways … with severe, irreversible impacts."
Holding warming to 1.5 degrees won't reverse climate change. In fact, the catastrophic impacts in that idealized scenario will be much worse than they are now.
Colin Carlson, an ecologist at Georgetown University who studies how climate change influences infectious diseases, said that one problem with imagining that we have 12 years until a huge disaster hits is that such thinking obscures the ongoing horrors of climate change in 2019.
"Climate change has already killed hundreds or thousands — or more — of people," Carlson said, "through malaria, through dengue, through a hundred other avenues that we're only now starting to be able to quantify."
Mosquito-borne diseases flourish in a warming world, his research has shown. And the world has already warmed enough that many people have gotten sick and died from those diseases — people who otherwise would have been spared.
"So this is not as simple as 'Can we stop this coming?' It's already here," he said.
Similarly, Wollenberg&rsquos work has shown that severe climate impacts are devastating food production worldwide in 2019. Vast regions of North and South America, Asia and Africa are becoming too hot for growing grains. The soil in low-lying, coastal regions of Bangladesh and China is getting saltier as rising seas contaminate groundwater, threatening rice production. (A few places are becoming more hospitable to certain crops. A warming Vermont, for example, is growing more hospitable to peaches, even as a shortened ski season threatens its economy.) The overall impact is to drive up food prices and create global unrest. Long term, these trends will make it impossible for some countries to produce enough food to feed their populations, she said.
To manage all that complexity, researchers tend to break down responses into two broad categories: mitigation and adaptation. Mitigation is, in short, the work of preventing climate change from worsening. Reducing emissions and growing forests fall into this category.
Adaptation is learning to deal with the warming that's already here and the additional warming that's coming: building sea walls and flood-abating salt marshes around coastal cities studying changes in precipitation so farmers know when to plant their crops and engineering crops to better withstand harsh environments.
But ultimately, all the researchers Live Science contacted said these problems become less catastrophic with less warming. Holding the world to a 1.5-C warming increase by the end of the century creates much more manageable short- and long-term problems than holding it to 2 C of warming, which is much less harmful to Earth than 3 C, which is much more survivable than 4 C, which is still less catastrophic than 6 C … and so on. None of those possible futures necessarily leads to a charred, lifeless global desert in our lifetimes. But each increase is almost unimaginably more dire for life on this planet than the one preceding it.
"It's always worth it to prevent more warming," Mach said.
With regard to the spread of mosquito-borne diseases, Carlson said, "We can stop it. Mitigating climate change is truly the silver bullet. Sometimes it is as simple as, 'If we stop climate change, we can stop a lot of the bad health impacts that are coming.'" (Though the devil is in the details, he added. The level of disease reduction will depend on how fast the carbon-mitigation project moves, and its effects won't be felt immediately or equally everywhere.)
The science points relentlessly to one reality: The best way to deal with climate change is to start cutting emissions now. It's easier to stop warming by keeping CO2 in the ground now than it is to pull carbon out of the air later. And mitigation makes adaptation much more effective.
Bringing up the 12-year time frame, then, is a way of drilling down on the first step the world has to take to move down the most effective mitigation path still available — even if it doesn't capture the full scope of the issue.
So, is it irresponsible for public figures to employ the 12-years rhetoric?
"I think the role of public figures is to set visions and create the urgency that we need," Wollenberg replied. "The scientific community is sometimes uncomfortable with that, but if you started talking to the general public about, 'Well, you could trade off your long-term emissions and delay the decline by 5%, or we could do a 4% reduction every year, but that would contrast with a 7% reduction where we could wait until 2035,' it would not be an effective message."
&ldquoI would blame the public figures who aren't taking steps more than I would blame the people who are trying to promote a vision," she said.
We're at a point in time when people are feeling the effects of climate change on their lives, said Jewel Tomasula, a doctoral student ecologist at Georgetown University, who studies the health of salt marshes in New Jersey. As Live Science has previously reported, the world in 2019 is hotter, monster storms are more frequent, diseases are on the move, and fires and floods are happening more often. Talking about 2030, Tomasula said, is about creating a window for activism to take effect — a decade of meaningful global movement on the problem.
"Science is great for understanding the problem," she said. "Climate change is a physical problem, and we can work on it with our data and really understand it. But that's not what's really going to fix it. … The way that problems like this have been addressed in the past is by having that political will and mobilization."
The notion of a 12-year deadline can be misleading and obscures some of the hedging and nuance scientists like to emphasize. But it also seems to offer climate mobilizers a focal point for their efforts, and people really are getting out into the streets.