Researchers have warned that by the end of the century, many parts of the world will have to cope with up to six weather catastrophes at once, ranging from heat waves and wildfires to deluge rains and deadly storms.
"Human society will face the devastating combined impacts of multiple interacting climate threats," said report co-author Dr. Erik Franklin, a researcher at the Institute of Marine Biology at the University of Hawaii.
"They are happening now and they will continue to get worse," he told the French news agency AFP.
Overburdening the atmosphere with carbon dioxide, methane and other greenhouse gases has unleashed a maelstrom of life-threatening forces.
It begins with rising temperatures, which, in normally dry regions, lead to droughts, heat waves, and deadly wildfires like the ones raging in California.
In more humid climates the result is heavy rain and flooding.
Over the oceans, global warming creates larger superstorms whose destructive power is enhanced by rising seas.
Until now, scientists have primarily studied these impacts of climate change one by one, hiding the possibility that human communities are hit by more than one at a time, according to the study.
Last year, for example, Florida experienced extreme droughts, record temperatures, more than 100 wildfires, and Hurricane Michael, the most powerful storm to ever hit its territory.
"A focus on one or a few hazards can mask the impacts of others, resulting in incomplete assessments of the consequences of climate change on humanity," said lead author Professor Camilo Mora of the University of Hawaii.
The future risk of facing multiple climate impacts at once depends on geography and on whether humanity is able to rapidly reduce greenhouse gas emissions.
If, against all odds, humanity succeeds in limiting global warming to two degrees Celsius above pre-industrial levels, for example, New York City will likely face a single climate hazard, one super-fast, perhaps, in a given year by end of the century.
The United Nations-sponsored Paris Agreement on climate change, signed by 195 countries in 2015, requires temperature rise to be “well below” 2.0 ° C.
Even under these optimistic scenarios, "increased cumulative exposure to the multitude of climate hazards will affect rich and poor countries alike," the study concluded.
However, if carbon pollution continues at its current rate, New York is more likely to be hit by up to four of these calamities at the same time, including extreme rain, rising sea levels, and storms.
The Australian city of Sydney and Los Angeles could face three weather calamities simultaneously, Mexico City four and Brazil, along its Atlantic coast, could face up to five.
In all scenarios, the tropical coastal areas will be the most affected.
To assess the risk of clustered climate catastrophes, Professor Mora and his international team collected data from several thousand peer-reviewed studies that looked at 10 specific impacts, mostly one at a time.
They included fires, floods, rains, sea level rise, changes in land use, ocean acidification, storms, warming, drought, and fresh water supplies.
The scientists analyzed how these by-products of global warming impact humans in six domains: health, food, water, economy, infrastructure, and security.
"Our health depends on multiple factors, from clean air and water to safe food and shelter," said co-author Professor Jonathan Patz, at the University of Wisconsin Institute for Global Health.
"If we only consider the more direct threats from climate change, heat waves or severe storms, for example, we will inevitably be surprised by even bigger threats that, in combination, can have even broader social impacts."
Scientists who were not involved in the research said it reinforces a point that should be obvious but remains highly controversial.
"The costs of inaction far outweigh the costs of taking action on climate change," said Professor Michael Mann of Penn State University.
"We can still reduce the harm and suffering in the future if we act quickly and dramatically to reduce carbon emissions."
The study, published in Nature Climate Change, also shows which parts of the world will likely be spared the worst ravages of climate change.
Several are found in temperate zones near polar regions, such as Tasmania and parts of Canada or Russia.
Original article (in English)