Climate change is a long-term change in the average weather patterns that have come to define Earth’s local, regional and global climates. These changes have a broad range of observed effects that are synonymous with the term.
Changes observed in Earth’s climate since the early 20th century are primarily driven by human activities, particularly fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth’s atmosphere, raising Earth’s average surface temperature. These human-produced temperature increases are commonly referred to as global warming. Natural processes can also contribute to climate change, including internal variability and external forcings.
Humans are increasingly influencing the climate and the earth’s temperature by burning fossil fuels, cutting down forests and farming livestock.
The main driver of climate change is the greenhouse effect. Some gases in the Earth’s atmosphere act a bit like the glass in a greenhouse, trapping the sun’s heat and stopping it from leaking back into space and causing global warming.
Many of these greenhouse gases occur naturally, but human activity is increasing the concentrations of some of them in the atmosphere, in particular:
- carbon dioxide (CO2)
- nitrous oxide
- fluorinated gases
- CO2 produced by human activities is the largest contributor to global warming.
Other greenhouse gases are emitted by human activity in smaller quantities. Methane is a more powerful greenhouse gas than CO2, but has a shorter atmospheric lifetime. Nitrous oxide, like CO2, is a long-lived greenhouse gas that accumulates in the atmosphere over decades to centuries.
Natural causes, such as changes in solar radiation or volcanic activity are estimated to have contributed less than plus or minus 0.1°C to total warming between 1890 and 2010.
The Effects of Climate Change
Climate change affects all regions around the world. Polar ice shields are melting and the sea is rising. In some regions extreme weather events and rainfall are becoming more common while others are experiencing more extreme heat waves and droughts. These impacts are expected to intensify in the coming decades.
Melting ice and rising seas
When water warms up it expands. At the same time global warming causes polar ice sheets and glaciers to melt. The combination of these changes is causing sea levels to rise, resulting in flooding and erosion of coastal and low lying areas.
Extreme weather, shifting rainfall
Heavy rain and other extreme weather events are becoming more frequent. This can lead to floods and decreasing water quality, but also decreasing availability of water resources in some regions.
Consequences for developing countries
Many poor developing countries are among the most affected. People living there often depend heavily on their natural environment and they have the least resources to cope with the changing climate.Risks for human health
Climate change is already having an impact on health: There has been an increase in the number of heat-related deaths in some regions and a decrease in cold-related deaths in others.
Sectors that rely strongly on certain temperatures and precipitation levels such as agriculture, forestry, energy and tourism are particularly affected.
Risks for wildlife
Climate change is happening so fast that many plants and animal species are struggling to cope. Many terrestrial, freshwater and marine species have already moved to new locations. Some plant and animal species will be at increased risk of extinction if global average temperatures continue to rise unchecked.