The effects of climate change span the physical environment, ecosystems and human societies. They also include the economic and social changes which stem from living in a warmer world. Human-caused climate change is one of the threats to sustainability.[1]
Many physical impacts of climate change are already visible, including extreme weather events, glacier retreat,[3] changes in the timing of seasonal events (e.g., earlier flowering of plants)
,[4] sea level rise, and declines in Arctic sea ice.
[5] The ocean has taken up between 20% and 30% of human-induced atmospheric carbon dioxide since the 1980s, leading to ocean acidification.
[6] Since 1970 the ocean has absorbed more than 90% of the excess heat in the climate system, raising temperatures and damaging coral reefs. Even if global surface temperature is stabilized, sea levels will continue to rise and the ocean will continue to absorb excess heat from the atmosphere for many centuries.[6]
Temperature increases faster over the surface of the land and in northern latitudes, so that for every 1 °C of global warming, temperatures in North America increase by almost 3 °F (1.6 °C).
[7] Climate change has already contributed to land degradation through changes to average conditions and increases in extreme weather
.[8] Changes to average conditions include raised temperatures and depleted soil moisture, increasing wildfire risk and impacting agriculture.
[9] Weather extremes that have increased in frequency and intensity include heat waves, drought, and storms. These changes are most acutely felt in natural ecosystems and developing countries where adaptation is most difficult. This can result in environmental migration for people that are dependent on land for food, feed, fibre, timber and energy.[10
The primary causes[12] and the wide-ranging effects[13
][14] of global warming and resulting climate change. Some effects constitute feedback mechanisms that intensify climate change and move it toward climate tipping points.[15]
The future impact of climate change depends on the extent to which nations implement prevention efforts, reduce greenhouse gas emissions, and adapt to unavoidable climate change effects.[16][17] Policy decisions made in the next few decades will have profound impacts on the global climate, ecosystems and human societies, not just for this century, but for the next millennia, as near-term climate change policies significantly affect long-term climate change impacts.[16][18][19] Stringent mitigation policies might be able to limit global warming (in 2100) to around 2 °C or below, relative to pre-industrial levels.[20][21] Without mitigation, increased energy demand and the extensive use of fossil fuels[22] may lead to global warming of around 4 °C.[23][24] With higher magnitudes of global warming, societies and ecosystems will likely encounter limits to how much they can adapt.[25]