Climate Change

In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The current rise in global average temperature is more rapid than previous changes, and is primarily caused by humans burning fossil fuels.[2][3] Fossil fuel use, deforestation, and some agricultural and industrial practices add to greenhouse gases, notably carbon dioxide and methane.[4] Greenhouse gases absorb some of the heat that the Earth radiates after it warms from sunlight. Larger amounts of these gases trap more heat in Earth's lower atmosphere, causing global warming.

Climate change is causing a range of increasing impacts on the environment. Deserts are expanding, while heat waves and wildfires are becoming more common.[5] Amplified warming in the Arctic has contributed to melting permafrost, glacial retreat and sea ice loss.[6][7] Higher temperatures are also causing more intense storms, droughts, and other weather extremes.[8] Rapid environmental change in mountains, coral reefs, and the Arctic is forcing many species to relocate or become extinct.[9] Even if efforts to minimise future warming are successful, some effects will continue for centuries. These include ocean heating, ocean acidification and sea level rise.[10]

Climate change threatens people with increased flooding, extreme heat, increased food and water scarcity, more disease, and economic loss. Human migration and conflict can also be a result.[11] The World Health Organization (WHO) calls climate change the greatest threat to global health in the 21st century.[12] Societies and ecosystems will experience more severe risks without action to limit warming.[13] Adapting to climate change through efforts like flood control measures or drought-resistant crops partially reduces climate change risks, although some limits to adaptation have already been reached.[14] Poorer communities are responsible for a small share of global emissions, yet have the least ability to adapt and are most vulnerable to climate change.[15][16]

Bobcat Fire in Monrovia, CA, September 10, 2020

Bleached colony of Acropora coral

A dry lakebed in California, which is experiencing its worst megadrought in 1,200 years.[17]

Some effects of climate change: Wildfire intensified by heat and drought, bleaching of coral caused by marine heatwaves, and worsening droughts compromising water supplies.

Many climate change impacts are already felt at the current 1.2 °C (2.2 °F) level of warming. Additional warming will increase these impacts and can trigger tipping points, such as the melting of the Greenland ice sheet.[18] Under the 2015 Paris Agreement, nations collectively agreed to keep warming "well under 2 °C". However, with pledges made under the Agreement, global warming would still reach about 2.7 °C (4.9 °F) by the end of the century.[19] Limiting warming to 1.5 °C will require halving emissions by 2030 and achieving net-zero emissions by 2050.[20]

Reducing emissions requires reducing energy use and generating electricity from low-carbon sources rather than burning fossil fuels. This change includes phasing out coal and natural gas fired power plants while vastly increasing electricity generated from wind, solar, and nuclear power. This electricity will need to replace fossil fuels for powering transportation, heating buildings, and operating industrial facilities.[21][22] Carbon can also be removed from the atmosphere, for instance by increasing forest cover and farming with methods that capture carbon in soil.[23]

Terminology

Before the 1980s, when it was unclear whether the warming effect of increased greenhouse gases was stronger than the cooling effect of airborne particulates in air pollution, scientists used the term inadvertent climate modification to refer to human impacts on the climate.[24]

In the 1980s, the terms global warming and climate change became more common. Though the two terms are sometimes used interchangeably,[25] scientifically, global warming refers only to increased surface warming, while climate change describes the totality of changes to Earth's climate system.[24] Global warming—used as early as 1975[26]—became the more popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate.[27] Since the 2000s, climate change has increased in usage.[28] Climate change can also refer more broadly to both human-caused changes or natural changes throughout Earth's history.[29]

Various scientists, politicians and media now use the terms climate crisis or climate emergency to talk about climate change, and global heating instead of global warming.[30]