Global warming is the ongoing rise of the average temperature of the Earth’s climate system and has been demonstrated by direct temperature measurements and by measurements of various effects of the warming. It is a major aspect of climate change which, in addition to rising global surface temperatures, also includes its effects, such as changes in precipitation. While there have been prehistoric periods of global warming, observed changes since the mid-20th century have been unprecedented in rate and scale.
Observed temperature from NASA vs the 1850–1900 average used by the IPCC as a pre-industrial baseline. The primary driver for increased global temperatures in the industrial era is human activity, with natural forces adding variability.
The Intergovernmental Panel on Climate Change (IPCC) concluded that “human influence on climate has been the dominant cause of observed warming since the mid-20th century”. These findings have been recognized by the national science academies of major nations and are not disputed by any scientific body of national or international standing. The largest human influence has been the emission of greenhouse gases, with over 90% of the impact from carbon dioxide and methane. Fossil fuel burning is the principal source of these gases, with agricultural emissions and deforestation also playing significant roles. Climate sensitivity to these gases is impacted by feedbacks, such as loss of snow cover, increased water vapour, and melting permafrost.
Land surfaces are heating faster than the ocean surface, leading to heat waves, wildfires, and the expansion of deserts. Increasing atmospheric energy and rates of evaporation are causing more intense storms and weather extremes, damaging infrastructure and agriculture. Surface temperature increases are greatest in the Arctic and have contributed to the retreat of glaciers, permafrost, and sea ice. Environmental impacts include the extinction or relocation of many species as their ecosystems change, most immediately in coral reefs, mountains, and the Arctic. Surface temperatures would stabilize and decline a little if emissions were cut off, but other impacts will continue for centuries, including rising sea levels from melting ice sheets, rising ocean temperatures, and ocean acidification from elevated levels of carbon dioxide.
Some effects of climate change
Heat wave intensification. Events like the June 2019 European heat wave are becoming more common.
Mitigation efforts to address global warming include the development and deployment of low carbon energy technologies, policies to reduce fossil fuel emissions, reforestation, forest preservation, as well as the development of potential climate engineering technologies. Societies and governments are also working to adapt to current and future global warming impacts, including improved coastline protection, better disaster management, and the development of more resistant crops.
Countries work together on climate change under the umbrella of the United Nations Framework Convention on Climate Change (UNFCCC), which has near-universal membership. The goal of the convention is to “prevent dangerous anthropogenic interference with the climate system”. The IPCC has stressed the need to keep global warming below 1.5 °C compared to pre-industrial levels in order to avoid some irreversible impacts. With current policies and pledges, global warming by the end of the century is expected to reach about 2.8 °C. At the current greenhouse gas (GHG) emission rate, the emissions budget for staying below 1.5 °C would be exhausted by 2028.