The phenomenon of rising average air temperatures close to the surface of the Earth over the previous one to two centuries is known as global warming. Since the middle of the 20th century, climate scientists have accumulated extensive data on a variety of weather events, including temperatures, precipitation, and storms, as well as on factors that have an impact on climate, such as ocean currents and the chemical makeup of the atmosphere. These findings show that Earth's climate has changed on practically every possible period from the beginning of geologic time. And that human activities have increasingly affected the rate and scope of current climate change since the beginning of the Industrial Revolution.
The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by the United Nations to give voice to a growing conviction among most of the scientific community. The United Nations Environment Program (UNEP) and the World Meteorological Organization (WMO) (UNEP). The rise in global average surface temperature between 1850 and 2019 was best estimated to have increased by 1.07 °C (1.9 °F), according to the IPCC's Sixth Assessment Report (AR6), which was released in 2021. The majority of the warming over the second half of the 20th century could be attributed to human activities, according to an IPCC special report published in 2018. It noted that humans and their activities have been responsible for a worldwide average temperature increase between 0.8 and 1.2 °C (1.4 and 2.2 °F) since preindustrial times.
Five greenhouse gas emission scenarios were modelled for AR6 to provide a set of global climate forecasts that took into consideration future emissions, mitigation (severity reduction) strategies, and uncertainties in models predictions . The precise function of feedback mechanisms and the effects of the industrial pollutants known as aerosols, which may partially counterbalance warming, are some of the biggest uncertainties. According to the lowest-emissions scenario, which presupposed significant reductions in greenhouse gas emissions starting in 2015, the average global surface temperature would rise between 1.0 and 1.8 °C (1.8 and 3.2 °F) by 2100 in comparison to the average between 1850 and 1900. This range contrasted sharply with the highest-emissions scenario, which assumed that greenhouse gas emissions would continue to climb throughout the 21st century and projected that the mean surface temperature would rise between 3.3 and 5.7 °C (5.9 and 10.2 °F) by 2100. By assuming that emissions will stabilize by 2050, the intermediate-emissions scenario forecast an increase of between 2.1 and 3.5 °C (3.8 and 6.3 °F) by 2100, before gradually falling.
Many climate experts concur that if the global average temperature increased by more than 2 °C (3.6 °F) in such a short period of time, serious societal, economic, and ecological harm would follow. Increased extinction rates of several plant and animal species, changes in agricultural practices, and increasing sea levels are only a few examples of this kind of harm. In accordance with the Paris Agreement, which aims to assist nations in limiting global warming to 1.5 °C (2.7 °F) above preindustrial levels in order to avoid the worst predicted effects, all national governments. With the exception of a few, had started the process of implementing carbon reduction plans by 2015. Considering that the 2018 The authors of the AR6 study projected that this barrier will be achieved by 2041 at the latest. A special analysis indicated that if carbon emissions keep increasing at the current rate, the average near-surface air temperature would rise by 1.5 °C anytime between 2030 and 2052.
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