What is Global warming ?

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.

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.

The effects of global warming include rising sea levels, regional changes in precipitation, more frequent extreme weather events such as heat waves, and expansion of deserts. Surface temperature increases are greatest in the Arctic, which have contributed to the retreat of glaciers, permafrost, and sea ice. Overall, higher temperatures bring more rain and snowfall, but for some regions droughts and wildfires increase instead. Climate change threatens to diminish crop yields, harming food security, and rising sea levels may flood coastal infrastructure. Environmental impacts include the extinction or relocation of many species as their ecosystems change, most immediately in coral reefs, mountains, and the Arctic. The IPCC includes ocean acidification with these effects because it is caused by the increased CO2 levels that drive climate change. Some impacts, such as loss of snow cover, increased water vapour, and melting permafrost, cause feedback effects that further increase the rate of global warming.

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 ultimate goal of the convention is to "prevent dangerous anthropogenic interference with the climate system".Although the parties to the UNFCCC have agreed that deep cuts in emissions are required and that global warming should be limited to well below 2 °C (3.6 °F) in the Paris Agreement of 2016, the Earth's average surface temperature has already increased by about half this threshold. With current policies and pledges, global warming by the end of the century is expected to reach just over 2 °C to 4 °C, depending on how sensitive the climate is to emissions. The IPCC has stressed the need to keep global warming below 1.5 °C (2.7 °F) compared to pre-industrial levels in order to avoid irreversible impacts. At the current greenhouse gas (GHG) emission rate, the carbon budget for staying below 1.5 °C (2.7 °F) would be exhausted by 2028