Climate change refers to global warming plus the large-scale shifts in weather patterns caused by the rising temperatures, driven by humans since the Industrial Revolution. While there have been previous periods of climatic change, observed changes since the mid-20th century have been unprecedented in rate and scale.
The human cause of climate change is not disputed by any scientific body of national or international standing. The largest influence has been the emission of greenhouse gases , with over 90% of the impact coming from carbon dioxide and methane. Fossil fuel burning is the main source of these gases; agricultural emissions and deforestation are also important. Temperature rise is accelerated or tempered by climate feedbacks, such as loss of snow and ice cover, increased water vapour, and changes to land and ocean carbon sinks.
Land surfaces are heating faster than the ocean surfaces, 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.
The Intergovernmental Panel on Climate Change (IPCC) assesses the scientific, technical and socioeconomic information relevant for the understanding of the risk of human-induced climate change. The IPCC has told policy makers that there is much greater risk to human and natural systems if warming goes above 1.5 °C (2.7 °F) compared to pre-industrial levels. Countries work together to "prevent dangerous anthropogenic interference with the climate system" under the umbrella of the United Nations Framework Convention on Climate Change (UNFCCC). Under the Paris Agreement , nations are making climate pledges to reduce greenhouse gas (GHG) emissions, but those promises — assuming nations follow through — would still allow global warming to reach about 2.8 °C (5.0 °F) by 2100. To limit warming to 1.5 °C (2.7 °F), methane emissions would need to decrease to near-zero levels and carbon dioxide emissions would need to reach net-zero by the year 2050.
Mitigation efforts include the development and deployment of low-carbon energy technologies, enhanced energy efficiency, 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 through improved coastline protection, better disaster management, and the development of more resistant crops.