Global warming

Global warming is long-term rise in the average temperature of the Earth's climate system, an aspect of current climate change shown by temperature measurements and by multiple effects of the warming, though there were also much earlier periods of global warming. The term commonly refers to the mainly human-caused observed increase in global surface temperatures and its projected continuation. In this context the terms global warming and climate change are commonly used interchangeably, but climate change includes both global warming and its effects, such as changes to precipitation and impacts that differ by region. Many observed changes since mid 20th century have been unprecedented compared to records over decades to thousands of years. In 2013, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded, 'It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.' The largest human influence has been the emission of greenhouse gases such as carbon dioxide, methane, and nitrous oxide. Climate model projections summarized in the report indicated that during the 21st century, the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) in a moderate scenario, or as much as 2.6 to 4.8 °C (4.7 to 8.6 °F) in an extreme scenario, depending on the rate of future greenhouse gas emissions and on climate feedback effects. These findings have been recognized by the national science academies of the major industrialized nations and are not disputed by any scientific body of national or international standing. 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, with the continuing 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 costal infrastructure and eventually force the abandonment of many coastal cities. Environmental impacts include the extinction or relocation of many species as their ecosystems change, most immediately the environments of coral reefs, mountains, and the Arctic. Because the climate system has a large 'inertia' and greenhouse gases persist in the atmosphere, climatic changes and their effects will intensify for many centuries even if further greenhouse emissions stop. Globally, a majority of people consider global warming a serious or very serious issue. Possible societal responses to global warming include mitigation by emissions reduction, adaptation to its effects, and possible future climate engineering. Every country in the world is a party to the United Nations Framework Convention on Climate Change (UNFCCC), whose ultimate objective is to prevent dangerous anthropogenic climate change. 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), the Earth's average surface temperature has already increased by about half this threshold. with efforts made to limit warming to 1.5 °C (2.7 °F). Some scientists call into question climate adaptation feasibility, with higher emissions scenarios, or the two degree temperature target. Multiple independently produced datasets confirm that the 2009-2018 decade was 0.93 ± 0.07 °C warmer than the pre-industrial baseline (1850-1900). Currently, surface temperature rise with about 0.2 °C degrees per decade. Since 1950, the number of cold days and nights have decreased, and the number of warm days and night have increased. Historical patterns of warming and cooling like the Medieval Climate Anomaly and the Little Ice Age were not as synchronous as current warming, but may have reached temperatures as high as late-20th century in a limited set of regions. Although the increase of the average near-surface atmospheric temperature is commonly used to track global warming, over 90% of the additional energy stored in the climate system over the last 50 years is in warmer ocean water. The rest has melted ice and warmed the continents and the atmosphere. Melting ice (including Arctic sea ice, ice sheets and glaciers) and warming of the continents and atmosphere account for the remainder of the change in energy.' The warming evident in the instrumental temperature record is consistent with a wide range of observations, documented by many independent scientific groups, for example in most continental regions the frequency and intensity of heavy precipitation has increased. Further examples include sea level rise, widespread melting of snow and land ice, increased heat content of the oceans, increased humidity, and the earlier timing of spring events, such as the flowering of plants. Global warming refers to global averages, with the amount of warming varying by region. Since 1979, global average land temperatures have increased about twice as fast as global average ocean temperatures. This is due to the larger heat capacity of the oceans and because oceans lose more heat by evaporation. Where greenhouse gas emissions occur does not impact the location of warming because the major greenhouse gases persist long enough to diffuse across the planet, although localized black carbon deposits on snow and ice do contribute to Arctic warming.