Effects of global warming

The effects of global warming are the environmental and social changes caused (directly or indirectly) by human emissions of greenhouse gases. There is a scientific consensus that climate change is occurring, and that human activities are the primary driver. Many impacts of climate change have already been observed, including extreme weather events, glacier retreat, changes in the timing of seasonal events (e.g., earlier flowering of plants), changes in agricultural productivity, sea level rise, and declines in Arctic sea ice extent. The physical effects of future climate change depends on the extent of prevention efforts (i.e., reducing greenhouse gas emissions). The social impact of climate changes will be further affected by our efforts to prepare for changes that do occur. Geoengineering is another policy option, although there are uncertainties regarding its effectiveness and little is known about potential side effects. Near-term climate change policies could significantly affect long-term climate change impacts. Stringent mitigation policies might be able to limit global warming (in 2100) to around 2 °C or below, relative to pre-industrial levels. Without mitigation, increased energy demand and extensive use of fossil fuels might lead to global warming of around 4 °C. Higher magnitudes of global warming would be more difficult to adapt to, and would increase the risk of negative impacts. This article doesn't cover ocean acidification, which is directly caused by atmospheric carbon dioxide, not the warming of global warming itself. In this article, 'climate change' means a change in climate that persists over a sustained period of time. The World Meteorological Organization defines this time period as 30 years. Examples of climate change include increases in global surface temperature (global warming), changes in rainfall patterns, and changes in the frequency of extreme weather events. Changes in climate may be due to natural causes, e.g., changes in the sun's output, or due to human activities, e.g., changing the composition of the atmosphere. Any human-induced changes in climate will occur against a background of natural climatic variations and of variations in human activity such as population growth on shores or in arid areas which increase or decrease climate vulnerability. Also, the term 'anthropogenic forcing' refers to the influence exerted on a habitat or chemical environment by humans, as opposed to a natural process. 'Detection' is the process of demonstrating that climate has changed in some defined statistical sense, without providing a reason for that change. Detection does not imply attribution of the detected change to a particular cause. 'Attribution' of causes of climate change is the process of establishing the most likely causes for the detected change with some defined level of confidence. Detection and attribution may also be applied to observed changes in physical, ecological and social systems. This article discusses the potential impact of climate change depending on different levels of future global warming. This way of describing impacts has been used in the IPCC (Intergovernmental Panel on Climate Change) Assessment Reports on climate change. The instrumental temperature record shows global warming of around 0.6 °C during the 20th century. More recent studies show that the 20th century was the hottest period recorded on Earth in the last 2,000 years.