Global warming is the increase in the average temperature of the Earth’s near-surface air and oceans in recent decades and its projected continuation. Natural phenomena such as solar variation combined with volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect from 1950 onward. These basic conclusions have been endorsed by at least 30 scientific society and academies of science, including all of the national academies of science of the major industrialized countries.
While individual scientists have voiced disagreement with some of the main conclusions of the IPCC, the overwhelming majority of scientists working on climate change are in agreement with them. Climate model projections summarized by the IPCC indicate that average global surface temperature will likely rise a further 1.1 to 6.4 °C during the 21st century. The range of values results from the use of differing scenarios of future greenhouse gas emissions as well as models with differing climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a millennium even if greenhouse gas levels are stabilized. The delay in reaching equilibrium is a result of the large heat capacity of the oceans. Increasing global temperatures will cause sea level to rise, and is expected to increase the intensity of extreme weather events and to change the amount and pattern of precipitation.
Other effects of global warming include changes in agricultural yield, trade routes, glacier retreats, species extinctions and increases in the ranges of disease vectors. Remaining scientific uncertainties include the amount of warming expected in the future, and how warming and related changes will vary from region to region around the globe. There is ongoing political and public debate worldwide regarding what, if any, action should be taken to reduce or reverse future warming or to adapt to it’s.