Global warming and climate change can both refer to the observed century-scale rise in the average temperature of the Earth's climate system and its related effects. Multiple lines of scientific evidence show that the climate system is warming. More than 90% of the additional energy stored in the climate system since 1970 has gone into ocean warming; the remainder has melted ice, and warmed the continents and atmosphere. Many of the observed changes since the 1950s are unprecedented over decades to millennia.
Scientific understanding of global warming has been increasing. In its fifth assessment in 2014 the Intergovernmental Panel on Climate Change reported that scientists were more than 95% certain that most of global warming is caused by increasing concentrations of greenhouse gases and other human activities. Climate model projections summarized in AR5 indicated that during the 21st century the global surface temperature is likely to rise a further for their lowest emissions scenario using stringent mitigation and for their highest. These findings have been recognized by the national science academies of the major industrialized nations.
Future climate change and associated impacts will be different from region to region around the globe. The effects of an increase in global temperature include a rise in sea levels and a change in the amount and pattern of precipitation, as well as a probable expansion of subtropical deserts. Warming is expected to be strongest in the Arctic, with the continuing retreat of glaciers, permafrost and sea ice. Other likely effects of the warming include more frequent extreme weather events including heat waves, droughts, heavy rainfall, and heavy snowfall; ocean acidification; and species extinctions due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields