Climate change includes anthropogenic global warming of greenhouse gases and its consequent large-scale changes in weather patterns. Although there have been periods of climate change in the past, since the mid-20th century humans have had an unprecedented impact on the Earth's climate system and caused change on a global scale.[ first]

The main contributor to climate warming is greenhouse gas emissions, of which more than 90% are carbon dioxide (CO2) and methane.[2] Burning fossil fuels (coal, petroleum, natural gas) for energy consumption is the main source of emissions, alongside emissions from agriculture, deforestation, and industrial production.[3] There is no reputable national or international scientific body that opposes the view that humans cause climate change.[4] Rates of temperature increase are accelerated or slowed down by climate feedback, such as the loss of light-reflecting snow and ice, increased water vapor (also a greenhouse gas), and changes in land and ocean carbon sinks.

Global warming, also referred to as climate change, is 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. Many of the observed changes since the 1950s are unprecedented in the instrumental temperature record which extends back to the mid-19th century, and in paleoclimate proxy records covering thousands of years.
Future climate change and associated impacts will differ from region to region. Anticipated effects include increasing global temperatures, rising sea levels, changing precipitation, and expansion of deserts in the subtropics. Warming is expected to be greater over land than over the oceans and greatest in the Arctic, with the continuing retreat of glaciers, permafrost and sea ice. Other likely changes include more frequent extreme weather events such as heat waves, droughts, heavy rainfall with floods 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 and the abandonment of populated areas due to rising sea levels. Because the climate system has a large “inertia” and greenhouse gases will remain in the atmosphere for a long time, many of these effects will persist for not only decades or centuries, but for tens of thousands of years to come.