Climate change consists of two main problems: (1) accelerated global warming caused by man-made emissions of greenhouse gases, especially carbon dioxide, and (2) the disruptive effects of global warming on the earth’s climate and human societies.
Science has made enormous progress in understanding climate change. We have a strong body of evidence that earth is warming. Recent warming is largely caused by human activities. Global warming is associated with a broad spectrum of other climate changes and impacts, including rising sea levels, increases in intense rainfall events, more frequent and intense heat waves, increases in number and intensity of wildfires, decreases in snow cover and sea ice, and ocean acidification.
CO2 levels spiked in the late 1800s and have continued to rise.
The earth naturally goes through a cycle of warming and cooling, but since the late 1800s, the warming cycle has sped up. In particular, accelerated warming is linked to human-generated emissions of carbon dioxide, a primary contributor to global warming. The presence in the atmosphere of carbon dioxide and other gases helps to trap sunlight and keep the earth warm. This is known as the greenhouse effect, which is why these heat-trapping gases are called greenhouse gases (GHGs). For more than 400,000 years, carbon dioxide (CO2) maintained a relatively stable concentration in the atmosphere. However, concentrations of greenhouse gases, and in particular, carbon dioxide, have risen dramatically since the mid-1800s – soon after human societies began to burn fossil fuels, including coal, oil, and gas, to power the engines of industrialization. The result has been a dramatically more rapid warming of the air and oceans.
Even small increases in temperature can affect climate. Shrinking glaciers, sea level rise, and changes to the air and ocean currents are all the result of global warming and are contributing to what we are already seeing: more frequent coastal flooding and extreme weather events across the country, migrations of some species including disease-carrying insects, and mass extinctions around the world.