Climate Change Evidence
Observations confirm that climate change is happening, and that extreme weather is becoming the new normal. In addition to the steady rise in air temperature, ocean heat content, and sea level, there has been a decline in glacier mass, increase in permafrost thaw, and ocean acidification. Quasi-regular oscillations, such as El Niños and La Niñas, that are internal to the climate system, modulate these trends, but do not alter the direction of the changes. Accompanying circulation changes lead to regional variations in weather and weather extremes. Precipitation patterns shift; rain rates intensify; and droughts last longer. Hurricanes and other tropical storms are also more intense. The impacts of these changes in the mean and variance of climate are evident in terrestrial, riverine, and marine ecosystems.