The Earth’s climate is constantly changing. Over the last 250 years, Earth’s average surface temperature has risen by about 1 degree Celsius (1.9 degrees Fahrenheit).
Climate change is the slow, cumulative effect of human activities that alters the natural balance of incoming and outgoing solar energy. Some of the incoming energy is reflected back into space by bright surfaces like ice and clouds, and some of it is absorbed by land or ocean water, air, and other parts of the atmosphere, where it re-emits heat back to the environment in longwave radiation known as infrared radiation. The atmosphere also contains a number of gases that absorb or reflect heat, the most significant being carbon dioxide and several other human-made gases with similar effects.
The concentrations of these gases, which are released into the atmosphere by burning fossil fuels, are largely responsible for recent warming. Trends in global surface temperatures, sea level rise, air temperature, arctic sea ice and snow cover loss, the depth of seasonal permafrost thaw, and other climate variables are consistent with global warming driven by human emissions.
We can reduce emissions to prevent the worst impacts and limit warming to a safer level. Taking action now can avoid tens of thousands of deaths and billions in damages from floods, drought, wildfires, and other hazards. This work will benefit everyone, but especially low-income communities and communities of color, which have contributed least to the problem and are most closely dependent on a healthy, functioning natural world for food, water, and income.
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