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Scientific evidence paints a clear picture: Climate change is happening, it is caused in large part by human activity, and it will have many serious and potentially damaging effects in the decades ahead. The primary cause is greenhouse gas emissions from cars, power plants and other human-made sources—rather than natural variations in climate. These emissions include carbon dioxide — the main greenhouse gas — which has reached a concentration level in our atmosphere that the Earth hasn’t seen for more than 400,000 years. Greenhouse gases act like a blanket, trapping the sun’s warmth near the earth’s surface, and affecting the planet’s climate system.
While we know much about the climate, scientists are still studying its effects and learning more every day. The climate system is very complex, and there are a lot of unknowns and uncertainties. However, through centuries of studies and experiments, we’ve been able to put together a strong picture of how the system works.
The Greenhouse Effect
The picture below shows the greenhouse effect. Light from the sun passes through the atmosphere and is absorbed by the Earth’s surface, warming it. Greenhouse gases, like carbon dioxide, act like a blanket, trapping heat near the surface and raising the temperature. It is a natural process that warms the planet. But human activities are increasing the amount of greenhouse gases and trapping more heat.
Greenhouse gases stay in the atmosphere for a long time. Although plants and the ocean absorb carbon dioxide, they can’t keep up with all the extra carbon dioxide that people have been releasing. So the amount of carbon dioxide in the atmosphere has been increasing over time.
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https://www.c2es.org/site/assets/uploads/2017/10/Observed-Climate.jpg
