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Greenhouse gas concentrations have increased rapidly, and human activities are the primary cause. The result is a worldwide, unnatural warming that's driving other changes in our environment.
Sunlight passes through the atmosphere. When it strikes surfaces or gases that can absorb it, heat is emitted. You can feel the effect directly by holding your hand over dark asphalt or your car’s hood on a warm, sunny day. The surface feels hot. It is re-emitting the energy it received from the sun.
Greenhouse gases in the atmosphere behave in a similar way. They absorb heat energy rising from the Earth’s surface and re-emit some of that heat back down towards the ground. The effect is similar to how an actual greenhouse works, thus the name. Greenhouse gases act like the windows of a greenhouse, allowing light through but trapping heat inside.
Greenhouse gases surround the Earth like a blanket. As we use burn more coal, natural gas, and oil, the blanket becomes excessively thick, dense, and less likely to allow heat to escape. Heat gets trapped inside the blanket of greenhouse gases and the Earth becomes too warm.
Greenhouse gases like carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4), trap heat in the atmosphere. With higher-than-natural concentrations, they lead to unnatural warming.
Since the Industrial Revolution, atmospheric carbon dioxide (CO2) concentration has increased by about 40% to above 400 parts per million (ppm).
Current CO2 levels are 100 ppm higher than at any time in the last million years and likely higher than any time in the last 25 million years. The dramatic increase of 100 ppm over 120 years is something that normally takes 5,000 to 20,000 years.
It’s this rapid, abrupt change that has massively disrupted Earth’s natural heat energy balance. It's leading to changes in temperature and chemistry that are happening much faster than natural ecosystems and built infrastructure can adapt to without help.