To understand global warming, we first must understand the greenhouse effect.

The greenhouse effect is a natural occurrence which keeps the lower 10 miles of our atmosphere livable.

Sunlight passes through the atmosphere. Light-colored surfaces, such as clouds or ice caps, radiate some heat back into space. But most warms the planet’s surface. The Earth then radiates some heat back into the atmosphere.

Human activity — such as burning fossil fuels — causes more greenhouse gases to build up in the atmosphere. As the atmosphere “thickens” with more greenhouse gases, more heat is held in.

Fossil fuels such as oil, coal and natural gas are high in carbon and, when burned, produce major amounts of carbon dioxide or CO₂. A single gallon of gasoline, when burned, puts 19 pounds of carbon dioxide into the atmosphere.

One way to think of it is like a car’s windshield. The sun’s energy passes through the windshield. The heat is trapped inside the car and cannot pass back out, causing the inside of the car to heat up.

So if we need the greenhouse effect to live, why is global warming damaging?

For millions of years, the amount of greenhouse gases in the atmosphere kept the planet’s temperature within a comfortable range for humans and other living creatures.

Human industries, transportation and cities are now sizable enough to alter the atmosphere’s chemistry.

The more CO₂ in the air, the warmer the temperature.

This graph shows CO₂ (the blue line) and temperature in Celsius (the red line). As CO₂ rises, so does temperature.

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