The greenhouse effect is a natural process responsible for keeping the earth at the temperature needed to sustain life. Acting just like the glass walls of a greenhouse, gases like carbon dioxide, methane, and nitrous oxide trap the sun’s heat in the atmosphere and prevent it from escaping into space.

About half of the sun’s radiation that travels toward the earth never makes it to the earth’s surface. Clouds and the atmosphere reflect about one-third of the radiation back toward the sun, and they also absorb another 20 percent. The rest of the radiation—about 50 percent—reaches the earth, where it is absorbed by oceans and land. This keeps the earth warm and sustains plant, animal, and human life. The earth also releases heat back toward space. Some of this heat passes through the atmosphere, but most of it is captured and retained by greenhouse gases before it can escape. This is the mechanism that keeps the earth warm.

Normally, the greenhouse effect keeps the earth just warm enough to sustain life. Scientists say that without the greenhouse effect, the average temperature of the earth would drop to as low as −18˚C (0˚F), compared to the twentieth-century average of 14˚C (57˚F). 

Enhanced greenhouse effect

The greenhouse effect has supported life on the earth for millions of years. Today, however, the greenhouse effect is growing stronger as human activities such as deforestation and fossil fuel use release more and more greenhouse gases into the atmosphere. This traps greater amounts of the sun’s radiation, which contributes to rising temperatures, also known as global warming.

In 2018, the United States alone emitted 14.7 trillion pounds of greenhouse gases. For reference, that weighs more than 20,000 Empire State Buildings—and the United States is not even the biggest emitter. In 2019, China emitted nearly twice as much greenhouse gas as the United States did that year.

Global Historical Greenhouse Gas Emissions

Due in large part to this enhanced greenhouse effect, the world today is more than 1˚C (1.8˚F) warmer than it was in the nineteenth century. While 1˚C may seem hardly noticeable on a sunny day, countries are already seeing the severe effects of planet-wide warming at this level. Heat waves are lasting longer, crop yields are shrinking, and rising sea levels are threatening coastal areas.

Scientists warn that human activity will likely raise global temperatures to 1.5˚C (2.7˚F) above nineteenth-century averages by 2050, and, without a significant reduction in greenhouse gas emissions, global temperatures could reach 2˚C (3.6˚F). Should this happen, the results would be catastrophic. And, in some cases—such as species going extinct, coral reefs dying, and sea levels rising—the effects would be irreversible.

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