What is the greenhouse effect?

Added on 16 January 2020

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Earth is said to be in a perfect "Goldilocks zone" away from the sun (not too cold, and not too hot), which enables life to thrive on the planet's surface. But Earth's balmy temperatures would not be possible without the greenhouse effect, which traps solar energy on Earth's surface and keeps the planet warm.

The greenhouse effect arises from Earth's atmosphere. Visible light from the sun, as well as invisible ultraviolet and infrared wavelengths, can penetrate the gaseous layer that blankets our world. Roughly 70% of these energetic rays are absorbed by Earth's oceans, land and atmosphere, while the remaining 30% are immediately reflected back into space, according to NASA Earth Observatory.

As the planet's surface heats up, it releases some of the infrared energy that it had absorbed, but that energy doesn't make it back out of Earth's gaseous atmosphere. Instead of shooting back out into space, the infrared energy closely hugs our planet and, therefore, raises Earth's overall temperature. This is similar to how a human-built glass greenhouse works, trapping heat from the sun to keep plants warm in the winter.

Without an atmosphere, our world would be as cold as the lifeless moon, which has an average temperature of minus 243 degrees Fahrenheit (minus 153 degrees Celsius) on its far side. Because of the greenhouse effect, Earth maintains an overall average temperature of around 59 F (15 C).

Greenhouse gases and climate change

Greenhouse gases include several naturally occurring molecules like water vapor, carbon dioxide, methane, nitrous oxide and ozone as well as several manufactured ones, like chlorofluorocarbons, according to the Australian Department of the Environment and Energy. Over the past century or so, human activities such as the burning of fossil fuels, intensive agriculture, livestock raising and land clearing have dramatically increased the concentrations of greenhouse gases in Earth's atmosphere, to the point where it's changing our planet's climate.

Since the middle of the 20th century, greenhouse gases produced by humans have become the most significant driver of climate change, according to the U.S. Environmental Protection Agency. Carbon dioxide levels in the atmosphere have increased by more than 40% since the start of the Industrial Revolution, from roughly 280 parts per million (ppm) to more than 400 ppm today.

The last time Earth's atmosphere had similar carbon dioxide concentrations was during the Pliocene epoch, between 3 million and 5 million years ago, according to the Scripps Institution of Oceanography in San Diego. That's at least 2.8 million years before modern humans roamed the planet. Fossils show that forests grew in the Canadian Arctic during the Pliocene, and savannas and woodlands spread over what's now the Sahara desert.

While some people still doubt the reality of human-induced climate change, the evidence for it is overwhelming. Since the 1850s, the average global surface-air temperature has risen by around 1.4 F (0.8 C), and ocean temperatures are now at the highest levels ever recorded.

Increases in greenhouse gases in the coming decades are expected to harm human health, increase droughts, contribute to sea level rise, and decrease national security and economic well-being throughout the world.

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Photo by Richard Gatley on Unsplash

Source: Space