Global warming, an extremely simple phenomenon

That carbon dioxide and other greenhouse gases trap heat is something scientists have known for more than 150 years. The basic concept of climate change is so simple that any child can replicate the physical and chemical aspects of that phenomenon.

Why and how it happens is a bit more complicated.


EDITOR’S NOTE: This dispatch is part of a series on the most serious problems associated with climate change, the role of science, the impact of global warming and what is being done to deal with this issue.


Just as the greenhouse effect traps heat and a blanket keeps you warm, carbon dioxide, methane and other gases — called greenhouse gases — trap heat from the sun that would normally bounce back and go off into space. The blanket and the greenhouse may not be perfect analogies, but they do give a good idea of ​​what’s going on, according to University of Pennsylvania climate scientist Michael Mann.

Without the greenhouse effect, scientists say, the Earth would freeze. The greenhouse effect — a natural phenomenon on steroids when met with carbon pollution — is responsible for the conditions that make life possible on Earth.

In excess, however, a good thing can stop being good. Scientists cite the runaway greenhouse effect of Venus as an example. In fact, James Hanson, NASA’s foremost climate expert, often considered the “Father of Climate Change,” was studying precisely what was happening on Venus before focusing on his own planet and warning that the same thing could happen here. same, albeit on a smaller scale.

The sun’s heat penetrates the atmosphere and bounces back, returning as infrared radiation, with another wavelength. If you put your hand on a dark rock on a sunny day, you will feel the heat given off by the Earth. The greenhouse effect occurs when heat tries to escape from the Earth and some of it is trapped by different chemicals in the atmosphere, such as water vapour, carbon dioxide and methane.

Around 1820, the French mathematician and scientist Joseph Fourier noticed that there is something in space that makes the Earth hotter than a rock: Our atmosphere.

“It works as a barrier that stops the terrestrial rays and makes the Earth’s temperature rise,” said the Irish physicist John Tyndall in 1862, the year in which he identified water vapor and carbon dioxide as greenhouse gases that trap the heat. In 1896, the Swedish chemist Svante Arrhenius went further and calculated that changes in carbon dioxide can affect the climate.

Numerous experiments, including some at home, show this phenomenon: You need two soda bottles, some carbon dioxide, air, a good light lamp or flame, and a thermometer. Heat one bottle containing normal air and one containing carbon dioxide using the same method. Measure their temperatures, and after a while, the one with carbon dioxide will have gotten much hotter.

This is because the geometry, spin and vibration of carbon molecules block the wavelength of light trying to escape from Earth, according to Mann. It is a different wavelength than the light that goes towards the sun.

Greenhouse gases, especially carbon dioxide, “correspond to sort of gaps” in the light spectrum that would allow heat to escape, but block those exits, Mann said.

Now, if there are natural greenhouse gases, what do small changes in carbon dioxide matter?

Carbon dioxide levels are about 240 parts per million, compared to 280 before the industrial revolution. Since then, the Earth has warmed by about 1.1 degrees Celsius (2 Fahrenheit).

Mann proposes another home experiment. Drop a few drops of water into a bowl and then a much smaller amount of black ink.

“The water will turn black,” Mann said. “Small concentrations of certain chemicals can have a big impact. Like with cyanide. That is why we avoid even the smallest concentrations of cyanide.”

“The experiment with the ink gives an idea of ​​the enormous impact that a small number of very powerful molecules can have… That is what is happening now.”


Seth Borenstein is on Twitter, a @borenbears


The Associated Press’ climate and environment coverage is supported by several private foundations. The HPD is solely responsible for the content.

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