Nature
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Greenhouse gases cause global warming – it’s a fact that we’ve all seen or heard at some point, perhaps more often than usual recently with climate conferences and elections. But how exactly do they have this effect?
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.The greenhouse effect
One of the simpler ways we can answer that question is by thinking about how a greenhouse works. The glass that it’s made from allows some energy from sunlight to pass through, warming up the inside of the greenhouse, but doesn’t let it back out again.
Earth has its own version of this called, funnily enough, the greenhouse effect. It works in a similar but slightly more complex way, where greenhouse gases like carbon dioxide and water vapor act a bit like the glass of a greenhouse.
Around 48 percent of the solar energy that reaches Earth is absorbed by the planet’s surface, which is then reradiated as infrared. Like delicious greenhouse tomatoes, we feel this infrared as heat.
The waves of infrared then make their way up to the atmosphere, but wait – greenhouse gas molecules are able to absorb it. That’s down to “their geometry and their composition,” climate scientist Jason Smerdon explained in an article that forms part of Columbia Climate School’s “You Asked” series.
It’s useful here to compare greenhouse gases with other molecules present in the atmosphere. Oxygen and nitrogen molecules, for example, are also there, but they’re only made up of two atoms, both the same element – that makes them pretty inflexible and thus unable to absorb a bunch of different wavelengths.
Greenhouse gases like carbon dioxide, on the other hand, have more than one element and more than two atoms, giving them the freedom to cut a whole lot more shapes and as a result, absorb a much greater span of wavelengths that includes infrared.
Absorbing all that energy causes the molecules to vibrate and then send the infrared back out into the atmosphere; about half of it will make it to space, but the remaining half stays on Earth, warming it up.
Greenhouse gone wrong
The greenhouse effect is one of the reasons why you’re reading this article right now – it helps to keep the Earth toasty enough to support life. If we didn’t have the greenhouse effect, then the planet would be a rather non-balmy -20°C (-4°F).
You can, however, have too much of a good thing. The concentrations of greenhouse gases in Earth’s atmosphere are far greater than they are naturally, which in turn exacerbates the greenhouse effect. As a result, the planet’s climate has been altered, seeing us smash an unprecedented number of climate records.
Significant greenhouse gas emissions also have effects other than warming; carbon dioxide, for example, can make its way down from the atmosphere and dissolve into seawater. This has caused ocean acidification, which comes with its own set of problems.
