Greenhouse gases

There are several different gases in the Earth's atmosphere. Some of these gases make the atmosphere function a bit like the glass walls of a greenhouse, increasing the temperature of the Earth. Those gases are called greenhouse gases. Different greenhouse gases have different abilities to contain the heat - they have different warming potentials. This means that a greenhouse gas that is only present in tiny amounts... ...

can have a stronger effect on global warming than another, more abundant gas. Other greenhouse gases might be very weak... ... but there is so much of them, that their total effect is large. That's the case with the gas mentioned the most in connection with global warming - carbon dioxide. It's a weak greenhouse gas, but there is a lot of it.

And the amount is increasing fast. In order to compare the effect of different greenhouse gases, they are usually converted to the equivalent amount of carbon dioxide that would give the same effect on the climate. The strongest greenhouse gas that we know of, sulphur hexafluoride, has a warming potential that is twenty-four thousand times that of carbon dioxide. That means that only one kilogram of that gas in the atmosphere, will heat the Earth as much as 24 tonnes of carbon dioxide! It's a good thing there are only tiny amounts of it in the atmosphere.

One group of greenhouse gases are the freons. Their warming potentials are between five thousand and fifteen thousand times higher than that of carbon dioxide. The emissions of freons have gone down a lot since they peaked in the 1980s, but the molecules will remain in the atmosphere for hundreds of years. A greenhouse gas that exists naturally is methane. It is released by decomposing plants in wetlands and swamps... ...

from extraction of fossil fuels... ... and a fifth of all methane emissions actually come from ... flatulent cows. While methane is a 'weak' greenhouse gas compared to freons - only about twenty times as strong as carbon dioxide - there is a lot of it. Also, the amount of methane in the atmosphere is increasing, as we drill for more fossil fuels, and breed more flatulent livestock.

Then there's one special greenhouse gas, not usually mentioned with the others... even though it is by far the most abundant: exceeding carbon dioxide by about fifty times more! What secret substance is that? Actually, it's ordinary water vapor! Water vapor is a greenhouse gas, but what makes it special is that it only stays in the atmosphere for a few days... ...

before it falls to the ground as rain or snow. When water molecules form water droplets or ice crystals - clouds that is - they also help to cool the Earth. Clouds reflect some of the solar radiation, before it penetrates too far into the atmosphere. So, how much do these gases affect the climate, converted to the equivalent amount of carbon dioxide? Let's start with the actual amount of carbon dioxide, 400 millionths of all the gas in the atmosphere, or 400 parts per million, ppm.

Then we add the effect of the other greenhouse gases, excluding water vapor. In total, they equal about 80 ppm of carbon dioxide. It's as if 480 millionths of the atmosphere was carbon dioxide, instead of only 400. And that number keeps increasing. So while carbon dioxide might be one of the weakest greenhouse gases...

The large amount of it means that it is still the one that has the strongest effect on the climate.