Watch the Earth breathe for one year

I like to think the French physicist Joseph Fourier appreciated the irony that he, of all people, was the one who discovered the greenhouse effect. Here was a man who kept his Paris apartment tropically hot, who wrapped himself in blankets and wore an overcoat even in summer — a man who, in short, usually felt cold. Yet his calculations showed that Earth was in fact far warmer than it ought to be.

It was the 1820s. Fourier, in his fifties and already a renowned scientist, decided to estimate the Earth’s temperature purely from scientific principles. He took the amount of sunlight that warms the Earth and then subtracted off the amount of energy the planet radiates back to space. He came up with a temperature some 30 degrees Celsius — more than 50 degrees Fahrenheit — colder than our actual planet.

Fourier knew the Earth was retaining extra heat, but he didn’t know how. It fell to later generations of scientists to reveal that certain gases, such as carbon dioxide and water vapor, block some of the infrared light that the planet radiates back to space. When these gases build up in the atmosphere, Earth temporarily emits less energy than it absorbs from the sun. To restore the energy balance, the planet warms.

Greenhouse gases absorb infrared light, which is invisible to the human eye but just as real as the light we can see. If your eyes could perceive light at the low wavelength of 6.3 microns, the air would look black with water vapor. At 7.5 microns, methane would obstruct your view. And at the 15-micron wavelength, you would see carbon dioxide.

That’s how NASA’s satellites detect greenhouse gases as they build up in our atmosphere, year after year. Let’s take another tour of the Earth to see how CO2 accumulates over the course of 2021, the most recent year for which NASA makes the data available.

Jan. 1

CO2 emitted by:

Fossil fuels

Fire

Land

Ocean

Loading data...

Explore

Using satellites, land-based monitoring stations and a physical model of the atmosphere, scientists identified four contributors to atmospheric CO2: combustion of fossil fuels, burning wood and other biomass, land ecosystems, and the ocean.

1 / 5

Most of the CO2 added to the atmosphere comes from humans burning fossil fuels like coal, oil and gas. Here, CO2 builds up above China, which for the past two decades has been the largest emitter of carbon dioxide.

2 / 5

In Africa, you can see how fires, such as from burning wood and clearing agricultural residue, also add carbon dioxide to the atmosphere.

3 / 5

Emissions are concentrated in the northern hemisphere, where most people live. Air spreads faster from east to west than north to south, but by year’s end, emissions have reached below the equator and cover most of the globe.

4 / 5

Spin the globe to explore it yourself.

5 / 5

What the globe doesn’t show is that the Earth also absorbs carbon dioxide, either when it dissolves in seawater or is taken up by plants during photosynthesis. The land and ocean together absorb about half of human emissions every year, helping slow global warming.

Most of the Earth’s land is in the northern hemisphere, where plants suck up CO2 all summer long. By September, there is less CO2 in the atmosphere than there was in January. Then winter comes, the plants die, and CO2 builds up in the atmosphere once more. By the end of the year, for every million molecules of air, there are about 2.5 extra molecules of CO2.

Carbon dioxide sticks around in the atmosphere for hundreds of years, so those extra molecules eventually start to add up. On Earth, atmospheric CO2 has risen from about 280 parts per million (ppm) before the industrial revolution to more than 420 ppm today.

As a proportion of all the air we breathe, it’s not much. Yet some molecules are potent, even in small concentrations. Consider that you can kill a full grown adult with as little as 70 milligrams of arsenic, or about 1 ppm.

Earth has not received a lethal dose of carbon dioxide, but as CO2 and other greenhouses gases build up in the atmosphere, the planet’s temperature must rise. Earth’s average temperature has increased 1.3 degrees Celsius since the Industrial Revolution. Most projections expect more than another degree by the end of the century.

A warmer planet will cause second-order effects, although they are harder to predict. Glaciers and ice caps will melt, but how much? How high will seas rise as a result? Will storms, which feed on heat, grow much stronger?

Every solution to slow down global warming essentially boils down to one of two categories: emit fewer greenhouse gases or absorb more of them. In the first category are low-carbon electricity sources; electric vehicles; and “green” cement. The second category includes ideas like planting a trillion trees; burying carbon-rich bricks; and deploying giant carbon-sucking vacuums. Energy and money are pouring in, but there are no magic bullets.

Fourier announced his discovery in 1824, so this year marks the bicentennial of humanity’s reckoning with the greenhouse effect (although Fourier never called it that). Since Fourier’s day, people have been trying to figure out what warms up the atmosphere or how to cool it down. We have been grappling with global warming for 200 years.

Note: At the request of readers, I changed the direction of the globe’s rotation to match that of the actual Earth. But I will only take this realism so far, and I categorically refuse to make it spin around 365 times in the year.