Enlarge / Carbon cycle, illustrated. (credit: Global Carbon Project)
Rarely has the future of Earth’s climate felt as malleable as it does this week. While substantive climate legislation morphs behind the scenes of the US Congress, nations have gathered in Glasgow to improve on their Paris Agreement pledges. Pledges, of course, require follow-through before they become reality, and it can be difficult to judge how encouraging each announcement is.
So how about a look backward instead of forward? The newly released global carbon budget report for 2021—an annual release from a huge group of scientists under the banner of the Global Carbon Project—actually includes a downward revision of total human-caused CO2 emissions for the last few years. Probably.
What have we done?
This annual publication includes our best estimates of each contributor to the Earth’s carbon cycle. That includes human-caused emissions but also uptake by land ecosystems and the oceans. Fossil fuel burning isn’t too hard to quantify, but the other elements are. Emissions from agriculture and deforestation—or conversely, uptake by reforestation—take more work and are therefore less certain. And estimates of the total amount of atmospheric carbon sequestered on land and in the oceans rely on models running with whatever observations we can feed them. But this whole-system perspective is crucial to understanding the consequences of our emissions.
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