Think about the sky is like a big bowl of blue soup. Its components include oxygen, nitrogen and carbon dioxide, which scientists can measure precisely. But since the Industrial Revolution, humans have added heaps of CO2 by burning fossil fuels, warming the planet 1.2 degrees Celsius so far and complicate those calculations.
Although it is easy to know what the total amount of CO is2 is that in that soup of air, it’s hard to analyze how much humanity is adding at any one time. That’s because Earth’s natural processes also produce gases, and because there are countless sources of civilization’s emissions, some of which grow or wane over the hour. It would be like throwing some salt in the actual soup and then trying to count exactly how many seeds went in. after they hit the liquid.
What atmospheric scientists can do, however, is create an inventory, a “bottom-up” attempt to fully count CO.2 because it’s made on Earth. For example, they can add up how much gasoline is being burned and how many fossil fuel power plants are operating at a given time, to calculate how much carbon is being released into the atmosphere. While fairly accurate, all inventory takes time, largely because some data is slow to come in. And timeliness is important when taking action on climate change, as we need to identify sources of CO.2 and get rid of them as quickly as possible, for example by replacing coal with renewable energygasonline cars with tramand gas furnace with heat pump.
You might wonder why the researchers couldn’t take a more “top-down” approach, training satellites on points on the planet and measuring CO2 go out of them. It has been tested on certain areas of the globe, for example when a NASA satellite takes readings across the Los Angeles Basin. But there are problems: The air is mixed and it is difficult to pinpoint exactly where the emissions are coming from. Another problem is that it is difficult to remove humanity’s emissions from CO .2 generated by the Earth’s natural carbon cycle. When plants photosynthesize, they take up carbon and lock it in their tissues, and in turn give off oxygen. As they die and rot, that carbon is released again.
But now the Covid-19 pandemic, oddly enough, has provided scientists with a better top-down tool for estimating small changes in fossil fuel emissions. A team of researchers used the UK’s coastal Weybourne Atmospheric Observatory to test the air for carbon dioxide and oxygen separately, then aggregate the measurements together. They then use a trick called atmospheric oxygen potential, or APO, to calculate the imbalance between oxygen and CO.2 from fossil fuel emissions.
The key to separating natural and anthropogenic emissions is the ratio between CO2 and oxygen. Plants treat both in a one-to-one ratio: They absorb the same amount of carbon dioxide as they give off oxygen, so the wholes cancel each other out. On the other hand, burning fossil fuels consumes more oxygen than produces CO2.
