think about The sky is like a big bowl of blue soup. Its components include oxygen, nitrogen and carbon dioxide that scientists can measure precisely.But since the industrial revolution, humans have been adding a lot of extra carbon dioxide2 By burning fossil fuels, it has so far warmed the planet by 1.2 degrees Celsius and complicates these calculations.

Although it is easy to know how much CO2 In that atmospheric soup, it’s hard to analyze how many humans have been added at any given time. That’s because Earth’s natural processes also produce gases, and because civilization’s own emissions come from so many sources, some of which increase or decrease hourly.It’s like adding a pinch of salt to the actual soup and then trying to count exactly how many grains are in it back They hit the liquid.

What atmospheric scientists can do, however, is to compile inventories, a “bottom-up” effort to exhaustively count carbon dioxide in the sky2 Because it was produced on earth. For example, they can add up the amount of gasoline burned and the number of fossil-fuel power plants operating at a given time to calculate how much carbon is being released into the atmosphere. While fairly accurate, all of these inventories take time, mainly due to the slow entry of some data.Timeliness is important when taking action on climate change as we need to identify the source of carbon dioxide2 And eliminate them as soon as possible, such as replacing coal with renewables, petrol cars with electric cars, and gas stoves with heat pumps.

You might wonder why researchers couldn’t take a more “top-down” approach, training satellites at various locations on Earth and measuring CO2 leave them. It has already been tried in some parts of the globe, for example, when a NASA satellite took readings over the Los Angeles Basin. But there are several problems: the air mixes, and it’s hard to pinpoint the exact source of the emissions.Another is that it is difficult to figure out human emissions from carbon dioxide2 Produced by Earth’s natural carbon cycle. When plants photosynthesize, they take carbon and lock it in their tissues, and then expel oxygen. When they die and decay, the carbon is emitted again.

But oddly, now the Covid-19 pandemic has helped scientists provide a better top-down tool for estimating small changes in fossil fuel emissions. A team of researchers used the Webern Atmospheric Observatory off the coast of the UK to test the air separately for carbon dioxide and oxygen, then put the measurements together.They then used a trick called atmospheric potential oxygen (APO), which calculates the imbalance between oxygen and carbon dioxide2 Emissions from fossil fuels.

The key to distinguishing natural and anthropogenic emissions is the ratio between carbon dioxide2 and oxygen. Plants deal with the two substances in a one-to-one ratio: they take in the same amount of carbon dioxide as they expel oxygen, so the totals cancel each other out.On the other hand, burning fossil fuels consumes more oxygen than produces carbon dioxide2.