World greenhouse gas balance“We still don’t see climate protection efforts in our numbers”

22 November 2024, by Thomas Merten

Just in time for the World Climate Conference, the Global Carbon Budget has once again been calculated this year. It reveals how much carbon dioxide there is in the atmosphere and where human beings stand with regard to climate protection. For the first time, the calculation also includes extensive prognoses for the coming year. These were developed at the Cluster of Excellence Climate, Climatic Change, and Society (CLICCS). Oceanography professor Tatiana Ilyina explains what the numbers mean.

How do you calculate how much CO₂ there is in the atmosphere?

We collect data that we have, all measurements, and all modeling possibilities that we have previously reviewed and that we trust. Using this, we calculate the amount of the climate gas CO₂ emitted worldwide and how much of it is bound in oceans and on land in so-called “carbon sinks.” We do this with, among other things, elaborate earth system models that incorporate climate fluctuations.

At the German Climate Computing Center, we are working with enormous amounts of data to simulate Earth’s carbon cycle. We begin in the pre-Industrial era in 1850 and let the models reproduce how the climate evolves. This way we can find out exactly what amounts of CO₂ remain in the atmosphere. It is a balance that starkly reveals where human beings stand with regard to climate protection: so far, we have not succeeded in reducing CO₂.

How do you get such exact numbers?

Naturally, there are uncertainties. Not all countries document their exact emissions. And emissions from wars are not reported. This is why we observe the CO₂ content at different places in the world and look to see if our numbers are plausible. We are transparent about reporting our remaining uncertainties. Nonetheless, our results are very precise.

What does the balance look like this year?

CO₂ emissions and concentration have increased because we continue to burn enormous amounts of oil, gas, and coal. On the other hand, oceans and soil absorb enormous quantities of CO₂. The sinks, therefore, still work and help us ameliorate the effects.

What is your team doing in Hamburg?

Every year, we provide numbers for the oceans. For us, that is business as usual. Now, however, my colleague Hongmei Li and our team have done something new: we have successfully calculated the exact prognoses about how much carbon dioxide will be in the atmosphere and in the sinks in the coming year. This was a veritable breakthrough. Using our special models in Hamburg, we were the first to accomplish this. Since last year, these data have been so robust that they are now being added to the Global Carbon Budget. I am really proud of that.

For what are the data useful?

They help us to determine exactly whether CO₂ fluctuations in the atmosphere can be traced back to humans or, for example, natural phenomena.

As a climate researcher, how do you see developments so far?

I always read in the media: “Despite efforts at climate protection.... “ Yet in our numbers, we have yet to see any efforts. At the World Climate Conference, there has so far been no talk of giving up on fossil fuels, only of vague reductions. In this year, we hoped in vain that the emissions curve would plateau. My wish is to live to see that.

Tatiana Ilyina and Hongmei Li do research at the Cluster of Excellence Climate, Climatic Change, and Society (CLICCS) at the University of Hamburg. Hongmei Li works at the Helmholtz-Zentrum Hereon GmbH and Tatiana Ilyina at the University of Hamburg. Ilyina was awarded the Fridtjof-Nansen-Medaille in April 2025 for excellent research.