Global Greenhouse-Gas Budget“When we look at our numbers, we can’t see any climate protection efforts”

25 November 2024

Photo: UHH

Right on time for the UN Climate Change Conference, this year a new update of the Global Carbon Budget was released. It shows how much CO₂ there is in the atmosphere and whether there has been progress in climate protection. For the first time, the new Budget includes extensive, reliable forecasts for the coming year, developed at the Cluster of Excellence for climate research (CLICCS) – a real breakthrough. In the following, Professor of Oceanography Tatiana Ilyina explains what the numbers mean.

How do you calculate the amount of CO₂ in the atmosphere?
We gather all the data we have, all the field data, all the modelling options that we’ve already vetted and trust. On that basis we calculate how much CO₂ is emitted worldwide and how much of the emissions are fixed in the ocean and on land, in what we call carbon sinks. We do so using e.g. complex Earth system models, which also reflect climate variability. The models, which we use to simulate the Earth’s carbon cycle at the German Climate Computing Center in Hamburg, produce massive amounts of data. We start in the preindustrial era, in 1850, and use the models to reproduce how the climate has changed. This allows us to precisely determine how much CO₂ remains in the atmosphere. The result is a budget that starkly shows where humanity stands when it comes to climate protection: we still haven’t reduced CO₂ emissions.

What makes the figures so accurate?
Needless to say, there are still sources of uncertainty. Not all countries report their emissions precisely. And emissions produced by wars aren’t recorded. That’s why we observe the CO₂ concentration at various sites around the globe and assess whether our numbers are plausible. The remaining sources of uncertainty are transparently listed in the report. Nevertheless, the results are highly robust.

What does this year’s budget look like?
The CO₂ emissions and concentration have risen again, because we continue to burn tremendous amounts of oil, gas and coal. On the other hand, the ocean and land have absorbed enormous amounts of CO₂. In other words, the sinks still work, helping to mitigate the impacts.

What does your team contribute at the Hamburg research hub?
Every year, we provide the numbers for the ocean; for us, doing so is business as usual. But this year, my colleague Hongmei Li and our team added something new: we succeeded in making detailed forecasts of how much carbon dioxide there will be in the atmosphere and the sinks next year. That was a real breakthrough; thanks to the unique models we have in Hamburg, we were the first to successfully do this. And since last year, the data has been sufficiently robust to be included in the Global Carbon Budget. That makes me very proud.

What can the data be used for?
It can help us precisely determine whether CO₂ fluctuations in the atmosphere are the result of human activities or, for instance, natural phenomena.

As a climate researcher, what’s your view on the developments so far?
In the media, I often come across the phrase “Despite climate protection efforts…”. But when we look at our numbers, we can’t see any such efforts. At the Climate Conference, so far no one has said anything about giving up fossil fuels; there have only been vague statements about reductions. This year, we hoped in vain that the emissions would flatten out. I hope to see that happen in my lifetime.

Tatiana Ilyina and Hongmei Li are researchers at the University of Hamburg’s Cluster of Excellence “Climate, Climatic Change, and Society” (CLICCS). Li works at the Helmholtz-Zentrum Hereon, Ilyina at the University of Hamburg. In April 2025, Ilyina will receive the Fridtjof Nansen Medal for outstanding research.