This is a giant postcard from the Jungfraujoch in Switzerland, consisting of 125,000 messages about climate change from children and young people. Photo credit: VALENTIN FLAURAUD

According to the latest data released by Nature Climate Change on October 30, the world must control future carbon dioxide emissions to about 220 billion tons to have a half chance of controlling warming within 1.5 degrees Celsius. Since annual global carbon emissions are now about 40 billion tons and rising, they will exceed this figure by 2029 or even earlier.

Joeri Rogelj of Imperial College London said that to achieve the 1.5°C target, humanity needs to achieve global net-zero carbon emissions by 2034 rather than 2050. "There aren't even any technical scenarios in the scientific literature describing how this would be possible," he said.

Robin Lamboll, also from Imperial College London, said it was still feasible to keep global warming below 2 degrees Celsius. To have a 50% chance of controlling global warming to less than 2 degrees Celsius, global carbon dioxide emissions cannot exceed 120 billion tons. If global carbon emissions continue at current levels, this figure will not be exceeded until 2046.

The rate at which the Earth warms depends largely on the amount of carbon dioxide in the atmosphere, which in turn depends on human emissions of carbon dioxide. Based on this, climate scientists can calculate a carbon budget, which is how much carbon dioxide people can emit before warming reaches a certain level.

In 2020, the Intergovernmental Panel on Climate Change (IPCC) estimated that the carbon budget for a 50% probability of staying below 1.5 degrees Celsius was about 500 billion tons of carbon dioxide. Now, a team including many of the researchers responsible for the IPCC assessment has updated that work.

The team estimates that as of January 2023, the remaining carbon budget will be approximately 250 billion tons of carbon dioxide. Since then, there have been another nine months of emissions, so the remaining carbon budget drops to about 220 billion tonnes of CO2.

One of the main reasons for the reduction in CO2 emissions from 500 billion tons to 250 billion tons is an additional 3 years of emissions since 2020, with much of the remainder due to better estimates of the impact of aerosol pollutants.

These pollutants, such as sulfur dioxide from burning fossil fuels, form tiny droplets in the atmosphere that have a cooling effect by reflecting sunlight and changing the brightness of clouds, but there has been much uncertainty about the extent of the cooling.

Today, the range of uncertainty has narrowed to the higher side. If aerosol cooling is high, the climate will warm further as fossil fuels are phased out and aerosol pollution decreases. This means that if people are to keep temperature rises within a certain level, they must emit less carbon dioxide.

Glen Peters of the Norwegian Center for International Climate Research estimates that global fossil fuel carbon dioxide emissions will be 1% higher in 2023 than in 2022. While some researchers believe emissions could eventually begin to decline in 2024, Peters remains unconvinced that carbon emissions will peak in 2023.

Chris Smith of the International Institute for Applied Systems Analysis in Austria said: "There is a good chance that warming will exceed 1.5 degrees Celsius in 2023, but that does not mean that in the long term we have exceeded 1.5 degrees Celsius." He said: "If we can "Limiting warming to 1.6, 1.65 or 1.7 degrees Celsius is much better than 2 degrees Celsius. We still have to fight for every 0.1 degrees Celsius."

Related paper information:

https://doi.org/10.1038/s41558-023-01848-5