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We have a larger-than-expected carbon budget for 1.5 degrees

carbon budget

credits Tim van der Kuip su Unsplash

University of Exeter presents new method to calculate carbon budget

( – A new method for calculating how many greenhouse gas emissions we can still afford to permanently exceed the Paris targets gives us a few more years. The world’s carbon budget could be 10% larger than previously estimated. But in any case, at the current emissive rhythms, we will squander it quickly.

While there is no single established method for calculating the global carbon budget, the underlying assumption is the same for everyone: greenhouse gas levels are a great indicator of current and future global warming. But how exactly to calibrate this relationship makes all the difference.

Previous estimates of the global carbon budget

According to the latest IPCC report published in 2021, to have a reasonable 66% probability of meeting the more ambitious target of the Paris Agreement, we can still emit 360 billion tons of CO2 equivalent (GtCO2eq). At the current rate, the IPCC argued, we would have exhausted them by 2030. If we choose a more risky probability, just 50%, the total rises to 500 GtCO2eq.

But a 2023 study updated the data and calculated that in three years the Earth has already consumed half of that carbon budget, anticipating the overrun to 2028. And he stressed that the number is subject to high uncertainty, especially because we do not know precisely how the climate system will react with the decrease in aerosols, which so far have had a cooling effect on the Planet. It is precisely at the lower concentration of aerosols that today is linked to the exceptional increase in temperatures of the global oceans, which in recent days have again marked the absolute record with 21.2°C.

A 10% larger budget

According to the model developed by the University of Exeter in Great Britain, historical global warming and estimated carbon emissions to date are an excellent indicator of the amount of carbon emissions left before exceeding the Paris climate targets. Researchers considered historical simulations of all available predictive models and future projections for a range of scenarios, combining them with observed estimates of global warming and anthropogenic CO2 emissions to this day.
The result is that the carbon budget for 1.5 degrees is 812 GtCO2eq (with an interval of 691-933 GtCO2eq, while that for 2 degrees is 1048 GtCO2eq (and a fork between 881 and 1216 GtCO2eq). Both are about 10% wider than the mean values derived from the set of predictive models. “The linearity between cumulative emissions and global warming is maintained at least up to 4 ºC,” the authors point out. But even with this expansion, we’ve only got about 10 years before we’ve really gone over 1.5 degrees.

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