Climate Overshoot is a Fantasy

Schleussner, CF., Ganti, G., Lejeune, Q. et al. Overconfidence in climate overshoot. Nature 634, 366–373 (2024).  https://doi.org/10.1038/s41586-024-08020-9

According to the data from the Global Carbon Project and the Rhodium Group, CO₂  emissions from mankind’s activities continue to grow . This brings CO₂  emissions to a record high above the pre -COVID-19 levels.

While emissions are declining in 26 countries, these efforts remain insufficient to reverse the growth in global emissions in China and India. Growth in total CO2 emissions for our planet – the sum of fossil and land-use change emissions has slowed down over the past decade, emissions continue to grow leading to a continued increase in CO2 in the atmosphere and continued global warming. 

The preliminary data for 2023 show global fossil CO2 emissions are set to reach a record high, with an increase of about +1.1% (range 0.0% to 2.d1%) relative to 2022 level, and expected growth in all fuel types. Projected 2023 emissions decrease in the European Union, USA, and to a lesser extent in the Rest of the World were exceeded by increases in emissions in India and China. CO2 emissions in India are now above those of the European Union.

As the  Intergovernmental Panel on Climate Change, IPCC sixth report showed that:

• Climate Change is already affecting ecosystems globally
• The planet is being impacted unevenly
• Despite pledges made the world is still on track for a 2-2.9 degree Celsius warming
• China and India are not our friends and their emissions will continue to grow significantly.

Last year the Washington Post analyzed 1,200 pathways to 1.5 degrees C. The Washington Post could not find a single pathways with  assumptions that did not involve magical technological development and that didn’t include temperature overshoot. A recent article in New Scientist Magazine summed up the situation perfectly.

“It is clear that the world is going to exceed the 1.5°C target for global warming, leading to an increasing focus on plans to cool it down again by removing carbon dioxide from the atmosphere..”

The article cited above and published this month in Nature magazine brings into question whether we will even be able to bring the temperature back down after an overshoot; and even if we can bring the planetary temperature back down, some changes in the plant can’t be reversed.  In the analysis cited above the authors adapted existing climate models to capture different elements of the climate response during the warming phase and the long-term phase after net zero emissions is achieved and carbon is removed from the environment. They modeled:

• The expected warming for a given quantity of cumulative emissions until net-zero CO₂.
• The expected warming or cooling for a given quantity of cumulative net-negative emissions after net-zero CO₂.
• The continued temperature response after net-zero CO₂ emissions are achieved and sustained

What they found was For a range of climate impacts, there is no expectation of immediate reversibility after an overshoot.  For a range of climate impacts, there is no expectation of immediate reversibility after an overshoot. This includes changes in the deep ocean, marine biogeochemistry and species abundance, land-based biomes, carbon stocks and crop yields, but also biodiversity on land. An overshoot will also increase the probability of triggering potential Earth system past tipping points that cannot be restored. Sea levels will continue to rise for centuries to millennia even if long-term temperatures decline.

The analysis also showed there is no guarantee that we will be able to bring the temperature back down. The sad truth appears to be that the climate change will impact life on earth. Species that go extinct due to loss of habitat cannot be brought back to life. If the ice sheet collapses, even if temperatures are restored it will take millennia to restore them and the list goes on. Restoring the temperature will not restore the lives that are lost. It is hoped that with adaptation to the changing climate some of mankind will survive this century. 

We have just passed the Jewish Days of Awe. On Yom Kippur, the Day of Atonement, Jews recite (more than once) the prayer Unetanneh Tokef, Jews believe God reviews our fates and decides who will live and who will die in the coming year. The older I get, the more appropriate the prayer feels for all of mankind. Below is a portion of the English translation. 

And on Yom Kippur it is sealed.

How many shall pass away and how many shall be born,

Who shall live and who shall die,...

Who shall perish by water and who by fire,

Who by sword and who by wild beast,

Who by famine and who by thirst,

Who by earthquake and who by plague,...