Global temperatures and atmospheric CO2

June 29, 2026

Peter Sainsbury is wrong when he states that global temperatures will stop rising when global CO2 emissions drop to net zero. It takes at least 2000 years for the earth’s surface temperature to equilibrate to any given increase in atmospheric CO2 (57 per cent after 100 years) and, for the consequent sea level rise, at least 10,000 years.

Global temperatures will only stop rising when atmospheric CO2 is reduced to near preindustrial levels. To reach even 350ppm CO2 will require the atmospheric removal of 1000Gt of CO2. For this to happen naturally will take hundreds of thousands of years. There are no feasible scaleable technologies for humans to remove that amount of CO2 with out further catastrophic environmental harm.

The last time earth had today’s CO2 level was in the mid Miocene, 16 million years ago. Surface temperature then was 4-6C higher than today and sea levels 10-25m higher. That is our future at best.

Furthermore, in the current geopolitical context it seems pure fantasy to believe we will stop burning fossil fuels to the extent we will keep global warming to a 1.5C. 1.5 is not a throwaway number. It’s science’s accepted risk limit to avoid climate tipping points.