Why every tenth of a degree C mean temperature increase by 2100 matters more than you may think
The world is presently headed towards a mean global temperature increase of ~3 degrees C or more by 2100, with a risk of a continued temperature rise in the 22nd century. After having wasted almost three decades, it seems increasingly difficult, if not impossible, for human civilization to stabilize the mean global temperature increase by 2100 at 1.5 degrees C. Instead, stabilizing at “well below 2 degrees C” might become the next best aspiration. Some economists might even find that a stabilization between 2 and 2.5 degrees C could be more “realistic” or even “optimal” from a cost-benefit perspective (optimal compared to what? What are short-term cost savings worth when the planet is ruined?). It is difficult to imagine a reality in which the costs and losses to human progress accumulating over centuries and millennia in case of even a 2.0–2.5 degrees C future could justify fleeting fossil fuel-based economic gains for a few more years.
Perhaps this can serve as a crude but insightful metaphor: If (future) human civilization was a pedestrian that is going to be hit by a vehicle, a 1.5 degrees C mean temperature increase by 2100 might correspond with an impact speed of 10 km/h, whereas 3 degrees C might correspond with 70 km/h (comparable to falling from a height of 19.3m, or from the 6th floor). 2 degrees C would then correspond with 30 km/h (comparable to falling from a height of 3.5 meters, or from the 1st floor) and 2.5 C with 50 km/h (comparable to falling 9.8 meters, or from the 3rd floor). Note that the risk of severe/fatal injury as a function of vehicle impact speed does not increase linearly but in accordance to a logistic function. When we say that “every tenth of a degree C matters” we are saying — to stay within this metaphore— that every 4km/h of vehicle impact speed reduction matters: disproportionately. The earlier and the more forcefully we hit the breaks, the more we can reduce the vehicle impact speed within the limited distance remaining in front of us. But as long as annual GHG emissions don’t start decreasing substantially, we are basically keeping our foot on the gas pedal.
