The Headlines:

Planet has just 5% chance of reaching Paris climate goal, study says - The Guardian

We only have a 5 percent chance of avoiding ‘dangerous’ global warming, a study finds - Chris Mooney/Washington Post  

Actual Study: 

“Less than 2°C warming by 2100 unlikely.” 

The Gist:

  • The authors developed a statistical model to forecast cumulative CO2 emissions to 2100. This model assumes the general range of emission trends over the past 50 years will continue into the future.
  • In line with trends over the past 50 years, the model assumes steady improvements in carbon intensity (CO2 emissions per dollar of GDP) over the 21st century. 
  • The model does not incorporate the possibility of future legislation or breakthroughs in alternative energy that could lead to larger and more abrupt changes in future emissions, which the authors say would be “speculative”.
  • Based on the model, the authors conclude that by 2100 the likely range of global temperature increase is 2.0–4.9°C, with median 3.2°C, and  a 5% chance that it will be less than 2°C.

Questions:

Did the headline accurately capture the gist of the study? Were the study's conclusions warranted?

My Take:

The headlines pretty well captured the gist of the study, but the study's conclusions are overly pessimistic because the authors' assumptions are unreasonable.  Why assume a slow and steady improvement in carbon intensity and not a quickening in the pace of improvement? After all, solar and wind have “gotten cheaper and scaled up faster than even the most optimistic forecasts of a decade ago, or even a few years ago."  And what about the potential for huge advances in energy efficiency? For instance, the American Council for an Energy-Efficient Economy recently recommended a long list of cost-effective "efficiency opportunities", which if implemented could:

"...roughly double the rate of efficiency improvement in the next 35 years relative to the past 35 years, and reduce 2050 energy use to half of current forecasts."

Technological progress tends to follow an 'S' curve: slow, then super-fast. Think of the automobile or Google.  Why should it be any different this time around?

Of course, we must remain vigilant! But measured optimism is not the enemy.

Reference:

Raftery, Adrian E., Alec Zimmer, Dargan M.W. Frierson, Richard Startz, and Peiran Liu (2017) “Less than 2°C warming by 2100 unlikely.” Nature Climate Change. DOI: 10.1038/NCLIMATE3352.  http://mfkp.org/INRMM/article/14409548