What are the chances?

14 04 2014
Mark Cochrane

Mark Cochrane

Another guest post from Mark Cochrane on the IPCC’s latest offering.


The final volume of IPCC Assessment Report 5 (AR5) from Working Group III: Climate Change 2014: Mitigation of Climate Change has been released by the IPCC. Press release here.

Although 2ºC is a somewhat arbitrary number, it is a level of warming that everyone with any involvement in the study of climate change and its impacts has agreed would be absolutely foolhardy to exceed before 2100 for human civilization. It’s not that the world would suddenly end but it is just so completely obvious that the negative consequences would be so unavoidably large that even Saudi Arabia, Russia, China and the U.S can agree that we do not want to go there. The only question is whether or not the human species is capable of any level of concerted action to avoid it.

wg2coverIn order to have a better than 50% chance of avoiding an average global temperature increase greater than  2C, the following guidance is given:

“Climate policies in line with the two degrees Celsius goal need to aim for substantial emission reductions,” Edenhofer said. “There is a clear message from science: To avoid dangerous interference with the climate system, we need to move away from business as usual.”

Scenarios show that to have a likely chance of limiting the increase in global mean temperature to two degrees Celsius, means lowering global greenhouse gas emissions by 40 to 70 percent compared with 2010 by mid-century, and to near-zero by the end of this century. Ambitious mitigation may even require removing carbon dioxide from the atmosphere.

The question obviously arises as to whether or not we can afford the cost of attempting to avoid what we certainly cannot afford to experience? Well, 235 authors and 38 review editors from 57 countries, together with nearly a thousand contributing or review experts, citing work from 10,000 scientific papers give us some insight there as well:

“Many different pathways lead to a future within the boundaries set by the two degrees Celsius goal,” Edenhofer said. “All of these require substantial investments. Avoiding further delays in mitigation and making use of a broad variety of technologies can limit the associated costs.”

Estimates of the economic costs of mitigation vary widely. In business-as-usual scenarios, consumption grows by 1.6 to 3 percent per year. Ambitious mitigation would reduce this growth by around 0.06 percentage points a year. However, the underlying estimates do not take into account economic benefits of reduced climate change.

If we cannot afford to invest such a paltry amount in the future then we have definitely reached the ‘limits to growth’ in collective human intelligence.

In any case:

1) Delaying action just increases the costs. Waiting until 2030 increases the estimates to 4% GDP.

2) The ongoing economic costs of climate change likely already exceed the proposed costs for mitigation activities by several-fold (e.g. link, link).

Mitigating activities are like trying to turn a fully laden oil tanker. Small rudder changes early on will do a lot more than large changes later on. Right now every decade sees global emissions levels not only going up but growing at increasing rates. This is like the captain of the Titanic spotting the iceberg and calling ‘full ahead’ to speed up their date with destiny.




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