Note: The following is a generalization of the approach I described in my blog posting last week.
“My goodness, look at _________ [fill in the blank with any of the following: glacial “retreat”, sea level rise, extreme weather, sea ice melt, temperature rise, insect infestation, drought, flood, and so on]. We must therefore reduce our carbon dioxide (CO2) emissions!” is typical of the excited cries from climate campaigners.
Instead of meekly accepting such emotional leaps in faith from simple observations about nature to expensive policy recommendations, we need to start holding our politicians, media and activists accountable for using logic in their assessments.
Here’s how.
Let’s say activists are using climate event X to promote policy action Y.
The normal questions a thinking individual would rationally ask are:
1 – How likely is it that event X is unusual?
We will assign a probability of 0% to 100% and call it P1.
2 – If X is unusual, what is the probability that it is dangerous?
The answer, in %, would be P2.
3 – If X is unusual and dangerous, how likely is it to be caused by warming?
P3 would be the answer.
4 – If X is unusual, dangerous, and caused by warming, what is the probability that the warming is caused by CO2 levels?
P4 would be the answer.
5 – If X is unusual, dangerous, and caused by CO2-induced warming, how likely is that higher CO2 level to be caused by human activities?
P5 would be the answer.
6 – If X is unusual, dangerous, and caused by human CO2-induced warming, what is the likelihood that it is more cost effective to reduce CO2 emissions than to simply prepare for and adapt to X?
P6 would be the answer.
Of course, the overall probability that reducing CO2 emissions is a good policy choice in response to event X is the product of the individual probabilities:
PX = P1P2P3P4P5P6
As we discussed last week, you need unrealistically high individual probabilities to end up with an overall PX that is anything more than trivial.
When people such as David Suzuki assert that we must enable a policy prescription X as a result of some climatic event Y, we must insist he start answering some basic questions about probability. Only then can we compare possible climate policy actions, the most basic of which is to simply promote development across the World so that societies have the strength to withstand whatever Mother Nature throws at us next.
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Tom Harris is Executive Director of the International Climate Science Coalition and an advisor to the Frontier Centre for Public Policy.
