Low ECS doubles the cost:benefit shortfall

Guest essay by Barry Brill

Topher Fields’ excellent documentary video http://topher.com.au/50-to-1-video-project/ explains that the overall costs of any global effort to reduce greenhouse gas emissions will be at least 50 times greater than its overall benefits.

But that was based on the UNIPCC’s 2007 report (AR4). Now that the 2013 summary report (AR5) has been leaked, we can see that Topher was much too generous. At the new revised rate of future warming, the assumed benefits will be sliced in half.

Since January 2012, no less than 19 scientific papers http://tinyurl.com/kjxs4kt have been published on the crucial question of climate sensitivity: ie how much warming would result from doubling the volumes of greenhouse gases in the atmosphere?  The latest draft of the AR5 summary tip-toes around this subject, but effectively recognises (in convoluted words and figures) that ‘equilibrium’ sensitivity (ECS) is probably around 2°C – about 33% less than the four previous reports had assumed.

But this doesn’t mean that future warming will reduce by only one-third!

Let’s make the following over-generous assumptions:

1. The ECS is immediately reflected in global average surface temperatures;
2. The IPCC models are valid in all other respects (except ECS);
3. The greenhouse effect is arithmetic rather than logarithmic;
4. The atmospheric concentration of CO2e will reach 560ppm in 70 years;
5. The discount rate for climate issues is way below any other investment rate.

The CMIP5 ensemble of models currently projects temperatures at 3°C above 1850 levels by 2085. According to NOAA (the median of the three surface datasets) we have already experienced 1.024 ±0.128°C over the last 160 years. So the official prediction is that temperatures will increase by a further 1.876°C over the next 70 years.

If those CMIP5 models were re-programmed with the updated ECS, the 2088 projection would reduce by one-third to 2°C. From this we deduct the 1.024°C already in the system, so the projected warming for the next 70 years falls to 0.976°C .

This is LESS THAN HALF the warming the IPCC was previously expecting –  a very dramatic reduction.

The updated projection suggests that the warming trend will be almost exactly the same as it has been over the past 100 years. During that period, there was no acceleration at all in the rise of sea levels, the retreat of glaciers or sea ice, the incidence of malaria, or the frequency of hurricanes or droughts.

In fact, it was an ‘optimum‘ temperature period. CO2 contributed to the ‘green revolution’, poverty levels and child mortality were decimated, while indicators like life expectancy and literacy boomed. Death rates from extreme weather have declined by 98% since 1920.
Then there is another reason why 50:1 might be a major over-estimate.

The current 16-year temperature standstill suggests that the climate optimum era may now be over. If so, and the world undertakes a crash programme to reduce greenhouse gases, we will presumably produce a cooling effect through the 21st century. Would that give rise to any benefits at all? Or would we be cutting our own throats?

Perhaps the AR5 report of WG3 (due March 2014) will address this scenario. The IPCC says it considers all possible futures without assigning probabilities to any one.

Now, let’s revert to those heroic assumptions we laid out above:

1. The ECS is the theoretical temperature response which continues long after emissions occur – hundreds of years into the future. The short-term impact of greenhouse doubling (Transient Climate Response) is only about 1.2°C – 40% less than the ECS.
2. The CIMP5 and CIMP3 models have actually been wrong by about 100%  over the past 20 years. The ECS is certainly not the only error.
3. The greenhouse effect is logarithmic, so (at 400ppm) we have already experienced more than half of the doubling effects.
4. The IPCC scenarios ignore technology change, the shale gas boom, etc and are long out of date.
5. The 50:1 project is conservatively based on the Stern report which opined that climate mitigation was uniquely different to investments in healthcare, education, disease and poverty eradication, climate adaptation, etc. This credo is based on an obscure moral philosophy which few economists can even follow let alone subscribe to.
Finally, the largest impact factor in all the economic models is the speed of temperature change, not just the amount. The AR4 results suggested a rate of change so fast as to exclude most opportunities for species (including humans) to adapt. With the long standstill and the new low sensitivity, this issue is now comfortably overcome.

So, if we were to apply updated science and normal economics to a cost:benefit study, the 50:1 ratio could easily blow out to 500:1.