Oct152009
Observations Show Climate Sensitivity Is STILL Not Very High
Written by Coby Beck

It's easy to see why Coby Beck, science blogger from A Few Things Ill Considered would allow me to republish this climate change denial argument over again even though it was written in 2006.  Unfortunately, it's not a very heartwarming reason.  The Climate Change denialist standpoint is still a very big and common issue that marine biologists and climate scientists alike still must deal with. The fact is, these skeptic don't understand that this climate change crisis is hurting our world, our marine life, and our bodies of water.

While e-mailing Coby Beck about republishing this piece, he told me that the denialist talking point found below is still a very common one and the fault of the argument remains the same. There is a fundamental flaw in its reasoning.  Despite this concept though, have we changed our ways? Have we improved our knowledge of the climate change crisis? Are we doing something to keep these climate change skeptics from remaining skeptical? 

June 27, 2006

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


Objection:

Taking into account the logarithmic effect of CO2 on temperature, the 35% increase we have already seen in concentrations represents about 3/4 of the total forcing to be expected from a CO2 doubling. Since we have warmed about .7oC so far, we should only expect about .3oC more for a doubling from pre-industrial levels, so about 1oC not 3oC as the scientists predict. Clearly the climate model sensitivity to CO2 is much too high.

Answer:

Even without addressing the numbers in this argument, there is a fundamental flaw in its reasoning.  We don't yet know exactly how much the climate will warm from the CO2 already in the air, there is a delay of several decades between forcing and final response.  Until an equilibrium temperature is reached, present day observations will not tell us the exact value of the climate's sensitivity to CO2.  The reason for this is primarily the very large heat capacity of the oceans. The enhanced greenhouse effect from higher CO2 levels is indeed trapping energy in the climate system according to expectations, but the enormous quantity of water on Earth is absorbing most of the resulting heat. Due to water's very high heat capacity, this absorbed energy shows up as only a very modest ocean warming, which in turn dampens the temperature change on land and lowers the global average trend.

This is commonly referred to as the climate system's thermal inertia. According to model experiments and consistent with data from past climate changes, this inertia results in a lag of several decades between the imposition of a radiative forcing and a final equilibrium temperature.

Now let's look at a couple of further details.  CO2 is not the only factor effecting the global temperature and in fact there is a phenomenon often called Global Dimming which is counteracting greenhouse gas warming.  Global dimming refers to the blocking of incoming sunlight by particulate pollution in the troposphere and airplane contrails in the stratosphere.  It is not a well quantified effect but it may well be masking a great deal more warming, definitely it is masking some.  

This is just one example, clearly an important one, of why we can not look at the temperature trends and pretend we can attribute everything to only CO2.  This same mistaken argument is made when looking at the mid-century cooling trend.

I believe it is Richard Lindzen who originated this argument, but it seems there is another problem as well, the numbers he is using don't add up.  35% increase in CO2 should correspond to 43% of the forcing from 2x CO2 (ln(1.35)/ln(2) = 43%) which is not 3/4.


This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


"Observations Show Climate Sensitivity Is Not Very High" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.

 

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