Mike Lockwood's 2/21/11 response to my email query


Hi Alec,


Thank you for your e-mail and you raise what I agree is a very interesting and complex point. In the case of myself and Claus Froehlich, we did address this issue in a follow-up to the paper of ours that you cite, and I attach that paper.


One has to remember that two parts of the same body can be in good thermal contact but not had time to reach an equilibrium. For example I could take a blow torch to one panel of the hull of a ship and make it glow red hot but I don't have to make the whole ship glow red hot to get the one panel hot. The point is that the time constant to heat something up depends on its thermal heat capacity and that of one panel is much less than that of the whole ship so I can heat it up and cool it down without an detectable effect on the rest of the ship. Global warming is rather like this. We are concerned with the temperature of the Earth’s surface air temperature which is a layer with a tiny thermal heat capacity and time constant compared to the deep oceans. So the surface can heat up without the deep oceans responding. So no we don’t assume Earth surface is in an equilibrium with its oceans (because it isn't).


So the deep oceans are not taking part in global warming and are not relevant but obviously the surface layer of the oceans is. The right question to ask is, "how deep into the oceans do centennial temperature variations penetrate so that we have to consider them to be part of the thermal time constant of the surface?" That sets the ‘effective’ heat capacity and time constant of the surface layer we are concerned about. We know there are phenomena like El-Nino/La Nina where deeper water upwells to influence the surface temperature. So what depth of ocean is relevant to century scale changes in GMAST [Global Mean Air Surface Temperature] and what smoothing time constant does this correspond to?


Jim Hansen has looked at ocean temperature profile changes and found that about a global average of 1Wm-2 is going into warming the oceans (compared to 235 Wm-2 of infrared (longwave) radiated by the top of Earth’s atmosphere back into space and (342-106) = 236 Wm-2 supplied by the solar shortwave (342 W is the daily mean supplied by the sun to every m2 of the top the atmosphere an 106 m-2 is reflected back into space (making the global albedo 106/342 = 0.31). This is why in climate model predictions even if you turn greenhouse emissions to zero the climate continues to rise for up to about 10 years (as the relevant part of the ocean that has warmed gives back the heat that it has stored) – its called the “temperature commitment”. (So climate models are given the relevant time constant is up to about 10 years).


In the attached paper, we cite a paper by Schwartz (2007) that discusses and quantifies the heat capacity of the oceans relevant to GMAST changes and so what the relevant response time constant is. It is a paper that has attracted some criticism but I think it is a good statement of the issues even if the numbers may not always be right. In a subsequent reply to comments he arrives at a time constant of 10 years. Almost all estimates have been in the 1-10 year range.


In the attached paper we looked at the effect of response time constants between 1-10 years and showed that they cannot be used to fit the solar data to the observed GMAST rise. Put simply. The peak solar activity in 1985 would have caused peak GMAST before 1995 if the solar change was the cause of the GMAST rise before 1985.


Incidentally, one thing I cannot agree on in your e-mail is that the response time is the only thing separating solar and anthropogenic “theories”. Our understanding of greenhouse trapping (by water vapour, CO2, methane etc) predicts the right level of GMAST (without it the GMAST would be -21 degrees) and it also predicts that changing from 280 ppm by volume of CO2 to 360 (which has happened since pre-industrial times) will have caused a GMAST change by a sizeable fraction of a degree – the science of the radiative properties of CO2 are too well understood and verified for that not to be true. (There are utterly false and unscientific statements around on the blogosphere that adding CO2 doesn’t add to the greenhouse trapping – this is completely wrong. It is true of some CO2 absorption lines but not of them all so if you integrate over the spectrum (rather than selecting bits of it!) one finds a radiative forcing rise that matches the observed GMAST rise very well indeed. Our best estimates of the corresponding radiative forcing by solar change are smaller by a factor of at least 10. So solar change is too small to have caused the rise we have seen, greenhouse trapping by extra CO2 is not.


I hope that helps


Mike Lockwood