Hansen Redux: service and disservice.
We thank Dr Davies for his response to our recent Drum article, as it provides an opportunity to discuss additional elements of the long, but interesting paper by Dr James Hansen.
There are many areas where we agree: the main being that most computer models of climate (1) have over-estimated the rate at which heat is being absorbed by the oceans, and (2) that the corresponding net human-made climate forcing is unrealistically large. Davies explains “All climate modellers know there are inaccuracies and poorly-constrained factors in the models.” Part of the reason for our original article was to inform the general reader, who is not a climate modeller, and is in general not accurately informed of the uncertainties, that these are very significant, pressing issues with the models. For instance from Hansen’s paper:
“A substantial effort is underway to isolate the causes of excessive vertical mixing in the GISS ocean model (J. Marshall, private communication)” [page 20]
“Continued failure to quantify the specific origins of this large forcing [from aerosols] is untenable” [Abstract]
By Hansen’s own account, the magnitude of the error by the models is almost half the entire forcing generally attributable to warming from human emissions of CO2 [AGW].This is a new development. It is not ‘business as usual’ as Davies portrays.
The widening gap between models and reality is shown by comparing the projections of Hansen’s 1988 paper where he predicts the future temperature from 3 scenarios of CO2 emissions. These 3 temperature scenarios were: (A) a rate of CO2 concentration growth at about 1.5% per annum; (B) decreasing CO2 growth rates and (C), growth of CO2 ceases after 2000. While CO2 levels have increased at a rate even greater than in Hansen’s scenario A, which should have led to temperatures increasing at a rate greater than scenario A, temperature has actually increased at a rate LESS than offered by scenario C.
Davies’s main complaint is that our article does not adequately highlight Hansen’s so-called “Faustian bargain”. This is that humanity has been getting away with CO2 emissions because aerosol cooling has been masking the CO2 heating. While we did mention it in the interests of balance, the problem is that the trade-off is a classic strategy of irrefutability of an auxiliary hypothesis, ala Popper, by correcting other errors such as ocean heat uptake and ocean warming with unmeasured aerosol cooling.
At this stage Hansen’s remedy of greater cooling from aerosols is only speculation; speculation that contradicts Hansen’s previous work which concluded some warming from aerosols. We wholeheartedly agree with Hansen on the need for direct empirical measurements of aerosols to diminish this major source of uncertainty. But this has not been done and in fact nearly all the forcings that Hansen relies on to support the worsening of AGW are, according to the IPCC’s 4th report, either unmeasured or very uncertain. Yet we are told by Davies that he and Hansen are certain of their effect, in conjunction with CO2, on the climate. How can that be?
This blurring of the distinction between fact and speculation is habitual in climate science and in our opinion tends to exasperate scientists from other fields.
Our article did not review well-known views, such as Hansen’s argument for CO2 climate sensitivity. It focused on the new information, which was the overestimation of heat absorption in the ocean by Hansen’s computer models. This is not in dispute. Davies concedes this. Like Hansen, Davies assumes that the estimation of the cooling effect of aerosols by the computer models must be less than the actual cooling by aerosols. Why? Because, he claims, the evidence for global warming by CO2 is NOT supplied by the models, but by other ‘real’ evidence.
In making the claim that the case for AGW does not rest on computer models and is therefore not vulnerable to the aerosol uncertainty, Davies unfortunately reverts to the churlish falsehood:
This misconception is part of the disinformation put about by the professional deniers funded by the likes of ExxonMobil.
If this is the case, then why then have IPCC computer modelling studies been used to determine the contribution of CO2 to global warming in the last half-century and why has Hansen been at the forefront of that process?
As noted, in our original article we did not deal with the wider issue of AGW, but in respect of Davies’ distinction between the computer models and ‘real’ evidence we can say that the ‘real’ evidence shows even greater departure of models from reality, as the most recent forcing estimates of 0.23 Watts per meter squared is significantly below the 0.6 Watts per meter squared predicted by Hansen from the GISS model for the time period 1993 to 2003 (see here).
In addition we are not professional deniers funded by anyone.
We are, however, familiar with Hansen’s palaeoclimatic ‘real’ evidence for 3C ‘fast’ climate sensitivity to CO2 doubling, as we are with a number of other findings of ‘fast’ climate sensitivity of less than 1.5C: Douglass, Shaviv, Spencer, Schwartz, Lindzen, Idso, McKitrick, and Scafetta to name a few.
The main palaeoclimatic ‘real’ evidence put forward by Davies concerns the infamous CO2 lag where CO2 changes supposedly follow temperature changes. Using the same graph, which Davies does to illustrate this supposed lag of a few hundred years, Frank Lansner, also retired, shows that, in fact, there is no relationship between CO2 and temperature. The supposed lag of CO2 disappears when the graph is examined properly. The graph shows that temperature actually drops when CO2 is at its maximum levels and therefore maximum warming capacity. Davies like other people makes the mistake of only looking at the graph when both temperature and CO2 are increasing not when CO2 is increasing and temperature is DECREASING. This lack of a relationship between CO2 and temperature is also seen in the recent record with temperature going the opposite direction to CO2 from 1940 to 1976. Then, as now, an unmeasured human aerosol cooling effect is invoked.
The remainder of Davies’s article are obvious non sequiturs.
He thinks the statement that “the world’s most prominent expert on the use of computer models for understanding of the Earth’s climate” implies “that Hansen is a great believer in the accuracy of computer models.”
He thinks the statement “free from the restraints of peer review” implies “that Hansen was engaging in a sly trick.”
It is not clear why, but Davies repeatedly draws attention to the draft status of Hansen’s paper (which has since been published at the Cornell archive), and so creates the impression that it contains significant inaccuracies. We simply found it refreshing that uncertainties raised by climate sceptics over the years are beginning to be acknowledged by someone like Hansen – that sea level rise has decelerated from 3.1 to 2.3 mm/year, the importance of enhanced indirect solar influences proven in recent cosmic ray studies, that CO2 sinks are not becoming less efficient, the large uncertainty associated with aerosols, clouds, and of course, that the climate models are more uncertain than are usually portrayed – but fear these may fail to make the final version.
Once again, we ask the question, based on the poor performance of the models against observations in recent years: do we really have an adequate scientific case that demands a policy response? More generally if policies are implemented on the back of a one-sided presentation of the science, then it is those policies and science which do society a “disservice”, not us.
It is not as though Climate sceptics do not have much of a case, as Davies implies; he should read the views of around 80 prominent climate scientists, geophysicists and related hard scientists expressed in a letter to the US Congress 8th February 2011:
Do the 678 scientific studies referenced in the CO2 Science document, or the thousands of studies cited in the NIPCC report, provide real-world evidence (as opposed to theoretical climate model predictions) for global warming-induced increases in the worldwide number and severity of floods? No. In the global number and severity of droughts? No. In the number and severity of hurricanes and other storms? No.
Do they provide any real-world evidence of Earth’s seas inundating coastal lowlands around the globe? No. Increased human mortality? No. Plant and animal extinctions? No. Declining vegetative productivity? No. More frequent and deadly coral bleaching? No. Marine life dissolving away in acidified oceans? No.
Quite to the contrary, in fact, these reports provide extensive empirical evidence that these things are not happening. And in many of these areas, the referenced papers report finding just the opposite response to global warming, i.e., biosphere-friendly effects of rising temperatures and rising CO2 levels.
Dr Davies should rethink his position.