This is a guest post by Matt Ridley.
Joe Romm of ThinkProgress described my Wall Street Journal op-ed as:
riddled with basic math and science errors
Yet he fails to find a single basic math or science error in my piece.
He says I :
can’t do simple math
and then fails to produce a single example of my failing to do simple math.
He says I apparently don’t know the difference between water vapor and clouds. He produces no evidence for this absurd claim, which is wrong. Water vapor is a gas; clouds are droplets of liquid water that condense from water vapor. I do know the difference.
He quotes a scientist as saying
it is very clear water vapor…is an amplifying effect. It is a very strong warmer for the climate.
I agree. My piece states:
water vapor itself is a greenhouse gas.
So there is no confusion there. At least not on my part.
However, I do discuss the possibility that clouds, formed from water vapor, either amplify or damp warming – and nobody at this stage knows which. This is the point that my physicist informant was making: the consequence of increased temperatures and water vapor in the atmosphere may be changes in clouds that have a cooling effect. You will find few who disagree with this. As the IPCC AR4 said:
Cloud feedbacks remain the largest source of uncertainty.
Joe Romm disagrees with this consensus, saying
The net radiative feedback due to all cloud types is likely positive.
He gives no backing for this dogmatic conclusion. By contrast, Professor Judith Curry of Georgia Tech says:
The key point is this. The cloud forcing values are derived from climate models; we have already seen that climate models have some fundamental problems in how clouds are treated (e.g. aerosol-cloud interactions, moist thermodynamics). So, climate model derived values of cloud forcing should be taken with a grain of salt. Empirically based determinations of cloud forcing are needed. At AGU, I spoke with a scientist that has completed such a study, with the paper almost ready for submission. Punchline: negative cloud feedback.
Joe Romm quotes Robert Kaufman as saying
I know of no evidence that would suggest that the temperature effect of sulfur emissions are small.
My piece never claimed that aerosols arising from sulfur emissions had a small effect, however as Nic Lewis points out, in the draft AR5 report,
Table 8.7 shows that the best estimate for total aerosol RF (RFari+aci) has fallen from −1.2 W/m² to −0.7 W/m² since AR4, largely due to a reduction in RFaci, the uncertainty band for which has also been hugely reduced. It gives a higher figure, −0.9 W/m², for AFari+aci. However, −0.9 W/m² is not what the observations indicate: it is a composite of observational, GCM-simulation/aerosol model derived, and inverse estimates.”
With regard to the rate of ocean heat absorption, which I wrote was fairly modest, Joe Romm quotes Kevin Trenberth as writing:
On the contrary there is now very good evidence that a lot of heat is going into the deep ocean in unprecedented ways…
and then provides a link to an article citing a study estimating the Earth's current heat absorption as 0.5 W/m². So what "fairly modest" figure does Nic Lewis use? Actually slightly higher: 0.52 W/m²!
Romm then says:
Ridley apparently doesn’t have the first clue what the climate sensitivity means
This is not true. I define sensitivity clearly as the temperature change for a doubling of CO2. I am not talking about the Transient Climate Response, which relates to temperature change only over a 70 year period. There is no confusion at my end.
Romm then says that
Schlesinger notes that an aggressive program of carbon mitigation can limit warming to 2Â°C and avoid the worst impacts
“It is worth pointing out that there is a healthy debate about Schlesinger’s low estimate”.
So maybe there is some confusion at Romm’s end about what Schlesinger concludes. This is what his paper says (in "Causes of the Global Warming Observed since the 19th Century" in Atmospheric and Climate Science 2012) –
"Additionally, our estimates of climate sensitivity using our SCM and the four instrumental temperature records range from about 1.5°C to 2.0°C. These are on the low end of the estimates in the IPCC’s Fourth Assessment Report. So, while we find that most of the observed warming is due to human emissions of LLGHGs, future warming based on these estimations will grow more slowly compared to that under the IPCC’s “likely” range of climate sensitivity, from 2.0°C to 4.5°C."
Many other recent papers have come to similar conclusions: For example, Schmittner et al. in Science Dec. 11, 2011 URL:
Combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations, we estimate a lower median (2.3 K) and reduced uncertainty (1.7 to 2.6 K as the 66% probability range, which can be widened using alternate assumptions or data subsets). Assuming that paleoclimatic constraints apply to the future, as predicted by our model, these results imply a lower probability of imminent extreme climatic change than previously thought.
Meanwhile for transient climate response, similar low estimates are also now being made. See for example Gillett et al.'s 2012 article "Improved constraints on 21st-century warming derived using 160 years of temperature observations" in Geophysical Research Letters:
Our analysis also leads to a relatively low and tightly-constrained estimate of Transient Climate Response of 1.3–1.8°C, and relatively low projections of 21st-century warming under the Representative Concentration Pathways.
Or Padilla et al.'s 2011 article "Probabilistic estimated of transient climate sensitivity subject to uncertainty in forcing and natural variability" in the Bulletin of the American Meteorological Association at URL::
For uncertainty assumptions best supported by global surface temperature data up to the present time, this paper finds a most likely present-day estimate of the transient climate sensitivity to be 1.6 K, with 90% confidence the response will fall between 1.3 and 2.6 K, and it is estimated that this interval may be 45% smaller by the year 2030. The authors calculate that emissions levels equivalent to forcing of less than 475 ppmv CO2 concentration are needed to ensure that the transient temperature response will not exceed 2 K with 95% confidence.
Mr Romm seems confused about methane outgassing feedbacks, arguing that even if climate sensitivity is low, these may dominate. Suffice to say that in this he has drifted a long way from the consensus.
Mr Romm seems determined to rule out even the possibility of low climate sensitivity in the teeth of strong evidence. I can see why he wishes to do so, his job depending on there being a dangerous future. I do not understand where he gets his certainty.
Finally, Mr Romm throws the term “anti-science” at me, again with no evidence. I cited peer reviewed papers and made the scientific argument that the latest data be considered in estimating sensitivity. That is pro science. What is anti-science is to make false accusations and try to shut down legitimate debate. Hard working people all over the world are now risking their lives as well as their wallets for the consequences of current climate policy (see Indur Goklany’s paper “Could biofuel policies increase death and disease in developing countries?”). They have a right to ask that those who determine the science behind such policies are open-minded. On the evidence of MrRomm’s astonishing outburst, my doubts about this are growing.