“ +++ climate sensitivity is an equilibrium concept. It tells you the temperature that you get to eventually. In a transient situation (such as we have at present), there is a lag related to the slow warm up of the oceans, which implies that the temperature takes a number of decades to catch up with the forcings. This lag is associated with the planetary energy imbalance and the rise in ocean heat content. If you don't take that into account it will always make the observed 'sensitivity' smaller than it should be.”

Comment: My article explicitly mentioned, took into account, and gave evidence for and against, the notion that the ocean was the cause of the difference between the transient and equilibrium climate responses to a given forcing.

Schmidt: “Therefore if you take the observed warming (0.6°C) and divide by the estimated total forcings (~1.6 +/- 1W/m²) you get a number that is roughly half the one expected.”

Comment: Using the UN’s CO2 forcing equation, and its all-ghg-to-CO2 ratio, I calculated the 1900-1998 forcing from all ghgs as 1.99wm^-2. Using the Stefan-Boltzmann equation for the Earth/troposphere system as a greybody with dT 0.6C, I calculated the 1900-1998 forcings from all sources as 1.98wm^-2. The two values are near-identical, suggesting either the cancellation of positive and negative feedbacks or the ocean notion, or some combination of the two. Either way, there is no cause for climate alarmism on these figures.

Schmidt: “ +++ If you ignore the fact that there are negative forcings in the system as well (chiefly aerosols and land use changes), the forcing from all the warming effects is larger still (~2.6 W/m²), and so the implied sensitivity even smaller.”

Comment: Again, I used the UN’s assumptions, which is that non-ghg forcings are not as well understood as ghg forcings, and that – as its table of forcings shows – all non-ghg forcings broadly self-cancel. This point was clearly explained, and illustrated with the UN’s forcings table, in the supporting calculations, which Schmidt had seen.

Schmidt: “Of course, you could take the imbalance (~0.33 +/- 0.23 W/m² in Hansen et al., 2005) into account and use the total net forcing, +++ ”

Comment: I cited Hansen et al. (2006), making a similar point.

Schmidt: “And finally, you can +++ imply that all the warming is due to solar forcing.”

My article correctly showed that, if one takes 1900 and not 1750 as the start-date for solar forcings, so as to coincide with the 20^th-century temperature rise of 0.6C relied upon by the UN, its own table of solar-irradiance proxies shows a base 20^th-century solar TSI increment of some 4wm^-2, equivalent to about 0.7wm^-2 outgoing at the tropopause after allowing for albedo and disc-to-sphere. This is before adding climate feedbacks, for which the UN’s current multiple of base forcing is approximately 2.7 according to Sir John Houghton in a reply to a question from me on the subject. Thus one multiplies the solar forcing by the feedback coefficient to get forcings plus feedbacks – i.e. 1.9wm^-2, which is close to the 2wm^-2 actually observed. However, the accompanying calculations, which Schmidt has seen, made it very clear that I had assumed, as a base case, no solar forcing above that mentioned by the UN, and that I had compared that case with others, some of which had considered 20^th-century solar forcings greater than those assumed by the UN.

Schmidt: “ +++. Either there are important feedbacks or there aren't. You can't have them for solar and not for greenhouse gases. Our best estimates of solar are that it is about 10 to 15% the magnitude of the greenhouse gas forcing over the 20th Century. Even if that is wrong by a factor of 2 (which is conceivable), it's still less than half of the GHG changes. And of course, when you look at the last 50 years, there are no trends in solar forcing at all. +++ ”

Comment: My article explicitly addressed the need to apply climate feedbacks to all forcings and said the UN had not done so. See Solanki and Usoskin (2005) for a conclusion that the Sun has been hotter, for longer, in the past 50 years than in the past 11,400 years. Recent papers apparently disputing this have failed to take account of Solanki’s point that it is the combination of the amplitude and duration of the recent solar activity that is exceptional, not the amplitude alone.

Chuck it again, Schmidt!

Commentary on a February 2007 posting by one Schmidt on a website owned by him with, inter alios, two authors of the discredited UN graph purporting to erase the mediaeval warm period

Schmidt: “+++ The WSJ is an influential paper in the US. However, the extent of its isolation on [climate change] is evident from the +++ reliance on +++ Christopher Monckton. They quote him saying that the sea level rise predictions were much smaller than in IPCC TAR (no they weren't), …”

Comment: My analysis of the Summary for Policymakers stated, correctly, that the UN’s upper-bound projection of sea-level rise to 2100, which had been 88cm in 2001, had been cut to 43-59cm in 2007, a reduction of between one-third and one-half depending on which scenario one uses. The Sunday Telegraph, the first newspaper to announce this reduction, verified it with the UN before printing it. The UN said the reduction in high-end forecasts on all scenarios had been made because “better data” were available. Quite.

Schmidt: “… that the human contribution to recent changes has been 'cut by a third' (no it hasn't), and that the Summary for Policy Makers (SPM) was written by politicians (no it wasn't - the clue is in the name).

Comment: The table of forcings in the UN’s 2001 report showed greenhouse-gas forcings summing to 2.43 watts per square meter, with all other forcings broadly canceling each other out. The equivalent table for 2007, albeit rotated by 90 degrees to make visual comparison less easy, reduces the 2001 report’s 2.43-watts-per-square-meter estimate of the anthropogenic greenhouse-gas contribution compared with 1750 by one-eighth to 2.3 watts per square meter despite a statement that radiative forcing from CO2 alone had increased by 20% since 1995. In addition, the report ascribes a large negative forcing to the effect of pollutant aerosol particles in the atmosphere for the first time. Also for the first time, taking into account negative as well as positive forcings, the UN states its estimate of total forcings, rather than allowing them to be deduced from the table of forcings. Its stated estimate of the anthropogenic forcing is 1.6 watts per square meter, down by a third from the previous report’s 2.43 watts per square meter.

Schmidt: “Even more wrong is the claim that "the upcoming report is also missing any reference to the infamous 'hockey stick' ". Not only are the three original "hockey stick" reconstructions from the IPCC (2001) report shown in the (draft) paleoclimate chapter of the new report, but they are now joined by 9 others. Which is why the SPM comes to the even stronger conclusion that recent large-scale warmth is likely to be anomalous in the context of at least the past 1300 years, and not just the past 1000 years.”

Comment: My analysis correctly stated that the UN, in its present report, had failed to apologize for the universally-discredited “hockey-stick” graph, and that its failure to apologize undermined its credibility and scientific integrity. I did not say that the “hockey-stick” had been dropped. I wish it had: then one could perhaps start to have some confidence in the IPCC process.

Schmidt: “Thus on any index of wrongness, this WSJ editorial scores pretty high. What puzzles us is why their readership, who presumably want to know about issues that might effect their bottom line, tolerate this rather feeble denialism. While we enjoy pointing out their obvious absurdities, their readers would probably be better off if the WSJ accepted Jeffery Sachs' challenge. For if they can't be trusted to get even the basic checkable facts right on this issue, why should any of their opinions be taken seriously?