But the SPM has been sidelined by momentous climate change events that occurred after its March cut-off date – and even after the date the draft was circulated.
The post is referring to recent papers on climate sensitivity and on the temperature standstill. In fairness an element of flexibility may be quite reasonable. However, the IPCC is an organisation that is heavily criticised by some involved in the climate change/global warming debate, and so sticking to their rules may be sensible. It’s partly a lose-lose for them, but at least sticking to the rules is harder to criticise than breaking the rules.
When it comes to climate sensitivity, two of the recent papers highlighted in the WUWT post is one by Otto et al. and another by Nic Lewis. Both of these have climate sensitivities lower than that of many other studies. If I remember correctly, both of these studies use recent observational data to estimate climate sensitivity (Added 2/9/2013 – it seems I did not remember correctly. Nic Lewis’s paper is a re-analysis of a Bayesian climate parameter study and is based on an earlier paper by Forest et al. 2006. Hence it doesn’t use the equations I describe below. My analysis below therefore doesn’t apply to Nic Lewis’s paper. If you want to know more, there is a Skeptical Science post about it.). The equations they use for the Transient Climate Response (TCR) and equilibrium climate sensitivity (ECS) are
In a sense these are quite clever approximations. Consider some time period over which the temperature is measured to changed by an amount ΔT. Use the change in CO2 concentration over the same time period to calculate the change in forcing ΔF. Use the known change in forcing ΔF2x for a doubling of CO2 to then calculate the TCR. Additionally, one can use the change in ocean heat content to determine the forcing, ΔQ, that has contributed to ocean heating. The difference between ΔF and ΔQ then gives the amount that has heated the surface during the time period considered and can then be used to estimate the ECS.
I can see a number of issues with using the above equations to estimate the TCR and ECS. One is that you have to assume that the forcings and feedbacks associated with the rising CO2 concentrations during the time period considered is a good representation of what will happen over the entire period during which CO2 will double. It may not be and the shorter the time period considered, the more likely there will be a mismatch. Another issue is that we now know that the surface temperature has a long-term anthropogenic trend on top of which short-term variations (due to natural variability) are super-imposed. There are periods during which the surface temperature trend is faster than the anthropogenic component, and other times when it is slower. Therefore the equations above should ideally use a time period over which the short-term natural variations average out. If not, the equations will either over-estimate or under-estimate the likely values of the climates sensitivities.
Another issue is that the equations above ignore any paleo-climatological evidence. This evidence suggests that the ECS is likely to be at least 2oC. In a similar vein, there are slow feedbacks that produce an equilibrium system sensitivity (ESS) which is expected to be higher than the ECS. In some sense, I would imagine that many would regard the equations above as sensible sanity check rather than truly independent estimates that should be seen as equivalent to those from much more detailed models. So, even though there are recent papers suggesting that the TCR and ECS could be lower than expected, the general views is (I believe) that it is unlikely that the ECS can be below 2oC.
Another thing that the recent WUWT post focuses on is recent work that has addressed the surface temperature “hiatus”. A paper they mention is one by von Storch & Zorita called can climate models explain the recent stagnation in global warming. Again, something I find frustrating about such papers is that they use the term global warming to mean surface warming. Ocean heat content data tells us that global warming has not stagnated. It’s only surface temperatures that are rising slower than expected. What this paper seems to do is establish how many climate models have trends – over the same time period – the same as or lower than the observed trend. They find that only 2% satisfy this condition. It, however, seems to have chosen the lowest of the possible trends (NCDC, HADCRUT4, GISS) and also doesn’t really seem to have considered the errors in the observed trends. The WUWT post summarises the von Storch & Zorita paper by saying
concludes that ‘natural’ internal variability and/or external forcing has probably offset the anthropogenic warming during the standstill. Overestimated sensitivity may also have contributed.
This makes it seem as though it is a combination of ‘natural’ internal variability, some unknown external forcing and overestimated sensitivity. The paper actually suggests these as 3 independent possibilities, although it does suggest that all 3 could contribute. However, the recent paper that blew Judith Curry’s mind seems to be suggesting that the surface temperature “hiatus” is most likely a consequence of reduced sea surface temperatures in the central to eastern tropical pacific. In other words, the suggestion is that anthropogenic global warming continues as expected, but internal variability means that we’re going through a period of reduced surface warming, not reduced global warming. So, there’s no real evidence that there is some unknown external forcing that is slowing global warming and not much evidence that the climate sensitivity is really lower than expected.
The WUWT concludes by saying
These new papers devastate the IPCC orthodoxy that current and future global temperatures are mostly driven by greenhouse gas emissions, and will reach dangerous levels later this century. On the other hand, all older papers are blindsided by their apparent failure to take account of the recent data (standstill).
I think this rather over-emphasises the significance of these recent papers. The ones on climate sensitivity might suggest slightly lower climate sensitivities than other studies, but their estimates are still consistent with earlier work and their method may be less reliable than more detailed calculations. Also, the von Storch & Zorita paper doesn’t really seem to conclude anything by itself and one of the suggestions made in the paper is what most suspect explains the surface temperature hiatus – internal variability resulting in a period where we’re undergoing a phase of slower than expected surface warming despite global warming continuing as expected.
So, I can’t see any real reason why the IPCC should change its rules and include these recent papers in the report it will be releasing later this month. They seem like perfectly fine bits of work, but they’re nowhere near as paradigm shifting as those at WUWT would like to believe.