The weblog Stoat has made a significant erroneous statement on the November 30 2007 Climate Science web posting
This Climate Science web posting corrects William M. Connolley’s scientific comments (I do appreciate, of course, that he is open-minded enough to read Climate Science!).
“RPs point appears to be that the IPCCs forcing-since-1750 of +1.6 W/m2 is not compatible with a current imbalance of about 0.85 W/m2. Sadly RPs link to the Hansen paper concerned is currently broken so I’m somewhat guessing what this figure is; I think its probably the earths current radiative imbalance. RP calls it the “the total observed radiative forcing and feedback” but I think he’s got this wrong.”
William is in error on the claim that the “the earths current radiative imbalance” is different than the “the total observed radiative forcing and feedback”. They are the same when both are for the same time period.
Indeed, this can easily be shown from a simple physics budget equation;
[Observed Global Radiative Forcing + Global Radiative Feedbacks (ocean heat content change + other Earth system heat changes) = Real World Global Radiative Imbalance] – Global Radiative Forcings (e.g. from the IPCC) = Global Radiative Feedbacks (e.g. which are consistent with the IPCC estimate of global radiative forcing)
The units of this equation can be in Joules per time or a global average Watts per meter squared. The history of these terms is not needed (such as back to 1750). The analysis of these terms can be made over any time period as long as it is the same for each term. [When the first term in the above budget equation is positive, there is global warming.]
There is an issue with the time of the IPCC forcings as the IPCC writes in the caption to Figure SPM-2 that they are presenting
“Global-average radiative forcing (RF) estimates and ranges in 2005…..”
Thus the IPCC states that the forcings in Figure SPM-2 are for 2005.
This is written differently in the footnote on page 2 of the IPCC report
In this report, radiative forcing values are for 2005 relative to pre-industrial conditions defined at 1750 and are expressed in watts per square metre (W m–2).
This is the apparent source of William’s misinterpretation. If William (or Gavin Schmidt) want to let the IPCC know of this error in the Figure caption, they should do that and let us know. Otherwise, we should assume thay agree with the Figure caption.
Even more importantly they (and the IPCC) should provide us with the actual best estimate of radiative forcings at the current time for each of the forcings listed in Figure SPM-2. Otherwise, we should assume that they agree with the IPCC caption that the plotted values are for 2005.
This issue of the time period of the forcings, which is contradictory within the IPCC SPM, is at the basis of the misinterpretation in the Stoat weblog.
I also include here the IPCC estimate of the total radiative forcing in global averaged Watts per meter squared which is +1.6 (0.6 to 2.4) for the total net anthropogenic forcing plus +0.12 (0.06 to 0.3) for the solar irradiance. Adding these two together yields +1.72 (0.66 to 2.7) which makes the conclusions on the negative feedbacks even stronger.
Thus if one accepts the IPCC central estimate of the global radiative forcings as being accurate for 2005 as they write in their figure caption (which is a premise of my November 30th weblog), then the Global Radiative Feedbacks are less than the Global Radiative Forcings. The global radiative feedbacks are negative! Any water vapor feedback, an increase in the surface long wave irradiance and all other climate effects, are included in these feedbacks.
If the IPCC value for the 2005 forcings are too large (since they are actually presenting the difference from the pre-industrial values), it is important that the IPCC provide us with a current estimate for each forcing and for the net value. Then we can reassess if global average radiative feedbacks are negative or not.
However, if one accepts the IPCC values of radiative forcing as being for 2005 (as stated in their figure caption), there is no other conclusion except that the climate system mutes the warming effect of positive radiative forcings.
New data, including recent sea surface temperature trends and upper ocean heat trends (which Climate Science will weblog on soon) further raise issues with the IPCC conclusion on the radiative forcings and feedbacks, as over the last few years, there has been no significant global warming using those two observed climate metrics.