In a recent post I came up with a 100-year global temperature trend of 1.64°C per century using the temperature history of 5 metrics of the satellite era. With satellite temperature updates of June and by using GISS land-ocean-index instead of “meteorological stations only” as in May, this trend is now being reduced to 1.59°C per century. Although this is still consistent with Special Report on Emission Scenarios SRES as used in the two recent reports TAR and AR4 of the IPCC, the slope points towards the lower end of any scenario.

First of all, lets have a look at the same global temperature trends. By using a running 4-year mean of the respective monthly temperature anomalies, the intention is to smooth out the effects of ENSO (El Nino - Southern Oscillation) as a natural variation influencing global temperature from one year to another. The professionals at Realclimate are the ones who have done it right I am sure. But this is not the main objective of the following graph. ENSO is probably the natural variability that is most cited by AGW proponents and the IPCC report is full of it alright. Yet another variable is the effect of two major volcanic eruptions: El Chichon and Mt. Pinatubo (see graph). And - surprise, surprise - the temperature was dropping worldwide for months or even years after the eruptions. Now, for the first time since Pinatubo erupted, the weather turns cooler again. But this time it is not just La Nina, it is not a major volcano, yes, it is also a lingering solar minimum, but there is something else in the picture that is not “unambigious” according to Prof. Gavin Schmidt of Realclimate.org. It is the pacific decadal oscillation once again. I used the same smoothing when embedding the PDO-index into the temperature history. The pacific decadal oscillation is still subject to debate among scientists. It is not clear whether it follows a cycle or if it just randomly switches on and off. But the index shows clearly warm and cold phases with a more long-term pattern in comparison with ENSO. It looks like PDO has switched into a cold phase with more La Ninas as a consequence.

In the middle of 2008, we have now a nice mix of a lingering La Nina together with a lingering solar minimum that encourages a continued disruption of the global warming trend. See also Keenlyside and Latif. The only thing that’s “missing” is a major volcano with global effects. But I digress…

Why does the title of this article claim that global temperature is about to fall below IPCC scenarios? Let’s look at one of the scenarios as outlined in AR4. SRES scenario A2 assumes a sort of “business-as-usual-attitude” on the planet until 2100. As far as the effect of the ongoing worldwide efforts to cut greenhouse gas emissions on the actual temperature  is concerned, I daresay that this emission scenario fits nicely up until now. So according this scenario, the temperature is projected to go up from 1990 to 2100 like this. The best estimate of the same scenario would rise the average temperature of 2071-2100 3°C above the 1961-1990-level.

With global warming taking a rest right now, temperature worldwide will have to accelerate nicely after - say - 2030 in order to reach the projected level. With each month of cool temperature reported, the dissenters of AGW alarmism will increase in numbers.

Update 2008/07/20:

References:
IPPC 2001, Working Group I, The Scientific Basis, Special Report on Emissions Scenarios SRES; , Graph 5 (d) The Global Climate of the 21st Century, Temperature change ( http://www.grida.no/climate/ipcc_tar/wg1/figspm-5.htm )

Model Average Surface Air Temperature Change: http://www.grida.no/climate/ipcc_tar/wg1/552.htm