I can look into how to factor in (or out) the Pinatubo eruption. Now that you have brought it to my attention, it probably dampens the growth rate for my first period, and amplifies it for my second period. So if I somehow control for it, and take it out, it will tend to increase the trend in the first period, and reduce the trend in the second. Given the timing of Pinatubo, if I do try to control for it, I’ll probably end up adjusting the time periods a bit.

Aaron, I’ve already controlled for the 98 El Nino. The trend you see before and after the data spike up in 98 is what is left after controlling for the El Nino.

you say

“To make my point clearer, are their any GCM models which can explain why temperatures in the 1993-2001 period increased at more than 3x the rate of increase from 1979 through 1992….”

Pinatubo probably explains the difference. Pinatubo erupted in June 1991 and caused considerable world-wide cooling in 1992, 1992 and possibly 1994 also. This will have the effect of exaggerating the 1993-2001 warming trend while reducing the 1979-1992 trend. Over short time periods the effect of major volcanos is significant.

I’m not sure if you can remove the Pinatubo effect but, as a rough guide, I think both 1991 and 1992 should (without Pinatubo) have been at least as warm as 1990 since there was a strong-ish El Nino in effect during 1991/92. There were also generally warmer ocean temps in the following years up to around late 1995, so 1993 and 1994 should also have recorded similar - if perhaps slightly lower - temperature anomalies.

I think the IPCC in AR4 only goes through 2005, so the “last six years” they would be talking about are not the last six years shown in my chart. And in 2005, it might have been harder to discern a downward trend from 2001 than it is today. However, I would venture the possibility that had they looked at the data for 1999 to 2005 carefully, they would have been forced to acknowledge that there was no trend, i.e. that any “trend” for those years was not significantly different than zero. You can almost see this just looking at the other chart I posted:

http://i27.tinypic.com/2r74myd.jpg

From 2001 to 2005, it is certainly hard to visualize any discernible trend, and given the monthly variation in the data it would be highly unlikely to find a “statistically significant” trend of any kind in the data.

While three of the four trend variables since 2001 are significantly different than zero, I wouldn’t be surprised to find them significantly different than the trend value for the preceding period. When I have time this week, I’ll check it out.

In my opinion, your calculations contradict the latter statement. It is true that the noisiness of the data is such that the downward trend in observed temperature between Jan 2002 and Jan 2008 may prove to be a blip in a long-term upward trend - but that remains to be seen.

I understand that it is the trend that would have to be adjusted by 1.2x. That’s why I called attention to the 1.36x trend difference for the period of greatest warming, 1993 through 2001. It is already there, no need to adjust the data. Since 2001, all the metrics show cooling, but the numbers are all over the place, and it doesn’t look like a similar simple comparison between land-sea and satellite metrics holds. This could be because the period is shorter and the data otherwise too uncertain or variable to yield any precise inferences. Do note that in the 1993-2001 period, all the trends are statistically significant, while that’s not the case for the period since 2001.

I’m not convinced that the 1.2x difference that should be there is going to be discernible. There is too much variation as it is, with the effects of ocean circulations, La Nina’s and El Nino’s, and such. It would probably take a century of steady warming to see a 1.2x difference that is statistically discernible. So far, we’ve only 28 years of satellite data. Let’s look at this again in 2079. ;)

What I really think is useful about all this analysis is in showing that there isn’t a discernible difference. I.e., the data are too noisy to meaningfully test a significant AGW/GCM hypothesis. And hypotheses that cannot be tested are not scientific. To make my point clearer, are their any GCM models which can explain why temperatures in the 1993-2001 period increased at more than 3x the rate of increase from 1979 through 1992, and then simultaneously explain a 3x cooling since then? Oh, and don’t anyone blame the 1993-2001 warming on the 1998 El Nino. I haven’t reported the statistics on my ‘98 El Nino variables, but the trend for 1993-2001 excludes the effect of the ‘98 El Nino. You can see that in the trend lines, though.