The bottom line is this: there is no global cooling trend. For the time being, until humanity brings its greenhouse gas emissions under control, we can expect each decade to be warmer than the preceding one. Weather fluctuations certainly exceed local temperature changes over the past half century. But the perceptive person should be able to see that climate is warming on decadal time scales.
The quote and figure are from a fascinating draft essay, “If It’s That Warm, How Come It’s So Damned Cold?” by NASA’s James Hansen, Reto Ruedy, Makiko Sato, and Ken Lo. It is posted on Hansen’s Columbia University website, and he sent out a note to his email list asking for comments:
Criticisms are welcome. This is a draft essay that I wanted to get out because we are releasing our December and annual surface temperature analysis on the GISS web site. We will prepare a write-up on 2009 temperatures for the GISS web site next week.
If you post comments I’ll get them to him.
Yes, Dr. Ruedy had told me they were going to get their write-up out Friday (see “Breaking: 2009 hottest year on record in Southern Hemisphere and tied for second globally”). But apparently there are just too many issues they wanted to address in it, including the long-term trend vs. the cold snap. The trend is unmistakable, you might even say unequivocal:
The long”term trends are more apparent when temperature is averaged over several years. The 60″month (5″year) and 132 month (11″year) running mean temperatures are shown in Figure 2 for the globe [above] and the hemispheres. The 5″year mean is sufficient to reduce the effect of the El Nino — La Nina cycles of tropical climate. The 11″year mean minimizes the effect of solar variability — the brightness of the sun varies by a measurable amount over the sunspot cycle, which is typically of 10″12 year duration.
The draft essay goes into great depth on how NASA knows 2005 was warmer than 1998 and why their dataset is better than the Hadley/CRU dataset (see also “Why are Hadley and CRU withholding vital climate data from the public?” and Finally, the truth about the Hadley/CRU data: “The global temperature rise calculated by the Met Office’s HadCRUT record is at the lower end of likely warming”).
There is a contradiction between the observed continued warming trend and popular perceptions about climate trends. Frequent statements include: “There has been global cooling over the past decade.” “Global warming stopped in 1998.” “1998 is the warmest year in the record.” Such statements have been repeated so often that most of the public seems to accept them as being true. However, based on our data, such statements are not correct.
The origin of this contradiction probably lies in part in differences between the GISS and HadCRUT temperature analyses (HadCRUT is the joint Hadley Research Centre, University of East Anglia Climate Research Unit temperature analysis). Indeed, HadCRUT finds 1998 to be the warmest year in their record. In addition, popular belief that the world is cooling is reinforced by cold weather anomalies in the United States in the summer of 2009 and cold anomalies in much of the Northern Hemisphere in December 2009.
Here we first show the main reason for the difference between the GISS and HadCRUT analyses. Then we examine the 2009 regional temperature anomalies in the context of global temperatures.
A key takeaway message is this:
Why are some people so readily convinced of a false conclusion, that the world is really experiencing a cooling trend? That gullibility probably has a lot to do with regional short”term temperature fluctuations, which are an order of magnitude larger than global average annual anomalies.
Short-term weather fluctuations are vastly greater than the long-term global warming anomaly in the climate (so far). Weather isn’t climate.