NOTE: This was posted on ICECAP today, and I’m copying it here. See my further notes below.
By Dr. John R. Christy.
I have been flooded this week with calls and e-mail messages concerning a story that has appeared on various Internet sites, in which the claim is made that cooling global temperatures over the past twelve months in some way negate or eliminate any global warming that might have happened over the past 100 years.
“Here is my perspective on this issue: Twelve months of data does not make a trend, especially in a system as complex and slow moving as global climate, and even more so when the cause for that short-term cooling is as reasonably well understood and well documented as a switch from a minor El Nino Pacific Ocean warming in January 2007 to the La Nina cooling event now taking place.
“The 0.59 C drop we have seen in the past 12 months is unusual, but not unprecedented; April 1998 to April 1999 saw a 0.71 C fall. The long-term climate trend from November 1978 through (and including) January 2008 continues to show a modest warming at the rate of about 0.14 C (0.25 degrees F) per decade.
“One cool year does not erase decades of climate data, nor does it more than minimally change the long-term climate trend. Long-term climate change is just that “long term” and 12 months of data are little more than a blip on the screen.”
Dr. John Christy is Professor of Atmospheric Science and Director, Earth System Science Center, The University of Alabama in Huntsville
Icecap Note: John is absolutely correct that we can’t make assumptions about one year’s trend either up or down. The story he references used the Hadley CRU land and ocean based data and of course John Christy, Roy Spencer and Phillip Gentry are using satellite derived lower tropospheric data. Satellite is widely recognized as the most accurate method for the assessment of change. The following plot of the last decade of the satellite derived global temperatures shows how the global climate is strongly influenced by El Nino and La Nina as John notes.
Note from Anthony: When the DailyTech first posted this story and referenced my blog as the source of th compilation, without ever interviewing me or asking me a single question, I notified them immediately of my concerns. Shortly after that I published this “Update and Caveat” (below) on the original post. Dailytech graciously made a changes to the wording at my request, but by then the genie was out of the bottle.
The website DailyTech has an article citing this blog entry as a reference, and their story got picked up by the Drudge report, resulting in a wide distribution. In the DailyTech article there is a paragraph:
“Anthony Watts compiled the results of all the sources. The total amount of cooling ranges from 0.65C up to 0.75C — a value large enough to erase nearly all the global warming recorded over the past 100 years. All in one year time. For all sources, it’s the single fastest temperature change ever recorded, either up or down.”
I wish to state for the record, that this statement is not mine: “–a value large enough to erase nearly all the global warming recorded over the past 100 years”
There has been no “erasure”. This is an anomaly with a large magnitude, and it coincides with other anecdotal weather evidence. It is curious, it is unusual, it is large, it is unexpected, but it does not “erase” anything. I suggested a correction to DailyTech and they have graciously complied.
This demonstrates how one story written in one place can often go repeated, without being challenged or double checked. This happens in many types of news reports. In my 25 years in TV, I’ve seen this happen at the local level, all the way up to the national level. We’ve seen it happen with global warming stories too. The ease of electronic immediacy in reporting often runs over the accuracy in reporting, be it blogs, websites, TV or radio, the issue is the same.