> From: David Sunfellow <nhne@n...>
> Date: Sat Feb 28, 2004 10:45 pm
> Subject: The Sun IS NOT Causing
> the Current Round of Global Warming
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The following excerpt comes from an informative letter that Jim Torson wrote to someone who believed that the sun was the cause of Earth's current rising temperatures. It summarizes what Jim recently learned from Dr. Caspar Ammann of the National Center for Atmospheric Research. Thanks to Jim for allowing me to share this information with all of you.
--- David Sunfellow
From Jim Torson
February 28, 2004
...Yesterday afternoon I attended a colloquium at Lowell Observatory on the subject of solar variation and climate change. (A copy of the colloquium announcement is included below.) The speaker was Dr. Caspar Ammann from the National Center for Atmospheric Research. I was able to chat with Dr. Ammann both before and after the colloquium to ask some questions. The following is a summary of a few important things he had to say.
At the beginning of the talk, Dr. Ammann mentioned the recent statements of James Schlesinger (former Secretary of Energy) on climate change and described why his statements are misleading and wrong. E.g., his statement that during the Middle Ages the Earth's temperatures were 1 to 2 degrees warmer than they are today is totally incorrect.
One criticism that has been made of the computer models (GCMs - Global
Circulation Models) is that they do not correctly model what we know to have happened in the past. However, this is no longer a valid criticism. (They have been running GCMs on the supercomputers at NCAR. Recently, they have been using the Earth Simulator computer in Japan because it is faster than the computers currently available at NCAR.) They have modeled the climate from 850 AD to the present. An important input to the model is the historical record of volcanic eruptions. Another important input is the solar variation, obtained from the amounts of Beryllium-10 in polar ice cores. Their model is quite good at describing the historical climate record, including the "Little Ice Age" and the "Medieval Warmperiod."
An important conclusion is that solar variation is an important factor in climate variation, which of course is no big surprise. However, the solar variations involved in the climate variations during the period they studied was quite small -- about one tenth (0.1) of one percent.
The bottom line of all this is that solar variation cannot possibly be the cause of the current warming. There is debate about whether or not the instrumental records show any clear evidence of recent solar variation. However, those who think there is evidence for variation say that it is about 0.1 percent. The recent warming is clearly much greater than the temperature variation over the past 1000 to 2000 years. If the recent warming were caused by solar variation, it would have to be much more than this 0.1 percent, and nobody is claiming there is any evidence for this larger variation. The only way to explain the current warming is to include the effects of the anthropogenic (human-caused) greenhouse gasses such as carbon dioxide.
There has been discussion of the possibility of rapid climate change
resulting from the slowing or stopping of the thermohaline circulation in the oceans, which would result in dramatic cooling is some areas such as England and western Europe (while the average temperature of the entire planet continues to rise). Interestingly, Ammann said he thought that was a possibility, but he thought that greenhouse warming might overwhelm this effect so that these areas have constant or rising temperatures. He said a more likely scenario would be that the warming could cause the release of large quantities of frozen methane from the ocean floor. (There is evidence that this happened millions of years ago.) Methane is a greenhouse gas, so this would accelerate the human-caused warming that is now in progress.
Another thing that Ammann said was that the planet is not currently in
radiative equilibrium. Thus, unfortunately, even if we stopped all emissions of greenhouse gasses, the planet would continue to warm for some time to come.
A final thing that Ammann said was that thirty years ago the general
thinking was that we might be headed for a cooling trend. This was based on examination of the natural climate change that had occurred in the past, e.g, from examining ice cores. However, in the past thirty years, there has been continuing new evidence that we are now in a warming trend and that human activity is an important cause of this.
Ammann is a co-author on the following paper:
Mann, Michael E., Caspar Ammann, Ray Bradley, Keith Briffa, Philip Jones, Tim Osborn, Tom Crowley, Malcolm Hughes, Michael Oppenheimer, Jonathan Overpeck, Scott Rutherford, Kevin Trenberth, and Tom Wigley, 2003. On Past Temperatures and Anomalous Late-20th Century Warmth, Eos, Vol. 84, No. 27.
This is available on-line as a PDF file at:
This contains a diagram that clearly shows that the recent warming is above what naturally occurred over the past 1000-2000 years. (In a response to Mark, you said that between 800 and 1300 AD the temperature was 4 to 5 degrees warmer than it is today. While this might be correct for some areas, Fig. 1 in this article shows that it is totally incorrect for the northern hemisphere average.)
Diagrams showing the comparison of the latest computer models with actual past climate are contained in the Powerpoint presentaion:
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Subject: Re: [Solar Threat] more debate....
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