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samboct -> RE: The myth of the "1970s global cooling hysteria" (12/5/2008 5:02:49 PM)
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An update on the science front-
I just got back from the 2008 Materials Research Society (MRS) meeting in Boston. One of the major invited talks was given by Susan Solomon of the NOAA on the 2007 IPCC report. There is effectively no debate any longer in the science community on global warming. Oh, I'm sure there are a few skeptics (Anybody remember Peter Duesberg who managed to convince Idi Amin that AIDS wasn't spread by HIV? The death toll from that one is only a few million or so, but who's counting?), but the theory is showing itself to be remarkably robust. The President of the MRS, Cynthia Volkaert characterized the talk as frightening and a call for action. Most people there agreed with Dr. Volkaert's description. Anybody who wants to argue with global warming at this point is now arguing with physics. A few points-
1) The temperature rise associated with anthropogenic sources of CO2 has been estimated at 0.75C (I'll get to how that estimation was made.)
2) Competing hypotheses such as variations in the sun cycle have shown to be independent of global warming.
3) Ice ages are due to variations in the Earth's orbit and are predictable. We're not due for another one in 10,000 years or so.
4) While CO2 levels were a lagging indicator of Earth's temperature in the past, CO2 levels are now forcing the temperature to rise.
5) Lifetimes of CO2 in the atmosphere are quite long. Most of the CO2 emitted is still in the atmosphere 25 years later, and a significant fraction is around for a century.
To some of the earlier posts- there is a difference between climate and weather. Climate changes are measured in decades- weather is measured on shorter time scales. Thus, natural processes such as an El Nino event can cool the planet for a year or so, but they do not affect the longer period of climate change. What's happened that has made the science more solid is that we have now largely measured 3 solar cycles and shown that the sun's output does not correlate to global warming- but CO2 concentration does.
How does CO2 cause global warming? Here's the physics- There are two sources of heat for the planet: the sun and radioactive decay which keeps the core molten. Unless there is a balance between the heat adsorbed from the sun, and heat losses to radiative cooling, the planet warms up. This assumes that the temperature of the core does not warm significantly over this time period- and there is no evidence to suggest that's happening. Thus, the sun provides the energy to heat the planet, and what we have to worry about are the cooling processes.
In a bit more detail, some photons from the sun pass through the atmosphere. (lots are reflected- thank you ozone layer. and please forgive me if this is in Al Gore's movie- haven't seen it.) These photons are high enough energy (low wavelength) so that they pass through the CO2 and the rest of the atmosphere to provide color, warmth, sunburn, tans, etc. After the photon hits the ground, water, cloud, etc. it gives up some of its energy and is reemitted at a longer wavelength (lower energy.) If there's no CO2 in the way- the photon gets all the way to space and is gone. If however, a photon of the right wavelength hits the CO2, it's reflected back to the earth- and we get toastier since it's energy has to do something.
Nobody is debating this mechanism- hence the comment that if you do- you're arguing with physics. The only question that was reasonable was if some other processes could cause the warming other than this lack of radiative cooling. Since the data weren't clear as to what caused previous ice ages and variations in the output of the sun were known, there were some competing hypotheses. However, better data on orbits and 30 years of monitoring the sun with modern instruments have shown that ice ages are due to orbital variations, and variations in solar output don't correlate with the temperature changes we've seen. In other words- the modeling is getting stronger, people aren't making guesses anymore.
How was the data analyzed? All the IPCC reports are meta studies. In other words- none of the authors actually goes into a laboratory and measures anything. The data is collected from the literature and consists of ice cores, sea water studies, air temperatures etc. Once the data has been gathered, its fit to a curve which plots temperature over time. Recent computer advances have refined the process and reduced the uncertainty. In order to either not burn people out or to reduce bias, 75% of the people that worked on the 2007 report were NOT affiliated with the 2001 report. In other words, 3/4ths of the people looking at the data for the 2007 report were a fresh set of eyes. The response was pretty clear and frightening- CO2 concentrations continue to rise, and global temperatures will continue to rise through this century. CO2 has a long lifetime in the atmosphere and reducing CO2 emissions immediately will still result in rising temperatures for decades. In short- the sooner we start reducing CO2, the less chance we have of cooking ourselves or creating massive deserts.
Sam
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