Tuesday, May 02, 2006

Global warming

Wasn't there a recent issue of Science with extensive coverage of global warming? Could you point to the flaws in the data sets they assembled? You might also be interested in the Wikipedia entry on Global Warming: http://en.wikipedia.org/wiki/User:Dragons_flight/ImagesI'd love to see some commentary on that data as well.

In response to Ashby's Query I have looked up some recent scientific publications, the abstract for the first of these is presented below.

Nature. 2006 Apr 20;440(7087):1029-32.

Climate sensitivity constrained by temperature reconstructions over the past seven centuries.
Hegerl GC, Crowley TJ, Hyde WT, Frame DJ.

The magnitude and impact of future global warming depends on the sensitivity of the climate system to changes in greenhouse gas concentrations. The commonly accepted range for the equilibrium global mean temperature change in response to a doubling of the atmospheric carbon dioxide concentration, termed climate sensitivity, is 1.5-4.5 K (ref. 2). A number of observational studies, however, find a substantial probability of significantly higher sensitivities, yielding upper limits on climate sensitivity of 7.7 K to above 9 K (refs 3-8). Here we demonstrate that such observational estimates of climate sensitivity can be tightened if reconstructions of Northern Hemisphere temperature over the past several centuries are considered. We use large-ensemble energy balance modelling and simulate the temperature response to past solar, volcanic and greenhouse gas forcing to determine which climate sensitivities yield simulations that are in agreement with proxy reconstructions. After accounting for the uncertainty in reconstructions and estimates of past external forcing, we find an independent estimate of climate sensitivity that is very similar to those from instrumental data. If the latter are combined with the result from all proxy reconstructions, then the 5-95 per cent range shrinks to 1.5-6.2 K, thus substantially reducing the probability of very high climate sensitivity.

This represents a typical paper regarding global warming predictions. They have defined a model and test assumptions. In this case the data set they generate contradicts the observational studies (cited as references 3-8) calling for acute climate sensitivity to elevated CO2. The key words to notice here are 'observational studies'. This means that there are no controls against which to measure the data and a scientific process was not executed (hypothesis-experiment-accept or reject hypothesis). This kind of study involves collecting as many pieces of information as you can (or want to) and try to explain them. The Wikipedia data from the link above is a prime example ofthis kind of data collection. Look at the data presented and ask what is missing. For the surface temperature record- where were the temperatures measured? Are these global averages or local phenomen. Whe the data says global temperatures how manylocations are tested? what is the standard deviation (are a few areas with a large increase skewing the average. For the reconstructed data (which is the bulk of the information) how are these temperatures determined and what is the margin of error.

If you examine the atmospheric CO2 concentrations you will notice that ther is a cyclic variation between 200 and 275 ppmv with a period of about 100,000 years. The industrial revolution began at the highpoint of one of these cycles. Since the onset of the industrial revolution the concentration has risen to 375 ppmv. Regardless this approximately a 36% increase in CO2 concentration. Based on the prediction above a 100% increase would increase the temperature 1.5 to 6.2 degrees C.

If the byproducts of production caused the increase in CO2 can be assumed but not proven.

If the industrial revolution coincided with a trough in the cycle rather than the peak the movement from 200 to 300 ppmv would not be outside of the normal variation. As this is an observational study that is based on reconstructed values (without information as to the method, accuracy or global reproducibility) over a 400,000 year period there is no information that predates this time period to demonstrate whether this is anomalous or an event that occurs on a regular basis.

I'll address this further as time permits


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