Trying to figure out who to believe on climate change

In Real Climate is an entry by Gavin Schmidt and Stefan Rahmstorf: Uncertainty, noise and the art of model-data comparison to contrast with one in Prometheus Updated IPCC Forecasts vs. Observations by Pielke. Same basic topic, two different ideas, opposing viewpoints, – but nothing to hang a hat on.

How can you tell what to think with all the back and forth? The tendency is to figure you have to become a climate scientist yourself and go to original data to run them through the models that you have dissected so you can thoroughly understand their strengths and weaknesses. Undertaking a career like this is no way to answer a question.

What you can do is to figure out what is actually being said and to consider their means of argument and how they respond to issues and questions.

Schmidt and Rahmstorf assert that there is a great deal of uncertainty in climate and weather that means that there is a significant variability in measure and model output. They attempt to discredit John Tierney and Roger Pielke Jr. as “flawed since they basically compare long term climate change to short term weather variability.”

So, it should be clear that short term comparisons are misguided, but the reasons why, and what should be done instead, are worth exploring.

The first point to make (and indeed the first point we always make) is that the climate system has enormous amounts of variability on day-to-day, month-to-month, year-to-year and decade-to-decade periods. Much of this variability (once you account for the diurnal cycle and the seasons) is apparently chaotic and unrelated to any external factor – it is the weather.

Problems can occur though if the estimate of the forced change is compared directly to the real trend in order to see if they are consistent. You need to remember that the real world consists of both a (potentially) forced trend but also a random weather component.

Finally, this subject appears to have been raised from the expectation that some short term weather event over the next few years will definitively prove that either anthropogenic global warming is a problem or it isn’t. As the above discussion should have made clear this is not the right question to ask. Instead, the question should be, are there analyses that will be made over the next few years that will improve the evaluation of climate models?

This is saying that the idea of these climate model studies is to learn about what is causing change and that they have many uncertainties that require significant averaging over time to discern quality.

But isn’t the question at hand the matter of governmental policy based on these models? That is what the stimulus post was for the Schmidt and Rahmstorf post. What started this discussion was Pielke’s observations about the IPCC, a governmental organization, predictions made in 1990, 1995, 2001, 2007) and various observations.

Both sides are ‘correct’ but the response is not answering the points raised in the stimulus. This is not an indication of good intellectual integrity. The pattern continues in the comments where Pielke offers explanation and observation and the response is defensive.

There are other things that should make one pause as well. A PBS show on the possibility of life on other planets tossed off the tundra melting as a human caused global warming effect. There are many such blatant assertions in the popular media. As the Real Climate post graph shows, the change in temperature is about 0.2C/decade or about a half a degree Celsius since 1980. The question is how a half a degree average temperature change is going to melt the Arctic tundra or do all of the other such things that are often given as a fact of human caused global warming.

The use of short term effects to support models and predictions whose effect can only be observed long term is something seen most often in the HCGW advocates. Perhaps its use in Real Climate is projection? That would be something to consider in evaluating the manner of argument.

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