August 19, 2007

Facts and theories

Tim writes,

I've been challenging people who question global warming (there are lots) and one argument I need help with is "human induced climate change is a theory" I need a way to explain that people making this argument don't really understand the word "theory".

The good short answer is, Yes, human induced climate change is a theory, a theory supported by the facts.

A while back I replied to Maureen Sheard's letter in the Owatonna People's Press. Her letter began: Facts on 'global warming' 1. It is a theory, not a fact.

The reply:

1. Global warming is a fact. If you and I were to look at a thermometer I think we could agree on the temperature. An observation like this is called a fact, and it's a fact that the global average surface temperature has increased by 1 F, give or take a few tenths, over the last hundred years. Theories are used to explain facts, and scientists use the word 'theory' in a special way. A scientific theory is not a guess or a hunch, but something supported by logic and evidence, and something that can be tested by experiment. Examples include the theories of gravitation and thermodynamics, and circuit theory. Current theories do a good job of explaining the global warming that has been observed since the agricultural and industrial revolutions.

Global warming is a fact, based measurements by thermometers, satellites, etc. Theories explain facts. A scientific theory is one that is supported by logic and evidence and can be tested by experiment. Accordingly intelligent design is not a scientific theory since it cannot be tested by experiment (God has forbidden us from testing him). In common usage a theory is speculative, a conjecture. In contrast, in science, facts support the succesful theory.

Some examples. Einstein's theory of relativity and has made all kinds of predictions about everything from stars to atoms that have been confirmed by many brilliant experiments. Darwin's theory of evolution has been confirmed again and again, for example by Mendelev's peas, DDT-resistant mosquitos, the finches of the Galapagos islands and the increasing number of infections by antibiotic-resistant flesh-eating bacteria.

Can we trust climate models, that is, is climate theory a good scientific theory? One test would be to try to duplicate a past period of the climate using the model-- letting it run free, and then compare the result with what actually happened. This is one of the best viable tests, since we cannot compare the results of a simulation of the 21st century's climate with the thermometer record for another hundred years.

This figure (click on it to enlarge) shows the climate record of the 20th century for different regions, the 'thermometer record', in black. (The figure is from the Summary for Policymakers put together by the IPCC.) It also shows the results of climate model simulations that were used to predict the climate of the 20th century. The blue band shows the results using only natural climate forcings, and the red band shows the results using both natural and anthropogenic climate forcings. This demonstrates that the models work and that it is necessary to include both natural and anthropogenic effects in order to successfully predict the climate of the 20th century over each continent, over the ocean, and over the planet as a whole.


At August 27, 2007 3:04 PM , Blogger rigtenzin said...

This is a very good post. I like your explanation of the difference between common usage and science of the term "theory." This little point could help rational people discuss global warming more clearly (or any other science related topics).

At September 08, 2007 8:18 PM , Blogger Papa Twister said...

I watched a NOVA last night that scared me more than anything I've seen yet on Global Warming. It was actually about Global Dimming. Apparently, particle pollution is reflecting the Sun's rays, and cooling the Earth. If not for Global Dimming, Global Warming would be much, much worse today. They said that as the worldwide temperatures have gone up, the evaperation rate of water has gone down. In fact, Global Dimming masked the intial effects of Global Warming. If not for Global Dimming, we would have been talking about Global Warming in the 70s. The problem is that particle pollution has direct effects on human health, therefore lawyers can sue industrial plants that are making people sick. And of course, money talks, so industry has been much more willing to reduce particle pollution than reduce greenhouse gasses. If particle pollution is reduced and greenhouse gasses continue to rise, we are in for catastrophe. There's more, but I want to hear what you think of this, Matt.


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