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Friday, December 15, 2006

Typical arguments about global warming

From time to time I get into conversation with people who have doubts about what is happening to our climate, usually based on their observations about the weather and what is happening in their garden. To come up with well thought out replies is not easy and so I've looked up such answers on the " How to talk to a Climate Sceptic Guide" blog and as an example I am copying one such answers here. If you wish to visit the blog you can use the link provided on this post or click here:

This is what you will find as a typical question and answer, using the statement: Climate change is just a natural cycle..

Thursday, February 23, 2006

This is Just a Natural Cycle

(Part of the How to Talk to a Climate Sceptic guide)


The current warming is just a natural cycle.

I always find this one a little amusing in the sense that you might as well call it "magic", because natural cycles do in fact have causes. So this is really just trying to insist that the climate science community is as ignorant as whoever it is writing this objection.


While it is undoubtedly true that there are some cycles and natural variations in global climate, anyone who wishes to insist that the current warming is purely or even just mostly natural has two challenges. Firstly, they need to identify just what this alleged natural mechanism is because absent a forcing of some sort, there will be no change in global energy balance. So natural or otherwise we should be able to find this mysterious cause. Secondly, a "natural cause" proponent needs to come up with some explanation for how a 30% increase in the second most important Greenhouse Gas does not itself affect the global temperature.

In other words, there is a well developed, internally consistent theory that predicts the effects we are observing, so where is the sceptic model, or theory whereby CO2 does not affect the temperature and where is the evidence of some other natural forcing?

There is a fine historical example of a very dramatic and very regular climate cycle that can be read in the ice core records taken both in Greenland and in the Antarctic. A naive reading of this cycle indicates we should be experiencing a cooling trend now, and indeed we were very gradually cooling over the length of the preindustrial Holocene, something around .5C averaged over 8000 years. It is informative to compare those fluctuations to today's changes. Leaving aside the descents into glaciation, which were much more gradual, the very sudden (geologically speaking) jumps up in temperature every ~100Kyrs actually represent a rate of change roughly ten times slower than the rate we are currently witnessing.

So could the current change be natural? Well, there is no identified natural cause (and they have been looked for), there is no theory of climate where CO2 does not drive the temperature and the natural cycle precedents do not show the same extreme reaction we are now witnessing.

(That would be a "No")

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posted by coby @ 2/23/2006 01:07:00 PM

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