Climate change is complex

By Ken Perrott 11/08/2010

I am always amazed at the way climate change sceptics, contrarians and deniers appear to think climatology is simple. They will latch on to one thing and claim it explains everything. They are the ultimate reductionists.

So, no! Climate is not influenced by greenhouse gases. The observed global temperatures can be “explained” by clouds. Or by cosmic rays, sunspots, volcanoes, El Nino, etc., etc.

On the other hand they will claim that climate scientists and the Intergovernmental Panel on Climate Change (IPCC) are ignoring natural influences. That they are considering only human caused effects.

Of course climate scientists are not that stupid. They are experts in the field, recognise the climate system is complex and attempt to consider all the relevant effects – natural and human caused.

Natural influences just can’t explain global temperature

You only have to look at the IPCC reports to see this. For example the figure below shows the results of simulations of global temperature from 1900 to 2005. Figure a included all the natural and anthropogenic influences.  The black line is the actual measured global temperature anomaly (obtained by subtracting the average temperature for 1901 to 1950).  The individual simulations are shown as thin yellow curves. The red line is the multi-model ensemble mean (see Figure 9.5 – AR4 WGI Chapter 9: Understanding and Attributing Climate Change).

Figure b is a similar plot using simulations which consider only the natural influences on climate. The individual simulations are shown as thin blue curves. The thick blue line is the multi-model ensemble mean.

So, climate scientist have considered both natural and anthropogenic influences. And they are unable to reproduce the global temperature changes since 1970 unless anthropogenic influences are included.

That is why the IPCC has concluded that there is a high probability (>90%) that human influences are contributing to the current observed global temperature increase.

Notice also that the experts talk about probabilities. It’s a complex field and things are rarely cut and dried. We are more certain about some influences than others. And the IPCC doesn’t hide this fact – far from it. It doesn’t make sweeping claims in the way that some of their opponents do.

Knowing what we don’t know

We can see this in another figure from the report (Figure 2.20 – AR4 WGI Chapter 2: Changes in Atmospheric Constituents and in Radiative Forcing). It shows the estimated influences of several human caused effect and solar radiation since 1750. Notice the error bars. They are much bigger in some cases than others. Notice the assessment of scientific understanding for these influences. We have a high understanding for some of them and a low understanding for others.

So, climate scientists aren’t hiding anything. They are not ignoring natural effects. They are up-front about probabilities. They acknowledge that we need more information is some areas. They are behaving like professionals.

Considering there are areas where scientific understanding is low there is clearly room for debate, discussion and more research. But deniers and contrarians who take an extreme reductionist stance, misrepresent the IPCC reports and attack honest scientists doing the research are not in a position to contribute to this.


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