Climate change is not simple

I have said this before – but it bears repeating Climate change is complex. And I feel the need to repeat it now because of a current myth being pushed very strongly by climate change deniers/contrarians/sceptics. The claim that “there has been no global warming for 16 years.”

If you doubt climate change is complex have a look at this global temperature record from NASA’s Goddard Institute for Space Studies.

Line plot of global mean land-ocean temperature index, 1880 to present, with the base period 1951-1980. The dotted black line is the annual mean and the solid red line is the five-year mean. The green bars show uncertainty estimates. [This is an update of Fig. 1A in Hansen et al. (2006).]

Isn’t cherry picky wonderful?

There’s a lot of noise in that graph but it does sort of support the conclusion that global temperatures have increased in the last 100 years. Mind you, if you want to create a contrary impression you can easily take a short time period – say around 1950, 1960 – 1980, 1985 – 1995 – or even the last 16 years. Cherry picking is a great thing – if your aim is to support a predetermined conclusion, and avoid (or even hide) evidence to the contrary.

So we get this sort of thing being promoted by climate change deniers (thanks to Andy for this one). Didn’t someone say a little knowledge is a dangerous thing? And isn’t cherry picking a great way of restricting knowledge?

So, just to repeat myself – here’s an extract from my post Climate change is complex. It indicates some of the scientific knowledge that climate change deniers/contrarians/sceptics ignore when they cherry pick to make this silly claims.

Natural influences just can’t explain global temperature

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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