The Earth is like a saucepan

If you measure transient temperature, don't expect it to tell you the final response. The earth takes time to warm up like a saucepan of water does.

I wrote this in response to comment-11843 of this blog post.

This graph purports to show that reality is on a different trajectory to the climate models. What in fact it shows is rather different. It compares a transient response of temperature to greenhouse gases to the final response ('equilibrium') response to that same forcing.

(It's a bit like if you say to me 'if you put a saucepan of water on the hob I predict it will boil eventually'; and I put it on the hob and then measure the temperature after 30 seconds which is only just above room temperature, and then I say to you 'you were wrong'. I would not comparing like with like; I should wait if I want my water to boil.)

This graph is COMPLETELY CONSISTENT with the IPCC models. The post could be confusing between transient response and equilibrium, and this post tries to clarify this.


IPCC TAR IS92a predicts that in 2060 there will be 550ppm CO2 only, forcing at 4.3W/m2, temperature change of 1.5C above the pre-industrial.
IPCC TAR (2001) IS92a scenario best guess:

This model result is consistent with the 'bottom graph' here

The IPCC also predicts climate sensitivity of 3C (best guess) - which would be the result if the CO2 level stabilised at 550ppmCO2(e), which is consistent with the 'top graph' from the same link.

In other words the bottom graph actually shows best guess 'transient response' and the top one best guess 'equilibrium response'. To compare the two graphs on the same basis (making the top one the 'model' and the bottom 'reality') is extremely misleading.


2060 - CO2 at 550ppm

Forcing at 4.3W/m2

Temperature change at 1.5C above preind

Climate sensitivity at 3C +/- 1.5C

Plotting on our graph

I'm afraid to say that I find this graph completely typical of all the 'sceptical' posts that I've seen - completely correct except for a 'minor' flaw in comprehension. This is usually the flaw in almost-experts - the 'minor' structural assumptions make a big difference!
Investigating this has taken me two hours in total; or about £40 in lost other work.

Let me say that I am completely open to scientific arguments and I find it very helpful in getting to the bottom of things to attack a problem sceptically (as long as there is no bias in that scepticism). But every time I feel that there may be a good argument, I feel disappointed and
that I have wasted my time, or that my points are viewed as marginal when they are actually structurally extremely important.

I do not want to have a political position on this, only listen to evidence and arguments. I do not have a closed mind but I won't be easily convinced on any structural point by anyone who has a 'position', because the mental effort in taking out the scientific 'signal' from the
political 'noise' is too great.

This particular case and the general question of climate change is emphatically is NOT closed. I am emphatically open to understanding the climate system more just in
non-political way (how does this system work; how can we represent feedbacks etc etc.) But I just won't be spending any more time considering this case in detail, or really other general points where people's motivation for scientific statements are political hobby horses (where people know in advance what result they want). I think I have to draw some sort of line under what you might call CSPNs 'Climate Science Political Movements' and 'Climate Sceptic Political Movements' (as opposed to the usual highly detailed structural scientific scepticism, which has no political bias).

Note that these criticisms can be applied to both 'sides'.