Thursday, December 03, 2009

What about the Medieval Warm Period?

source (note that I have flipped the above graph horizontally so that it matches the first graph)


Another common theme of the skeptics: How come it was so warm in the years 800-1300 AD?

On the top graph down we see that the temperatures nearly touched modern values, yet there was no industrial carbon dioxide release then.

The second graph shows that there was an increase in sunspot activity at that time, and unusually long period of increased solar activity. That is one possible candidate for the causation of the Mediaeval Warm Period.

The third graph shows that there is no correlation between modern temperatures and solar activity. The fit is much better for CO2 levels.

The lesson here is that the earth's temperature is a result of six variables:
a. the distance from earth to sun, which varies very slowly
b. sunspot activity, which has a cycle of about 11 years
c. Albedo - the reflectivity of the earth's surface - mainly clouds and snow
d. aerosols and soot, mainly from volcanoes, which can cool the atmosphere by throwing dust into the air. Industrial soot plays a part here
e. greenhouse gases, which trap the sun's heat
f. Ocean currents, notably El Nino and La Nina

We are affecting d and e, but they are enough, in a finely balanced system, to create serious problems.

Note that there is some doubt about whether the MWP was local or global.

More here


Rob Stanley said...

I watched a very interesting lecture given by Lord Monckton which raises many points on,amongst other things,the way data is collected and consequently presented by scientists working for the IPCC.He quotes an email from David Deming in 2005 which says 'we must get rid of the mediaeval warm period' in an attempt to make our impact on the climate more alarming.An original IPCC graph from 1990 is shown in which we can clearly see the warm period then we see the later famous hockey stick graph which he claims has been manipulated by omission.Can you shed some light on this?

DocRichard said...

Hi Rob
I'm sorry, I have no time for "Lord" Monckton, who is a conspiracy theorist and a purveyor of falsehoods Here

The MWP does show, just about, on the "spaghetti" graph. There is an old graph which some denialists use, which is well out of date, showing a big MWP.

The thing about the "hockey stick" is that the ground has been covered and re-covered from so many angles that it is clear that modern temperatures are way above the MWP, even if it was global and not just regional. I know that the skeptics point to global sources to support MWP, and the climate scientists have called their data into question. I'm not too bothered either way. The MWP coincided with an unusually sustained burst of solar activity. This is the key point: we are not claiming GHGs are the ONLY cause of CC: just that we cannot explain present temperatures WITHOUT factoring in man made GHGs.

Rob Stanley said...

It seems to be the done thing to simply dismiss Lord Monckton as a nut.I wish Al Gore or anyone else would accept his offer of a public debate on the subject to show us who is talking more sense.By the way,the page you referred me to about Lord Monckton's purveyed falsehoods was unavailable so I cannot comment on those.I assume your interpretation of Dr Deming's email is different to that of Lord Monckton.The 1990 graph does show a big MWP but it was produced by the IPCC presumably using facts so how can it become outdated?Are you telling me that the IPCC could be capable of mistakes?

DocRichard said...

Sorry, I just do not do conspiracy theories. Life is too short. I imagine Al Gore feels the same way. Wittgenstein said if you see your enemy drowning in a bog, it is best not to jump in after hime with a knife.

Sorry, I gave you a link to a search page.
Here's one link on Lord Monckton.

"I assume your interpretation of Dr Deming's email is different to that of Lord Monckton. The 1990 graph does show a big MWP but it was produced by the IPCC presumably using facts so how can it become outdated? Are you telling me that the IPCC could be capable of mistakes?"

Of course science changes all the time, that is in its nature. 1990 is 20 years ago. That is a very long time in science.

Could you give a link to the picture you are referring to? I have an idea which item it is.

Of course, the IPCC makes mistakes. How many items do we have now? Three? Ten? I'm sure you could find a hundred, if you really put your mind to it. But the case for AGW is built on thousands of papers, and hundreds of thousands of observations. The case is sound. Have a look at Iain Stewart in my next blog.

Simon said...

Just for you Rob :)

Simon said...
This comment has been removed by the author.
Rob Stanley said...

The graph was published as graphic 7c on page 202 of the first progress report of the IPCC 1990 and the link I have is the climate audit by Steve Mcintyre Where did the IPCC 1990 figure 7c come from? And to Simon thank you for the link I had no idea about this.I was sent to a blog with some interesting opinions so I tried to watch the debate on youtube to form my own but its unavailable as yet.I'm sure it will be there before long.I look forward to seeing it and will get back to you when I have.