Monday, July 27, 2015 Evaluation of CMIP5 palaeo-simulations to improve climate projections

Our latest paper has just appeared in Nature Climate Change: "Evaluation of CMIP5 palaeo-simulations to improve climate projections". It was mainly the brainchild of Sandy Harrison, intended as a response/update to the "preview" paper "Evaluation of climate models using palaeoclimatic data" which promised that the PMIP component of CMIP5 would
provide assessments of model performance, including whether a model is sufficiently sensitive to changes in atmospheric composition, as well as providing estimates of the strength of biosphere and other feedbacks that could amplify the model response to these changes and modify the characteristics of climate variability.
So, how did PMIP do? Well, when we started writing the paper, we looked to see what work had been published that addressed these questions. There was not perhaps quite as much as we might have hoped, but enough to say that
Palaeo-evaluation has shown that the large-scale changes seen in twenty-first-century projections, including enhanced land–sea temperature contrast, latitudinal amplification, changes in temperature seasonality and scaling of precipitation with temperature, are likely to be realistic. Although models generally simulate changes in large-scale circula- tion sufficiently well to shift regional climates in the right direction, they often do not predict the correct magnitude of these changes. Differences in performance are only weakly related to modern-day biases or climate sensitivity, and more sophisti- cated models are not better at simulating climate changes. Although models correctly capture the broad patterns of climate change, improvements are required to produce reliable regional projections.

We started work on the paper around the time we visited Reading last summer, and mostly finished it during our trip to France. Most of the time since then it’s been sitting in limbo waiting for space to be published. It’s pleasing that this travel actually generated a tangible result, which doesn’t always turn out to be the case. And also pleasing that jules and I can continue to make contributions to the literature despite the lack of grey cubicles to spend our days in :-)

4 figures summarise the main results. The first shows that large scale behaviour of the models is consistent between past and future climates (top plots) and that the past climates are consistent with data (bottom plots).
However, when we look at some smaller (but still quite large) areas there are substantial problems, with the modelled mid-Holocene monsoon not adequate to support the vegetation that was present in what is now the Sahara desert. In some places, the models barely register any changes at that time, or move in the opposite direction to the data.
We summarised the climatologies with a Taylor diagram: the Last Glacial Maximum results show at least a positive correlation between models and data (the temperature results are fairly good), whereas for the mid-Holocene, the model results are clustered close to the zero correlation line (vertical line in the diagram below) and have far too little spatial variability. Pale colours are the older PMIP2/CMIP3 results where available, showing that things have not changed significantly with the new generation of models.
We also re-examined the question of equilibrium climate sensitivity. This had been raised in the context of CMIP3 by Hargreaves et al in 2012 who asked "Can the Last Glacial Maximum constrain climate sensitivity?" Our answer there did point to the importance of checking this somewhat tentative result with the new CMIP5 results when they became available, and the new results are not so encouraging. In short, there is no detectable correlation between the equilibrium sensitivity of the models, and their simulated LGM cooling. Not that the results are particularly incompatible with the correlation we had previously found either, they just form a rough ball in the right place without a slope either way. There is, perhaps, room to explore this in more detail, and a new paper by Hopcroft and Valdes (which seems to have been written while our paper was in the publication queue) does exactly this. There are question marks over one or two of the models but it’s perhaps a mistake to go too far down this route, as the risks of cherry-picking and post-hoc justification are strong when the ensemble is so small to begin with.

Not much of Harrison et al. will come as a huge surprise to those working in the field, as this paper is basically a review of recent literature rather than hot-off-the-press results. We hope it will serve as a useful summary and perhaps provoke further research in this area.


Thursday, July 16, 2015

[jules' pics] Baaaa!

A sheeps
Lake District Lamb.

Posted By Blogger to jules' pics at 7/16/2015 12:45:00 PM

Sunday, July 12, 2015

'Mini ice age' coming in next fifteen years!

Oh no it isn't, despite what you can read in the Indescribablyoverhyped. At most, a solar min might make a detectable reduction in the warming trend. It won't cause significant cooling.

It is not clear to me who is responsible for this made-up story, it could be due to exaggeration from the scientists, a badly worded press release, or a journalist trying to get their story published. But in any case, it's not true.

Oh, thanks to ATTP, the press release seems ok, I can see how the journalist might have got confused. I wonder if she actually spoke to any scientists - solar or climate - before writing her piece.

Thursday, June 25, 2015

Wha daur say mass in ma lug?

All this fawning over the pope leaves me rather depressed. So, maybe he happened to say something that was not completely stupid and backward. I suppose perhaps if you are feeling particularly optimistic, that's something to be mildy positive about. But that hardly outweighs the downside of having some cult-leader wielding such authority. It would be far better to not listen to him at all.

(sits back and anticipates first comment about living in glass houses...though it's more stone than glass)

Wednesday, June 17, 2015

[jules' pics] Lovely James

awww, i'n't 'ee sweeet?

In photos on the internets, James makes most things look smaller than they are, because he is larger than you think, but maybe the little hill behind James was once a big mountain, before the glaciers scraped most of it away. It is fun to ride by bicycle as the track starts at a gentle slope and gets gradually steeper and steeper almost all the way up. 

Posted By Blogger to jules' pics at 6/17/2015 04:21:00 PM

Sunday, June 14, 2015

[jules' pics] Englefield v Myohoji

Englefield seems to date from the mid 1500s, and Myohoji goes back to the 1200s. How much of which buildings may be "original" is another question, of course...

Anyway... in 2010, I blogged the Deva gate and famous moss steps at Myohoji

Both places have a large number of trees, but at Englefield I found no red gate with protective angry monsters - there was just a little metal gate with an "honesty box", into which you are expected to put 6 quid. In November I expect you'd feel more moved to put in about tuppence, and with no red monsters to chase you down, why not? However, to make up for this lack of impressive gate-ness, the main building is very grand and the landscaped garden very large. 

Oh look - a Japanese maple!
But the thing that really caused me to think of Myohoji was, of course, the daisy staircase.
daisy steps

Myohoji's moss steps repeated for those who can't click links back as far as 2010
Myohoji moss stairs
Clearly Englefield need to grow more steps to make it proper zen, but there is potential, for example with  the correct ferniness at bottom right hand side.

Posted By Blogger to jules' pics at 6/14/2015 05:20:00 PM

Which Hunt?

So the Tim Hunt thing rumbles on and on... the story for anyone who missed it, is that an old entitled and successful Nobellist said some stupid and sexist and unfunny things in a public lecture at a meeting on science journalism. Unsurprisingly, some of the journalists reported this, which led to a deluge of twittering and Guardian articles. Old entitled and successful Nobellist clumsily attempted an apology but said that he meant it really. UCL rapidly removes him from his honorary post, ditto European Research Council. Now there's the latest woe is me apologia.

On one side, we have his defenders saying that he's a great scientist and has supported many female scientists through his career. On the other, his detractors point out that his comments add to the hostile environment that many women have to put up with on a regular basis, and have no place in modern research culture. I have to say I come down pretty firmly on the latter side. It's not like UCL or ERC are short of old white men to fill up honorary positions and committees.

Wednesday, June 10, 2015

[jules' pics] Parking!

I've been missing Starbucks Parking on Sundays. In fact I've been missing all the colourful, shiny, expensive and overpowered cars of Kamakura and Yokohama. Here it is mostly Land Rovers with dogs in the back, Quad Bikes with dogs on the steering wheel, and Caravans full of dogs and holiday makers. But then last Sunday there appeared, just down the road at Falcon Manor... 

woo hoo!

Posted By Blogger to jules' pics at 6/10/2015 02:04:00 PM

Tuesday, June 09, 2015

That hiatus thing

The hiatus is no more, apparently. Or rather, it never was. “Nature Hiatus” might have to change its name, or at least its main focus of publication.

I never really understood why the “hiatus” was such a thing. Whether or not the warming trend since some carefully chosen date is positive, negative, and “significantly” so or not, is mostly an exercise in cherry-picking and the abuse of significance testing (The Difference Between “Significant” and “Not Significant” is not Itself Statistically Significant), not to mention the sort of “gotcha” that belongs in the political domain if anywhere. What matters is how well the obs agree with model projections, and there is no particular threshold of zero trend that has any special importance in that respect. Furthermore, whether or not there is an interval with zero or negative trend, no-one with any clue would dispute that we will continue to see warming in the long term, with some natural variability overlaid on top of that.

Lots of people have blogged this in some detail. RC, Doug MacNeall (Doug can you please change your name to a sensible spelling?) and Stoat, to name but three. I am still somewhat unconvinced by some of the model-data comparisons which smack rather too much of move-along-nothing-to-see-ism for my taste. The models do generally overestimate the trend over quite a long period, it is pretty marginal to claim that they agree with the data, and we've been waiting for the long-promised acceleration in warming for some time. As recently as 2006 or so, many prominent scientists were proclaiming an expected warming of 0.72C over the inerval 2000-2030. That's not looking too likely right now. Even with the multiply-promised El Ninos (and 2015 looks set for being another record year), the recent warming is no more than steady.

Thursday, June 04, 2015

[jules' pics] Our garden

Almost everything in our garden is doing flowering at the moment. It is the British way, to bloom in May and June and hibernate the rest of the year.

Posted By Blogger to jules' pics at 6/04/2015 07:20:00 PM