EGU: thursday

Rowan Sutton: on the amplification of warming over land. That the land warms more than the oceans is well know; but as RS points out the *why* is somewhat less well known. I would have said, unthinkingly, its because of the ocean heat capacity. But… you get the same effect (or similar) in equilibrium runs so its not that, or not all that. He says its because the oceans are wet and so can lose heat through evap, which is harder for the drier land, and this seems likely. Its interesting how well-known-things like this turn out not to have been much investigated.

Some talk of precipitation and its variability between different predictions… keyed to the usual water stress will be a problem in future stuff. Which brings me back to the Australian drought and the stick I got in comments by belittling it. But doesn’t help in knowing what is to come.

Fichefet – LOVECLIM simple climate model – total melting in 3kyr (depending on scenario) with half gone in about 1kyr. Which isn’t very fast (probably slower than the hadcm3 estimates. Mikolajewicz, later, gets 3.4m after 600 y but I think he is using 4*CO2). 6 mm/yr at max. In Q’s: is your model reliable: its quite simple? Maybe. Could the recent glacier speed-up remove it faster? A (from Huybrechts): no. Climate and melting is more important.

Gregory: wot the IPCC did re SLR from ice sheets. Mostly the obvious: that Ant will gain mass and Gr lose (ablation at margins bigger than gain in interior). But high-res models are needed to do this well. Thermal expansion is biggest, followed by small ice caps. But recent Gr/Ant speed-up isn’t modellable, so in the absence of knowing what to do with it, it gets added in as a term scaled with temperature. This then roughly balances the gain of Antarctica. Points out that AR4 ests v sim to TAR, but with reduced error range due to greater certainty.

Rahmstorf think we are underestimating future sea level rise. He has an empirical model simply correlating T to SLR over the 20th C, and gets 3.4mm/yr per 1 oC above pre-ind. Applying this to future T projections gets him a higher rise than IPCC – quite a lot higher, 50-150 cm by 2100. It will be out in Science soon. He does note that obs SLR is higher than the GCMs currently predict. Q: when will the difference between you and IPCC estimates become clear? A: about 20 years. Most of the Q’s focus on individual components, and he answers with “but I’m not looking at individual components”. Best Q: mountain glaciers will run out as a source, so the linear assumption is wrong. Slightly unsatisfactory answer is that other things will take over.

Nathan Gillett: detecting changes in humidity.

Treat of the day is to be Singer, in the anthro session. Wot will he come up with this time? His first point is unclear, possibly even to him… something about pattern correlations apparently taken from IPCC ’95. The second point is back to the trop temperature trends… the tropical problem. Which appears to amount to cherry-picking from the CCSP report (as someone who was familiar with the report and its review points out in the questions). He is pushing the mis-match between the models (warming inc with altitude in the trop) and the obs (not really in the tropics). But to do this he has to ignore all the stuff about problems found with the sondes, and indeed the conclusions of the report itself. So, unsurprisingly, he doesnt actually address any of the detection and attribution stuff at all.

Now its lunchtime. A little chat with that Alistair McDonald. I fear we still disagree about radiative param and LTE.

van Oldenborg: why does Europe warm more than the ar4 runs say it should? Globally, the ar4 models are on the obs trend. But in Europe, they are below it, by 3 SD. And especially over the one Netherlands grid point which they care about (is tis pushing local stuff too hard?). And the suggestion is that this may be due to problems with the THC: which is too southwards (and too deep in the oceans?) in the ar4 runs.

Comments

  1. #1 Alexander Ac
    2007/04/19

    Dear William,

    I would be interested, if in these discussions was included the argument about the evidence from paleoclimatology, that at a time, when the warming was *slower* as that of predicted by IPCC, the ocean rose by several meters in a century (Hansen). This was around 125 000 years ago. I think that non-linear fasion of glacier (sheets) melting is quite possible…

    [Not sure exactly what you mean. 125kyr might be the end of the previous glacial. The end of the last glacial 12kyr ago might be better to study. But since that would be the end of the Laurentide ice sheet its a bit different from now -W]

  2. #2 Eli Rabett
    2007/04/19

    Land can also lose energy through evaporation, at lest if the top layer is moist or there are puddles. What kind of Brit are you?

    Since the top layer of soil can warm/cool faster than the top layer of an ocean, this process can actually be more efficient for land, with dew forming in the morning after the evening cooldown and being evaporated during the day as the sun shines. (Of course, being a Brit, you would not know about sunshine….:)

    [Um yes. But land is often limited in how much evap can occur. Unlike the sea -W]

  3. #3 SCM
    2007/04/19

    I hope you didn’t take my comment re Aussie drought too hard :-) I do appreciate the EGU updates (keep it up and all that).

    [Ah no you need to keep on at me -W]

  4. #4 Magnus W
    2007/04/20

    Interesting and it seems like my little university is going to precipitate in some research about water vapour (water cycle in the atmosphere) and climate change. And next door they study snow in different ways, partly evaporation… not my area though.
    One link one person

  5. #5 Steve Bloom
    2007/04/20

    Alexander, Hansen does refer to glacial termini as times of very rapid SLR, but simply by way of showing that such rapid collapse of ice sheets associated with rising temperatures is a known physical phenomenon. He points out that while the present ice sheet configuration is different (much less and in different places), the rate of temperature increase to which we are subjecting the ice is also different (much more rapid than under natural conditions and on a trajectory to very quickly reach levels where in the past there was much less ice than now). Given this, he says that it’s thus a question of how rapidly rather than whether the present ice sheets will go (starting with the WAIS and GIS, but moving on to the EAIS if things get warm enough).

    Having at present no model for this process and therefore no ability to predicts its course, Hansen concludes that it would be prudent to keep temperatures below those levels. He suggests that keeping CO2 to 450 ppm and thus temperature to no more than about 1C above present is approximately what is needed to avoid the risk of substantial SLR, and that to do so strong action will be necessary starting within the next decade. See Hansen’s pubs on this subject at his Columbia page.

    [I don't think that "we don't know, but it would be prudent" is going to work -W]

  6. #6 Eli Rabett
    2007/04/20

    Well, yes and no, and it depends where, that’s hydrology folks.

  7. #7 Timothy Chase
    2007/09/20

    William M. Connolley wrote:

    Now its lunchtime. A little chat with that Alistair McDonald. I fear we still disagree about radiative param and LTE.

    Hard to believe.

    Every argument which he has posed has been responded to several times. Over at Real Climate we have pointed him to all sorts of data. There is of course partial-LTE and non-LTE which he is aware of at this point – but he also knows that the difference between either of these and LTE is a matter of degree and gradual.

    He knows about the long tails on the Maxwell distribution, that collisional energy can and is transformed into thermal radiation by greenhouse gases. He knows that the part of the spectrum that carbon dioxide is sensative to is already saturated near the ground.

    And the list goes on – like Don Giovanni’s list of conquests rolling along the stage and into the orchestral pit.

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