04 August 2009

Question place

Been a while since I put up a note for you to ask questions/make comments/suggest topics/ etc.. So, here goes. Have at it.

12 comments:

Jesús said...

I would be interested in learning about the way formal attribution is done, or the way in which specific climate feedbacks are estimated, but trying to focus more on your line, I would be interested in learning something about the role that oceans play in the climate system, as some people usually try to point to them as the cause of global warming. More specifically, an acquaintance suggested a skeptical hypothesis: that in a past warm climate (let's say the MWP) oceans might have accumulated positive temperature anomalies that sank into the deep ocean with the ocean streams and might be arising now, transferring that positive anomaly to the troposphere. I think this hypothesis has several pitfalls (hemisphere trends, ocean-land trends, TOA energy balance...), but I would be curious to know whether the hypothesis makes any sense.

And regarding the oceanic oscillations (ENSO, NAO, AMO, PDO...), a friend says that the longer the period (low frequency) the shorter the amplitude. Implying that longer ocean oscillations have a lesser impact on climate. I don't know if that's true.

Or maybe some comment on this recent paper that a skeptic used to defend that the Copenhagen Report was wrong when saying that "The updated estimates of the future global mean sea level rise are about double the IPCC projections from 2007".

And last (and least), my English teacher suggested that magma in the interior of the Earth may have an effect on surface temperatures. I said it doesn't, because of the distance, but I'm afraid I didn't sound very persuasive and I couldn't find an authoritative source rejecting it... :-/

Cheers.

Penguindreams said...

A couple of quick comments:

It's a general truism about the earth system that the longer the period, or the larger the area, the smaller the deviation from the mean. In other words, while my local temperature could be 20 degrees away from normal tomorrow, it's extremely unlikely that the continental average temperature would be that deviant, and all but impossible for the planetary mean to be that far off.

There are some extremely localized effects on surface temperatures from magma. It has to get very near the surface, as in Hawai'i, Yellowstone, and Iceland. But the hot springs, geysers, and lava flows do affect surface temperature.

At large scale, however, it's an ignorable term. Solar variation gives us a variation of 0.25 W/m^2 (varying with the solar cycle) averaged over the whole planet. The magma (geothermal source) is 0.05 W/m^2 averaged over the planet, and varies only on the many millions of years time scale.

Sinking a warm temperature anomaly into the deep ocean doesn't work. The deep ocean waters are cold, and get that way by being near freezing at the surface. Warming up the source regions means no new deep water, not warm deep water. (There are additional factors, notably salinity, but that doesn't help either -- how are you getting the water salty? The usual way is to freeze ice from the ocean.)

Eric L said...

You seem to know a lot about ice, so I was wondering if you would do a series explaining the behavior of Antarctic sea ice. Lots of questions come to mind. So the sea ice extent seems to have risen gradually over the past 30 years, but also it seems to me that it rises a little more in relatively warm years (though maybe also after volcanic eruptions, I haven't analyzed it much beyond generating this graph.) Is this strictly an area/extent phenomenon? Do we have data on the volume of sea ice? Is this primarily driven by salinity, precipitation, or are there other processes as well? Does this have any relation to ice over land? What is expected in the future?

Thanks!

Penguindreams said...

Eric: You raise a point I've been meaning to give a full post to. Namely, increased Antarctic ice area is expected from a greenhouse warming. This goes back to Manabe in the early 1990s. The mechanism he saw in his model was that in the warmed climate, there was more snowfall onto the ice pack. The snow gets converted to ice (if there's enough of it to sink the top of the floe below the sea level), or simply acts as an insulator for the ice. The rising trend in Antarctic ice was not statistically significant until much later. But then we (Markus and Cavalieri) also observed that there was more snow on the Antarctic ice pack.

So, a very successful prediction out of the climate model.

Jesús said...

Thanks for your answer! :-)

jg said...

Thank you for inviting questions. Here are few topics I'm eager to learn more about:

Ocean chemistry: especially, how to understand the ocean's ability to absorb CO2 from the atmosphere against it's outgassing of CO2. (I went off topic with this question at InitForTheGold so MT may be working on this too).

Firn models: Understanding how the lag between CO2 levels and temperatures is corrected. How do the models used to determine this lag differ from models of other climate processes.

Astronomical forcing (though I've made a lot of progress - with help from you and others, I'd enjoy your treatment of the subject).

If any of your posts would be assisted by illustrations I could draw under your direction, please let me know.

thanks
jg

Didjeridust said...

One question that came up in a local debate on net:
Is the amount of warming due to urbanisation through the last 150 years quantified?
I'm thinking of change in albedo due to tarmac and concrete and buildings(roofs) and wassits...
(I took the liberty of using the simplified climate-"model" presented on this site some time ago with a change in albedo from 0.3 to 0.2 for 1% of the earths surface and came up with 0.18 degrees celcius/kelvin - anyone have a better/more realistic figure?)

Jesús said...

Didjeridust,

I just know that the IPCC deals with it on page 182 of Chapter 2, WG I.

Cheers.

jyyh said...

What are the current verified studies/graphs indicating the seasonal variability of the flow rates of the land based glaciers that have oceanic terminus? And more specifically, when was this measured for the first time? Probably I could dig this up myself, too, but don't just bother since the increase in the yearly flow rates has been demonstrated.

Bayesian Bouffant, FCD said...

Which name do you use, woodchuck or groundhog? How about garbanzo bean vs. chickpea?

connor said...

The deniers I argue with keep referring to this Arctic sea ice data

http://ocean.dmi.dk/arctic/meant80n.uk.php

And claiming it shows a return to baseline levels earlier than at any time since 1958.

Can you explain the discrepancy between this data and the NDSIC?

Penguindreams said...

Connor:
The obvious thing is that the DMI data are not sea ice data. They are about mean atmospheric temperature north of 80 N. They are also using a climate baseline of 1958-2002, as opposed to the 1979-2000 that NSIDC uses for sea ice.

So, given that they're different figures, calculated against a different baseline, the folks you're talking to should really explain why it is we should expect the two curves to look the same. And what it means if they don't.

Bayesian:
I probably use all 4. Woodchuck more often than hedgehog, and garbanzo more than chick pea. Unless it's the other way around.

Didjeridust:
As Jesus showed, yes, it's something computable, and has been examined.

all:
I do make note of questions here for later articles, so don't worry that if there's no answer here, there will be no response at all.