14 December 2010
AGU, Day 2
Posted by Callan Bentley
Man, this meeting is intense. There’s so much going on all the time that for every session or talk you commit to, you’re missing literally dozens of others. This is kind of like going to the library and picking out a book, knowing that there are many other books you’re not reading — but with the exception that every 20 minutes, the old choices are gone, and they’re replaced with another several dozen options. If the library evaporated every 20 minutes and re-congealed into hundreds of new books, that would give some of the flavor. And the posters! There are so many posters. My own back-of-the-envelope calculations (based on a 2 m long by 1 m tall individual poster area), coupled with a tally of the total number of walls (81 full walls, each double-sided and with 12 to 16 poster slots per side, plus 4 partial walls) suggest that there is ~4.5 km of available lateral poster space. That, my friends, is a lot. And they turn over completely every day… thankfully not every 20 minutes, but still, you can’t dawdle. See ’em while you can.
I went to sessions today on submarine landslides (very cool: a lot of different approaches, ranging from computer modeling to a physical model where a batch of gravel was dumped into a wave tank, to seismic imaging of actual submarine landslide deposits in the deep sea), geoengineering (title of session: “Can We Counteract Global Warming?”), and carbon sequestration by reacting CO2 with ultramafic rocks*. I was particularly struck during the day at how prevalent and accepted climate change is at this meeting. Among the specialists, the people who are trained to know how climate works, there is a remarkable consensus on the reality of this issue. I mean, could you even have a session called “Can We Counteract Global Warming?” if there was a debate as to whether global warming is real? Certainly there are sessions at AGU where scientists are teasing out attribution of warming due to various factors, including albedo, solar input, and individual classes of greenhouse gases. No doubt there are some good arguments there about why the change is occuring. But I have yet to see a talk title or poster which suggests that the troposphere isn’t warming**. Sadly, this profound misconception is still persistent among the general public. I encountered it again this evening on Facebook, where a friend of a friend commented along those lines. I don’t actually expect that individual to cite a specific dataset in support of his “marked cooling trend for the past decade” contention (he quoted something from the Bible at me instead, I think to indicate that science is hubris), but it drove home to me that somehow the acceptance of global warming as an issue isn’t fully leaking out of the Moscone Center.
Anyhow, enough about that. If it wasn’t a climate change denier, it would be someone claiming the Earth was only a few thousand years old, and that brings me to the next highlight of the day: I attended a terrific talk in the afternoon by Sam Bowring of MIT, who talked about refinements in U/Pb dating of rocks in the Wopmay Orogen of northwestern Canada and the Bishop Tuff of eastern California. I ran into some old friends after Sam’s talk, and others in the poster session. All in all, I ended up feeling a bit burned out by the end of the day. It’s a long haul, this AGU Fall Meeting. I’ve got two more days to go, and maybe I would do well to heed Brian Romans’ advice to pace myself.
* The fate of civilization could hinge on mineral physics? Whoa… I’ll admit I didn’t see that one coming.
**Although I did see some posters claiming that hot spots aren’t hot.
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I attended a presentation on Quaternary Geomorphology today, and the person talked about CO2 in ice cores. Something about the CO2 increase FOLLOWING or lagging behind the warming event. Odd. Need to know more. I just did a google search for the reference, looking for .gov sites. This may be it.
Here is what it says.
Ice Core Records of Atmospheric CO2 Around the Last Three Glacial Terminations
Air trapped in bubbles in polar ice cores constitutes an archive for the reconstruction of the global carbon cycle and the relation between greenhouse gases and climate in the past. High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 +/- 400 years after the warming of the last three deglaciations. Despite strongly decreasing temperatures, high carbon dioxide concentrations can be sustained for thousands of years during glaciations; the size of this phase lag is probably connected to the duration of the preceding warm period, which controls the change in land ice coverage and the buildup of the terrestrial biosphere.
OK, so CO2 increases 200-1000 years AFTER the warming of the deglaciation.
Ideas I came up with –
Continental shelf is flooded and plants are killed off?
It is too dry after the cold, wet(?) glacial and plants die off? (Are glacial periods dry? Great Salt Lake was pretty deep during the last glaciation, so there was a lot of precipitation some places.)
Warm water can’t hold as much gas? So gas is released into atmosphere. But why CO2?
Freshwater from melting icecaps floods sea surface and kills off phytoplankton, so there is less photosynthesis.
Does anybody know anything about this?
From what I understand, in general, it works like this in the pre-anthropogenic era:
1) Milankovitch cycles tweak total insolation up a bit more or down a bit less. Summer insolation in the northern hemisphere is apparently the key driver.
2) CO2 and albedo are part of two amplifying feedbacks, reinforcing the insolation “forcing” — snowcover melts, baring more ground which has a lower reflectivity, which absorbs more heat, which melts more snow, which bares more ground, etc. And: permafrost melts, releasing carbon to the atmosphere both as CO2 from the breakdown (oxidation) of organic carbon in the soil and CH4 from methanogenic bacteria in the anoxic sectors of the subsurface. These greenhouse gases act as amplifiers of the Milankovitch signal.
Your brainstorming has generated some ideas which seem valid to me at first blush – they doubtless play into the “amplification” signal too.
Once humans came along and discovered fossil fuels, that natural signal got booted offline, and the novelty of the anthropogenic pulse of carbon took over as the driver (dominant forcing) of the system. When exactly fossil carbon replaced Milankovitch insolation as the driver is uncertain to me — some claim as recently as the 1950s, which Bill Ruddiman of UVA thinks it was actually shortly after the dawn of agriculture ~7000-5000 years ago. He makes the argument in “Plows, Plagues, and Petroleum” that anthropogenic greenhouse gases actually saved us from a new ice age. An interesting read. I recommend it.