AMS Climate briefing rundown

Yesterday I attended a climate change briefing hosted by the American Meteorological Society (in conjunction with NSF, AGU, AAAS, and the American Statistical Association). It was in the Hart Senate Office Building, but I didn’t see any senators at the briefing.

It was an interesting format: 3 talented speakers giving 3 “fifteen-minute” presentations (really more like 25 minutes apiece), each focusing on a different aspect of climate change: Mike Oppenheimer (Princeton) spoke about the science, Jon Krosnick (Stanford) spoke about public perception, and Norm Ornstein (American Enterprise Institute) spoke about the current political landscape.

Oppenheimer gave some of the basics about the greenhouse effect, etc., then showed the striking graph from Solomon, et al. (2009):

This is a sobering chart: the ~100 ppm increase in CO₂ in the past century has a radiative forcing of about ~1.5 Watts/m², and that’s yielded a bit less that 1°C of global warming. But when you project emissions into the future, you see that the CO₂ we’ve emitted has a really long residence time in the atmosphere. If emissions were to stop completely at different points in the next century, we would see peak emissions of 450, 550, 650, 750, 850, or 1200 ppm, after which the numbers would slowly decline, but then ~stabilize at levels well above the preindustrial background level of 285 ppm. In other words, we’re locked in to irreversible climate change to some extent; it’s only a question of degree (pun intended). With reinforcing feedbacks, the resulting temperature changes could be severe.

Oppenheimer then moved on to discuss ice melting. He talked about the precipitous 2007 decline in Arctic sea ice, and pointed out that in 2008 and 2009 the ice there had rebounded to the (negative) trend line. “This means it wasn’t terrible,” he said. “It was just really bad.”

Next, he used a good visualization to talk about potential melting in the future. He showed maps of Greenland and Antarctica, with the relevant ice masses overprinted with their potential contribution to sea level rise. He soberly reminded the audience that while melting of Greenland and West Antarctica were immediate concerns, East Antarctica was “likely not going anywhere soon.”

Jon Krosnick was next to speak. He is interested in the intersection of communication, psychology, and politics, and conducts a lot of survey research. He pointed out that there has been a lot of talk in the mainstream media lately about pronounced declines in public acceptance of climate change science. For instance, a Pew poll found a decrease from 71% to 57% of the public who accept anthropogenic climate change. In a critique of the questions pollsters used to arrive at that conclusion, Krosnick found significant methodological flaws, and showed how his team have countered those pitfalls with better question wording. Tenses were mixed up, questions asked only about the “last few decades,” questions were not about responders’ opinions but about what they “had read and heard,” or the questions were laughably complex, “which increases the cognitive burden for the responder,” Krosnick said. He also pointed out that the Pew survey compared a summer poll with a winter poll, and suggested that the time of year you ask people questions about global warming influences how they respond.

So his research group used better questions, and came up with a shift from 80% to 75% over the same time period. Yes, that’s a decline. Yes, that’s statistically significant. But it’s also 75% of those surveyed. Krosnick reminded the audience that 3/4 is a big number, a huge number of people who think anthropogenic climate change is real. There is not a huge decline, and “believers” are in a solid majority.

Still, what’s behind the decline? Krosnick postulated five potential explanations: (1) Trust in science was declining, (2) the economic situtation has made people reluct to shoulder the burden of dealing with climate change, (3) Republican political leaders (he didn’t say “Inhofe,” but that’s surely who he was referring to) are making headway with the public, (4) “skeptical” scientists are making headway with the public, or (5) 2008 broke the warming trend and had the lowest temperatures in the most recent decade. He then evaluated each of these using his survey research methods.

He found no significant change in the trust in scientists. It remains at ~70%. So much for explanation #1. He actually found a (small) increase in the willingness to pay for remedial policies, in spite of the bad economy, so #2 is out, too. In addressing the influence of the Inhofes, he found no real chance among Republicans as compared to Democrats (presumably Republicans would be more willing to be influenced by Inhofe’s statements). He also ruled out the skeptical scientists’ influence, as people who have a low trust in scientists have both a correct perception of scientific consensus and a correct perception of the overall temperature change. And that left #5, the 2008 break in temperature trends. He suggested that when it warms up again, they will shift back. As with a year’s cooler weather, the cooler perception is a temporary aberration which will vanish as soon as people “stick their finger out the window” and find it to be hot again.

The final speaker was Norm Ornstein. I was very impressed by Ornstein’s diction and mastery of the Washington political landscape. He’s a very smart guy, who assumed the podium and stuck his hands in his pockets and (sans PowerPoint) spoke extemporaneously and in great detail about why politicians do what they do. I was impressed with his erudition and competent demeanor. He noted that there is a deep dysfunction in the American political system, and that this dysfunction is systematic: that is, it doesn’t change with the election of new officials. In 40 years of observing Washington politics from the inside, Ornstein said that this is the most dysfunctional he has ever seen it. He said that it’s really unlikely to get meaningful climate legislation passed unless the health care bill passes first. Obama needs a record of success in order to push his other agenda items forward, and the obstinacy of the Republican caucus has made his first year ineffective, which puts Democratic Congresspeople in a tricky spot “going out on a limb” to support him in his second year (as they are up for re-election then).

I tend to think about policy rather than politics, so this “reality check” about how Congresspeople think was insightful to me. In spite of strong science (Oppenheimer) and strong public sentiment (Krosnick), the reality of the political landscape suggests we’re not going to see meaningful climate legislation any time soon.

And with that, I went to Union Station and got some lunch.

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Solomon, S., Plattner, G., Knutti, R., & Friedlingstein, P. (2009). Irreversible climate change due to carbon dioxide emissions Proceedings of the National Academy of Sciences, 106 (6), 1704-1709 DOI: 10.1073/pnas.0812721106

Pew Research Center for the People and the Press. (Oct. 11, 2009) Fewer Americans See Solid Evidence of Global Warming. Washington, DC.

Better shot of glacial striations in Central Park

The one I posted earlier came via iPhone, and iPhone cameras are rather low in resolution, especially after pocket-lint accumulates on the unprotected lens. I took this one with my normal camera & I think it came out a bit better:

Penny (upper center-left) for scale. I’ve got high-resolution versions of this if anyone needs them for teaching.

Folds of New York

Thursday is ‘fold day’ here at Mountain Beltway.

Let’s take a look at some folds I saw last weekend in New York City. We’ll start with a bunch seen in the Manhattan Schist in Central Park. Here’s an example of the foliation in the schist. It’s got finer-grained regions and coarser, schistier regions with big honking muscovite flakes. Metamorphic petrologists: Does this correspond to paleo-bedding? (i.e. quartz-rich regions that metamorphose less spectacularly, and mud-rich regions that converted more totally to muscovite during metamorphism?)

Anyhow, here’s what it looks like when it’s folded (accented with a small granite dike):

And another, with some boudinage thrown in for flavor:

This was one of the best outcrops I saw that weekend (on the edge of the ‘lake’), but it was inaccessible to closer photography. Sorry about all the branches in the image. What you’re looking at here is a series of folds with axes plunging at ~45° towards the lake:

Crudely annotated version:

Granite dike:

Boudinaged granite dike:

Folded and boudinaged granite dike #1:

Folded and boudinaged granite dike #2:

Lastly, here’s a couple of folds from inside the American Museum of Natural History. A metaconglomerate:

A little model mountain belt made out of compressed sand layers:

The thing that really struck me about this sand model is the folds visible in the green and yellow central part of the mountain belt: There are refolded folds there. The lower-central antiform with dark green atop yellow is the best example. I had the idea in my head that two generations of folds meant two generations of deformation, but here you’ve got two generations of folds resulting (presumably) from a single episode of ‘mountain building.’

Such beautiful complexity! I want a sand model like this for my lab.

Pyrolusite on a pterosaur

All the photos I posted over the weekend here were via iPhone, and hence not particularly high-quality, despite their excellent geological content. Now I’ve downloaded the photos from my real camera, and have a few good ones to show. Here’s a succession of photos of the same specimen of Pterodactylus longirostrus, each progressively more zoomed in than the last. It’s a late Jurassic pterosaur (140 Ma) from the Solnhofen limestone of Germany.

I mainly took these for the pyrolusite dendrites rather than the fossil itself…

Emriver in action

Today, a few photos of my spring Environmental Geology class doing a New Orleans Case Study lab using our lovely Emriver river process simulator:

That’s it. I mainly shot these photos for Steve Gough, as NOVA is participating in the new grant he submitted to NSF, but I figured I would share them here, too. The students gave permission for the use of their images. I’ll blog up the Emriver itself someday: a fun toy indeed!

When the Sturtian happened

Last Friday, I spent the evening riding up to New York on a bus. To pass the time, I had my iPod and a new paper by Francis Macdonald and colleagues in Science. The paper examines the timing of one of the episodes of “Snowball Earth” glaciation. There’s some important new data in this paper, and it helps constrain the “Sturtian” glaciation in time.

So here’s the deal with Precambrian glaciations: there have been several. Generally speaking, there was a big episode of glaciation around 2.5 Ga (“Ga” = billion years ago, for those new to geo-temporal argot, and “Ma” = million years ago). There were also a series of at least two, and maybe upwards of four episodes during the Neoproterozoic era (~700 Ma). These latter glaciations have been collectively dubbed the Snowball Earth glaciations for evidence which suggests that they were global in extent. The evidence was high-precision paleomagnetic signatures which suggest some of the glacial sediments were deposited within a few degrees of the equator. If the equator was frozen over, it follows that the rest of the planet was too, due to ice-albedo feedback. That’s kind of a big deal, and the Snowball Earth hypothesis has been a rich source of research inspiration over the past decade and a half.

Now, figuring out just when the Snowball Earth glaciers flowed is a bit tricky. You can’t directly date glacial sediments using radiogenic isotopes, as they will be composed of the pulverized remains of pre-existing rock bodies, and will yield older-than-actual ages. It would be cool to find volcanic layers within the sedimentary package, because we can date those, or to find igneous intrusives (like dikes) which cut across the glaciogenic sediments, because those too are worthy of dating. The younger of the two “main” Neoproterozoic glaciations is called the Marinoan glaciation, and it has been dated using methods like these in Namibia (635.5 ± 0.6 Ma) and China (between 636 ±4.9 Ma and 635.2 ± 0.2 Ma). Locations as farflung as China and Namibia and other Canada can be correlated with one another on the basis of stable isotope chemostratigraphy. Basically, the idea is that there are global fluctuations in the carbon (or sulfur, or oxygen, or whatever) isotope “signature” that gets locked in the sediments, due to whatever was happening in the world at that time (e.g., life gobbling up certain isotopes, or climatic shifts, or other “big picture” events). So the chemostratigraphy allows us to match up rock units of the same age, and the few places where we are lucky enough to get igneous units interacting with the sedimentary package allow us to pin the whole lot to a specific date.

Great… for the Marinoan.

But an earlier “Snowball” episode, the Sturtian glaciation, has not been as precisely dated. Enter the Macdonald, et al. (2010) study. They report four new high-precision U/Pb dates from igneous rocks in the Ogilvie Mountains of northwestern Canada. Three of these are part of the Sturtian stratigraphic package, following the paradigm I outlined above. One, from a tuff unit, yielded a date of 717.43 ± 0.14 Ma, and another yielded a date of 716.47 ± 0.24 Ma: both of these were essentially right at the bottom of the Upper Mount Harper Group, which includes strata that are interpreted as belonging to the Sturtian glaciation on the basis of dropstones (A) and striated clasts (C) like these (from the supporting figure S2 for the paper):

They also found evidence of “grounded ice”: soft-sediment folds that resulted when (they interpret) the nose of the glacier shoved its way forward. So this wasn’t just a floating glacier above: the glacier was in the muck, suggesting it was right there at sea level.

This is a lucky find: a datable volcanic ash layer right at the base of a big stack of glacial sediments. It’s a major advance for understanding the Sturtian in its own right.

They also report a date of 811.51 ± 0.25 Ma for strata deeper down in the stack, right before a global isotopic ‘excursion’ (a big, distinctive leftward squiggle on the carbon chemostratigraphy plot) called the Bitter Springs isotopic stage. Here’s a detail from the paper’s Figure 2, showing how this new date integrates absolute time with the relative time illustrated by the isotopic curve:

That’s δ¹³C data plotted from three Neoproterozoic sections (in Namibia, Svalbard, and the Yukon). The thick central vertical black line is 0‰, with the left bound being -8‰ and the right bound being +8‰. The horizontal green lines show the new dates from this paper.

So all that is good, and a significant new batch of data for helping pin down the timing of these ancient glacial episodes. We’ve been able to date some Sturtian glacial units and a pre-Sturtian isotopic excursion.

The paper presents a fourth date, too: this is from a diabase sill that is part of the Franklin Large Igneous Province (LIP) exposed on Victoria Island, over 1000 km to the northeast of the Ogilvie Mountains (where the other three dates come from). The Franklin diabase gives a U/Pb age just like those from the Sturtian glacial sediments: 716.33 ± 0.54 Ma. But is this relevant, considering how different the rocks are, and how very far apart they are? Check out this map to see their lack of proximity, from the paper’s supporting figure S1:

Why would the paper’s authors bother with a rock unit so far away from the Ogilivie section? Well, the Franklin LIP is integral to the Snowball story on at least three fronts that I can think of. It ties this story together quite nicely, and I think that it is just as important as the Ogilvie data.

First, on a tectonic note, it’s a mafic unit that is associated with the breakup of Rodinia, a Proterozoic supercontinent. (Rodinia’s position on the paleo-equator is supposed to have sped up weathering of the continental crust and resulting CO₂ drawdown, cooling the planet.) Second, it has paleomagnetic orientations which suggest it was emplaced within 10° of the magnetic equator. (This is important because it demonstrates that grounded ice was present within 10° of the equator at the time the Franklin LIP erupted… and due to ice-albedo feedback, it implies higher latitudes were frozen-over at that time, too.) Third, the Franklin LIP has been fingered as a possible culprit in causing Snowball Earth. This is because mafic igneous rocks suck CO₂ out of the atmosphere when they are chemically weathered, producing carbonate rocks. The Franklin LIP has the potential to be a major driving force for the CO₂ drawdown which initiated the Sturtian Snowball via global cooling. A big package of mafic rock delivered raw right to the tropical weathering belt could be sufficient to trigger an ice age, some workers have suggested. The Franklin LIP was in the right place at the right time: was it the culprit, or only an accomplice? Witness the way that the authors (properly) hedge their bet in their conclusion’s penultimate sentence:

…the synchrony among continental extension, the Franklin LIP, and the Sturtian glaciation is consistent with the hypothesis that the drawdown of CO₂ via rifting and weathering of the low-latitude Franklin basalts could have produced a climate state that was more susceptible to glaciation.

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Macdonald, F., Schmitz, M., Crowley, J., Roots, C., Jones, D., Maloof, A., Strauss, J., Cohen, P., Johnston, D., & Schrag, D. (2010). Calibrating the Cryogenian Science, 327 (5970), 1241-1243 DOI: 10.1126/science.1183325

Video on carbon sequestration in Oman ophiolite

http://www.whoi.edu/oceanus/viewArticle.do?id=61206

(from one of the Skepchicks)

Suevite from Vrederfort

One of my students brought this sample in the other day:

She said her father collected it in South Africa. It was labeled “suevite.” I learned the term suevite about a year ago, while touring the USGS Chesapeake Bay Impact Crater coring project samples at the USGS Headquarters in Reston, Virginia. Wright Horton taught me that suevite is impact-generated melt that chills with other chunks of the pre-impact rock mixed into it. Sometimes, it is glassy. There was a bunch of it deep in the Chesapeake Bay Impact Crater core.

So I put this together in my head and asked “Where in South Africa did this come from?” The student couldn’t remember, but it was “some weird name.” “Was it the Vrederfort Structure?” I asked? Her eyes lit up: “Yes! That’s it! How did you know?” I didn’t know: but that’s the only impact site in South Africa I could name offhand. So I think that’s what this is. A pre-Vrederfort Impact granite smashed and melted during the impact, with individual mineral grains breaking off and mixing into the melt, which then solidified into suevite. Pretty neat little sample! I’d love to have one of my own, but settled for making a digital scan of hers. E-mail me if you want a bigger copy.

Rusty weathering rind

On a granite block

Giant ground sloths

In the American Museum of Natural History:

These mylodontids reminded me of Puerto Natales…