Watch a YouTube video

This guy on YouTube has spelled out a very nice approach to how "skeptics" should look at the possibility of a changing climate.


blog action day

If time permits, which is a big if right now, I will try to participate in blog action day.

Bloggers Unite - Blog Action Day


Shipping Lanes

I've been sitting on the idea for this post for almost a week, but haven't had a chance to work it up. Since it doesn't look like I'm going to get to do it the way I originally wanted, I'm giving in and just going for the gusto. Maybe (yeah right) I'll come back and round out the rough edges later, but for now I want to get the basic ideas out there.

Ship tracks are the contrails of the sea. Perhaps more accurately, ship tracks are to the marine atmospheric boundary layer what contrails are to the upper troposphere. They are lines of what we will call clouds that form behind a ship. They are the focus of a recent article that I found very interesting. A news summary can be found on the Science (LINK) web site, while the paper appears in GRL. For a good picture of ship tracks, NASA's MODIS is a good resource.

The idea in the paper is to establish the radiative forcing associated with ship tracks on the global scale. This hasn't been done before using observations because ship tracks are very low, very small clouds that cover a tiny amount of Earth's surface area. However, they are common, as the paper points out, in several regions, notably off the coast of Africa and in the North Pacific. These are, somewhat coincidentally (but not really), the same regions where we think about extensive stratocumulus decks.

Schreier et al. use one year of satellite imagery, from the ENVISAT-AATSR, and go through a straight forward but intensive process of identifying ship tracks and then estimating their radiative forcing. The bottom line is that in some regions the radiative impact of ship tracks, lets call it the local radiative effect, can be a non-trivial -0.05 W/m2, but on the global scale the effect is miniscule at -0.4 to -0.6 mW/m2 (plus or minus 40%). Note that the global value is in milliWatts, so is 100 time smaller than the largest regional radiative effect (-0.05 W/m2 = -50 mW/m2). The negative sign arises because ship tracks are very low clouds that are very white (i.e., reflective), so when they appear they provide a more reflective surface for sunlight to bounce off, which to first order reduces the amount of energy in the climate system (because most of the reflected light goes back out to space) and cools the climate. This is familiar if you've been exposed to cloud "feedback" ideas, in which more low cloud cover increases the albedo of Earth and cools it. In fact, this is a terrific example of that effect, but we'll come to that shortly. It is also good to note that the radiative forcing associated with a doubling of atmospheric carbon dioxide is about 4 W/m2, which is itself a small signal in the total radiative budget (with 1365 W/m2 of incoming sunlight at the top of the atmosphere, distributed over a day (divide by 4) and an albedo of about 0.3 you're talking in the neighborhood of a 225 W/m2 of sunlight being absorbed at the surface, and all of global warming comes down to 4W/m2 give or take!).

Okay so before I sign off, leaving you totally confused. I wanted to point out a couple of interesting things about ship tracks that aren't necessarily in the article. First of all, it is helpful to remember why ship tracks form. The ships are steaming ahead, burning fairly dirty fuel to get where they are going, and the exhaust goes right out into the atmosphere. This exhaust contains particulate matter as well as precursors for particles, so the ship is basically making a trail of particles behind it. These particles act as nucleation sites for water, forming small cloud droplets. Because the ships spew out so much stuff, there are enough nucleation sites available to grow lots of droplets and form these linear clouds. Why don't the clouds form anyway if there's that much water in the atmosphere already? Well, a couple of reasons. One is that the relative humidity isn't quite 100% in fair weather conditions, but even if it were, water doesn't like to condense unless there are surfaces (supplied by the particles). At a relative humidity of about 80%, there just aren't enough particles floating around the clean maritime boundary layer to let the water condense into clouds. The ships provide the extra nucleation sites necessary, and make it even easier by supplying the boundary layer with hygroscopic particles, meaning the particles effectively decrease the saturation specific humidity (http://en.wikipedia.org/wiki/Hygroscopic). That just means that the particles are very efficient at turning water vapor into liquid water. So a ship goes by, spews out water-loving particles, water condenses on those particles forming droplets, and a big collection of droplets is a cloud. Fine, what else?

So okay, the ships go by and make lines of clouds, but we now know (or strongly suspect) based on Schrier et al. that the global effect of these cloud is negligible and the local effect is also pretty small. Can we be done with it then? Not quite. These clouds are a great example of the Twomey effect, which is an old idea now and just says that by increasing the number of particles in the air, the size of cloud droplets gets smaller, and when clouds are made up of small droplets they are brighter (i.e., more reflective). Coakley et al. (1987) presented ship tracks as such an example, showing with satellite data that the reflectivity of ship tracks is higher than the surrounding low-level cloud cover. This is exactly what leads to the radiative forcing that has now been estimated by Schreier et al. The important thing to recognize here is that the Coakley et al. study is essentially a proof of concept, showing that pollution can impact atmospheric radiative transfer. They definitely did not say ships were impacting global climate.

There is a related effect, sometimes called the Albrecht effect, which takes into account the change in cloud fraction associated with changes in particles in the atmosphere. It is presented by Albrecht (1989), and is also a pretty simple idea. When extra particles are put into the atmospheric boundary layer, they form droplets and brighter clouds, as discussed above. Smaller droplets can also change the formation of raindrops, or more precisely in the case of shallow maritime clouds, drizzle drops. The change is to reduce the precipitation efficiency, which increases the liquid water in the cloud layer, and can lead to an increase in the fractional cloudiness. The important point here is that not only could increased particle concentration in the marine atmospheric boundary layer make brighter clouds, but could actually increase the overall cloudiness. This would amplify the effects discussed by Coakley et al. because there would now be a larger area covered by brighter clouds. The Albrecht study makes use of ship tracks only in the sense of the Coakley et al. study, and only suggests that changes in precipitation could account for the sustained difference in ship tracks from the stratiform cloud in which they are embedded. This is supported to some extent by aircraft observations.

And finally, since we're covering so many bases, there's another effect that should be mentioned. Pincus and Baker (1994) present a study that extends the Albrecht study in that it accounts for the change in the thickness of clouds in the presence of varying particle concentration. They use a model of a cloudy boundary layer and account for changes in absorption and precipitation with cloud thickness and droplet number, respectively. This effect is not quite as "obvious" as the other indirect effects, but the bottom line is that more droplets can make thicker clouds with a higher albedo, which is thus another facet of this negative feedback associated with changes in atmospheric aerosol (particles). They note, however, that you'd expect to see ship tracks extend higher than surrounding clouds, which at that time was not observed. I'm not sure where this effect really stands, but it is interesting to consider.

So these are the indirect effects of aerosol on climate. We came a long way in this post, from a recent study showing that the globally averaged radiative forcing due to ship tracks is small all the way through aerosol effects on cloud albedo, precipitation processes, and horizontal and vertical cloud distribution. Well done. There are a lot more details that could have been added, and tons more studies. These will be left for future posts, though. I've included some references below for those of you who want to follow up.


Schreier, Mathias; Mannstein, Hermann; Eyring, Veronika; Bovensmann, Heinrich
Global ship track distribution and radiative forcing from 1 year of AATSR data
Geophys. Res. Lett., Vol. 34, No. 17, L17814
10.1029/2007GL030664 (LINK)

Effect of Ship-Stack Effluents on Cloud Reflectivity
Science 28 August 1987:
Vol. 237. no. 4818, pp. 1020 - 1022
DOI: 10.1126/science.237.4818.1020

Aerosols, Cloud Microphysics, and Fractional Cloudiness
Science 15 September 1989:
Vol. 245. no. 4923, pp. 1227 - 1230
DOI: 10.1126/science.245.4923.1227

Effect of precipitation on the albedo susceptibility of clouds in the marine boundary layer
Nature 372, 250 - 252 (17 November 2002); doi:10.1038/372250a0


The Arctic and its role in the climate change discourse

I spend most of my time thinking about clouds in the tropics and subtropics, but lately there's been a lot of mainstream coverage of the Arctic and how it relates to climate chage. I've posted about Arctic issues before, of course, but today I not only want to highlight a little of the coverage that I've noticed lately, but also warn you, gentle reader, that this is really just going to be one of myriad posts, articles, stories, and sundry coverage of the Arctic over the coming 2-3 years (and probably beyond). Why? Because of the "International Polar Year," which is a big enough deal to have its own domain: ipy.org. It is, as the name implies, an international effort to better understand the Earth system near the poles, from their web site:

IPY, organized through the International Council for Science (ICSU) and the World Meteorological Organization (WMO), is actually the fourth polar year, following those in 1882-3, 1932-3, and 1957-8. In order to have full and equal coverage of both the Arctic and the Antarctic, IPY 2007-8 covers two full annual cycles from March 2007 to March 2009 and will involve over 200 projects, with thousands of scientists from over 60 nations examining a wide range of physical, biological and social research topics. It is also an unprecedented opportunity to demonstrate, follow, and get involved with, cutting edge science in real-time.

Don't fool yourself either, this is not a group of environmental activists who are out trying prove something; this is a concentrated period of study of the Arctic and Antarctic by the people who do that work anyway. It should lead to some great collaborations and synthesis of datasets that haven't been able to be compared or incorporated in meaningful ways before.

So that is the future, what is going on now?

Well, just over the past few days I've read a few interesting tidbits about the Arctic, which people seem to enjoy discussing more than the Antarctic (but more on that later). One of the poster children for climate change awareness is the polar bear, which relies on big pieces of sea-ice floating around near other pieces of sea-ice. The bears hang out on the ice, get hungry, dive in after fish or seals, and come up onto more ice. Apparently they aren't so well adapted to feeding on land, plus there isn't as much food available on land for them. Anyway, a quick article from the BBC, which came to be via ClimateArk, reports on a study that suggests two-thirds (2/3) of the polar bear population will be gone by the middle of the century [LINK]. That's 30-50 years from now, if you're keeping score at home. Why are the bears going to disappear? Because the ice is going away. So what does that mean for a species that relies on ice rafts as hunting platforms? It means that the bears are going to starve and drown. That is a fact. There is already evidence that some populations of polar bears are losing weight, and it probably isn't in preparation for beach season (Regehr et al 2006, also Roberson 2005 (news), Obbard et al. 2006).

This leads directly into our topic number two: sea-ice. This is one of the reasons it's more interesting to talk about the Arctic than the Antarctic, actually. Think about the globe, and picture the poles; the south pole is covered by a landmass (Antarctica) which is actually pretty large, extending far from the pole before giving way to the Southern Ocean. The fact that it is land, combined with the fact that it is surrounded by a continuous ring of ocean, makes climate change near the pole more difficult to understand: the ice in the middle of Antarctica isn't melting. And the sea-ice is much more seasonal (for the most part, though don't forget the Larson B ice shelf!) than in the Arctic (we're painting with a broad brush here). The Arctic is just an ocean, really, which provides easy passage among North America, Europe, and Asia, you remember the Northwest Passage [news], except that it has historically been blocked up by sea-ice. Lately this isn't so true [news, Randy Boswell].

The opening of the Northwest Passage is due to summertime melting of sea-ice, as discussed in Randy Boswell's very nice piece above. There has always been a lot of seasonal sea-ice around the Arctic. During the winter there is little to no sunshine available to deliver energy to warm the surface or melt ice, so as temperatures drop, ice forms, and it stays there until summer when the sun comes out. So that happens every year, and is perfectly normal and expected. However, what has happened over the past few years is a tremendous summertime melting, and just about every year now we hear about how sea-ice extent and sea-ice area are reaching record lows. One of the problems with this is that there is a potential feedback, since the "permanent" sea-ice (that ice that does not melt during the summer) is being reduced each year, so during the winter the ice that grows is thin, leading to quick melting in the summer, which exposes more permanent sea-ice to warm water and sunshine, leading to more loss and a diminished base amount of ice going into the winter. This most recent report suggests that the speed of this cycle might have been underestimated, and now some experts (yes, they are experts in Arctic sea-ice) say that an ice-free Arctic (in the late summer) could exist by 2030 (Serreze et al 2007a,b), which is right around the corner. This bodes ill for the polar bears.

Finally on this subject, it is interesting to note the relationship between the absurd observed sea-ice melt in the last few years compared with our best comprehensive climate models (Serreze et al. 2007b, Overland & Wang 2007). Some of the current-generation models do sort of okay, while basically all of them show a strong trend in the Arctic, but none of the models accurately predict the magnitude of the observed trend. Let me reiterate that these models don't know anything about the observations; they are physical models of climate system forced by atmospheric composition (carbon dioxide) and sunshine, so this isn't a matter of poor data assimilation or statistical techniques or a poor model (in the sense of statistical modeling). This is a dramatic underestimation of the impact of climate change on a region of the world known to be prone to positive feedbacks. What this means is that our "uncertainty" about the future of climate change goes in both directions. Climate change deniers like to point out problems with the models that they think lead to unlikely warming, but here we have a beautiful example of the models underestimating what is actually happening. Perhaps the models are too conservative? Not really, I just wanted to be provocative for a moment. My interpretation is that we need to improve the physics in the models, and probably spend more effort in doing atmosphere-ocean-ice interactions much better than this round of climate models. That is a rant I'll save for later though, as this post is stretching the average blog reader's patience.

Some references:

Regehr, E.V., Amstrup, S.C., and Stirling, Ian, 2006, Polar bear population status in the southern Beaufort Sea: U.S.
Geological Survey Open-File Report 2006-1337, 20 p. [PDF]

Obbard, Martyn E., Marc R.L. Cattet, Tim Moody, Lyle R. Walton, Derek Potter, Jeremy Inglis, and Christopher Chenier, 2006, Temporal Trends in the Body Condition of
Southern Hudson Bay Polar Bears. Climate Change Research Information Note, Issue 3. Ministry of Natural Resources, Ontario, Canada, 8 p. [PDF, see also MNR SIT]

Serreze, M. C., M. M. Holland, and J. Stroeve. 2007. Perspectives on the Arctic's shrinking sea-ice cover. Science 315(5818): 1533-1536, doi:10.1126/science.1139426. [pdf]

Stroeve, J., M. M. Holland, W. Meier, T. Scambos, and M. Serreze. 2007. Arctic sea ice decline: Faster than forecast. Geophysical Research Letters 34, L09501, doi:10.1029/2007GL029703.

Overland, J. E., and M. Wang (2007), Future regional Arctic sea ice declines, Geophys. Res. Lett., 34, L17705, doi:10.1029/2007GL030808. [pdf]


hurricanes again

It has been far too long since my last post... the casual blogger's constant lament. In my own defense, a lot has happened in the past few months, not the least of which is that I finished my PhD program and moved to Fort Collins, Colorado as a postdoc. I am now affiliated with both UCLA and CSU via the CMMAP project. Of course, anything I say on this blog has nothing to do with those institutions, and could still be wrong even though I am now officially an "expert."

Now to what I was going to write....

After a rather slow start, the Atlantic hurricane season is really getting going now. Early this morning Hurricane Felix came ashore along the Mosquito Coast in central America as a powerful category 5 hurricane. This is the second category 5 storm to make landfall in the past 3 weeks (following Dean), and apparently is the first time two category 5 storms have made landfall in the same season. It is also worth noting that only about 31 category 5 storms have been recorded in the Atlantic since 1928. Of course, reliable observations were not available until the 1960s; there have been 18 category 5 storms since 1966. Eight of those have occured over the past five years [2003,2007]!

The big storms are not the only story though. There is a lot of tropical activity already, including three tropical storms (Barry, Chantal, and Erin) and numerous disturbances that haven't developed. There is currently an area off the Florida coast that is probably going to develop into a tropical storm over the next few days (although there is significant wind shear). There's also a region out in the central Atlantic that could still develop, basically following the same path as Dean and Felix. These all originate as "easterly waves" coming off the west coast of Africa, and it is starting to look like it's going to be a very active season; don't be surprised to see another category 5 by the end of the month. If that does happen, it will only be the second year with more than two category 5 storms in the Atlantic.

By the way, yes there are tropical cyclones in the Pacific too! Henriette is the third East Pacific hurricane of the year (Cosme, Flossie), and although it is only a category 1 right now (possibly 2 by landfall), it is bringing substantial rain to the west coast of Mexico. In the western Pacific there have already been 7 typhoons this season and 2 tropical storms.


ye olde iron fertilizing effect

So apparently people now think they can make money by throwing iron into the ocean... YES, throwing iron into the ocean.

Here's the, actually very good, story on NYTimes.com: [The Energy Challenge: Recruiting Plankton to Fight Global Warming]

The basic idea is that plankton reproduce like mad when the conditions are right, and in large swaths of the ocean the conditions are right. Except there isn't enough iron. So, when you dump some iron on those areas, plankton bloom, creating regions of increased biological activity. The upside to this, according to some, is that the plankton use carbon from the ocean to make their little calcium carbonate exoskeletons, which when the critters die, can sink to the bottom of the ocean. This means that carbon is removed from the atmosphere-ocean system... it is sequestered, like an OJ juror. So now at least two companies, so cleverly named Planktos and Climos, think they can get governments (or companies working under cap and trade systems) to pay them to go throw some iron into the ocean.

I do not reject this idea outright. There are clearly some good ideas here, but we have to be careful. Here are a couple of my primary concerns.

First, I'm worried that these plankton species will produce a lot of methane waste, possibly negating any decrease in atmospheric CO2 that they might be responsible for. There is similar concern with nitrous oxide, apparently.

Second, the amount of carbon actually deposited might be less than has been thought recently. This is actually in this week's Science [LINK].

Third, as these operations scale up, will they account for their own carbon emissions. Boats are notoriously bad for emissions, and there's going to have to be a lot of boating involved. Also, where is this iron coming from, and how much energy (i.e., carbon) is going into collecting and transporting it?

Finally, there are possible feedbacks that could negate any good this will do. Including the old DMS-cloud condensation nuclei, in which more biology produces more aerosol (in the form of dimethylsulfide, DMS) which acts as nucleation sites for cloud droplets, making more cloud. The effect could be to shade the surface, reduce SST, and thus reduce biological productivity, leaving a rusty sea surface instead of a nice, healthy green one. I don't know if this is feasible, but things like this always seem to come up.

Also consider the amount of carbon dioxide that needs to be removed from the atmosphere. I've just come from a talk that reminded me of this. Carbon dioxide, when frozen, has about the same density as water. That means that a ton of CO2 is about one cubic meter (size of a coffee table). You're now talking about removing billions of tons of carbon dioxide annually, which is an enormous mass, many cubic kilometers of frozen CO2. The ocean is a big place, but we've got to be careful about how and where such deposits are made, or they'd just be mixed back up to the atmosphere. There's just so many potential pitfalls that it is hard to imagine a successful implementation. But as I said at the beginning, I'm willing to keep an open mind on the subject, and would be happy to see a successful strategy.


US Army getting into supercomputers

Here's a quick story that seems like it is important. I will refrain from any interpretation of speculation here.

Army funds supercomputing center [LINK]


IPCC AR4 - Summary for Policymakers

So you by now know, I hope, that the Intergovernmental Panel on Climate Change has issued it's Fourth Assessment Report of working group I (i.e. the "physical scientists). Okay, actually, it has only released an abstraction of the AR4 called the Summary for Policymakers. The full report will be available in a couple months. For now, get the summary from the UCAR site [PDF].

There are a lot of issues about this report and the IPCC in general that I'm tempted to start spouting. Instead, I'm going to let those thoughts roll around a little more, and perhaps wait for the full report. For today, I just want to point out some key points, about the summary, along with some cautionary words.

The report is written by climate scientists (so is the summary). All the writers, both lead authors and contributing authors, work on a voluntary basis. I think the idea, at least for the north American and European scientists, is that the IPCC is an important way for scientists to interface with the policymakers and general public, and that working on the report is an important outreach activity. The IPCC as an entity is organized under the auspices of the World Meteorological Organization (WMO) and the United Nations Nations Environment Programme (UNEP), and as such it is open to members of those organizations. That means that a lot of scientists are eligible to contribute to the report, but it also means that there are a lot of governments that have vested interests in what the report ultimately says.

Do governments influence the content of the report? Well, from what I've heard ('round the proverbial water cooler), there is very little direct interaction with world governments. Drafts of the reports are sent out to tons and tons of people, including governments, so there are notes sent back. Those notes have to be addressed individually, but I'm sure that most of them are insignificant and are basically ignored. The indirect influence is probably more important. The scientists writing the report are aware of the political/societal implications, and try to protect themselves by explicitly avoiding making prescriptive suggestions; they don't say what to do about climate change, they just evaluate the scientific evidence to evaluate the extent of climate change and projections of future change. The indirect influence of governments and economics makes the authors, in my opinion, even more conservative in their language than scientists normally are. I think the report generally does not embrace more extreme projections and predictions, which is to their credit, but is a caveat when reading the report or the summary. That is, some of the key points are probably more conservative than individual scientists would suggest.

Of course, there is also pressure to put new and important results into the report. This pressure comes less from external sources and more from the drive to show how much we've learned since the last report. There are a few points in the summary that I was surprised to see, not because they aren't important, but because I think there have to be many, many caveats. The two examples that stick out are (1) that tropical cyclones are getting more intense with global warming and (2) that patterns of precipitation will change in the future, with specific patterns emerging as robust. I'll blog more about both of these in the future, but here I'll just say that I look forward to reading the specifics in the full report. I generally believe the first claim, while the second one seems extremely poorly constrained by climate models.

Even with these opposing pressures, the results of the summary are largely unsurprising and in line with the Third Assessment Report (2001). The lower range of climate sensitivity has inched up a bit from 1.5C to 2.0 C. That basically has had to move up as we've seen more and more warming over the past decade. They are also making the upper range of possible sensitivity more hazy by mentioning some projections of greater than 5C or so, even though they don't necessarily incorporate those very sensitive projections in the non-analysis that goes into writing the report. (I'll also talk about what I mean by non-analysis in a future post.)

So, yes, global warming is happening. Oh, and yes, it is because of humans emitting carbon dioxide into the atmosphere.


Newsflash? No.

Well, according to NOAA's National Climatic Data Center, 2006 was even warmer than 2005. That means, if you haven't been keeping score, that 2006 was the warmest year on record (for the USA). I didn't find an actual ranking for the global mean temperature, but I think we can safely assume 2006 was in the top 5 (if not the top 2). The press release blames (rightly, for a change) ENSO (which is El Nino) for the getting 2006 into the top seat. It turns out December was really hot, mostly because there weren't very many storms crossing the country. My suspicion is that this El Nino will continue to make this winter much warmer than average, and 2007 will beat 1998 and 2006 as the warmest year in the past 1000+ years.