Tuesday, December 15, 2009

The Earth is Blue

“Mankinds footprint in the oceans is now clearly detectable - it is warmer, more acidic, and less diverse.” (Stein 2009)

There are people here from the Meteorological Office at the Hadley Center in Britain talking about what they do best - models. Theirs is one of a number of climate models that churns out results telling us how the atmosphere is likely to behave under different sets of circumstances. These are the famous/infamous GCM's we have heard a lot about.

These models are incredibly complicated because they are trying to replicate or mimic really complicated patterns in environmental systems. They do have their blind spots though and it is worth knowing what and where these are because they tell us something about the limitations of the model, and ultimately it is as important to know what the models do not tell us as it is to know what they do tell us. It is also helpful in knowing whether the models are likely to over-predict or under-predict warming trends looking into the future.

Let's start simple. There is a great deal of concern about Arctic sea ice (think of the plight of the Polar Bears). So much of it has melted back seasonally in recent years that shipping companies have started placing bets on new east-west routes being open in the Arctic Ocean. The great search for the Northwest Passage may finally be over. Even where the ice does not completely melt away, it is thinner than we have ever seen it before. It is expected that atmospheric warming in the high latitudes will result in an ice free Arctic Ocean during the summer months sometime between 2030-2060.

Once the Arctic goes ice free in summers, there are a number of feedbacks expected to occur. What is unknown is the rate at which these feedback mechanisms will kick in or the secondary effects these changes will likely have on other aspects of the environmental system.

As ice disappears, surface reflectance decreases tremendously resulting in an overall increase in the amount of sunlight which will be absorbed by the seawater and transformed into heat (where previously it would have been reflected back to space without ever being transformed into heat). Think of putting something reflective in your cars windshield in the summertime. The net effect is to keep the sunlight from entering your car and being transformed into heat. Now take away that reflector and imagine how hot that seat will feel when you sit down. In effect, this is what is happening in the Arctic as the ice melts back.

The melting icepack won't increase sea levels any because it is already floating over the Arctic Ocean in the same way that drinks don't overflow the glass when the ice melts. However, as water warms it expands slightly in volume. This means that worldwide warming of seawater will result in thermal expansion which will result in higher sea levels even if not one extra drop of glacial water enters the oceans.

As ice disappears, it is expected that the Arctic will quickly begin absorbing atmospheric CO2 at a rate higher than is occurring now in other areas of the world's oceans. This will, in turn, dramatically accelerate ocean acidification.

The oceans are capable of absorbing tremendous amounts of CO2 from the atmosphere, which is a good thing unless you reach conditions of saturation. That is because as saturation is reached, ocean water will literally become corrosive to exoskeletons and shells of ocean critters. Any animal that has a hard exoskeleton or shell (mussels, snails, shrimp, lobster, coral, clams, etc) is likely to be affected by this. Especially disturbing is this effect on phytoplankton and zooplankton. They don't sound very interesting but they are the base of the food chain for a tremendous number of things that swim.

We are already seeing hints of this occurring now. Many oyster larvae off the west coast of the U.S. no longer survive to maturity. Losing or even damaging such an important commercial fishery would be a huge economic blow to fishermen who have already taken severe hits because of local salmon populations declining.

Earlier in the week we heard a couple of NOAA researchers discuss ocean acidification and how this problem was different from the atmospheric complexities and uncertainties of global climate change. They made three essential points:

1) Ocean acidification is mechanistically simple. We know how it works. It is based on simple principles we understand and is no more complicated chemically than soda water. It is essentially the same process that causes water to have a corrosive effect on the subsurface and create caves.

In an interesting side note, one proposal floated recently by the authors of Superfreakonomics was to shoot large quantities of sulfur dioxide into the atmosphere to increase reflectance and temporarily cool the atmosphere. One of the many problems with this proposal is that most of this material shot up into the stratosphere would eventually also be absorbed by the oceans. This in turn would make the ocean water absorb CO2 much more efficiently - it would speed it up. So the Superfreakonomics guys are advocating a simple solution to atmospheric warming that will sell a lot of books but will almost certainly kill the oceans, or at least kill them much, much faster.

2) There are fewer options for dealing with ocean acidification. Pretty much the only option for reducing the rate and extent of the problem is to reduce the amount of CO2 in the atmosphere that the oceans can absorb. That's it. There are no quick fixes or other ways to forestall the inevitable absorption of CO2 by the oceans.

3) Lastly this issue of ocean acidification is more urgent than atmospheric warming. While the models predict very bad scenarios driven by atmospheric warming still a few decades away, acidification levels for most oceans around the world left the "safe" range back in the 1990's. Many waters are currently at a critical stage where they become corrosive at the surface for extended periods of time in the summer months. Hope you don't like oysters. If nothing is done quickly, NOAA describes acidification reaching catastrophic levels by 2040, way too soon for the development of complicated technologies such as carbon capture and storage (think "Clean Coal"). The good news is that by the time the Arctic sea ice melts back and causes a spike in ocean acidification, much of the wildlife with hard shells and exoskeletons may already be long gone as will the fish that depend on them for their survival. They won't have to endure that last indignity.

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