A Hot Topic
Today’s issue of Nature features several interesting articles about the effects of global warming. Two are research articles, with one revising estimates of the expected increase in sea level due to global warming and the other demonstrating how certain important marine ecosystems could be vulnerable to changes in ocean currents due to global warming. The journal also contains an editorial and a news feature about the need to monitor ocean currents more closely to better assess the consequences of global warming and to warn us of impending climate shifts.
One of the most obvious effects of global warming will be an increase in sea levels, both from melting snow and ice and the natural tendency of water to expand slightly as it warms up. In “Low sea level rise projections from mountain glaciers and icecaps under global warming,” scientists Sarah Raper and Roger Braithwaite provide a more conservative prediction for the expected increase in sea level over the next century. According to the sources used in the paper, current models vary, but the average predicted increase over the next century is 0.387 meters (just over 15 inches). Although about 60% of the increase is expected to come from water expansion, this study focuses specifically on sea level rise due to melting mountain glaciers and icecaps.
Although previous models predict a contribution of 0.106 meters in sea level increase from mountain glaciers and icecaps, this paper cuts that estimate in half. The rationale for this is that the authors in the current study accounted for changing patterns in snowfall, with increased snowfall in some areas expected to slow the melting process. The study is interesting and rigorous, but even if the results are correct, this would only reduce the total expected sea level increase by roughly 10%, and an increase in the sea level of 12 or 13 inches instead of 15 inches would still be very significant.
An ongoing themes in climate change research is that global warming can manifest itself in a variety of ways (see my previous post on this topic). In “Reduced mixing generates oscillations and chaos in the oceanic deep chlorophyll maximum,” scientists Jef Huisman, Nga Pham Thi, David Karl, and Ben Sommeijer model variation in the deep cholophyll maximum (DCM), an important layer of plankton around 100 meters below the surface of the ocean, and they find that it is much less stable than originally thought, a finding which has important implications for global warming:
What exactly the broader implications of a change in the DCM would be remain unknown, but such jarring disruptions to natural ecosystems are rarely good.
The current issue of Nature also features an editorial and news piece on the potential for global warming to cause drastic weather and climate changes by shutting down thermohaline circulation, the scenerio that was recently dramatized into the film The Day After Tomorrow. It is thermohaline circulation in the Atlantic Ocean, for example, that carries warm water northward, allowing Europe to enjoy a relatively mild climate for its latitude. Although the editorial is lukewarm to the potential for major climate changes, it calls for governments and scientists to step up efforts to monitor this phenomenon more closely worldwide. The news feature by Quirin Schiermeier, called “Climate change: a sea change” goes into much more detail on the issue.
Clearly, we do not understand all of the effects global warming could have on our planet, which is a reason to be even more cautious than we already are, not less. Although global warming is a very timely topic and a source of numerous ongoing research projects, this week was particularly interesting. Hopefully the pace of research will continue to increase, giving us a better idea of just what kind of an effect we are having on our environment and how we can change to counteract this.
One of the most obvious effects of global warming will be an increase in sea levels, both from melting snow and ice and the natural tendency of water to expand slightly as it warms up. In “Low sea level rise projections from mountain glaciers and icecaps under global warming,” scientists Sarah Raper and Roger Braithwaite provide a more conservative prediction for the expected increase in sea level over the next century. According to the sources used in the paper, current models vary, but the average predicted increase over the next century is 0.387 meters (just over 15 inches). Although about 60% of the increase is expected to come from water expansion, this study focuses specifically on sea level rise due to melting mountain glaciers and icecaps.
Although previous models predict a contribution of 0.106 meters in sea level increase from mountain glaciers and icecaps, this paper cuts that estimate in half. The rationale for this is that the authors in the current study accounted for changing patterns in snowfall, with increased snowfall in some areas expected to slow the melting process. The study is interesting and rigorous, but even if the results are correct, this would only reduce the total expected sea level increase by roughly 10%, and an increase in the sea level of 12 or 13 inches instead of 15 inches would still be very significant.
An ongoing themes in climate change research is that global warming can manifest itself in a variety of ways (see my previous post on this topic). In “Reduced mixing generates oscillations and chaos in the oceanic deep chlorophyll maximum,” scientists Jef Huisman, Nga Pham Thi, David Karl, and Ben Sommeijer model variation in the deep cholophyll maximum (DCM), an important layer of plankton around 100 meters below the surface of the ocean, and they find that it is much less stable than originally thought, a finding which has important implications for global warming:
Climate models predict that global warming will increase the stability of the vertical stratification in large parts of the oceans. This will reduce vertical mixing and suppress the upward flux of nutrients, leading to a decline in oceanic primary production. Our model predicts that the same process of reduced vertical mixing may induce oscillations and chaos in the phytoplankton of the DCM, generated by the difference in timescale between the sinking flux of phytoplankton and the upward flux of nutrients. Thus, counter-intuitively, increased stability of the water column due to global warming may destabilize the phytoplankton dynamics in the DCM, with implications for oceanic primary production, species composition and carbon export.
What exactly the broader implications of a change in the DCM would be remain unknown, but such jarring disruptions to natural ecosystems are rarely good.
The current issue of Nature also features an editorial and news piece on the potential for global warming to cause drastic weather and climate changes by shutting down thermohaline circulation, the scenerio that was recently dramatized into the film The Day After Tomorrow. It is thermohaline circulation in the Atlantic Ocean, for example, that carries warm water northward, allowing Europe to enjoy a relatively mild climate for its latitude. Although the editorial is lukewarm to the potential for major climate changes, it calls for governments and scientists to step up efforts to monitor this phenomenon more closely worldwide. The news feature by Quirin Schiermeier, called “Climate change: a sea change” goes into much more detail on the issue.
Other possible effects of a shutdown predicted by models include warming in the tropics, or, rather surprisingly, over Alaska and Antarctica. Rainfall patterns might change, too. A southern shift of the thermal equator — which has accompanied thermohaline circulation shutdowns during ice ages — could lead to monsoon failures, and droughts in Asia and the Sahel region, says Severinghaus, and these effects seem to be independent of sea ice. Such shifts could have severe consequences for poor farmers in many parts of the world, consequences that may be considerably more disruptive than colder winters in affluent northern Europe, says Severinghaus. And, as Schlesinger points out, a weakening or stopping of the thermohaline circulation would reduce the carbon dioxide uptake of the ocean, which would mean a positive feedback on global warming. The oceans currently absorb about a third of the carbon dioxide released from fossil fuels, although the proportion is set to decrease as emissions climb.
Clearly, we do not understand all of the effects global warming could have on our planet, which is a reason to be even more cautious than we already are, not less. Although global warming is a very timely topic and a source of numerous ongoing research projects, this week was particularly interesting. Hopefully the pace of research will continue to increase, giving us a better idea of just what kind of an effect we are having on our environment and how we can change to counteract this.
posted by Nick Anthis at
6:03 PM
2 Comments:
Hi there
The global warming situation is clearly an interesting one, particularly the way it's commonly discussed in the media. In one respect it highlights a fundamental issue in science with regards to the limits of its reliability - we're reminded of the skepticism required in scientific thought. When discussing the relevant topics, one has to disentangle what the situation "is" from the methods we use to analyse and describe it. The idea that the observer's view of the world is impossibly disconnected from an independent reality is not a new one but is easily forgotten. Science is based on constructing and re-evaluating hypotheses through the measurement of relevant parameters and subsequent development of explanatory models. Hence there is a potential to find what you're looking for and not what you're not. This statement may sound nonsensical, but the capacity that Science retains to find what is not looked for is one which is fundamental to achieving breakthroughs in understanding - breakthroughs that we believe paint in some more of the picture that brings our understanding closer to the "real" world.
Mathematical modelling holds a prominent role in climate change. In finding out the causes, rate of change and future consequences of global warming, our sight is sharpened by the models that play out the parameters we know to be important. The threats that current ecosystems are under are often graphically displayed in their disastrous and possibly unstoppable power. I stress the threats that ecosystems are under because it is these consequences of climate change that are given the most space in the media - from rising sea levels to tropical London. I suspect that this is because the models devised to make such predictions are easier to make and re-evaluate. However, in our attempts to reverse the trends of climate change, we are utterly dependent on our understanding of its causes. Here the models are of such challenging complexity, the only thing we know for certain is that we don't know nearly enough. What are the causes of climate change? What is the weather going to be next weekend? These are questions that are simply a very long way from having satisfactory answers.
September 11 provided an opening in the skies that allowed the measurement of a parameter previously underemphasised in models of the causes of climate change. On September 12 and 13, the clear skies over the USA permitted a comparison and therefore calibration of the effect of particles in the atmosphere resulting from air traffic. These particles deflect the sun's rays, reducing the amount of energy reaching the surface of the earth. This has been given the name "Global Dimming" by some in the field. The realisation that this effect actually has an important role in the earth's climate demonstrated that the models of the causes climate change, and its rate of change, had to factor in this new variable. In fact the skies over the globe have cleared in many areas as cleaner technologies have been introduced over the 20th century and so more of the sun's energy reaches the earth's surface. This means that, potentially, climate change could accelerate faster than old models predicted.
What has this to do with your blog entry?
My writing is in response to a couple of comments in your blog where you, quite rightly, depart from simply reporting what's written in Nature and express some of your reactions to the reports. These reactions are widely uttered and are hard to find disagreement with as, on the face of it, they express a conservationist desire not to damage the biosphere and in particular the human element of it.
Firstly, your natural conclusion to the changes in ocean water column mixing, "such jarring disruptions to ecosystems are rarely good". My questions is: when have there previously been such jarring disruptions to ecosystems where bad consequences have been seen? Are you sure that this conclusion is rational, or is it something that just seems sensible and therefore probably right.
Secondly, your instinctively modest style in the final paragraph presents an argument that, behind the optimistic and idealistic tone, suffers in its advice from the uncertainty behind climate change research. What exactly is meant, by you and others, by the statement "be even more cautious than we already are"? How cautious? Is Kyoto enough...are its parameters relevant? What things should we be cautious with? Everything? Fossil fuels? Nuclear fuels? Cows? Plants? The advice to be cautious is well received by many with an unquestioning and conservative mind, but in itself it rings hollow when knocked by the realisation that we don't know what it means. Which way is cautious, and how hard do we have to row to get there?
I have enjoyed reading your blog and I am impressed by the objective of providing a forum for report and reflection. It would be interesting to read your comments about the nature of the way things are reported as well as the nature of the things that are being reported - after all, this is what Nature et al have been doing so well for so long.
Please don't mistake my arguments for criticism, it's been fun to read your reports and it's been fun to write in response. Hope you enjoyed reading my comments too...
By
Anonymous, at Sat Jan 21, 10:01:00 PM
Hi Anonymous,
Thanks for your comments--there's definitely a lot there. In regards to objectivity in science, what you are saying is important and is probably the reason why scientists are so hesitant to join the political dialogue. However, this reticence can be costly when scientists fail to accurately convey the significance of their conclusions to the public. It would be irresponsible for scientists to sit back and stay out of the political debate on climate change, especially when others have a strong economic interest in the public not believing global warming is significant.
The current research, although it has many holes in it, is convincing enough for us to be concerned about climate change, and it should be reason enough for us to act on that. Your comments highlight many of these holes, though, such as our lack of understanding of basic weather patterns and other factors, such as reflection by particles, that may moderate the effects of global warming. This will obviously be a very rich area of research for quite a while.
I can think of a few examples off of the top of my head of jarring disruptions in ecosystems that have been damaging. For example, large scale agriculture in Australia has lead to increased nutrient-rich runoff at the Great Barrier Reef. This has allowed algae to grow much more prolifically, making the water cloudier and limiting the sunlight reaching the coral, which depend on sunlight for energy. This is slowly killing the reef. Another broader example is habitat fragmentation in general, which is leading to the extinction of many animals. When an animal population’s habitat is divided up by manmade structures, even if the total area of the habitat is not decreased by a great deal, it can have a very negative impact on the survival of that population, especially if it is a population of large animals that require a large amount of space over which to roam.
On the other hand, slow disruptions to ecosystems are not necessarily bad, since they are responsible for causing animals and other life forms to evolve to the great diversity we see in nature today. The problem, though is that humans are currently altering the environment much too quickly for many organisms to evolve to survive under these conditions.
How can we be more cautious, then? I wish I had the answer to that, although I know that we need to cut back on greenhouse gas emission in whatever way possible. Nuclear power, despite its drawbacks, looks like a strong alternative to fossil fuels, although renewable resources should be the goal. Research and development on these methods, including hydrogen fuel cells, need to be a major priority, especially since this will not only help us protect the environment, but will also have economic and political benefits as oil production peaks and begins to decline.
By
Nick Anthis, at Sun Jan 22, 06:27:00 PM
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