正文
The Gathered Storm: An Examination of Global Warming at Yale
By Jason Wu
Yale Scientific Magazine, Cover Story, Spring issue, 2007
Projected surface temperatures for the 21st century, relative to the period from 1980-1999.
The story of the human response to global warming is one fraught with institutional inertia, intermittent insight, and, at times, anexasperating incrementalism. Unlike other environmental causes, such as the prevention of oil spills, global warming as an issue has tended to lack the flashbulb appeal of a crisis—an Exxon Valdez moment.
Instead,the public has been fed a series of scientific abstracts, white papers and bureaucratic reports as the evidence has mounted. There seems to be a disturbing symmetry between the ponderous public response and, to the uninitiated, the apparently glacial speed of climactic change.
Although scientists and environmental groups have sounded the alarm for years,the political ice has only recently been broken on the issue of global warming. But the crack-up has come quickly. Cities and states are moving to address the issue and Congress is now brimming over with proposed climate legislation.
Identifying the Problem
The latest major governmental examination of global warming, the Intergovernmental Panel on Climate Change (IPCC) report, reflected the growing scientific consensus on the issue.
The IPCC commission found “warming of the climate system is unequivocal,”and the bulk of the warming is “very likely due to the observed anthropogenic greenhouse gas concentrations.” The report defines a“very likely” event as one that will occur over 90 percent of the time.
Scientific backing for the report comes from an unusual variety of sources. Since reliable surface temperature records have only been kept for the past century or so, scientists have had to turn to an increasingly creative set of records.
According to Karl Turekian,Sterling Professor of Geology & Geophysics, some of the most telling marks of past temperature trends can be found in deep water,recorded in corals and in the calcium carbonate shells left behind by tiny single-celled protists known as Foraminifera.
During periods of especially pronounced atmospheric carbon dioxide concentrations, such as the Paleocene-Eocene Thermal Maximum, a period of intense warming 55 million years ago, the equilibrium between carbon dioxide and carbonic acid in the oceans shifted in favor of the carbonic acid. The elevated acidity in many cases dissolved large sections of the calcium carbonate shells, leaving a physical record of past carbon dioxide levels.
More conventional means of identifying features of past climates include records gleaned from ice cores, which contain air bubbles that form snapshots of past isotopic ratios of atmospheric gases.
Because gases condense at different rates that depend on the mass of the isotopes that constitute them, the relative concentrations of various isotopes in the ice can serve as records of past temperature trends.
Since different sources of different gases often leave isotope signatures,these ice cores can also provide reference levels of greenhouse gases,helping scientists determine the extent of natural climatic variation and the magnitude of anthropogenic effects on greenhouse gas concentrations.
Other significant sources of climatic information include the advance and retreat of glaciers,which, according to Turekian, leave their records in the debris they deposit on the ocean bottom, and the growth of stalagmites in caves.
Models and Predictions
The vast array of climate data may, however, paradoxically serve to limit the power of current scientific models to predict future trends. “How well they describe the present climate” is simultaneously “a strength and a weakness,” explains Alexey Fedorov, an Assistant Professor of Geology & Geophysics.
The problem with “the amount of effort put into current climate” simulations, Fedorov says,is that the level of specificity generated “may be detrimental to your ability to predict” future climates. Turekian agreed, arguing that “the real problem is that every step of the way, they need to ground their models with results.”
Compounding this problem“are many unknowns,” according to Fedorov. In the near term, these factors can range from cooling resulting from volcanic eruptions to natural variations in sunlight. “The two most uncertain factors in climate models are the effects of clouds and the atmospheric aerosols that may or may not reduce the future warming trends,” Fedorov said.
Another significant theoretical impediment comes from the inherently chaotic nature of climate systems. Although nonlinear, chaotic systems play a smaller role in climate than they do in weather forecasts, “there is still a certain amount of chaos in the system,” Fedorov said. “You have to do ensemble calculations.”
Taken together,these variables often frustrate scientific attempts to create complete models for future climates. Such variations are “not [huge factors],but [they’re] important factor[s] if you want to reproduce climate for the past 1,000 years,” Fedorov cautions.
Unfortunately,in the coming years the shortcomings of prediction and measurement may only intensify, as scientists are set to lose significant sections of their ability to collect climate data from space. The “climate monitoring system from space is in a crisis,” explains Geology &Geophysics Associate Professor Steven Sherwood. “This could cause gaps in our climate records.”
The prospect of these gaps in the data collection seem counterintuitive at a time when global warming is finally commanding mainstream attention as a major policy crisis, and Sherwood conceded the point. “You would think people would be more resolute about getting good data and the opposite is happening.”
The net result, according to Sherwood, is that “our ability to measure climate is not what any of us would like,” and will likely continue to stay that way unless significant policy changes occur.
A Layered Crisis
Although it is the prospect of sea level rise and heat waves that have so far captured the public imagination, a sustained increase in greenhouse gas emissions may bring a whole host of other consequences.
Perhaps the clearest sign of the complexity of the climate change issue lies in the fact that in actuality, “the biggest climate change we have now is in the Stratosphere, which is cooling at a half to one degree (Celsius) per decade,” Sherwood said.
“People don’t notice because we don’t live there, but if you did you’d notice it big-time,”Sherwood explained. The IPCC report found that by contrast, the temperature in the inhabited Troposphere, the lowest level of the atmosphere, has increased by 0.13 degrees Celsius per decade in the past fifty years.
The consequences of stratospheric cooling may be difficult to predict, because “the cooling is not the same everywhere,” Sherwood explains. “It’s more towards the poles, and this we believe is influencing the jetstreams of both hemispheres. It’s making them stronger.”
Apart from shifting weather patterns in both hemispheres, such an effect would also form “stratospheric clouds, which destroy ozone,” Sherwood warned. Indeed, the temperature ranges conducive to the destruction of ozone explain “why the hole is in the southern hemisphere,” and will “definitely make it worse.”
An increase in humidity, to complement the increase in temperature, may also be in store. “Humidity increases at the rate of 7% per degree of surface warming,” and “the total amount of water vapor in the tropics is going up 1% per decade,” Sherwood said. “That starts to be significant.”
Skeptics and apologists for global warming often look for a silver lining to the temperature and CO2 increases in the potential corresponding boost to vegetation and plant growth. Sherwood doesn’t contest the point, but does note that “the nutritive value of plants decreases when you have high CO2.”
The corollary to the apologists’ argument— that this vegetation increase will preclude or offset damage to ecosystems—falls short in the eyes of Mark Pagani, Associate Professor of Geology & Geophysics, who argues that “ecosystems that exist in those colder regions have nowhere to go.”
On the biggest charge of many environmental groups, a link between global warming and hurricane Katrina, however, Sherwood is reticent. “You’re really talking about statistics,” Sherwood demurred. “Hurricanes happen regardless.”
More potential facets of the global warming crisis appear through study of and analogy with past climates.Fedorov has focused much of his examination of this issue through this angle, centering his research on the Pliocene epoch, specifically the period between three and five million years ago, before the glaciers and ice ages, during which the mean global temperatures were “maybe three degrees (Celsius) warmer than today.”
“You basically have the same world,” Fedorov elaborates. Carbon dioxide levels were “very close to the current level,” and “all important factors, at least what we know, were very similar to the present climates,” with the notable difference of temperature.
The result? “At that time, the conditions were what we call permanent El Niño,” Fedorov noted. In the normal cold upwelling zones off the coasts of California, Peru, and South Africa, which are rich regions for fisheries, “the temperatures were ten degrees (Celsius) higher.”
“There were no cold upwelling regions in the world.” The prevailing present tendency for El Niño to produce flooding in South America, along with drought, fires, and haze in Southeast Asia and Australia, would presumably strengthen. The complementary phenomenon of La Niña, would,“if the past data are right,” “quite [possibly]” cease to exist, Fedorov said.
Approaches and Solutions
The path to a solution for global warming is one troubled by scientific,technological, and political obstacles. Ultimately, “a proper solution will require a very tough international treaty,” argues James Gustave Speth, co-founder of the Natural Resources Defense Council and Dean of the Yale School of Forestry and Environmental Studies. “It has to layout the responsibilities for different classes of countries.”
In the case of the U.S., the professed goal of California, to reduce emissions by 80% by the year 2050, “should be the goal for the U.S.,” Speth said.
Speth explains the severity of these cuts by the imminent risks, he says, of “serious degeneration of the Greenland and the West Antarctic ice sheets and shelves,” if the warming is not stopped before a specific threshold, one he sets at below 2°C above the pre-industrial level.
The difficulty of stopping emissions before the threshold is breached is compounded by the fact that the world would experience “0.6 degrees(Celsius) additional warming even if we stopped all emissions today,”and the fact that the world has already experienced 0.7 degrees(Celsius) of warming.
“It’s very important to underscore how late we are at picking this up,” Speth warns. Compared to previous atmospheric challenges, “this is a lot more serious as a problem, and a lot more difficult to address,” Speth said.
Many experts believe merely modest cuts in emissions will not solve the issue. According to Fedorov, “it will give you maybe ten, twenty years delay.” “It’s not a solution.” Fedorov stresses the need to combine technological advances with conservation.
“We need to invest more money in research in Carbon Sequestration,” he says, an idea Pagani and Sherwood second.
“If you drink Coca-Cola, the CO2 is captured from a way stream. Instead of making soft drinks out of it, you pump it into a hole in the ground and hope it will stay,” Sherwood explained.
More specifically, carbon sequestration could be performed through a passive extractor in which CO2 is pulled out of air flowing through and converted into an inorganic mineral that would then be buried.
It may also be possible to pump liquid CO2 into holes in the ground, such as those in dried aquifers or oil holes. A third option, Pagani clarifies, would be to “pump liquid CO2 to a depth of 3000 meters in the deep ocean, where it will stay liquid.” It’s “a little bit crazy,”he concedes, but “[Carbon Sequestration] is our best solution, as far as I can tell.”
Sherwood holds a similar view.“In the term of the next few decades, that’s the best option we have for progress.” “We have the technology to do it.”
Carbon sequestration also has the economic advantage of allowing continued use of fossil fuels, if performed at a high enough level. It is “the only way we’ll be able to use our vast coal reserves,” Speth said. Still,“it’s not the most promising” solution. “Energy efficiency is by far the most cost effective thing we have and can make the largest single contribution.”
Sherwood is less discriminating in his analysis of the correct approach for policymakers. “We need to create markets for new technologies” as well as for “technologies that have been around for decades. There is also more basic research that needs to be done.” “We need to do everything.”
If we don’t, we’ll see the acidification of the oceans, the elimination of specific ecosystems, and potentially disastrous changes in ocean circulation, Pagani argued. “Because it’s anthropogenic, there is a choice.”
ABOUT THE AUTHOR
JASON WU is a freshman in Branford College. He admits to a furtive hope for global warming during February morning treks up Science Hill.
ACKNOWLEDGEMENTS
The author would like to thank James Gustave Speth, Steve Sherwood, Alexey Fedorov, Karl Turekian, Mark Pagani, and David Bercovici for their gracious help and direction with this article.
FURTHER READING
Speth, James Gustave. (2004). Red sky at morning: America and the crisis of the global environment. New Haven, CT: Yale University Press.
National Research Council. (2006). Surface Temperature Reconstructions for the Last 2,000 years. Washington, DC: National Academies Press.
Intergovernmental Panel on Climate Change (2007). Climate Change 2007. Cambridge, England: Cambridge University Press.
Sherwood, S. C. and C. L. Meyer, (2006) The general circulation and robust relative humidity. Journal of Climate, 19, 6278-6290.
Posted 星期三, 06/16/2010 - 16:12 by Fishville
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