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Over the last 200 years, the amount of carbon in Earth's atmosphere has increased by about 100 ppm, to its current level of about 360 ppm. Meanwhile, average temperatures have begun to creep up. Most scientists agree that this increase in temperature is caused, in part, by the heat-trapping effects of atmospheric CO2.

So, CO2 reduction--or dealing with the consequences of a failure to reduce CO2--will be an important theme of applied environmental science in the coming decades. But research on approaches to carbon mitigation is already big, diverse, and growing, with many career opportunities in many scientific fields right now (see sidebar).

Environmentalists believe that the best approach to solving the CO2 problem is phasing out industrial processes that liberate CO2 from organic carbon compounds, particularly fossil fuel energy production. But phasing out fossil fuels is a hard sell in certain political and business circles. Though it is yet to find favor with environmentalists, an alternative approach has the support of big business and the current U.S. Administration: Go ahead and burn those fossil fuels, but remove and sequester the CO2 they contain.

One prominent research center, the Carbon Mitigation Initiative (CMI) based at Princeton University's Princeton Environmental Institute, is sponsored by two companies with a large stake in the outcome of the CO2 debate: BP and the Ford Motor Co. CMI's pragmatic objective is to "identify the most credible methods of capturing and sequestering a large fraction of carbon emissions from fossil fuels" in a way that accounts for political and economic realities. CMI seeks solutions to the CO2 problem that won't rock the economic (and political) boat.

Global Carbon Mitigation Links

International: The CO2 Capture Project

Norway: Klimatek

UK: IEA's Greenhouse Gas R&D Programme

U.S.: DOE's National Energy Technology Laboratory

U.S.: DOE's Carbon Sequestration Page

U.S.: MIT's Carbon Sequestration Initiative

U.S.: Princeton's Carbon Mitigation Initiative

The technological problem by itself is daunting. "To solve the problem," said CMI co-director Robert Socolow at a meeting earlier this year, "new technologies for the capture and storage of carbon in fossil fuels must be implemented on a fantastic scale. The majority of the roughly one thousand billion tons of carbon in the fossil fuels consumed over the 21st century will need to be redirected from the atmosphere and sequestered elsewhere."

Currently, carbon mitigation is expensive: At current rates--about $300 per ton--getting rid of half the carbon emitted each year will cost at least $500 billion, which constitutes a considerable portion of the federal budget. And even if the Bush Administration's ambitious target of $10 per ton can be met, eliminating or mitigating half the world's carbon emissions will still cost $20 billion to $30 billion dollars a year, making carbon mitigation a pretty big industry. And getting the cost down to anywhere near that 10-dollar-a-ton figure will require a major research investment in the near term.

So, there's little doubt that the number of people working to solve the CO2 problem will increase dramatically in the coming decades. The hard part for career-seeking scientists is to figure out how to prepare for a carbon-mitigation career. The field is so diverse, and most of the technologies are so young, that no obvious career path or training scheme presents itself.

Researchers at academic and industrial research centers worldwide are studying a range of technologies. One approach is simply to grow more trees, since young softwood forests are prolific carbon fixers. No one thinks that trees will solve the problem by themselves, but forestry may be a part of the solution. In the short term there are bound to be research opportunities in CO2-related forestry; in the longer term--if this approach pans out--applied forestry may prove to be a promising professional career track.

The U.S. government is also funding research that aims to determine which nutrients limit the growth of carbon-fixing photosynthetic microorganisms (cyanobacteria and phytoplankton) in oceans. The theory is that providing the limiting nutrients should increase microbial growth rates and, in turn, the rate at which carbon from the atmosphere is sequestered by microbes and carried to the bottom of the sea. So perhaps a marine biology background--especially one combined with environmental analytical chemistry skills--will get your environmental science career off to a good start.

Rather than relying on microbes to do the job, some scientists seek to capture CO2 from fossil fuels as part of an energy-transforming process, and then inject it deep into the Earth where it will--hopefully--remain until the fossil-fuel-burning era is well past. Experts consider this to be one of the more promising approaches, since Earth's deep aquifers can, in principle, store vast quantities of CO2. But CO2-sequestration technology is young: Problems remain with both the extraction of carbon from fossil fuels and its sequestration in underground aquifers. "It is pretty early to scope this out," writes Princeton economist David Bradford via e-mail, "since there is as yet no obvious winner in the technology, or obvious timetable according to which it would be deployed."

Another industry-friendly approach to solving the carbon mitigation problem is to burn fossil fuels more cleanly and efficiently. The U.S. President's budget for the current year includes 150 million dollars for his "clean coal power initiative," which he calls a "down payment" on his promise of $2 billion over the next decade. A large portion of America's new energy needs in the coming years is expected to be met by another currently abundant fossil fuel--natural gas--making the design of new, more efficient turbines a national priority and an active area of research. In fact, a high-efficiency, low-carbon-emission natural gas turbine has just been developed by a joint U.S. Department of Energy and General Electric research project, at an overall cost of $600 million with DOE footing $100 million of the bill. With the global market for natural gas power expected to approach $100 billion per year over the next decade, this, too, may be another promising direction for up-and-coming scientists and engineers.

Lowering the costs and improving the efficiency of alternative energy technologies--fuel cells, solar panels, nuclear fusion, etc.--is likely to be an important part of the solution to the CO2 problem. In recent months, important advances have been made in both hydrogen fuel cell and nuclear fusion research, and manufacturing cheaper and more efficient solar cells is a major objective of materials research, with slow, steady gains being made.

A third approach to the CO2 problem--after mitigation and conservation--is to deal with the consequences of doing nothing. If, as most scientists expect, global temperatures continue to rise as a result of increased atmospheric CO2, the consequences would likely be profound and expensive--and would potentially mean a lot of jobs for future environmental scientists.

Jim Austin is the editor of Science Careers. @SciCareerEditor on Twitter