There's been a great deal of uproar this past week over the controversial awarding of the 2007 Nobel Peace Prize jointly to the UN's Intergovernmental Panel on Climate Change (IPCC) and former vice president Al Gore for their work on raising awareness of climate change and global warming. For all the inevitable politicizing of the issue, what the Nobel Prize Committee's decision truly augurs is the recognition by the international community that global warming is real, and we're quickly running out of time to reverse the potentially catastrophic trends.

Honestly? It's probably already too late for merely implementing mitigation strategies, according to Rosina Bierbaum of the University of Michigan. Nor will simply relying on adaptation strategies be sufficient to deal with the impending impacts of climate change. "Any measures are only going to get more costly and difficult to implement" as time goes on, she said, quoting an old proverb: "It is easier to close the jaws of an alligator when they are small." Our alligator is entering its rebellious adolescence.

By now, the science of climate change is well-documented, bolstered by a solid accumulation of evidence of global warming that is strong enough to cause the IPCC to declare the conclusion "unequivocal." And as Bierbaum cheekily observed, this is from a scientific body "not prone to declarative sentences." There may be minor quibbles about the science here and there, and a few naysaying holdouts, but by and large, the scientific consensus on this is pretty clear.

Even tiny "degrees" of warming matter, so aggressive mitigation -- while not sufficient on its own -- can nonetheless make a significant difference, she said. One could start by drastically reducing the amount of CO2 emissions, and hence the levels of atmospheric carbon, which are higher than they have ever been (roughly 380 parts per million) over several hundred thousand years. The levels began rising in the 19th century when we began using coal as a major energy source, and they've been on the rise ever since, most dramatically in the last two decades.

(One questioner pointed out that when you consider the entire geologic record dating back billions of years, there have been periods with comparable levels of atmospheric CO2, and that eventually a cap would be reached. Bierbaum countered that she's concerned about the faster rate of change that's now occurring, since there is far less time for species -- including humans -- to adapt.)

How much carbon are we talking about, to hold future temperature increases to no more than 2 to 2.5 degrees Celsius higher than the pre-industrial era? Per Robert Burruss of the US Geological Survey, we need to reduce present emissions by 70% over many years, removing hundreds, if not thousands, of gigatons of CO2 from our energy processes, in order to stabilize atmospheric CO2 concentrations at around 500 ppm (it's around 360 ppm today) -- which, by the way, is still kinda high, but should hold the temperature increases to the less catastrophic levels. It's important to set attainable goals. Just how are we going to do that? Well, the IPCC Special Report on Carbon Capture and Storage (issued in 2005) estimates that geological sequestration of CO2 could eliminate about half of those emissions.

This would involve injecting supercritical CO2 into porous and permeable rock formations some 1 to 3 km below low-permeability seals (to prevent leakage). That includes oil and gas reservoirs, saline aquifers, coal beds, and organic-rich shale. We actually have some experience with CO2 injection since oil companies use it for enhanced oil recovery. So such a scheme is perfectly possible with existing technology and an infrastructure is already in place to build upon. In fact, there are already carbon capture and storage (CCS) projects underway in Norway, Canada, and Algeria; collectively they store about 3 megatons of CO2 every year.

The bad news is that your average 1000 MW coal-fired power plant emits about 4 MTs of CO2 every year. At best, CO2 separation plants will break even. "Clearly, CO2 capture and storage to eliminate a significant fraction of atmospheric emissions will require deployment of new energy systems at an enormous scale," said Burruss. We could decrease emissions an additional 15% by switching all existing coal-fired electricity to natural gas, but this would require doubling our natural gas consumption -- we just don't have those kinds of resources in the US and importing it from other countries is not a workable solution (as we have learned to our detriment with oil imports). When it comes to energy, there's always a tradeoff, somewhere.

One of the biggest concerns regarding CCS is identifying sites with adequate storage capacity. Burruss estimates that using low-density storage, US oil reserves could hold around 20.8 gigatons of CO2 -- 31.2 gigatons if high-density storage is used. Are you wondering what 1 gigaton of carbon might look like? According to Burruss, it translated into 69.4 trillion cubic feet (TCF) of CO2. For comparison, the entire US gas consumption per year is only 22 TCF, while US natural gas production amounts to 20 TCF. Storing the CO2 emissions from a 1000 MW power plant for 50 years would require a volume equivalent to a two-to-three billion barrel oil field. (Yikes!)

Then there's the geographical mismatch between the largest sources of those CO2 emissions and the largest oil and gas traps available for sequestration and storage. The largest storage sites are (obviously) located in Texas, the Gulf Coast and southern California, but the biggest power plants producing CO2 emissions are located up and down the Ohio and Mississippi Valley. Transporting all that CO2 into storage adds extra costs to CCS strategies; the other option would be to build new plants at the storage sites and take the old ones offline. Neither option is especially appealing.

We also must be able to insure that the seals maintain their integrity over long periods of time, and to develop mechanisms to mitigate any incidental leakage before the sequestered CO2 makes its way back to the surface. Finally, we'll need excellent sensors to accurately monitor the CO2 distribution once its stored, and to identify any leakage.

Frankly, I came away from the session feeling a wee bit depressed, convinced that while CCS is a necessary stop-gap measure, it's not quite up to the task of removing sufficient CO2 emissions to have a significant impact on climate change. That may have been the take-home message. Both Bierbaum and Burruss insist that we're going to need every possible means of carbon management at our disposal. This includes not just CCS, but also enhanced carbon storage in biomass and soils; shifting from fossil fuels to renewable biomass; drawing electricity from renewable sources like solar and wind, or nuclear power, and continuing to make improvements in generation and usage efficiencies. CCS is only one part of the solution.