Overview & Relevance:
The Intergovernmental Panel on Climate Change finding that the balance of evidence suggests that there is already a discernible human impact on global climate (Santer et. al., 1996) is buttressed by recent studies: One showed that satellite measurements which first appeared to contradict surface temperature warming were inadvertently distorted by the satellites’ orbital decay; and that when corrected for this effect both records agreed within their measurement accuracy (Wentz and M. Schabel, 1998). Another study by a team of paleoclimatologists reconstructed Northern Hemisphere temperature over the past millennia (Mann et al., 1998). Their results indicate that the temperature rise of the past century is significantly larger than expected from natural climate variability.
In principle, one can never conclusively “prove” a scientific theory. There are still geologists who don’t accept plate tectonics, and immunologists who don’t believe the HIV virus causes AIDS. Incorrect theories are eliminated when they fail empirical tests. Those left standing, like the greenhouse gas theory of global warming, are accepted until they are “falsified” by data or a better theory comes along (Popper, 1969).
There is at this point in time a huge amount of data consistent with the CO2 greenhouse warming hypothesis first advanced by Svante Arrhenius over a hundred years ago (Arrhenius, 1896). Although we recognize other anthropogenic greenhouse gases, CO 2 from fossil fuel burning is the major player. It produces most of the radiative forcing, and it has the longest lifetime of any greenhouse gas. Some fossil fuel CO2 will remain in the atmosphere longer than Homo sapiens has been on Earth — what Wallace Broecker called “man’s unseenartifact.” “Global warming theory” as presently construed is deeply connected to our understanding of how the atmosphere and climate work. It continues to pass risky tests; and confidence is building to the point where we should think seriously about mitigation. There are vocal critics of the fossil fuel greenhouse theory. But in my opinion they are fighting a rearguard action. You can’t fool Mother Nature.
Climate change mitigation is another matter. It gets “political” fast. In the U. S. Congress, “global warming” is seen primarily as a political issue, perhaps because of the early endorsement of the theory by Vice President Al Gore, in his book, Earth in the Balance. There are at this point sufficient “nay” votes in the Senate to block ratification of the Kyoto Protocol. Some have characterized global warming as “liberal clap trap” designed to transfer U. S. taxpayers’ dollars to the developing world. Indeed, authors of IPCC chapters have been attacked in the press for suggesting that a discernible effect on global climate has already occurred.
There is a danger in launching into ideological arguments before we understand green-house gas stabilization. Yet such arguments are a mainstay of political debate about global warming. These ideological arguments are about some of the most important and value-laden trade-offs of the next century: about the roles of governments versus industry, about emission cuts by developing versus developed nations, about energy conservation versus energy supply, about economic growth versus preservation of ecosystems versus population control. But the climate issue is too important to politicize too early because this can prematurely limit the range of policy options.
Editorially, The New York Times stressed the importance of early implementation and emissions trading within the framework of the Kyoto Protocol which commits the industrialized world to an average 5% reduction in greenhouse emissions below 1990 levels between 2008 and 2012 (Remember Global Warming? Nov. 11, 1998). These are politically ambitious and psychologically important targets even though scientists familiar with the problem know that atmospheric CO2 levels will continue to rise almost as much under the Kyoto Protocol as in “business as usual.”
A paper published last October in Nature found that stabilizing atmospheric carbon dioxide will require a massive transition in the next century away from our predominantly fossil fuel system to some as yet undetermined source of primary power (Hoffert et al., 1998). To stabilize with continued economic growth at twice the preindustrial CO2 concentration — an oft-cited target but still high enough to cause significant climate change — we will, by the year 2050, have to provide 100-300% of today’s global power from carbon-emission-free sources. The implied transition in the world energy system to non-CO2 emitting sources of this magnitude fifty years hence is mind-boggling. To put this in perspective, consider that Enrico Fermi’s “atomic pile,” the first nuclear reactor in 1943, is more distant in the past than the year 2050 is in the future. And nuclear power still provides less than 5% of the global energy supply.
On the positive side, a response to the challenge of global climate change through the development of carbon-free energy technologies — renewables, space solar power and fusion, and even fission (if problems of radioactive waste disposal, weapons proliferation, public perception of risk, and inadequate supplies of uranium-235 can be overcome) — could stimulate technological innovation and entirely new industries of the twenty-first century, as World War II and the Cold War did in the twentieth century.
We sought, in this AGCI Workshop, to address the quantitative challenge of carbon-emission-free power while attempting to limit preconceptions. Our impression was that the range of options presently under consideration for climate change mitigation was too limited. At this point, the most advanced concept actively being investigated by the Department of Energy under its Carbon Management Program is CO2 capture and sequestration, with continued primary dependence on gas, oil and increasingly coal well into the twenty-first century (Parson and Keith, 1998). This is a promising technology and was considered seriously at our Workshop. But there are other options.
Perhaps the most immediate response to the need for carbon emission reductions is to increase the efficiency of energy end use — an approach associated since the energy crisis of the 1970s with Amory Lovins and his Rocky Mountain Institute (Lovins, 1977). Indeed, the presentation by Lovins at our Workshop can be construed as the demand reduction end of an innovative technology spectrum in which innovative energy supplies from extraterrestrial sources formed the other end. In between, a series of innovative renewable, fission and fusion ideas, as well as geoengineering schemes were presented, and subjected to lively debate at our Workshop. The very definition of “geoengineering,” which involves some of the most futuristic technologies (Keith, in press; Teller et al., 1997), is controversial, and underscores the complex socio-political-technical interactions one encounters in mitigation studies. Some argued at our Workshop that the term “geoengineering” should be applied only to compensatory global-scale changes in the Earth’s radiation balance (from space mirrors or artificial aerosol layers) and perhaps changes in the carbon cycle from fertilization of the oceans, but that capture and sequestration of CO2 by burial in depleted natural gas reservoirs or the deep ocean should be called something else. It needs its own category like “Carbon Management,” because of pejorative overtones of “geoengineering” as destructive of natural ecosystems.
That may be; but based on estimates of carbon-emission-free power needed by the year 2025, we computed huge rates of carbon sequestration to subterranean reservoirs needed. These numbers are a limiting case, because they assume all carbon-emission-free primary power required comes from fossil fuel energy. A carbon emission factor of 0.56 GtC/TW is assumed for the primary energy part which increases for capture and burial. The factors f = 1.5 and 4.5 are lower and upper bound estimates of additional carbon per unit of primary power to separate, compress and sequester the CO2.
On the positive side, carbon dioxide is already pumped into depleted oil and gas reservoirs for secondary recovery of hydrocarbon fuels - a factor tending toward near-term adoption. One can make hydrogen, an energy carrier suited for use as motor vehicle fuel whose combustion doesn't emit CO2 to the atmosphere, from fossil fuels, if one is willing to pay the price of more total carbon emitted and entombed in subsurface sarcophagi. CO2 capture and sequestration would leave in place, and even expand, the infrastructure of fossil fuel as a primary energy source; which may be why it is under active consideration by some oil companies as a fallback if emission controls are imposed.
But can we guarantee the integrity (non-leakage) of massive amounts of subsurface CO2? For how long? And can we maintain such burial cost-effectively as fossil fuel use reverts from gas and oil back to coal? Granted the technological readiness of Carbon Management, it is mind-boggling to imagine stuffing six to sixteen gigatonnes of carbon per year into deep reservoirs less than thirty years from now to stabilize atmospheric CO 2 at 550 ppm. Six gigatonnes of carbon per year is humankind's present total emission rate of carbon in the form of carbon dioxide.
In fairness, it is a massive challenge to any carbon-free energy technology to supply the amounts of primary power needed by 2050. At our Workshop, we considered a broad range of global primary power sources: fossil fuels (coal, oil and gas), fission, renewables (hydro, wind, geothermal, terrestrial solar, tides, biomass, and ocean thermal), fusion (D/T and D/3He fuel cycles) and space power including low earth orbits (LEO), geo-stationary orbits (GEO) and lunar-based power systems. For each source, we endeavored to estimate maximum energy inventory, time to deplete, maximum useful power, limiting factors, and key research issues. This analysis, which builds on pioneering work by David Criswell (1998), should be regarded as very preliminary. But it indicates the kind of cross- cutting research issues involved in global energy systems. These are not only technical but involve the evolution of social and economic infrastructures that support a given technology.
Workshop Topic (s):
- Carbon Cycle
- Climate Variability and Change (including Climate Modeling)
- Human Contributions & Responses