|The Week That Was
March 16, 2002
1. COMPARATIVE RISKS TO LIFE in the US (and other industrialized nations), as presented by Prof. Bernard Cohen. Risks from pollutants are minute -- and practically non-existent from nuclear power.
2 Nuclear power plants study in Britain. Getting ready to replace Britain's nuclear capacity -- while the Government whistles in the wind.
3. Nuclear bomb detection is difficult but possible
4. Atmospheric aerosols found to brighten clouds, partially offsetting greenhouse effect. But estimates are still highly uncertain.
5. Satellite data confirm negative feedback from water vapor. This may explain why climate models consistently overestimate future increase in temperature.
6. Sea Level Rise: The experts disagree with IPCC forecast -but they could all be wrong
2 NUCLEAR POWER PLANTS STUDY IN BRITAIN.
British Energy is teaming up with British Nuclear Fuels to conduct a feasibility study into the construction of new nuclear power plants in the UK. The agreement, which will be announced today, is likely to focus on the Westinghouse AP-1000 design, the most up-to-date reactor-type in BNFL's portfolio.
British Energy, as yet, has no plans to build a new nuclear facility. However, the agreement to conduct research will be seen as an attempt to push the nuclear power option higher on the government's agenda.
An agreement with British Energy is essential for BNFL if it is to remain a contender in the design and development of nuclear power plants. BNFL is not the only candidate to replace Britain's ageing nuclear plant and British Energy has taken care to find a foreign competitor against which to measure BNFL's product. In December, British Energy signed a similar agreement with Atomic Energy of Canada, to carry out groundwork to establish the suitability of CANDU reactors in the UK power market.
British Energy has expressed interest in building 10 new plants to replace its own portfolio of reactors, which will gradually go offline during the next quarter century.
DAVID KING, the Government's chief scientific adviser, last night called for more nuclear power stations to be built in Britain. Unless existing plant is replaced as it wears out, he said, all those wind farms will do nothing to boost the share of energy that we generate from sources that do not pump carbon dioxide into the atmosphere. The threat of global warming is more important, he argued, than the dilemma of nuclear waste. This must be tackled anyway, since dismantling old nuclear stations will raise the amount of stored radioactive waste from 10,000 tons to nearer 250,000. An official body is quietly trawling for a dump site. The Sellafield area, the only one where there would be any local support for such a store, has been ruled out on geological grounds.
3. DETECTION OF FISSIONABLE MATERIALS is becoming of increasing importance because of the fear of nuclear terrorism. Scenarios include material smuggled in by suitcases or by ship-borne containers to bombs carried into harbors by ships.
Nuclear expert Ed Zebroski believes that airport detection is readily possible, but like baggage monitors depends on the setup, discipline and the discrimination tools provided to the watchers. The ordinary X-ray inspection should screen out anything like a nuclear device, but if somehow that is bypassed there are other good detection methods.
Plutonium 239 emits soft x-rays at about 30 and 50 kev. Even weapons-grade Pu has some 240 and 241 isotopes. Pu-241 over time produces increasing amounts of Am-241, which has an appreciable rate of spontaneous fission, emitting fast neutrons. With suitable detectors, small amounts of plutonium can be detected. Still more sensitive detection makes use of a small neutron generator, producing ample n-gamma and fast neutron signals from either plutonium or U-235.
There is a patent (T. Gozani and Zebroski) for a portal monitor that can readily detect a few tens of milligrams of plutonium. With kilogram amounts, as in a weapon, detection should be highly reliable unless substantial shielding is provided for both x-rays and fast neutrons. That, of course, should raise other alarms.
Remote detection, suitable for identifying fissionable material carried
in ships can rely on a method published for discriminating nuclear warheads
from decoys. It "interrogates' using fast neutrons and relies on
the detection of penetrating gamma rays emitted by fission products.
4. ATMOSPHERIC AEROSOLS FOUND TO BRIGHTEN CLOUDS
Atmospheric scientists have long suspected that microscopic aerosol particles from industrial processes increase the brightness of clouds, resulting in greater reflection of sunlight and cooling of Earth's climate. However, this supposition is based on model calculations rather than observations, and these model calculations are very uncertain.
Now, Stephen Schwartz and colleagues at the U.S. Department of Energy's Brookhaven National Laboratory and Purdue University have combined satellite measurements of cloud brightness, water content, and other variables with model calculations of atmospheric aerosols to demonstrate the brightening effect. This effect, described in the February 19, 2002 issue of the Proceedings of the National Academy of Sciences, should be accounted for in assessing the magnitude of global climate change, the researchers say.
One difficulty in measuring the effect of aerosols is knowing their concentration. Aerosols such as sulfur compounds result from emissions by fossil-fuel-burning power plants and other industrial processes. They are typically found in the lowest three to four kilometers above Earth's surface and precipitate out of the atmosphere, typically in about a week. "Because of this short residence time, aerosols are highly variable as a function of location and time, which makes it tough to measure their concentrations on a global scale," Schwartz said.
Schwartz's team has been working for more than a decade to develop and refine a "chemical transport model" to calculate aerosol distribution. The model uses archived weather data and weather prediction models to track the distribution of aerosols from industrial sources to various parts of the atmosphere. "This model is the key to knowing where and when to look for the aerosol effect," Schwartz said.
By analyzing data from the model, the Brookhaven-Purdue team identified two one-week episodes during April 1987 when the modeled concentration of sulfate aerosol over the North Atlantic Ocean -- far from any local sources of aerosol emissions -- increased significantly and then decreased over the course of each week. These large variations in aerosol concentration and the fact that there were no high-atmosphere (obscuring) clouds during these events made them ideal episodes for studying the effect of aerosols on cloud brightening.
The next challenge was to get the data on cloud brightness for that area over the same time period. For this, the scientists retrieved satellite measurements of radiance (how much light the clouds reflect) and optical depth (a value related to how much light is transmitted through the cloud), and used these measurements to calculate the size of the cloud droplets and the liquid water path (the amount of liquid water in the cloud). They were also able to analyze how these variables were related to one another.
The findings show that, for a given liquid water path, cloud reflectivity was indeed higher on the days with higher aerosol content than on the days with lower aerosol levels. "If the effect is as widespread as we think it is, it would produce quite a substantial cooling effect on climate," Schwartz said. "This new study," he added, "provides a method of quantifying the phenomenon globally over the past 15 years using archived satellite data. Once this is done, we will have a much better idea of the true magnitude of the greenhouse effect."
Could aerosols be deliberately employed to offset the greenhouse effect? "This is an attractive thought," Schwartz said, "but it cannot work in the long run -- because aerosols are so short-lived in the atmosphere, whereas greenhouse gases accumulate over time. An ever-increasing amount of aerosols would be required. We'd never solve the long-term problem."
Also, says Schwartz, the aerosol effect may have a different geographical
distribution from the greenhouse effect, and "the consequence of
this mismatch is unknown." One key to assessing the overall impact
of aerosols, he said, will be further development of the satellite-based
5. NEGATIVE FEEDBACK FROM WATER VAPOR Two research papers have recently analyzed trends in the energy balance of the atmosphere: Chen et al, 2002; Wielecki et al, 2002; see also Hartmann 2002)
Outgoing long-wave (heat) radiation increased between 1985 and 2000 (at a rate of 3.7 Watt/m2/decade, acc to Chen et al 2002. Fig 1). The LW maximum occurs in two bands in the subtropics of each hemisphere.
These results confirm a mechanism long advocated by Hugh Ellsaesser (1984) that depletes the upper troposphere water vapor (UTWV). It starts by enhanced GH heating of the tropical oceans, producing more evaporation and increased convective activity with strong cumulus action. This upward energy transfer strengthens the existing Hadley circulation and thereby also the downward return flow in the extra-tropical zones. This subsidence enhances the drying of these zones.
The IR radiation from WV now comes from a deeper warmer layer and emits more energy into space (as just observed), cooling the atmosphere and providing a negative feedback to GH warming.
Once climate models take this effect into account, they will calculate a lower climate sensitivity (more in line with what is currently observed) and, of course, much reduced future temperatures.
Chen, J., Evidence for Strengthening of the Topical General Circulation in the 1990s, Science 295, 838-841, 2002.
Ellsaesser, H.W., The Climatic Effect of CO2: A Different View, Atmospheric Environment 18(2), 431-434, 1984.
Hartman, D.L, Tropical Surprises, Science 295, 811-812 ,2002.
Wielicki, B.A. et al., Evidence for Large Decadal Variability in the Tropical Mean Radiative Energy Budget, Science 295, 841-844, 2002.
6. "THE PUZZLE OF GLOBAL SEA LEVEL RISE" is the title of a comprehensive article in the March 2002 issue of Physics Today by Bruce Douglas and Richard Peltier.
Their disagreement with the IPCC TAR report comes on the heels of that of glaciologist Mark Meier (U of Colo) and the biting criticism of Swedish sea-level expert Nils-Axel Moerner. But they all have different problems with the IPCC - and so do we at SEPP.
D-P give 18 cm/century as the best value for SL rise in the 20th century (after correcting land movements for Glacial Isostatic Adjustment from the weight of the ice sheets that covered No Europe and No America until 5000 years ago). [We agree with this value, which is about double that allowed by the IPCC.]
But then comes a problem we have long pointed to: Thermal expansion from ocean warming and melting mountain glaciers can explain only half that value. We think the discrepancy is even worse -- since ice accumulation on the Antarctic Continent (leading to a drop in SL) was not considered by D-P. They give various imperfect solutions to the "puzzle."
Our explanation is straightforward but politically incorrect (see our book Hot Talk, Cold Science): With thermal expansion plus glacier melting nearly canceled by Antarctic ice accumulation, SL rise is reasonably insensitive to decadal scale climate changes - including any that might be brought about by human activities. The observed rise - which has not been accelerating - can be explained by the slow (millennial timescale) melting of Antarctic ice sheets.
Hence we predict that SL rise during the 21st century will again be 18 cm - and there is nothing anyone can do about this!