Research M Watch A 300-million-year record of atmospheric CO2 concentrations
In its latest assessment of global warming, the Intergovernmental Panel on Climate Change (IPCC) noted that substantial uncertainties still need to be resolved concerning the role of atmospheric aerosols on cloud formation and ultimately on climate change. According to a perspective article appearing in the June 15th issue of Science, the IPCC observation is understated, and uncertainties are even greater than previously suspected. “Recent studies indicate that both the forcing [associated with atmospheric aerosols] and its magnitude may be even larger than anticipated,” writes the international group of scientists from Finland, Italy, and the United States. Forcing refers to perturbations of the climate system that change its radiative balance, which in turn influences global temperatures. Clouds are the most important factor controlling Earth’s temperature because they have such a pronounced effect on the planet’s albedo (reflectivity), which influences the radiative forcing. In addition to what has already been estimated, the scientists note recent evidence suggesting that chemical factors, such as the effects of soluble gases, slightly soluble solutes, and surface tension lowering by organics in cloud water, lead to additional negative forcing (cooling). According to the team of scientists, the marked lack of global data on these important aspects of atmospheric aerosols means there are additional uncertainties beyond those already noted by the IPCC. This makes the largest uncertainty (effect of clouds) in estimating climate forcing even larger, they say. These uncertainties must be resolved to better understand how human activities, which generate aerosols, affect climate change. (Science 2001, 292 (5524), 2025–2026)
Are atmospheric concentrations of carbon dioxide (CO2) and global temperature linked? A new technique reveals that such a coupling has probably existed for at least 300 million years. The method, conceived by Gregory Retallack at the University of Oregon, relies on the relationship between pores in leaves and concentrations of CO2 in the atmosphere. By examining pores in plant fossils up to 300 million years old and those of existing plants, Retallack has been able to estimate atmospheric concentrations of CO2 and demonstrate that the gas has been an important driver of climatalogical conditions on earth. Retallack’s analysis also suggests that some inconsistencies in other proxies of long-term CO2 trends, such as use of carbon isotopes, may be compromised by episodic outbursts of isotopically light methane catastrophically released from permafrost and marine gas hydrate reservoirs. Further examination of these issues may refine scientists’ understanding of longterm climatological phenomena. In a second companion piece, Wolfram Kürschner of Utrecht University, the Netherlands, comments, “It seems to me that the new [Retallack’s] data point to a long-term coupling between CO2 and temperature that is similar to the well-established coupling between the two during the most recent ice ages, roughly, the past 400,000 years.” Kürschner cautions, however, that the method will need further scrutiny, such as examining the fossil record of different plant species, to become more firmly established and that interdisciplinary efforts will be necessary to resolve apparent discrepancies between other proxies of atmospheric gas concentrations. Interestingly, Retallack’s analysis suggests that on several occasions in the past, atmospheric CO2 concentrations exceeded 2000 ppm, and dur-
ing some periods, they even exceeded 4000 ppm. For comparison, the current atmospheric concentration of CO2 is slightly over 365 ppm. (Nature 2001, 411 (6835), 287–290, 247–248)
Butyltins in marine sediment Organotin compounds, such as tributyltin (TBT) and triphenyltin, are common additives used in antifouling paints, wood preservatives, and fungicides. Although many countries have banned or at least restricted TBT as a paint additive because of its toxicity, it is still present in marine environments. TBT does break down to less toxic forms, such as dibutyl (DBT) and monobutyltin (MBT), with exposure to light and microorganisms, but the process slows greatly as TBT accumulates in sediments. PHOTODISC
Climate prediction uncertainties greater than realized
Tributyltin from ship paintisaccumulating in marine sediments.
Quantifying the amount of TBT and its breakdown products typically involves several analytical preparatory steps, but J. Ignacio Garcia Alonso and colleagues at the University of Oviedo in Spain have now developed a method using gas chromatography–inductively coupled plasma mass spectrometry with isotope dilution for simultaneously determining TBT, DBT, and MBT in sediments. Before analysis, the samples must be derivatized. The researchers acknowledge that the derivitization step may not be as effective or reproducible in sediment samples if the butylated tins aren’t completely extracted. More work is necessary to develop extraction procedures that are sensitive to different types of sediments. (Anal. Chem. 2001, 73 (13), 3174–3180)
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