Search

The paper reviews measurements of glacier mass balance in the period 1946-95. There are data for 246 glaciers but most records are quite short. The available mass-balance data are biased to Western Europe, North America and the former USSR with too few measurements from other parts of the world. The data are also biased towards wetter conditions with too few data from the dry-cold glaciers that are typical of many regions. There is no sign of any recent global trend towards increased glacier melting, and the data mainly reflect variations within and between regions. The 'direct method' of measuring glacier mass balance is with stakes and snowpits but it is a very laborious way of measuring long-term glacier changes. Stake/snowpit measurements should be more integrated in future with geodetic and remote sensing methods, especially laser profiling, and with modelling. [ABSTRACT FROM AUTHOR]

This paper begins to identify the relative roles of climate change, people and fire as factors in the late-Pleistocene and Holocene evolution of one of the most diverse terrestrial ecosystems in southern Australia. Our research illustrates that pollen from mediterranean-type heathlands can be recognized from sediments taken from small basins in semi-arid ecosystems. The use of pollen and carbonized particle analyses from sediment cores, in conjunction with ecological research on plant-fire relationships, establishes a role for palaeoecological techniques in the interpretation of long-term processes in semi-arid heathlands in Australia. Radiocarbon dates indicate that the treeless structure at our study site in the Little Desert of western Victoria has existed since at least the early Holocene. Pollen evidence indicates an increase in plant diversity, especially in Proteaceae and fire ephemerals, and a decrease in fire-sensitive taxa (e.g., Callitris spp., Allocasuarina muelleriana type) over the last 4000 years. This decline occurs in conjunction with increases in the frequency of carbonized particles. [ABSTRACT FROM AUTHOR]

Assessment of the degree of decay of peat (humification) in ombrotrophic mires has become a standard technique for palaeoclimatic reconstruction, based on the finding that decay is primarily determined by surface wetness and temperature at the time of peat deposition. Determination of humification is undertaken by colorimetric measurement of an alkali extract of the peat at 540 nm. Humification is proportional to the amount of humic matter dissolved by this extraction process, although few researchers convert results to a quantitative measure of humification expressing results as percentage light transmission through the peat. This paper uses luminescence spectroscopy to assess the chemical composition of these extracts. Luminescence excitation and emission wavelengths suggest that high molecular weight acids (‘humic acids’) are altered by the extraction procedure to form lower molecular weight acids (‘fulvic acids’), amino acids and polysaccharides. Percentage transmission is principally related to luminescence emission wavelength and thus to molecular weight of the compounds present. Luminescence emission shows much more sensitivity to peat composition and demonstrates that different plant species may be affected to different degrees by the NaOH extraction process. The findings broadly support the underlying principle of colorimetric determination of ‘humification’ whereby transmission levels decrease with increasing plant breakdown, but show that it is based on an inadequate understanding of the chemical processes occurring in peat decay and preparation procedures. Luminescence spectroscopy provides a technique for resolving these issues. [ABSTRACT FROM AUTHOR]

This paper adds a new dimension to the role of scientific knowledge in policy by emphasizing the multivalent character of scientific consensus. We show how the maintained consensus about the quantitative estimate of a central scientific concept in the anthropogenic climate-change field—namely, climate sensitivity—operates as an ‘anchoring device’ in ‘science for policy’. In international assessments of the climate issue, the consensus-estimate of 1.5°C to 4.5°C for climate sensitivity has remained unchanged for two decades. Nevertheless, during these years climate scientific knowledge and analysis have changed dramatically. We identify several ways in which the scientists achieved flexibility in maintaining the same numbers for climate sensitivity while accommodating changing scientific ideas. We propose that the remarkable quantitative stability of the climate sensitivity range has helped to hold together a variety of different social worlds relating to climate change, by continually translating and adapting the meaning of the ‘stable’ range. But this emergent stability also reflects an implicit social contract among the various scientists and policy specialists involved, which allows ‘the same’ concept to accommodate tacitly different local meanings. [ABSTRACT FROM AUTHOR]

In a comment on the paper by Sundqvist et al. (2007a), Hammarlund and Edwards suggest that the oxygen isotope signal of the speleothem records K1 and L4 from northwestern Sweden as well as for the earlier published stalagmite SG93 from northern Norway should mainly reflect variation in the δ18O of mean annual precipitation. The main argument used by the authors is that the SG93 dδ18O record should show remarkable similarities with the lacustrine carbonate dδ18O record from Lake Tibetanus. The similarities between SG93 and Lake Tibetanus are mainly seen for the period between 10 and 9 ka BP, which is a period where both records have higher dδ18O values compared with later in the Holocene. If true, this would indicate that temperatures in northern Scandinavia would have reached their Holocene maximum between 10 and 9 ka BP, which is contrary to what has been reported from other archives in the region which place the Holocene climatic optimum somewhere between 8 and 5 ka BP. Several factors affect the dδ18O of speleothems and definitely also by annual mean dδ18O of the local precipitation. However, for Holocene speleothems from northern Scandinavia as well as from the Alps this signal seems to be overridden by other factors, such as variable mixing of summer and winter precipitation of cave drip water as well as the temperature-dependent fractionation between calcite and water. But the relative importance of the factors can differ between different timescales, caves and even speleothems from the same cave, depending on hydrological pathways. To better understand the factors controlling the stable oxygen isotopes in precipitation and proxy archives back in time there is a need for more highly resolved records as well as for more atmospheric and hydrological modelling. [ABSTRACT FROM AUTHOR]