Characterisation of macrogel composition from industrial natural rubber samples: Influence of proteins on the macrogel crosslink density

The insoluble (macrogel) and soluble fractions of 11 commercial natural rubber (NR) samples (Technically specified rubber) were separated. Nitrogen titrations and lipid extractions enabled a quantitative assessment of the proteins and extractable lipids in each fraction. Swelling was measured in tetrahydrofuran in order to evaluate the crosslink density (Mc –1) of each macrogel. While the soluble fraction had a high lipid concentration, the majority of non-isoprene compounds of the macrogel were found to be proteins, which accounted for 4.6 to 50.8% (w/w) of the macrogel. Indeed, the macrogels contained less than 0.5% (w/w) extractable lipids. However, our results showed that the soluble fraction contained large quantities of proteins (16–66% of the nitrogen content of the raw NR sample), probably structuring microaggregates. An exponential correlation (R2 > 0.96) was found between the crosslink density and the protein concentration of macrogel, suggesting that proteins are involved in the majority of crosslinks in macrogel. (Résumé d'auteur

Extending the record of photosynthetic activity in the eastern United States into the presatellite period using surface diurnal temperature range

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 32 (2005): L08405, doi:10.1029/2005GL022583.In this study, we demonstrate that mid-latitude surface measurements of diurnal temperature range (DTR) can be used to reconstruct decadal variability of regional-scale terrestrial photosynthetic activity 1) during and prior to the period with satellite retrievals of land greenness and 2) without the need for moisture data. While the two relative maxima present in the seasonal evolution of DTR can determine the beginning and the end of the growing season, the summertime average DTR can be used as a proxy of summertime terrestrial photosynthesis. In a case study in the eastern United States (1966–1997), the DTR reconstructions indicate significant natural decadal variability in photosynthetic activity, but no secular, long-term trend. The summertime photosynthesis was found to be controlled primarily by moisture availability. Also, contrary to existing model parameterizations, the timing of spring onset was found to depend on both temperature and moisture.This work is supported by National Science Foundation grant ATM-9987457, NASA EOS-IDS grants NAG5-9514 and NNG04GK34G, NASA Carbon Cycle Program grant NAG5-11200, and the WHOI Ocean and Climate Change Institute

Projected Changes to Hydroclimate Seasonality in the Continental United States

Future changes to the hydrological cycle are projected in a warming world, and any shifts in drought risk may prove extremely consequential for natural and human systems. In addition to long-term moistening, drying, or warming trends, perturbations to the annual cycle of regional hydroclimate variables may also have substantial impacts. We analyze projected changes in several hydroclimate variables across the continental United States, along with shifts in the amplitude and phase of their annual cycles. We find that even in regions where no robust change in the annual mean is expected, coherent changes to the annual cycle are projected. In particular, we identify robust regional phase shifts toward earlier arrival of peak evaporation in the northern regions, and peak runoff and total soil moisture in the western regions. Changes in the amplitude of the annual cycle of total and surface soil moisture are also projected, and reflect changes to the annual cycle in surface water supply and demand. Whether changes become detectable above the background noise of internal variability depends strongly on the future scenario considered, and significant changes to the annual cycle are largely avoided in the lowest-forcing scenario

On the detection of summertime terrestrial photosynthetic variability from its atmospheric signature

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 31 (2004): L09207, doi:10.1029/2004GL019453.We identify the climatic signatures of the summertime terrestrial photosynthesis variability using a long simulation of pre-industrial climate performed with the NCAR coupled global climate-carbon model. Since plant physiology controls simultaneously CO2 uptake and surface fluxes of water, changes in photosynthesis are accompanied by changes in numerous climate variables: daily maximum temperature, diurnal temperature range, Bowen ratio, canopy temperature and tropospheric lapse rate. Results show that these climate variables may be used as powerful proxies for photosynthesis activity for subtropical vegetation and for tropical vegetation when photosynthetic variability may be limited by water availability.Support for this work was provided by National Science Foundation grant ATM-9987457, NASA EOS-IDS grant NAG5-9514, WHOI contribution #11077 and the NCAR Climate Simulation Laboratory (CSL)

Causes of differences in model and satellite tropospheric warming rates

In the early twenty-first century, satellite-derived tropospheric warming trends were generally smaller than trends estimated from a large multi-model ensemble. Because observations and coupled model simulations do not have the same phasing of natural internal variability, such decadal differences in simulated and observed warming rates invariably occur. Here we analyse global-mean tropospheric temperatures from satellites and climate model simulations to examine whether warming rate differences over the satellite era can be explained by internal climate variability alone. We find that in the last two decades of the twentieth century, differences between modelled and observed tropospheric temperature trends are broadly consistent with internal variability. Over most of the early twenty-first century, however, model tropospheric warming is substantially larger than observed; warming rate differences are generally outside the range of trends arising from internal variability. The probability that multi-decadal internal variability fully explains the asymmetry between the late twentieth and early twenty-first century results is low (between zero and about 9%). It is also unlikely that this asymmetry is due to the combined effects of internal variability and a model error in climate sensitivity. We conclude that model overestimation of tropospheric warming in the early twenty-first century is partly due to systematic deficiencies in some of the post-2000 external forcings used in the model simulations

Rapidly evolving aerosol emissions are a dangerous omission from near-term climate risk assessments

Anthropogenic aerosol emissions are expected to change rapidly over the coming decades, driving strong, spatially complex trends in temperature, hydroclimate, and extreme events both near and far from emission sources. Under-resourced, highly populated regions often bear the brunt of aerosols' climate and air quality effects, amplifying risk through heightened exposure and vulnerability. However, many policy-facing evaluations of near-term climate risk, including those in the latest Intergovernmental Panel on Climate Change assessment report, underrepresent aerosols' complex and regionally diverse climate effects, reducing them to a globally averaged offset to greenhouse gas warming. We argue that this constitutes a major missing element in society's ability to prepare for future climate change. We outline a pathway towards progress and call for greater interaction between the aerosol research, impact modeling, scenario development, and risk assessment communities