Chemosphere - Global Change Science最新文献

The 1979–1999 response of the climate system to variations in solar spectral irradiance is estimated by comparing the global averaged surface temperature anomalies simulated by a 2-D energy balance climate model to observed temperature anomalies. We perform a multiple regression of southern oscillation index and the individual model responses to solar irradiance variations, stratospheric and tropospheric aerosol loading, stratospheric ozone trends, and greenhouse gases onto each of five near-surface temperature anomaly data sets. We estimate the observed difference in global mean near-surface air temperature attributable to the solar irradiance difference between solar maximum and solar minimum to be between 0.06 and 0.11 K, and that 1.1–3.8% of the total variance in monthly mean near-surface air temperature data is attributable to variations in solar spectral irradiance. For the five temperature data sets used in our analysis, the trends in raw monthly mean temperature anomaly data have a large range, spanning a factor of 3 from 0.06 to 0.17 K/decade. However, our analysis suggests that trends in monthly temperature anomalies attributable to the combination of greenhouse gas, stratospheric ozone, and tropospheric sulfate aerosol variations are much more consistent among data sets, ranging from 0.16 to 0.24 K/decade. Our model results suggest that roughly half of the warming from greenhouse gases is cancelled by the cooling from changes in stratospheric ozone. Tropospheric sulfate aerosol loading in the present day atmosphere contributes significantly to the net radiative forcing of the present day climate system. However, because the change in magnitude and latitudinal distribution of tropospheric sulfate aerosol has been small over the past 20 years, the change in the direct radiative forcing attributable to changes in aerosol loading over this time is also small.

This paper discusses the dual contribution of rice paddy soils to atmospheric greenhouse effect. On one hand, the paddy soils store more organic carbon than the upland soils by 12–58% in China. The amount of organic carbon stored in paddy soils increased by 120.8–584.0 Tg (Teragram=$\text{10}{}^{12}\text{g}$) in 0–100 cm soil depths due to the conversion of upland soils to paddy soils in the past 600 years in China. On the other hand, the paddy soils are another important source of atmospheric CH₄. Among the factors governing the CH₄ emission, the water regime was mainly reviewed in this paper. Mid-season aeration is one of the means to mitigate the CH₄ emission and also contribute to the higher rice yield. However N₂O emission does occur during the drainage period, and its global warming potential (GWP) is higher in long term. Therefore, it is important to properly control the water regimes and judiciously use nitrogen fertilizers in paddy soils in order to maximize its sinks and minimize its sources of atmospheric greenhouse gases (GHGs).

Context abstract: Methane is an important greenhouse gas. Livestock production constitutes a large part of total UK methane emission. By comparing livestock derived methane production with three theoretical sinks, the possibility of balancing methane production with direct consumption is assessed.

Ruminant livestock production contributes up to 40% of methane emission in the UK. With the increasing environmental and economic costs of greenhouse gas release, ways in which emission can be balanced with consumption must be explored. Three hypothetical sinks for ruminant livestock derived methane were examined. Only one sink appeared at all practicable in the context of modern farming. Under optimal conditions, high capacity methane oxidation in soil could conceivably reduce methane emissions where high concentrations of methane (>1%) were consistently supplied.

An important focus of climate-change research is the understanding of the role of ecosystems in shaping climate. Central to this aim is the identification of any feedbacks by which ecosystems may moderate anthropogenic forcing of climate. One possible ecosystem feedback involves the marine food-web and the biogenic sulfur compound dimethylsulfide (DMS). DMS is produced by algae containing the precursor compound dimethylsulfoniopropionate (DMSP), and once ventilated to the atmosphere can be transformed to sulfate aerosols and global climate. It was hypothesized that an increase in biogenically produced sulfate aerosols leading to formation of more cloud condensation nuclei (CCN), and brighter clouds, could stabilize the climate against perturbations due to greenhouse warming.

Although a large database of DMS seawater measurements exist, attempts to statistically correlate DMS concentrations with other biological parameters, such as chlorophyll a or nutrients, have failed. This underscores the complex and dynamic nature of the DMS cycle, and means that simple regression-type predictive models are unlikely to be useful, except at local scales. Regional-scale simulations of the DMS cycle have involved multi-parameter, deterministic formulations based on ecological food-web approaches but with the added challenge of properly simulating the behavior of coupled sulfur and nitrogen (or carbon) cycles.

Here we review the current DMS modeling approaches, outline the parameterization of key processes, and identify areas where our knowledge is poor and improvements should be made. Model skill can only be assessed against detailed regional and global data sets, however data have not always been collected in a form suitable for model parameter estimation or model calibration/validation. DMS time series, which are essential for calibration of seasonal or multi-annual simulations, are rare. We discuss the minimum requirements for a successful future integration of observational and theoretical efforts.

In a technique for measuring methane emitted by grazing ruminant livestock, a calibrated source of inert tracer sulfur hexafluoride (SF₆) is inserted into the rumen of each participating animal prior to collection of “breath” samples for gas analysis. Each source comprises a “permeation tube” from which an SF₆ charge slowly escapes through a permeable membrane, to be sampled with the breath. This paper reports analyses of the permeation characteristics of such tubes and provides evidence that the permeation rate slowly changes rather than stays constant as the technique supposes. This feature has been observed routinely over several generations of tube fills in our laboratory. Failure to take account of a changing permeation rate can lead to a systematic error in the inferred methane emission rate of up to about 15%. A quality control strategy is proposed that enables permeation rates to be extrapolated with confidence, based on the monitored performances of control tubes as proxies for inserted tubes.

During the FIELDVOC campaign in a eucalyptus forest in Portugal the distributions of monoterpenes compounds and particulate carbon were measured in the ambient air above the forest. Monoterpenes compounds in the eucalyptus forest atmosphere consisted mainly of β-pinene, α-pinene, 1,8-cineol, limonene and trans-ocimene.

For several monoterpenes, such as β-pinene and α-pinene, atmospheric levels were higher at night than during the day. This was partially attributed to a decrease in atmospheric turbulence and transport of emissions from nearby pine forests during the night by the low intensity of easterly winds. β-Pinene, which is emitted by pine trees but not in any noticeable amount by eucalyptus, was used as a tracer.

Particulate carbon was measured as organic carbon and black carbon (BC). The measurement of particulate carbon levels was also done during the FIELDVOC'94 campaign at a coastal site, where clean air masses arriving from the Atlantic were sampled. The concentrations of atmospheric particulate carbon were higher in the forest than along the coast. Based upon a mass balance, it was possible to estimate an upper limit to the inclusion of biogenic volatile organic emissions into the organic aerosol component when air masses were transported from the coast inland during sea breezes. A value of as much as 40% of the particulate organic carbon (POC) can be attributed to emissions from vegetation of compounds such as monoterpenes which, after oxidation to less volatile products, are transferred to the particulate phase.