Atmospheric CO(2) concentration ([CO(2)]) is now higher than it was at any time in the past 26 million years and is expected to nearly double during this century. Terrestrial plants with the C(3) photosynthetic pathway respond in the short term to increased [CO(2)] via increased net photosynthesis and decreased transpiration. In the longer term this increase is often offset by downregulation of photosynthetic capacity. But much of what is currently known about plant responses to elevated [CO(2)] comes from enclosure studies, where the responses of plants may be modified by size constraints and the limited life-cycle stages that are examined. Free-Air CO(2) Enrichment (FACE) was developed as a means to grow plants in the field at controlled elevation of CO(2) under fully open-air field conditions. The findings of FACE experiments are quantitatively summarized via meta-analytic statistics and compared to findings from chamber studies. Although trends agree with parallel summaries of enclosure studies, important quantitative differences emerge that have important implications both for predicting the future terrestrial biosphere and understanding how crops may need to be adapted to the changed and changing atmosphere.
Mercury (Hg total) fluxes were calculated for rainwater, throughfall and stream water in a small catchment located in the northeastern region of the Brazilian Amazon (Serra do Navio, Amapa State), whose upper part is covered by a natural rainforest and lower part was altered due to deforestation and activities related to manganese mining. The catchment area is 200 km from the nearest gold mining (garimpo). Minimum and maximum Hg concentrations were measured monthly from October 1996 to September 1997 and were 3.5-23.4 ng l(-1) for rainwater, 16.5-82.7 ng l(-1) for throughfall (March-August 1997) and 1.2-6.1 and 4.2-18.8 ng l(-1) for stream water, in natural and disturbed areas, respectively. In the natural area, the inputs were 18.2 microg m 2 year(-1) in rainwater and 72 microg m(-2) year(-1) in throughfall. This enrichment was attributed to dry deposition. The stream output of 2.9 microg m(-2) year(-1) indicates that Hg is being recycled within the forest as other chemical species or is being retained by the soil system, as confirmed by the cumulative Hg burden in the 0-10 cm surface layer, which was 36480 microg m(-2). When the disturbed area of the catchment was included, the stream output was 9.3 microg m(-2), clearly indicating the impact of the deforestation of the lower part of the basin on the release of mercury. The Hg burden in the disturbed area was 7560 microg m(-2) for the 0-10 cm surface layer.
Animal husbandry, aquaculture and fishery have major impacts on the environment. In order to identify the range of impacts and the most important factors thereof, as well as to identify what are the main causes of the differences between products, we analysed 52 life cycle assessment studies (LCAs) of animal and vegetal sources of protein. Our analysis was focused only on land requirement and carbon footprints.
In a general conclusion it can be said that the carbon footprint of the most climate-friendly protein sources is up to 100 times smaller than those of the most climate-unfriendly. The differences between footprints of the various products were found mainly to be due to differences in production systems. The outcomes for pork and poultry show much more homogeneity than for beef and seafood. This is largely because both beef and seafood production show a wide variety of production systems.
Land use (occupation), comprising both arable land and grasslands, also varies strongly, ranging from negligible for seafood to up to 2100 m2 y kg−1 of protein from extensive cattle farming. From farm to fork the feed production and animal husbandry are by far the most important contributors to the environmental impacts.
House J, Brovkin V. Climate and Air Quality. In: Kabat P, Nishioka S Millennium Ecosystem Assessment (Program). Condition and Trends Working Group. Ecosystems and human well-being : current state and trends : findings of the Condition and Trends Working Group of the Millennium Ecosystem Assessment. Washington, DC: Island Press ; 2005. Publisher's Version
Exposure to elevated concentrations of surface ozone (O3) causes substantial reductions in the agricultural yields of many crops. As emissions of O3 precursors rise in many parts of the world over the next few decades, yield reductions from O3 exposure appear likely to increase the challenges of feeding a global population projected to grow from 6 to 9 billion between 2000 and 2050. This study estimates year 2000 global yield reductions of three key staple crops (soybean, maize, and wheat) due to surface ozone exposure using hourly O3 concentrations simulated by the Model for Ozone and Related Chemical Tracers version 2.4 (MOZART-2). We calculate crop losses according to two metrics of ozone exposure e seasonal daytime (08:00e19:59) mean O3 (M12) and accumulated O3 above a threshold of 40 ppbv (AOT40) e and predict crop yield losses using crop-specific O3 concentration:response functions established by field studies. Our results indicate that year 2000 O3-induced global yield reductions ranged, depending on the metric used, from 8.5e14% for soybean, 3.9e15% for wheat, and 2.2e5.5% for maize. Global crop production losses totaled 79e121 million metric tons, worth $11e18 billion annually (USD2000). Our calculated yield reductions agree well with previous estimates, providing further evidence that yields of major crops across the globe are already being substantially reduced by exposure to surface ozone e a risk that will grow unless O3-precursor emissions are curbed in the future or crop cultivars are developed and utilized that are resistant to O3.
A number of studies show that significant reductions in solar radiation reaching the Earth’s surface have occurred during the past 50 years. This review analyzes the most accurate measurements, those made with thermopile pyranometers, and concludes that the reduction has globally averaged per year, equivalent to a reduction of 2.7% per decade, and now totals 20 W m−2, seven times the errors of measurement. Possible causes of the reductions are considered. Based on current knowledge, the most probable is that increases in man made aerosols and other air pollutants have changed the optical properties of the atmosphere, in particular those of clouds. The effects of the observed solar radiation reductions on plant processes and agricultural productivity are reviewed. While model studies indicate that reductions in productivity and transpiration will be proportional to those in radiation this conclusion is not supported by some of the experimental evidence. This suggests a lesser sensitivity, especially in high-radiation, arid climates, due to the shade tolerance of many crops and anticipated reductions in water stress. Finally the steps needed to strengthen the evidence for global dimming, elucidate its causes and determine its agricultural consequences are outlined.