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Timing of climate variability and grassland productivity
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Future climates are forecast to include greater precipitation variability and more frequent heat waves, but the degree to which the timing of climate variability impacts ecosystems is uncertain. In a temperate, humid grassland, we examined the seasonal impacts of climate variability on 27 y of grass productivity. Drought and high- intensity precipitation reduced grass productivity only during a 110-d period, whereas high temperatures reduced productivity only during 25 d in July. The effects of drought and heat waves declined over the season and had no detectable impact on grass productivity in August. If these patterns are general across ecosystems, predictions of ecosystem response to climate change will have to account not only for the magnitude of climate variability but also for its timing.
Konza | net primary production | streamflow | critical climate periods
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The Influence of Climate, Soils, Weather, and Land Use on Primary Production and Biomass Seasonality in the US Great Plains
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Identifying the conditions and mechanisms that control ecosystem processes, such as net primary production, is a central goal of ecosystem ecology. Ideas have ranged from single limiting-resource theories to colimitation by nutrients and climate, to simulation models with edaphic, climatic, and competitive controls. Although some investigators have begun to consider the influence of land-use practices, especially cropping, few studies have quantified the impact of cropping at large scales relative to other known controls over ecosystem processes. We used a 9-year record of produc- tivity, biomass seasonality, climate, weather, soil conditions, and cropping in the US Great Plains to quantify the controls over spatial and temporal patterns of net primary production and to esti- mate sensitivity to specific driving variables. We considered climate, soil conditions, and long-term average cropping as controls over spatial patterns, while weather and interannual cropping varia- tions were used as controls over temporal vari- ability. We found that variation in primary production is primarily spatial, whereas variation in seasonality is more evenly split between spatial and temporal components. Our statistical (multi- ple linear regression) models explained more of the variation in the amount of primary produc- tion than in its seasonality, and more of the spatial than the temporal patterns. Our results indicate that although climate is the most important variable for explaining spatial patterns, cropping explains a substantial amount of the residual variability. Soil texture and depth con- tributed very little to our models of spatial vari- ability. Weather and cropping deviation both made modest contributions to the models of temporal variability. These results suggest that the controls over seasonality and temporal variation are not well understood. Our sensitivity analysis indicates that production is more sensitive to climate than to weather and that it is very sen- sitive to cropping intensity. In addition to iden- tifying potential gaps in out knowledge, these results provide insight into the probable long- and short-term ecosystem response to changes in climate, weather, and cropping.
Key words: primary production; carbon; land use; agriculture; climate; weather; soil; seasonality; cropping; grassland; US Great Plains.
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SOME REFLECTIONS ON CLIMATE CHANGE, GREEN GROWTH ILLUSIONS AND DEVELOPMENT SPACE
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Many economists and policy makers advocate a fundamental shift towards “green growth” as the new, qualitatively-different growth paradigm, based on enhanced material/resource/energy efficiency and drastic changes in the energy mix. “Green growth” may work well in creating new growth impulses with reduced environmental load and facilitating related technological and structural change. But can it also mitigate climate change at the required scale (i.e. significant, absolute and permanent decline of GHG emissions at global level) and pace? This paper argues that growth, technological, population-expansion and governance constraints as well as some key systemic issues cast a very long shadow on the “green growth” hopes. One should not deceive oneself into believing that such evolutionary (and often reductionist) approach will be sufficient to cope with the complexities of climate change. It may rather give much false hope and excuses to do nothing really fundamental that can bring about a U-turn of global GHG emissions. The proponents of a resource efficiency revolution and a drastic change in the energy mix need to scrutinize the historical evidence, in particular the arithmetic of economic and population growth. Furthermore, they need to realize that the required transformation goes beyond innovation and structural changes to include democratization of the economy and cultural change. Climate change calls into question the global equality of opportunity for prosperity (i.e. ecological justice and development space) and is thus a huge developmental challenge for the South and a question of life and death for some developing countries (who increasingly resist the framing of climate protection versus equity).
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GREEN-TREE RETENTION IN HARVEST UNITS: BOON OR BUST FOR BIODIVERSITY?.pdf
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etween trees and man there is a rift in the perception of time, and forest managers have no choice but to yield to the pace of the trees. This can make innovations in forest management difficult to evaluate. Nonetheless, innovation is key to meeting society’s changing expectations. It is not just timber anymore. Biodiversity, recreation, aesthetics, and clean water all share top billing with a sustainable crop of timber. And although novel silvicultural strategies are being promoted to meet these complex demands, without the benefit of time, it is difficult to know exactly how well they will achieve their goals.
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Greenhouse Gassed: Carbon Dioxide Spells Indigestion for Food Chains
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The author closes with a quote from a biologist who asks who will be chasing wild ungulates with nutrition supplements. CO2 is a fertilizer, with side effects. Plants may grow more rapidly, but at the cost of their nutritional value. Hessman interviews researchers studying this effect on a range of animals from insects to mammals.
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High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Years
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The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition, reflecting the wetting of Asian deserts. A northern shift of the Intertropical Convergence Zone could be the trigger of these abrupt shifts of Northern Hemisphere atmospheric circulation, resulting in changes of 2 to 4 kelvin in Greenland moisture source temperature from one year to the next.
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Climate effects of global land cover change
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When changing from grass and croplands to forest, there are two competing effects of land cover change on climate: an albedo effect which leads to warming and an evapotranspiration effect which tends to produce cooling. It is not clear which effect would dominate. We have performed simulations of global land cover change using the NCAR CAM3 atmospheric general circulation model coupled to a slab ocean model. We find that global replacement of current vegetation by trees would lead to a global mean warming of 1.3°C, nearly 60% of the warming produced under a doubled CO2 concentration, while replacement by grasslands would result in a cooling of 0.4°C. It has been previously shown that boreal forestation can lead to warming; our simulations indicate that mid- latitude forestation also could lead to warming. These results suggest that more research is necessary before forest carbon storage should be deployed as a mitigation strategy for global warming.
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How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006
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To distinguish between simultaneous natural and anthropogenic impacts on surface temperature, regionally as well as globally, we perform a robust multivariate analysis using the best available estimates of each together with the observed surface temperature record from 1889 to 2006. The results enable us to compare, for the first time from observations, the geographical distributions of responses to individual influences consistent with their global impacts. We find a response to solar forcing quite different from that reported in several papers published recently in this journal, and zonally averaged responses to both natural and anthropogenic forcings that differ distinctly from those indicated by the Intergovernmental Panel on Climate Change, whose conclusions depended on model simulations. Anthropogenic warming estimated directly from the historical observations is more pronounced between 45°S and 50°N than at higher latitudes whereas the model-simulated trends have minimum values in the tropics and increase steadily from 30 to 70°N.
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Reduction of spring warming over East Asia associated with vegetation feedback
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Over East Asia, surface air temperature displays a significant increasing trend particularly in early months of the year for the period of 1982 – 2000. Warming per decade is strongest in late winter, 1.5°C in February and 1.1°C in March, but is significantly reduced in spring, 0.4°C in April and 0.1°C in May. During the analysis period, the reduced temperature increase from late winter to spring is found to be in contrast with the increased vegetation greenness derived from the satellite-measured leaf area index over the domain. We examined this inverse relationship using two climate model experiments— coupled with and without a dynamic vegetation model. In both experiments, strong warming in winter is relatively well reproduced, but weak warming in spring is observed only in the coupled experiment. Analysis of the surface energy budget indicates that weaker spring warming results from an evaporative cooling effect due to the increased vegetation greenness. Over East Asia, the vegetation-evaporation feedback, therefore, may produce seasonal asymmetry in the warming trend.
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Rising temperature depletes soil moisture and exacerbates severe drought conditions across southeast Australia
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Over the past decade the southern catchments of the Murray Darling Basin (MDB), responsible for much of Australia’s agricultural output, have experienced a severe drought (termed the ‘‘Big Dry’’) with record high temperatures and record low inflow. We find that during the Big Dry the sensitivity of soil moisture to rainfall decline is over 80% higher than during the World War II drought from 1937 – 1945. A relationship exists between soil moisture and temperature independent of rainfall, particularly in austral spring and summer. Annually, a rise of 1°C leads to a 9% reduction in soil moisture over the southern MDB, contributing to the recent high sensitivity. Since 1950, the impact from rising temperature contributes to 45% of the total soil moisture reduction. In a warming climate, as the same process also leads to an inflow reduction, the reduced water availability can only be mitigated by increased rainfall. Other implications for future climate change are discussed.
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