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Sökning: WFRF:(Prentice IC)

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1.
  • Arneth, Almut, et al. (författare)
  • CO2 inhibition of terrestrial isoprene production stabilises tropospheric oxidation capacity
  • 2007
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 1944-8007. ; 34, L18813:18
  • Tidskriftsartikel (refereegranskat)abstract
    • [1] Isoprene is the dominant volatile organic compound produced by the terrestrial biosphere and fundamental for atmospheric composition and climate. It constrains the concentration of tropospheric oxidants, affecting the lifetime of other reduced species such as methane and contributing to ozone production. Oxidation products of isoprene contribute to aerosol growth. Recent consensus holds that emissions were low during glacial periods ( helping to explain low methane concentrations), while high emissions ( contributing to high ozone concentrations) can be expected in a greenhouse world, due to positive relationships with temperature and terrestrial productivity. However, this response is offset when the recently demonstrated inhibition of leaf isoprene emissions by increasing atmospheric CO2 concentration is accounted for in a process-based model. Thus, isoprene may play a small role in determining pre-industrial tropospheric OH concentration and glacial-interglacial methane trends, while predictions of high future tropospheric O-3 concentrations partly driven by isoprene emissions may need to be revised.
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2.
  • Bigelow, NH, et al. (författare)
  • Climate change and Arctic ecosystems: 1. Vegetation changes north of 55 degrees N between the last glacial maximum, mid-Holocene, and present
  • 2003
  • Ingår i: Journal of Geophysical Research. - : Wiley-Blackwell. - 2156-2202. ; 108:D19
  • Forskningsöversikt (refereegranskat)abstract
    • [1] A unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55degreesN at the last glacial maximum (LGM) and mid-Holocene (6000 years B. P.). The pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups. Five tundra types (cushion forb tundra, graminoid and forb tundra, prostrate dwarf-shrub tundra, erect dwarf-shrub tundra, and low- and high-shrub tundra) were distinguished and mapped on the basis of modern pollen surface samples. The tundra-forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed. During the mid-Holocene the tundra-forest boundary was north of its present position in some regions, but the pattern of this shift was strongly asymmetrical around the pole, with the largest northward shift in central Siberia (similar to200 km), little change in Beringia, and a southward shift in Keewatin and Labrador (similar to200 km). Low- and high-shrub tundra extended farther north than today. At the LGM, forests were absent from high latitudes. Graminoid and forb tundra abutted on temperate steppe in northwestern Eurasia while prostrate dwarf-shrub, erect dwarf-shrub, and graminoid and forb tundra formed a mosaic in Beringia. Graminoid and forb tundra is restricted today and does not form a large continuous biome, but the pollen data show that it was far more extensive at the LGM, while low- and high-shrub tundra were greatly reduced, illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types.
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3.
  • Claquin, T, et al. (författare)
  • Radiative forcing of climate by ice-age atmospheric dust
  • 2003
  • Ingår i: Climate Dynamics. - : Springer. - 1432-0894. ; 20:2-3, s. 193-202
  • Tidskriftsartikel (refereegranskat)abstract
    • During glacial periods, dust deposition rates and inferred atmospheric concentrations were globally much higher than present. According to recent model results, the large enhancement of atmospheric dust content at the last glacial maximum (LGM) can be explained only if increases in the potential dust source areas are taken into account. Such increases are to be expected, due to effects of low precipitation and low atmospheric (CO2) on plant growth. Here the modelled three-dimensional dust fields from Mahowald et al. and modelled seasonally varying surface-albedo fields derived in a parallel manner, are used to quantify the mean radiative forcing due to modern (non-anthropogenic) and LGM dust. The effect of mineralogical provenance on the radiative properties of the dust is taken into account, as is the range of optical properties associated with uncertainties about the mixing state of the dust particles. The high-latitude (poleward of 45degrees) mean change in forcing (LGM minus modern) is estimated to be small (-0.9 to +0.2 W m(-2)), especially when compared to nearly -20 W m(-2) due to reflection from the extended ice sheets. Although the net effect of dust over ice sheets is a positive forcing (warming), much of the simulated high-latitude dust was not over the ice sheets, but over unglaciated regions close to the expanded dust source region in central Asia. In the tropics the change in forcing is estimated to be overall negative, and of similarly large magnitude (-2.2 to -3.2 W m(-2)) to the radiative cooling effect of low atmospheric (CO2). Thus, the largest long-term climatic effect of the LGM dust is likely to have been a cooling of the tropics. Low tropical sea-surface temperatures, low atmospheric (CO2) and high atmospheric dust loading may be mutually reinforcing due to multiple positive feedbacks, including the negative radiative forcing effect of dust.
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6.
  • Hickler, Thomas, et al. (författare)
  • CO2 fertilisation in temperate forest FACE results not representative for global forests.
  • 2008
  • Ingår i: Global Change Biology. - : Wiley-Blackwell. - 1354-1013. ; 14:7, s. 1531-1542
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract in UndeterminedResults from free-air CO(2) enrichment (FACE) experiments in temperate climates indicate that the response of forest net primary productivity (NPP) to elevated CO(2) might be highly conserved across a broad range of productivities. In this study, we show that the LPJ-GUESS dynamic vegetation model reproduces the magnitude of the NPP enhancement at temperate forest FACE experiments. A global application of the model suggests that the response found in the experiments might also be representative of the average response of forests globally. However, the predicted NPP enhancement in tropical forests is more than twice as high as in boreal forests, suggesting that currently available FACE results are not applicable to these ecosystems. The modeled geographic pattern is to a large extent driven by the temperature dependence of the relative affinities of the primary assimilation enzyme (Rubisco) for CO(2) and O(2).
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7.
  • House, J, et al. (författare)
  • Climate and air quality
  • 2006
  • Ingår i: Millennium Ecosystem Assessment 2005 - Current State and Trends. Findings of the Condition and Trends Working Group (Ecosystems and Human Well-being). - : Island Press. ; 1, s. 350-390
  • Bokkapitel (övrigt vetenskapligt)
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10.
  • Schroter, D, et al. (författare)
  • Ecosystem service supply and vulnerability to global change in Europe
  • 2005
  • Ingår i: Science. - : American Association for the Advancement of Science. - 1095-9203. ; 310:5752, s. 1333-1337
  • Tidskriftsartikel (refereegranskat)abstract
    • Global change will alter the supply of ecosystem services that are vital for human well-being. To investigate ecosystem service supply during the 21st century, we used a range of ecosystem models and scenarios of climate and land-use change to conduct a Europe-wide assessment. Large changes in climate and land use typically resulted in large changes in ecosystem service supply. Some of these trends may be positive (for example, increases in forest area and productivity) or offer opportunities (for example, "surplus land" for agricultural extensification and bioenergy production). However, many changes increase vulnerability as a result of a decreasing supply of ecosystem services (for example, declining soil fertility, declining water availability, increasing risk of forest fires), especially in the Mediterranean and mountain regions.
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