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  • 2010-2014  (2)
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  • 1
    Publication Date: 2011-02-16
    Description: Precipitation changes are a key driver of climate change impacts. On average, global precipitation is expected to increase with warming. However, model projections show that precipitation does not scale linearly with surface air temperature. Instead, global hydrological sensitivity, the relative change of global-mean precipitation per degree of global warming, seems to vary across different scenarios and even with time. Based on output from 20 coupled Atmosphere-Ocean-General-Circulation-Models for up to 7 different scenarios, we discuss to what extent these variations can be explained by changes in the tropospheric energy budget. Our analysis supports earlier findings that long- and shortwave absorbers initially decrease global-mean precipitation. Including these absorbers into a multivariate scaling approach allows to closely reproduce the simulated global-mean precipitation changes. We find a sensitivity of global-mean precipitation to tropospheric greenhouse gas forcing of −0.42 ± 0.23%/(W/m2) (uncertainty given as one std of inter-model variability) and to black carbon emissions of −0.07 ± 0.02%/(Mt/yr). In combination with these two predictors the dominant longer-term effect of surface air temperatures on precipitation is estimated to be 2.2 ± 0.52%/K – much lower than the 6.5%/K that may be expected from the Clausius-Clapeyron relationship.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2022-05-26
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Climate of the Past 9 (2013): 1111-1140, doi:10.5194/cp-9-1111-2013.
    Description: Both historical and idealized climate model experiments are performed with a variety of Earth system models of intermediate complexity (EMICs) as part of a community contribution to the Intergovernmental Panel on Climate Change Fifth Assessment Report. Historical simulations start at 850 CE and continue through to 2005. The standard simulations include changes in forcing from solar luminosity, Earth's orbital configuration, CO2, additional greenhouse gases, land use, and sulphate and volcanic aerosols. In spite of very different modelled pre-industrial global surface air temperatures, overall 20th century trends in surface air temperature and carbon uptake are reasonably well simulated when compared to observed trends. Land carbon fluxes show much more variation between models than ocean carbon fluxes, and recent land fluxes appear to be slightly underestimated. It is possible that recent modelled climate trends or climate–carbon feedbacks are overestimated resulting in too much land carbon loss or that carbon uptake due to CO2 and/or nitrogen fertilization is underestimated. Several one thousand year long, idealized, 2 × and 4 × CO2 experiments are used to quantify standard model characteristics, including transient and equilibrium climate sensitivities, and climate–carbon feedbacks. The values from EMICs generally fall within the range given by general circulation models. Seven additional historical simulations, each including a single specified forcing, are used to assess the contributions of different climate forcings to the overall climate and carbon cycle response. The response of surface air temperature is the linear sum of the individual forcings, while the carbon cycle response shows a non-linear interaction between land-use change and CO2 forcings for some models. Finally, the preindustrial portions of the last millennium simulations are used to assess historical model carbon-climate feedbacks. Given the specified forcing, there is a tendency for the EMICs to underestimate the drop in surface air temperature and CO2 between the Medieval Climate Anomaly and the Little Ice Age estimated from palaeoclimate reconstructions. This in turn could be a result of unforced variability within the climate system, uncertainty in the reconstructions of temperature and CO2, errors in the reconstructions of forcing used to drive the models, or the incomplete representation of certain processes within the models. Given the forcing datasets used in this study, the models calculate significant land-use emissions over the pre-industrial period. This implies that land-use emissions might need to be taken into account, when making estimates of climate–carbon feedbacks from palaeoclimate reconstructions.
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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