The biogeophysical climatic impacts of anthropogenic land use change during the Holocene
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Abstract. The first agricultural societies were established around 10 ka BP and had spread across much of Europe and southern Asia by 5.5 ka BP with resultant anthropogenic deforestation for crop and pasture land. Various studies have attempted to assess the biogeochemical implications for Holocene climate in terms of increased carbon dioxide and methane emissions. However, less work has been done to examine the biogeophysical impacts of this early land use change. In this study, global climate model simulations with HadCM3 were used to examine the biogeophysical effects of Holocene land cover change on climate, both globally and regionally, from the early Holocene (8 ka BP) to the early industrial era (1850 CE). Two experiments were performed with alternative descriptions of past vegetation: (i) potential natural vegetation simulated by TRIFFID but no land-use changes, and (ii) where the anthropogenic land use model, KK10 (Kaplan et al., 2009, 2011) has been used to set the HadCM3 crop regions. Snapshot simulations have been run at 1000 year intervals to examine when the first signature of anthropogenic climate change can be detected both regionally, in the areas of land use change, and globally. Results indicate that in regions of early land disturbance such as Europe and S.E. Asia detectable temperature changes, outside the normal range of variability, are encountered in the model as early as 7 ka BP in the June/July/August (JJA) season and throughout the entire annual cycle by 2–3 ka BP. Areas outside the regions of land disturbance are also affected, with virtually the whole globe experiencing significant temperature changes (predominantly cooling) by the early industrial period. Large-scale precipitation features such as the Indian monsoon, the intertropical convergence zone (ITCZ), and the North Atlantic storm track are also impacted by local land use and remote teleconnections. We investigated how advection by surface winds, mean sea level pressure (MSLP) anomalies, and tropospheric stationary wave train disturbances in the mid- to high-latitudes led to remote teleconnections.Keywords:
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Deforestation
Land Cover
Biogeochemical Cycle
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Return period
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Abstract Atmosphere–land–ocean coupled model simulations are examined to diagnose the ability of models to simulate drought and persistent wet spells over the United States. A total of seven models are selected for this study. They are three versions of the NCEP Climate Forecast System (CFS) coupled general circulation model (CGCM) with a T382, T126, and T62 horizontal resolution; GFDL Climate Model version 2.0 (CM2.0); GFDL CM2.1; Max Planck Institute (MPI) ECHAM5; and third climate configuration of the Met Office Unified Model (HadCM3) simulations from the World Climate Research Programme (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) experiments. Over the United States, drought and persistent wet spells are more likely to occur over the western interior region, while extreme events are less likely to persist over the eastern United States and the West Coast. For meteorological drought, which is defined by precipitation (P) deficit, the east–west contrast is well simulated by the CFS T382 and the T126 models. The HadCM3 captures the pattern but not the magnitudes of the frequency of occurrence of persistent extreme events. For agricultural drought, which is defined by soil moisture (SM) deficit, the CFS T382, CFS T126, MPI ECHAM5, and HadCM3 models capture the east–west contrast. The models that capture the west–east contrast also have a realistic P climatology and seasonal cycle. ENSO is the dominant mode that modulates P over the United States. A model needs to have the ENSO mode and capture the mean P responses to ENSO in order to simulate realistic drought. To simulate realistic agricultural drought, the model needs to capture the persistence of SM anomalies over the western region.
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Atmospheric models
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This paper describes an analysis of different ways of constructing climate change scenarios using output from three climate models. It focuses on using the HadRM3H regional climate model applied across southern Africa and a macroscale runoff model operating at a scale of 0.5 × 0.5° to simulate river runoff. HadRM3H has a spatial resolution of 0.44 × 0.44° and is driven by boundary conditions from HadAM3H, a global atmosphere general circulation model with a spatial resolution of 1.875 × 1.25°. This, in turn, used sea‐surface boundary conditions from HadCM3, a coupled global ocean‐atmosphere general circulation model that operates at a spatial resolution of 3.75 × 2.5°. Sixteen climate scenarios were constructed from the three models, representing different combinations of model scale, whether the climate model simulations were used directly or changes were applied to an observed baseline, and whether observed or simulated variations from year‐to‐year were used. The different ways of deriving climate scenarios from a single initial climate model experiment result in a range in change in average annual runoff at a location of at least 10%, and often more than 20%. There is a clear difference in the large‐scale spatial pattern of change in runoff from HadCM3 to HadRM3H. Many of the climate features in HadRM3H are already present in HadAM3H simulations, as would be expected from the experimental design. This suggests that for studies over a large geographic domain, an intermediate‐resolution global climate model can produce useful scenarios for impact assessments. HadRM3H overestimates rainfall across much of southern Africa and so results in too much runoff: This leads to smaller estimates of future change in runoff than arise when changes in climate are applied to an observed climate baseline. It is concluded that under these circumstances it is preferable to apply modeled changes in climate to observed data to construct climate scenarios rather than derive these directly from the regional climate model simulations. Incorporating increases in interannual variability as simulated by HadRM3H leads to little change in simulated annual mean runoff. However, it has a larger impact on the frequency distributions of runoff, with extreme flows predicted to increase more than mean flows and even to increase in areas where the mean flow decreases. This demonstrates the importance of considering not only changes in mean climate but also climate variability.
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Transient climate simulation
Baseline (sea)
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Abstract The annual cycle of precipitation and the interannual variability of the North American hydroclimate during summer months are analyzed in coupled simulations of the twentieth-century climate. The state-of-the-art general circulation models, participating in the Fourth Assessment Report for the Intergovernmental Panel on Climate Change (IPCC), included in the present study are the U.S. Community Climate System Model version 3 (CCSM3), the Parallel Climate Model (PCM), the Goddard Institute for Space Studies model version EH (GISS-EH), and the Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1 (GFDL-CM2.1); the Met Office’s Third Hadley Centre Coupled Ocean–Atmosphere GCM (UKMO-HadCM3); and the Japanese Model for Interdisciplinary Research on Climate version 3.2 [MIROC3.2(hires)]. Datasets with proven high quality such as NCEP’s North American Regional Reanalysis (NARR), and the Climate Prediction Center (CPC) U.S.–Mexico precipitation analysis are used as targets for simulations. Climatological precipitation is not easily simulated. While models capture winter precipitation very well over the U.S. northwest, they encounter failure over the U.S. southeast in the same season. Summer precipitation over the central United States and Mexico is also a great challenge for models, particularly the timing. In general the UKMO-HadCM3 is closest to the observations. The models’ potential in simulating interannual hydroclimate variability over North America during the warm season is varied and limited to the central United States. Models like PCM, and in particular UKMO-HadCM3, exhibit reasonably well the observed distribution and relative importance of remote and local contributions to precipitation variability over the region (i.e., convergence of remote moisture fluxes dominate over local evapotranspiration). However, in models like CCSM3 and GFDL-CM2.1 local contributions dominate over remote ones, in contrast with warm-season observations. In the other extreme are models like GISS-EH and MIROC3.2(hires) that prioritize the remote influence of moisture fluxes and neglect the local influence of land surface processes to the regional precipitation variability.
HadCM3
Atmospheric research
Atmospheric models
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It is central to understand climate of the past if the importance of changes in present day climates are to be assessed and for reducing uncertainties in predictions of future climate changes. The climate system has, in general, only been instrumentally observed for the past hundred and fifty years. Hence proxy data must be used to represent earlier climates, using measures that are considered responsive to changing climatic conditions. Previous studies comparing proxy and climate model data have been based on only a handful of climate models, which is not a representative approach given the lack of understanding in the climate system and the assumptions made to produce climate models, and also given the large degree of randomness in climate trajectories given a certain climate forcing history. The EU funded Millennium Project was specifically established to aid understanding of these issues. Firstly, by generating a number of synthesized regional proxy-based climate reconstructions for Europe stretching back to 1000 AD, and secondly in the development of a fast variant of the fully-featured HadCM3 UK Met. Office climate model (FAMOUS) to generate a vast model ensemble of experiments. This ensemble can be used to develop statistical distributions for determining the climate sensitivity and likely future climate changes, as many model experiment permutations allow for the large uncertainty in historical forcings, model parameterizations and internal climate variability to be accounted for. This study involves the development of methods for comparing climate data reconstructed from European regional proxy syntheses from the Millennium Project with the FAMOUS model ensemble.
HadCM3
Proxy (statistics)
Climate system
Transient climate simulation
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This study shows climate projections of air temperature and precipitation over South America (SA) from the Regional Climate Model version 3 (RegCM3) nested in ECHAM5 and HadCM3 global models. The projections consider the A1B scenario from Intergovernmental Panel on Climate Change (IPCC) and three time-slices: present (1960–1990), near- (2010–2040), and far-future (2070–2100) climates. In the future, RegCM3 projections indicate general warming throughout all SA and seasons, which is more pronounced in the far-future period. In this late period the RegCM3 projections indicate that the negative trend of precipitation over northern SA is also higher. In addition, a precipitation increase over southeastern SA is projected, mainly during summer and spring. The lifecycle of the South American monsoon (SAM) was also investigated in the present and future climates. In the near-future, the projections show a slight delay (one pentad) of the beginning of the rainy season, resulting in a small reduction of the SAM length. In the far-future, there is no agreement between projections related to the SAM features.
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