skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Potential bias of model projected greenhouse warming in irrigated regions

Abstract

Atmospheric general circulation models (GCMs) used to project climate responses to increased CO{sub 2} generally omit irrigation of agricultural land. Using the NCAR CAM3 GCM coupled to a slab-ocean model, we find that inclusion of an extreme irrigation scenario has a small effect on the simulated temperature and precipitation response to doubled CO{sub 2} in most regions, but reduced warming by as much as 1 C in some agricultural regions, such as Europe and India. This interaction between CO{sub 2} and irrigation occurs in cases where agriculture is a major fraction of the land surface and where, in the absence of irrigation, soil moisture declines are projected to provide a positive feedback to temperature change. The reduction of warming is less than 25% of the temperature increase modeled for doubled CO{sub 2} in most regions; thus greenhouse warming will still be dominant. However, the results indicate that land use interactions may be an important component of climate change uncertainty in some agricultural regions. While irrigated lands comprise only {approx}2% of the land surface, they contribute over 40% of global food production. Climate changes in these regions are therefore particularly important to society despite their relatively small contribution to average globalmore » climate.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
897972
Report Number(s):
UCRL-JRNL-221969
TRN: US200706%%163
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geophysical Research Letters, vol. 33, N/A, July 14, 2006, L13709, doi:10.1029/2006GL026770
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; AGRICULTURE; CLIMATES; FEEDBACK; FOOD; GENERAL CIRCULATION MODELS; GREENHOUSE GASES; IRRIGATION; LAND USE; MOISTURE; PRECIPITATION; PRODUCTION; SOILS

Citation Formats

Lobell, D, Bala, G, Bonfils, C, and Duffy, P. Potential bias of model projected greenhouse warming in irrigated regions. United States: N. p., 2006. Web. doi:10.1029/2006GL026770.
Lobell, D, Bala, G, Bonfils, C, & Duffy, P. Potential bias of model projected greenhouse warming in irrigated regions. United States. doi:10.1029/2006GL026770.
Lobell, D, Bala, G, Bonfils, C, and Duffy, P. Thu . "Potential bias of model projected greenhouse warming in irrigated regions". United States. doi:10.1029/2006GL026770. https://www.osti.gov/servlets/purl/897972.
@article{osti_897972,
title = {Potential bias of model projected greenhouse warming in irrigated regions},
author = {Lobell, D and Bala, G and Bonfils, C and Duffy, P},
abstractNote = {Atmospheric general circulation models (GCMs) used to project climate responses to increased CO{sub 2} generally omit irrigation of agricultural land. Using the NCAR CAM3 GCM coupled to a slab-ocean model, we find that inclusion of an extreme irrigation scenario has a small effect on the simulated temperature and precipitation response to doubled CO{sub 2} in most regions, but reduced warming by as much as 1 C in some agricultural regions, such as Europe and India. This interaction between CO{sub 2} and irrigation occurs in cases where agriculture is a major fraction of the land surface and where, in the absence of irrigation, soil moisture declines are projected to provide a positive feedback to temperature change. The reduction of warming is less than 25% of the temperature increase modeled for doubled CO{sub 2} in most regions; thus greenhouse warming will still be dominant. However, the results indicate that land use interactions may be an important component of climate change uncertainty in some agricultural regions. While irrigated lands comprise only {approx}2% of the land surface, they contribute over 40% of global food production. Climate changes in these regions are therefore particularly important to society despite their relatively small contribution to average global climate.},
doi = {10.1029/2006GL026770},
journal = {Geophysical Research Letters, vol. 33, N/A, July 14, 2006, L13709, doi:10.1029/2006GL026770},
number = ,
volume = ,
place = {United States},
year = {Thu Apr 27 00:00:00 EDT 2006},
month = {Thu Apr 27 00:00:00 EDT 2006}
}
  • Theoretical and modeling studies suggest that increasing greenhouse gases will cause the global mean temperature to rise a few degrees centigrade during the next century. Current global coupled GCMs have shown a distinct pattern of warming associated with this global mean rise. It is important to know how well our observing network will be able to capture the global mean temperature rise associated with this pattern if it occurs. The authors consider if a sampling bias exists as a result of the spatial distribution of observations as they are now located (1950-1979) when detecting a pattern of temperature change thatmore » should be typical of a warming due to increasing atmospheric CO[sub 2]. The observations prove adequate to estimate the globally averaged temperature change associated with the pattern of CO[sub 2] warming from a general circulation model with a bias whose absolute value is generally less than 2%. 15 refs., 3 figs.« less
  • Climate changes during the next 100 years caused by anthropogenic emissions of greenhouse gases have been simulated for the Intergovernmental Panel on Climate Change Scenarios A ({open_quotes}business as usual{close_quotes}) and D ({open_quotes}accelerated policies{close_quotes}) using a coupled ocean-atmosphere general circulation model. In the global average, the near-surface temperature rises by 2.6 K in Scenario A and by 0.6 K in Scenario D. The global patterns of climate change for both IPCC scenarios and for a third step-function 2xCO{sub 2} experiment were found to be very similar. The warming delay over the oceans is larger than found in simulations with atmospheric generalmore » circulation models coupled to mixed-layer models, leading to a more pronounced land-sea contrast and a weaker warming (and in some regions even an initial cooling) in the Southern Ocean. During the first forty years, the global warming and sea level rise due to the thermal expansion of the ocean are significantly slower than estimated previously from box-diffusion-upwelling models, but the major part of this delay can be attributed to the previous warming history prior to the start of present coupled ocean-atmosphere model integration (cold start). 38 refs., 17 figs.« less
  • Two 100-yr equilibrium simulations from the NCAR Community Climate Model coupled to a nondynamic slab ocean are used to investigate the activity of northern winter extratropical cyclones and anticyclones under a greenhouse warming scenario. The first simulation uses the 1990 observed CO{sub 2}, CH{sub 4}, N{sub 2}O, CFC-11, and CFC-12 concentrations, and the second adopts the year 2050 concentrations according to the Intergovernmental Panel on Climate Change business-as-usual scenario. Variables that describe the characteristic properties of the cyclone-scale eddies, such as surface cyclone and anticyclone frequency and the bandpassed root-mean-square of 500-hPa geopotential height, along with the Eady growth ratemore » maximum, form a framework for the analysis of the cyclone and anticyclone activity. Objective criteria are developed for identifying cyclone and anticyclone occurrences based on the 1000-hPa geopotential height and vorticity fields and tested using ECMWF analyses. The potential changes of the eddy activity under the greenhouse warming climate are then examined. Results indicate that the activity of cyclone-scale eddies decreases under the greenhouse warming scenario. This is not only reflected in the surface cyclone and anticyclone frequency and in the bandpassed rms of 500-hPa geopotential height, but is also discerned from the Eady growth rate maximum. Based on the analysis, three different physical mechanisms responsible for the decreased eddy activity are discussed: (1) a decrease of the extratropical meridional temperature gradient from the surface to the midtroposphere, (2) a reduction in the land-sea thermal contrast in the east coastal regions of the Asian and North American continents, and (3) an increase in the eddy meridional latent heat fluxes. Uncertainties in the results related to the limitations of the model and the model equilibrium simulations are discussed. 45 refs., 10 figs., 1 tab.« less
  • This paper describes El Nino-Southern Oscillation (ENSO) interannual variability simulated in the second Handley Centre coupled model under control and greenhouse warming scenarios. The model produces a very reasonable simulation of ENSO in the control experiment--reproducing the amplitude, spectral characteristics, and phase locking to the annual cycle that are observed in nature. The mechanism for the model ENSO is shown to be a mixed SST-ocean dynamics mode that can be interpreted in terms of the ocean recharge paradigm of Jin. In experiments with increased levels of greenhouse gases, no statistically significant changes in ENSO are seen until these levels approachmore » four times preindustrial values. In these experiments, the model ENSO has an approximately 20% larger amplitude, a frequency that is approximately double that of the current ENSO (implying more frequent El Ninos and La Ninas), and phase locks to the annual cycle at a different time of year. It is shown that the increase in the vertical gradient of temperature in the thermocline region, associated with the model's response to increased greenhouse gases, is responsible for the increase in the amplitude of ENSO, while the increase in meridional temperature gradients on either side of the equator, again associated with the models response to increasing greenhouse gases, is responsible for the increased frequency of ENSO events.« less
  • Cited by 10