Reducing uncertainty in prediction of wheat performance under climate change

Projections of climate change impacts on crop performances are inherently uncertain. However, multimodel uncertainty analysis of crop responses is rare because systematic and objective comparisons among process-based crop simulation models are difficult. Here we report on the Agricultural Model Intercomparison and Improvement Project ensemble of 30 wheat models tested using both crop and climate observed data in diverse environments, including infra-red heating field experiments, for their accuracy in simulating multiple crop growth, N economy and yield variables. The relative error averaged over models in reproducing observations was 24-38% for the different end-of-season variables. Clusters of wheat models organized by their correlations with temperature, precipitation, and solar radiation revealed common characteristics of climatic responses; however, models are rarely in the same cluster when comparing across sites. We also found that the amount of information used for calibration has only a minor effect on model ensemble climatic responses, but can be large for any single model. When simulating impacts assuming a mid-century A2 emissions scenario for climate projections from 16 downscaled general circulation models and 26 wheat models, a greater proportion of the uncertainty in climate change impact projections was due to variations among wheat models rather than to variations among climate models. Uncertainties in simulated impacts increased with atmospheric [CO2] and associated warming. Extrapolating the model ensemble temperature response (at current atmospheric [CO2]) indicated that warming is already reducing yields at a majority of wheat-growing locations. Finally, only a very weak relationship was found between the models’ sensitivities to interannual temperature variability and their response to long-term warming, suggesting that additional processes differentiate climate change impacts from observed climate variability analogs. In conclusion, uncertainties in prediction of climate change impacts on crop performance can be reduced by improving temperature and CO2 relationships in models and are better quantified through use of impact ensembles

High-energy gamma-ray emission from the Galactic Center

The EGRET instrument on the Compton Gamma-Ray Observatory has observed the Galactic Center (GC) region with good coverage at a number of epochs. A strong excess of emission is observed, peaking at energies >500 MeV in an error circle of 0.2 degree radius including the position l=0 and b=0 . The close coincidence of this excess with the GC direction and the fact that it is the strongest emission maximum within 15 degrees from the GC is taken as compelling evidence for the source's location in the GV region. The history of the emission intensity, observed over 5 years, leaves room for possible time variation; however, it does not provide evidence. The angular extent of the excess appears only marginally compatible with the signature expected for a single compact object. The emission therefore may stem from one or more compact objects or may originate from diffuse interactions within 85 pc from the center of the Galaxy at 8.5 kpc distance. The spatial distribution of the emission does not correlate with the details of the CO-line surveys. Thus, in spite of the existence of a strong emission peak, earlier conclusions based on an apparent 'gamma-ray deficit', postulating the masses of the 'wide-line' clouds in the GC area to be an order of magnitude lower than indicated by naive CO interpretation, are supported. However, the total gas mass if the Nuclear Bulge (NB) derived from the gamma-ray emission is found to be in agreement with the mass which in recent studies has been derived from molecular-line and FIR surveys. The #gamma#-ray emission spectrum is peculiar and different from the spectrum of the large-scale galactic diffuse emission. A diffuse emission scenario requires an enhanced and peculiar Cosmic Ray (CR) spectrum as suggested for the electrons in the 'Radio Arc'. A compact sources model hints at an origin in pulsars. While the spectrum suggests middle-aged pulsars like Vela, too many are required to produce the observed flux. The only detected very young pulsar, the Crab pulsar, has an incompatible spectrum. However, it is not proven that the Crab spectrum is characteristic for all young pulsars: thus, a single or a few very young pulsars (at the GC not detectable in radio emission), provided their gamma-ray emission is larger than that of the Crab pulsar by a factor of 13, are likely candidates. Alternatively, more exotic scenarios, related to the postulated central black hole or dark matter (neutralino) annihilation, may be invoked. (orig.)Available from TIB Hannover: RN 9303(440) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman