Reply to comment by A. Givati and D. Rosenfeld On the paper by Alpert, P., N. Halfon and Z. Levin: Does air pollution really suppress precipitation in Israel?. Alpert, P., N. Halfon, Z. Levin.
JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY:
This report describes, implements, and compares options for representing groundwater in regional water resource system management models.
Response of Pacific subtropical-tropical thermocline water pathways and transports to global warming. Luo, Y. Y.; Rothstein, L. M.; Zhang, R. H..
Geophysical Research Letters:
Global warming may change the thermocline water pathways and transports from the subtropics to the tropics in the Pacific Ocean, which are known to have profound implications for the El Nino-Southern Oscillation (ENSO) and thereby global climate. This study investigates the changes by comparing solutions between a present-day climate and a future, warmer climate from a set of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) models. As the climate warms, although the total transport from the subtropics to the tropics exhibits no significant change, transport via western boundary pathways increases and via interior pathways decreases. This shift is due to high potential vorticity (PV) zones that extend further westward, thus dynamically guiding thermocline water away from interior pathways to prefer western boundary pathways from the subtropics to the tropics. Additionally, a warmer climate induces a large temperature increase near the sea surface in the eastern tropics and a significantly enhanced Equatorial Undercurrent (EUC) in the western and central Pacific; the former is related to the decreased transport through interior pathways and the latter is linked to the increased transport through western boundary pathways. Implications of the results of this study are also discussed. Citation: Luo, Y., L. M. Rothstein, and R.-H. Zhang (2009), Response of Pacific subtropical-tropical thermocline water pathways and transports to global warming, Geophys. Res. Lett., 36, L04601, doi:10.1029/2008GL036705.
Review of Literature on Climate Change and Forest Diseases of Western North America. John T. Kliejunas, Brian W. Geils, Jessie Micales, Glaeser, Ellen Michaels Goheen, Paul Hennon, Mee-Sook Kim, Harry Kope, Jeff Stone, Rona Sturrock, Susan J. Frankel.
United States Department of Agriculture:
A summary of the literature on relationships between climate and various types of tree diseases, and the potential effects of climate change on pathogens in western North American forests is provided. Climate change generally will lead to reductions in tree health and will improve conditions for some highly damaging pathogens. Sections on abiotic diseases, declines, canker diseases, root diseases, Phytophthoras, foliar diseases, stem rusts of pine, mistletoes, and wood decays present some examples of potential disease effects with predicted climate change. The effects of climate change on hosts, pathogens, and their interaction will have numerous, mostly adverse, consequences to forest ecosystems.
Risk aversion, time preference, and the social cost of carbon. David Anthoff, Richard S J Tol, Gary W Yohe.
Environmental Research Letters:
The Stern Review reported a social cost of carbon of over $300/tC, calling for ambitious climate policy. We here conduct a systematic sensitivity analysis of this result on two crucial parameters: the rate of pure time preference, and the rate of risk aversion. We show that the social cost of carbon lies anywhere in between 0 and $120 000/tC. However, if we restrict these two parameters to matching observed behaviour, an expected social cost of carbon of $60/tC results. If we correct this estimate for income differences across the world, the social cost of carbon rises to over $200/tC.
satellite-derived direct radiative effect of aerosols dependent on cloud cover. D. Chand, R.Wood, T. L. Anderson, S. K. Satheesh, R. J. Charlson.
Aerosols from biomass burning can alter the radiative balance of the Earth by reflecting and absorbing solar radiation1.n Whether aerosols exert a net cooling or a net warming effect will depend on the aerosol type and the albedo of the underlying surface2. Here, we use a satellite-based approach to quantify the direct, top-of-atmosphere radiative effect of aerosol layers advected over the partly cloudy boundary layer of the southeastern Atlantic Ocean during July–October of 2006 and 2007. We show that the warming effect of aerosols increases with underlying cloud coverage. This relationship is nearly linear, making it possible to define a critical cloud fraction at which the aerosols switch from exerting a net cooling to a net warming effect. For this region and time period, the critical cloud fraction is about 0.4, and is strongly sensitive to the amount of solar radiation the aerosols absorb and the albedo of the underlying clouds. We estimate that the regional-mean warming effect of aerosols is three timeis higher when large-scale spatial covariation between cloud cover and aerosols is taken into account. These results demonstrate the importance of cloud prediction for the accurate quantification of aerosol direct effects.
Satellite observations indicate rapid warming trend for lakes in California and Nevada. P. Schneider, S. J. Hook, R. G. Radocinski, G. K. Corlett, G. C. Hulley, S. G. Schladow, T. E. Steissberg.
GEOPHYSICAL RESEARCH LETTERS:
Large lake temperatures are excellent indicators of climate change; however, their usefulness is limited by the paucity of in situ measurements and lack of long-term data records. Thermal infrared satellite imagery has the potential to provide frequent and accurate retrievals of lake surface temperatures spanning several decades on a global scale. Analysis of seventeen years of data from the Along-Track Scanning Radiometer series of sensors and data from the Moderate Resolution Imaging Spectroradiometer shows that six lakes situated in California and Nevada have exhibited average summer nighttime warming trends of 0.11 ± 0.02 C yr 1 (p < 0.002) since 1992. A comparison with air temperature observations suggests that the lake surface temperature is warming approximately twice as fast as the average minimum surface air temperature.
Scale effects in species distribution models: implications for conservation planning under climate change. Changwan Seo, James H Thorne, Lee Hannah, Wilfried Thuiller.
Predictions of future species’ ranges under climate change are needed for conservation planning, for which species distribution models (SDMs) are widely used. However, global climate model-based (GCM) output grids can ias the area identified as suitable when these are used as SDM predictor variables, because GCM outputs, typically at least 50!50 km, are biologically coarse. We tested the assumption that species ranges can be equally well portrayed in SDMs operating on base data of different grid sizes by comparing SDM performance statistics and area selected by four SDMs run at seven grid sizes, for nine species of contrasting range size. Area selected was disproportionately larger for SDMs run on larger grid sizes, indicating a cut-off point above which model results were less reliable. Up to 2.89 times more species range area was selected by SDMs operating on grids above 50!50 km, compared to SDMs operating at 1 km2. Spatial congruence between areas selected as range also diverged as grid size increased, p rticularly for species with ranges between 20 000 and 90 000 km2. These results indicate the need for caution when using such data to plan future protected areas, because an overly large predicted range could lead to inappropriate reserve location selection.
Selecting global climate models for regional climate change studies. Pierce, D. W.; Barnett, T. P.; Santer, B. D.; Gleckler, P. J..
Proceedings of the National Academy of Sciences of the United States of America:
Regional or local climate change modeling studies currently require starting with a global climate model, then downscaling to the region of interest. How should global models be chosen for such studies, and what effect do such choices have? This question is addressed in the context of a regional climate detection and attribution (D&A) study of January-February-March (JFM) temperature over the western U. S. Models are often selected for a regional D&A analysis based on the quality of the simulated regional climate. Accordingly, 42 performance metrics based on seasonal temperature and precipitation, the El Nino/Southern Oscillation (ENSO), and the Pacific Decadal Oscillation are constructed and applied to 21 global models. However, no strong relationship is found between the score of the models on the metrics and results of the D&A analysis. Instead, the importance of having ensembles of runs with enough realizations to reduce the effects of natural internal climate variability is emphasized. Also, the superiority of the multimodel ensemble average (MM) to any 1 individual model, already found in global studies examining the mean climate, is true in this regional study that includes measures of variability as well. Evidence is shown that this superiority is largely caused by the cancellation of offsetting errors in the individual global models. Results with both the MM and models picked randomly confirm the original D&A results of anthropogenically forced JFM temperature changes in the western U. S. Future projections of temperature do not depend on model performance until the 2080s, after which the better performing models show warmer temperatures.
Sensitivity studies of aerosol-cloud interactions in mixed-phase orographic precipitation. Andreas Muhlbauer, Ulrike Lohmann.
Journal of the Atmospheric Sciences:
Anthropogenic aerosols serve as a source of cloud condensation nuclei (CCN) as well as ice nuclei (IN) and affect microphysical properties of clouds. Increasing aerosol number concentrations is assumed to retard the cloud droplet coalescence and the riming process in mixed-phase orographic clouds thereby decreasing orographic
precipitation. In this study, idealized 3D simulations are conducted to investigate aerosol-cloud interactions in mixed-phase orographic clouds and the possible impact of anthropogenic and natural aerosols on orographic precipitation. Two different types of aerosol anomalies are considered which are naturally occuring mineral dust and anthropogenic black carbon. In the simulations with a dust aerosol anomaly the dust aerosols serve as efficient ice nuclei in the contact mode leading to an early initiation of the ice-phase in the orographic cloud. As a consequence, the riming rates in the cloud are increased leading to an increased precipitation efficiency and to an enhancement of orographic precipitation. The simulations with an anthropogenic aerosol anomaly suggest that the mixing state of the aerosols plays a crucial role since coating and mixing may cause the aerosols to initiate freezing in the less efficient immersion mode than by contact nucleation. It is found that externally mixed black carbon aeroso s increase riming in orographic clouds and enhance orographic precipitation. In contrast, internally mixed black carbon aerosols decrease the riming rates which in turn leads to a decrease in the orographic precipitation.