Detection and attribution

posted by Prof. Dr. Hans von Storch, Director emeritus of Institute for Coastal Research

The two manuscripts „Detectable anthropogenic shift toward heavy precipitation over eastern China“ by Ma S., Zhou T., D. Stone, D. Polson, A. Dai, P. Stott, H. von Storch, Qian Y, C. Burke; Wu P., Zou L., and A. Ciavarella, and „An attempt to deconstruct recent climate change in the Baltic Sea Basin“ by A. Barkhordarian, H. von Storch, E. Zorita, and J. Gómez-Navarro has been accepted for publication by Journal of Climate and Journal of Geophysical Research – Atmospheres.

Apart of the general scientific interest in these results, the papers provides evidence for the significance of the Geesthacht-work on regional detection and attribution. The former article demonstrates the successful cooperation between Chinese leading laboratories and the KlimaCampus Hamburg, and in particular the Institute for Coastal Research in Geesthacht.

The abstracts reads:

  • Changing precipitation characteristics directly affect society through their impacts on drought and floods, hydro-dams and urban drainage systems. Global warming increases the water holding capacity of the atmosphere and thus the risk of heavy precipitation. Here, we analyze daily precipitation records from over 700 Chinese stations from 1956-2005. The results show a significant shift from light to heavy precipitation over eastern China. An optimal fingerprinting analysis of simulations from 11 climate models driven by different combinations of historical anthropogenic (greenhouse gases, aerosols, land use, and ozone) and natural (volcanic and solar) forcings indicates that anthropogenic forcing on climate including increases in greenhouse gases (GHG) have had a detectable contribution to the observed shift towards heavy precipitation. We find some evidence that anthropogenic aerosols (AA) partially offset the effect of the GHG forcing, resulting in a weaker shift towards heavy precipitation in simulations that include the AA forcing than in simulations with just the GHG forcing. In addition to the thermodynamic mechanism, strengthened water vapor transport from the adjacent oceans and by midlatitude westerlies, resulting mainly from GHG-induced warming, also favors heavy precipitation over eastern China. Further GHG-induced warming is predicted to lead to an increasing shift towards heavy precipitation, leading to increased urban flooding and posing a significant challenge for mega-cities in China in the coming decades. Future reductions in AA emissions resulting from air pollution controls could exacerbate this tendency towards heavier precipitation.
  • We investigate whether the recently observed temperature and precipitation trends over the Baltic Sea Basin are consistent with state-of-the-art regional climate model projections. To address this question we use several data sources: 1) multi-decadal trends derived from various observational data sets, 2) estimates of natural variability provided by a 2,000-year paleoclimatic model simulation, and 3) response to greenhouse gas forcing derived from regional climate simulations driven by the A1B and RCP4.5 scenarios (from ENSEMBLES and CORDEX projects). Results indicate that, over the past decades, the climate in the Baltic Sea Basin has undergone a change that is beyond the estimated range of natural variability. We test the hypothesis that this change may be understood as a manifestation of global warming due to increasing concentrations of greenhouse gases (GHGs). We find that changes in near-surface temperature support our hypothesis that the effect of GHG is needed to simulate the observed changes. The pattern correlation and regression results clearly illustrate the concerted emergence of an anthropogenic signal consistent with the GHG signal in summer and autumn in the 21st century. However, none of the 19 regional climate simulations used in this study reproduce the observed warming. The observed trends in precipitation and surface solar radiation are also partially inconsistent with the expected changes due to GHG forcing. We conclude that, besides the regional response to GHG forcing, other human-made drivers have had an imprint. Regional emission of industrial aerosols has been strongly reduced in this region, and we suggest that this reduction may be the missing driver.

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