Attribution of changes in precipitation patterns in African rainforests
Philosophical Transactions of the Royal Society B: Biological Sciences 368:1625 (2013)
Abstract:
Tropical rainforests in Africa are one of the most under-researched regions in theworld, but research in the Amazonian rainforest suggests potential vulnerability to climate change. Using the large ensemble of Atmosphere-only general circulation model (AGCM) simulations within the weather@home project, statistics of precipitation in the dry season of the Congo Basin rainforest are analysed. By validating the model simulation against observations, we could identify a good model performance for the June, July, August (JJA) dry season, but this result does need to be taken with caution as observed data are of poor quality. Additional validation methods have been used to investigate the applicability of probabilistic event attribution analysis from large model ensembles to a tropical region, in this case the Congo Basin. These methods corroborate the confidence in the model, leading us to believe the attribution result to be robust. That is, that there are no significant changes in the risk of low precipitation extremes during this dry season (JJA) precipitation in the Congo Basin. Results for the December, January, February dry season are less clear. The study highlights that attribution analysis has the potential to provide valuable scientific evidence of recent or anticipated climatological changes, especially in regions with sparse observational data and unclear projections of future changes. However, the strong influence of sea surface temperature teleconnection patterns on tropical precipitation provides more challenges in the set up of attribution studies than midlatitude rainfall. © 2013 The Author(s) Published by the Royal Society. All rights reserved.The record winter drought of 2011-12 in the Iberian peninsula
Bulletin of the American Meteorological Society 94:9 (2013) S41-S45
Quantifying uncertainty in future Southern Hemisphere circulation trends
Geophysical Research Letters 39:23 (2012)
Abstract:
The Antarctic polar night jet has intensified during spring in recent decades due to stratospheric ozone depletion and rising greenhouse gas (GHG) concentrations and this has had substantial effects on the region's climate. GHG concentrations will rise over the 21st century whereas stratospheric ozone is expected to recover and there is uncertainty in future southern hemisphere (SH) circulation trends. We examine sensitivity to the physics parameterisation of the 21st century SH circulation projection of a coupled atmosphere-ocean General Circulation Model and the sensitivity of the contribution from stratospheric ozone recovery. Different model parameterizations give a greater range of future trends in the position of the tropospheric jet than has been found in previous multi-model comparisons. Ozone recovery causes a weakening and northward shift of the DJF tropospheric jet. Varying the physics parameterization affects the zonal wind response to ozone recovery of the SON stratosphere by ∼10% and that of the DJF troposphere by ∼25%. The projected future SAM index changes with and without ozone recovery and the SAM index response to ozone recovery alone are found to be strongly positively correlated with projected 21st century global warming. © 2012. American Geophysical Union. All Rights Reserved.Equivalence of greenhouse-gas emissions for peak temperature limits
Nature Climate Change 2:7 (2012) 535-538
Abstract:
Climate policies address emissions of many greenhouse gases including carbon dioxide, methane, nitrous oxide and various halogen-containing compounds. These are aggregated and traded on a CO2-equivalent basis using the 100-year global warming potential (GWP100); however, the GWP 100 has received scientific and economic criticism as a tool for policy1-4. In particular, given international agreement to limit global average warming to 2°C, the GWP100 does not measure temperature and does not clearly signal the need to limit cumulative CO 2 emissions5-7. Here, we show that future peak temperature is constrained by cumulative emissions of several long-lived gases (including CO2 and N2O) and emission rates of a separate basket of shorter-lived species (including CH 4). For each basket we develop an emissions-equivalence metric allowing peak temperature to be estimated directly for any emissions scenario. Today's emissions of shorter-lived species have a lesser impact on ultimate peak temperature than those nearer the time of peaking. The 2°C limit could therefore be met by setting a limit to cumulative long-lived CO2-equivalent emissions while setting a maximum future rate for shorter-lived emissions. © 2012 Macmillan Publishers Limited. All rights reserved.Broad range of 2050 warming from an observationally constrained large climate model ensemble
Nature Geoscience 5:4 (2012) 256-260