Search Results

You are looking at 1 - 10 of 16 items for

  • Author or Editor: Fraser C. Lott x
  • Refine by Access: All Content x
Clear All Modify Search
Fraser C. Lott and Peter A. Stott

Abstract

Although it is critical to assess the accuracy of attribution studies, the fraction of attributable risk (FAR) cannot be directly assessed from observations since it involves the probability of an event in a world that did not happen, the “natural” world where there was no human influence on climate. Instead, reliability diagrams (usually used to compare probabilistic forecasts to the observed frequencies of events) have been used to assess climate simulations employed for attribution and by inference to evaluate the attribution study itself. The Brier score summarizes this assessment of a model by the reliability diagram. By constructing a modeling framework where the true FAR is already known, this paper shows that Brier scores are correlated to the accuracy of a climate model ensemble’s calculation of FAR, although only weakly. This weakness exists because the diagram does not account for accuracy of simulations of the natural world. This is better represented by two reliability diagrams from early and late in the period of study, which would have, respectively, less and greater anthropogenic climate forcing. Two new methods are therefore proposed for assessing the accuracy of FAR, based on using the earlier observational period as a proxy for observations of the natural world. It is found that errors from model-based estimates of these observable quantities are strongly correlated with errors in the FAR estimated in the model framework. These methods thereby provide new observational estimates of the accuracy in FAR.

Full access
Lixia Zhang, Tianjun Zhou, Xiaolong Chen, Peili Wu, Nikolaos Christidis, and Fraser C. Lott
Free access
Chunhui Lu, Fraser C. Lott, Ying Sun, Peter A. Stott, and Nikolaos Christidis

Abstract

In China, summer precipitation contributes a major part of the total precipitation amount in a year and has major impacts on society and human life. Whether any changes in summer precipitation are affected by external forcing on the climate system is an important issue. In this study, an optimal fingerprinting method was used to compare the observed changes of total, heavy, moderate, and light precipitation in summer derived from newly homogenized observation data with the simulations from multiple climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5). The results demonstrate that the anthropogenic forcing signal can be detected and separated from the natural forcing signal in the observed increase of seasonal accumulated precipitation amount for heavy precipitation in summer in China and eastern China (EC). The simulated changes in heavy precipitation are generally consistent with observed change in China but are underestimated in EC. When the changes in precipitation of different intensities are considered simultaneously, the human influence on simultaneous changes in moderate and light precipitation can be detected in China and EC in summer. Changes attributable to anthropogenic forcing explain most of the observed regional changes for all categories of summer precipitation, and natural forcing contributes little. In the future, with increasing anthropogenic influence, the attribution-constrained projection suggests that heavy precipitation in summer will increase more than that from the model raw outputs. Society may therefore face a higher risk of heavy precipitation in the future.

Free access
Chunhui Lu, Jie Jiang, Ruidan Chen, Safi Ullah, Rong Yu, Fraser C. Lott, Simon F. B. Tett, and Buwen Dong
Full access
Jianping Duan, Liang Chen, Lun Li, Peili Wu, Nikolaos Christidis, Zhuguo Ma, Fraser C. Lott, Andrew Ciavarella, and Peter A. Stott
Full access
Seung-Ki Min, Yeon-Hee Kim, Sang-Min Lee, Sarah Sparrow, Sihan Li, Fraser C. Lott, and Peter A. Stott
Free access
Nicholas J. Leach, Sihan Li, Sarah Sparrow, Geert Jan van Oldenborgh, Fraser C. Lott, Antje Weisheimer, and Myles R. Allen
Free access
Rafael C. de Abreu, Christopher Cunningham, Conrado M. Rudorff, Natalia Rudorff, Abayomi A. Abatan, Simon F. B. Tett, Buwen Dong, Fraser C. Lott, and Sarah N. Sparrow
Open access
Seung-Ki Min, Min-Gyu Seong, Dong-Hyun Cha, Minkyu Lee, Fraser C. Lott, Andrew Ciavarella, Peter A. Stott, Maeng-Ki Kim, Kyung-On Boo, and Young-Hwa Byun
Full access
Cheng Qian, Jun Wang, Siyan Dong, Hong Yin, Claire Burke, Andrew Ciavarella, Buwen Dong, Nicolas Freychet, Fraser C. Lott, and Simon F. B. Tett
Open access