| dc.description.abstract | Regional temperature change over the twentieth century has been strongly influenced by aerosol forcing [1, 2]. The aerosol effect is also expected to be pronounced on regional precipitation change [3]. Changes in historical precipitation—for the global mean and land mean of certain regions—should be more sensitive to spatially heterogeneous aerosol forcing than greenhouse gas forcing [4, 5, 6, 7]. Here, we investigate whether regional precipitation and temperature respond predictably to a significant strengthening in mid-twentieth-century Northern Hemisphere mid-latitude (NHML) aerosol forcing. Using the latest climate model experiments, we find that observed regional temperature changes and observed Northern Hemisphere tropical land precipitation changes are consistent with the IPCC Fifth Assessment Report [8] aerosol forcing estimate, but observed NHML land precipitation changes show little evidence of an aerosol response. This may be a result of changes in precipitation measurement practice that increased observed precipitation totals at the same time that aerosol forcing was expected to reduce them [9]. Investigating this inconsistency, we calculate the required increase in early-twentieth-century observed NHML land precipitation to bring this result in line with aerosol forcing. Biases greater than this calculated correction have been identified in countries within the NHML region previously, notably the former Soviet Union [9, 10]. These observations are frequently used as a metric for the quality of model-simulated precipitation. More homogeneity studies would be of huge benefit. | en_GB |
