We found that aerosols and greenhouse gases produce similar but opposite signed patterns in extreme temperatures over the United States (see image), leading to large scale cancellations over the historical period ( Mascioli et al., 2016 ).  Extreme precipitation over the eastern United States decreases in response to aerosols, particularly in winter, and increases over the eastern and central United States in response to greenhouse gases, particularly in spring. In the future, aerosol emissions are projected to decrease while greenhouse gas concentrations continue to rise.  As a result, the patterns of extreme temperature and precipitation associated with
greenhouse gas forcing are expected to dominate over the twenty-first century. We found that the U.S. Southeast was less sensitive to climate change than other regions, whether forced by greenhouse gases or aerosols. This finding, along with our interest in reconciling conflicting reports in the literature regarding the U.S. warming hole (a region over the eastern U.S.A. that did not warm over at least some of the 20 th century), led to a systematic examination of observed eastern U.S. temperature trends. Rather than a single ‘warming hole’, we found that different ‘holes’ emerge depending on the season, region, and time period, possibly reflecting different combinations of anthropogenic aerosol forcing and internal climate variability ( Mascioli et al., 2017 ). [EPA]