Warming Hole-fact or fiction? Vasu Misra Florida State University

Trend for May-June Climatological daily precipitation for March-June period (earlier months included because effects of precipitation can persist for several months) May-June period is shown because it shows the strongest linkage between temperature trends and precipitation climatology From Portmann et al. 2009

There is marked change in trends of Tmax across the dry line across spatial scales (even near California coast [cyan]) 100W is the dryline From Portmann et al. 2009

Precipitation trend is not related to Tmax trend in the southeastern US Precipitation trend is comparable or smaller than the variability From Portmann et al. 2009

Annual average temperature in the west has outpaced the east by about a factor of 2 in the second half of the 20 th century. Owing to this change in the mean there is a similar differential change in the ratio of record high to record lows Ensemble average shows similar east-west differential in surface heating but does not show the cooling trend in the southeastern US Off the 7 ensemble members of CCSM3, one showed the warming hole This ensemble member shows a decline in temperature for a couple of decades after 1950 and then an increase thereafter. Figs. 1 and c show warming trends in tropical Pacific and northeast Pacific and cooling north of Hawaii and northern Atlantic From Meehl et al. 2012

1.Time evolving radiatively forced model (volcanoes, sunspots, GHG’s, ozoen, sulfate direct aerosol affect) with climatological SST did not produce warming hole. 2.Model forced with observed SST and fixed radiative forcing produced the warming hole. From Meehl et al. 2012

SST pattern that tends to force the warming hole in the southeastern US. We compute 451 overlapping 50-yr surface air temperature trends from the 500-yr CCSM3 control run. By calculating pattern correlation values over the continental United States between each of these temperature trend patterns and the warming hole surface air temperature trends in the single twentieth century ensemble member and then picking the 42 cases for which the correlations are greater than 0.5, we produce a composite linear trend pattern of surface air temperature associated with warming-hole-like events generated by internal processes (Fig. b). From Meehl et al. 2012

Trends ending in From Wu et al. (2014)

The instantaneous temperature trend in From Wu et al. (2014)

Conclusions Earlier studies have diagnosed linear trends and suggest the so called warming hole Portmann et al. (2009) claim it is because southeast rains so much that leads to this warming hole Meehl et al. (2012) claim it is the natural variability of SST called IPO that causes this warming hole If you consider non-linear trends, then you begin to see that the warming hole in the Southeast US is shrinking and in the last couple of decades has disappeared