Warming Hole-fact or fiction?
Vasu Misra
Florida State University
Trend for May-June
May-June period is shown because it
shows the strongest linkage between
temperature trends and precipitation
climatology
Climatological daily precipitation
for March-June period (earlier
months included because effects
of precipitation can persist for
several months)
From Portmann et al. 2009
100W is the dryline
There is marked change in
trends of Tmax across the dry
line across spatial scales (even
near California coast [cyan])
From Portmann et al. 2009
Precipitation trend is
comparable or smaller than the
variability
Precipitation trend is not related to
Tmax trend in the southeastern US
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 20th 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
1950
1960
1970
1980
1990
2000
2009
1901-2009
From Wu et al. (2014)
The instantaneous
temperature trend in
1950
1960
1970
1980
1990
2000
2009
1901-2009
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