"a coherent cooling pattern across the Northern Hemisphere mid-latitudes that has emerged in the recent 15 years and is not reproduced by the models. This regional inconsistency between models and observations might be a key to understanding the recent hiatus in global mean temperature warming."Thus, although warm extremes are getting warmer, cold nights in the N Hemisphere are getting colder, not warmer as predicted by global warming theory. How could increased CO2 cause "a coherent cooling pattern across the Northern Hemisphere mid-latitudes" over the past 15+ years? Inquiring minds want to know; according to the authors,
"precisely identifying the mechanisms behind the observed regional cooling patterns in extreme cold temperatures lies beyond the scope of this paper."
Excerpts from the discussion and conclusion:
We analyzed observed and model-simulated trends in
annual temperature extremes for the past 40 years
(1971–2010) in comparison to the recent 15 years
(1996–2010) using climate extreme indices from the HadEX2
observational dataset and a large set of CMIP5 models.
Simulated trends over the two periods are generally comparable
to observed trends for absolute temperature extremes
(i.e., coldest night (TNn) and warmest day (TXx) of the year)
on a global scale. The observed trends in hot extremes (i.e.,
TXx) are well represented in climate simulations, showing
warming trends similar to those seen in the observations in
both periods. Observed warming trends in cold extremes
(TNn) are less well represented in climate simulations, but
simulated trends are nevertheless consistent with observed
trends globally and in many regions. The largest discrepancy
between observed and simulated trends in cold extremes is
found in the Northern mid-latitudes (20 °N–45 °N), where
observations indicate a coherent zonal band of decreasing
trends over the recent 15 years. This might be connected to
the recent hiatus in the warming of global Tmean, which has
been characterized mainly as a winter phenomenon (e.g.,
Kosaka and Xie 2013, Cohen et al 2012). Only a few individual
model realizations simulate a cooling trend in TNn.
Our findings are consistent with the suggestion that the
recent 15-year period largely represents a highly unusual
(extreme) realization of climate as part of internal variability
(e.g., Meehl et al 2013, Kosaka and Xie 2013, England
et al 2014). Other recent studies (Fyfe et al 2013, Fyfe and
Gillett 2014) argue that internal climate variability is unlikely
to be the only explanation for the discrepancy seen between
model and observed trends and that some external forcing
components not fully represented in current climate models
could have contributed to the local cooling trends in cold
extremes. While precisely identifying the mechanisms behind
the observed regional cooling patterns in extreme cold temperatures
lies beyond the scope of this paper, the results
presented here provide relevant details to complete the overall
picture of recent temperature changes beyond globally averaged
Tmean.
We conclude that while there appears to be a discrepancy
in global Tmean trends between observations and simulations
over the hiatus period (e.g., Fyfe et al 2013), that discrepancy
does not generally extend to temperature extremes, with the
exception of a recent cooling in Northern mid-latitude TNn
that is particularly apparent regionally in South Asia. In
general, temperature extremes continue to increase in most
regions of the world consistent with the long-term projections
under global warming scenarios (e.g., Seneviratne et al 2012,
Sillmann et al 2013b).
 |
| Observations in red, modeled results in black |
Environmental Research Letters Volume 9 Number 6
Jana Sillmann et al 2014 Environ. Res. Lett. 9 064023 doi:10.1088/1748-9326/9/6/064023
Observed and simulated temperature extremes during the recent warming hiatus
OPEN ACCESS
Jana Sillmann1, Markus G Donat2, John C Fyfe3 and Francis W Zwiers4
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Letters
The discrepancy between recent observed and simulated trends in global mean surface temperature has provoked a debate about possible causes and implications for future climate change projections. However, little has been said in this discussion about observed and simulated trends in global temperature extremes. Here we assess trend patterns in temperature extremes and evaluate the consistency between observed and simulated temperature extremes over the past four decades (1971–2010) in comparison to the recent 15 years (1996–2010). We consider the coldest night and warmest day in a year in the observational dataset HadEX2 and in the current generation of global climate models (CMIP5). In general, the observed trends fall within the simulated range of trends, with better consistency for the longer period. Spatial trend patterns differ for the warm and cold extremes, with the warm extremes showing continuous positive trends across the globe and the cold extremes exhibiting a coherent cooling pattern across the Northern Hemisphere mid-latitudes that has emerged in the recent 15 years and is not reproduced by the models. This regional inconsistency between models and observations might be a key to understanding the recent hiatus in global mean temperature warming.
You mean to tell us that the climate "scientists" can't work out that it's not getting warmer because it's getting cooler.
ReplyDeleteNo wonder they're loosing the debate.