Speculation is rife as to why there has been no global warming for the last 17 or 18 years. Some of this speculation is by those who believe the science is settled and is merely to try and “save” the discredited climate models used by the IPCC. Others – the real scientists – actually use it as an opportunity to investigate something that is not very well understood at all.
The lack of warming has been “blamed” on a variety of reasons. Some have blamed mysterious heat storage in the deep ocean where the heat has actually been transported from and through colder temperatures to higher temperatures! Others say that aerosols and soot in the atmosphere – due to pollution – have distorted the warming trend by hiding the sun. Some few point out that the models really don’t know how to treat clouds and moisture in the atmosphere and what actually drives cloud formation is still an unknown unknown. And there are those – like me – who put it down to natural variation which in turn is ultimately driven – via many still unknown mechanisms – by the Sun.
The El Nino-Southern Oscillation, has a major impact on global climate and is usually acknowledged but a new paper in Nature now suggests that the lack of warming is due to the Pacific Decadal Oscillation that lasts for a much longer period of time (15 – 30 years). There may well be some influence of the Pacific Decadal Oscillation and no doubt it should be investigated further. But it does first need an acknowledgement that there is something to be investigated. As the authors begin “Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century, challenging the prevailing view that anthropogenic forcing causes climate warming”.
Yu Kosaka & Shang-Ping Xie, Recent global-warming hiatus tied to equatorial Pacific surface cooling, Nature Letter (2013),
doi:10.1038/nature12534
Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century, challenging the prevailing view that anthropogenic forcing causes climate warming. Various mechanisms have been proposed for this hiatus in global warming, but their relative importance has not been quantified, hampering observational estimates of climate sensitivity. Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model. Although the surface temperature prescription is limited to only 8.2% of the global surface, our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970–2012 (which includes the current hiatus and a period of accelerated global warming). Moreover, our simulation captures major seasonal and regional characteristics of the hiatus, including the intensified Walker circulation, the winter cooling in northwestern North America and the prolonged drought in the southern USA. Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-Niña-like decadal cooling. Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase.
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