The Pacific And The Pause
Every few weeks along comes another explanation or contributing factor to the post-1997 global surface temperature pause. The list of factors is now a long one, which is curious considering that often the pause is dismissed as non-existent. We now have stratospheric water vapour variations, the Sun’s low activity, lack of wind in the Pacific, the oceans absorbing more heat, aerosols both from small-scale volcanic eruptions and from burning stoves in India and China, the cyclical patterns in the Pacific or is it the Atlantic, lack of data coverage in the polar regions, and Stadium waves not forgetting the all-purpose, hand-waving explanation that it’s down to vague natural climatic variability. The increasing number of explanations for the pause has revealed much about our level of understanding of the climate. The pause is now a well-established phenomenon requiring an explanation, although some still think it doesn’t exist, most scientists do.
And now comes another one. The latest previously unappreciated effect concerns trade winds in the Pacific, this time getting stronger. England et al 2014 writing in Nature Climate Change contend that the East-West equatorial winds in the Pacific have been unusually strong in the past two decades and they have pushed warmed surface water towards Asia where it has pooled and diffused its heat into subsurface waters. The effect has been to replace warm surface waters with cooler ones that have a concomitant effect on global temperatures, as long as the exceptional Pacific trade winds persist. A few years ago we were told that the pause was due to the weakening of Pacific trade winds.
Fig 1 is from England et al 2014 (click on image to enlarge). It shows the well-known surface temperature graph as well as Pacific wind stress and the state of the Interdecadal Pacific Oscillation (IPO), which was only discovered in 1997, coincidently the start of the pause. It will be noted that -IPO tends to be associated with unchanging global temperatures and +IPO with rising temperatures no matter what the state of the Pacific wind stress. One could argue that the Pacific wind stress has been increasing since 1990 in an “unprecedented” manner, as England et al do. However, one could also argue that there was nothing unprecedented going on until about 2000!
Natural climatic variability, according to this research, is therefore in control of the recent 17-year pause in global surface temperatures. The general implication of this growing realisation is that natural variability must have played a strong role in the warming seen between 1980 – 97. One cannot have one without the other.
The England et al 2014 paper continues a trend seen in many papers in the past few years, that of combining and using in evidence the pre and post anthropogenic eras implicitly taking the 0.8 deg warming seen in the ‘thermometer’ era (about post 1880) as support for man-made warming.
One of the problems with the conclusions drawn from the output of England et al’s climate models is that their predicted increase in sub-surface ocean temperature between 100m and 300m below sea level is not born out by the observations. Another interesting question is, why did the Pacific winds change just after the strongest El Nino seen? Another question is if the rise in global surface temperature seen between 1910 – 40 is also related to the Pacific trade winds.
In any case, the trade winds theory is only a partial explanation for the pause giving a modelled cooling of 0.11 deg C by 2012 whereas it would require 0.2-0.3 deg C to explain the pause completely.
The best thing about this paper is that it leads to a specific prediction: When the Pacific winds desist global temperature should increase rapidly, by about 0.5 deg C in a decade – an unprecedented amount. Fig 2 (click on image to enlarge) shows England et al’s predictions that strike me as already running much warmer than the data, but time will tell.
Next Week’s News
The Nature Climate Change paper received uncritical coverage from reporters who consider their role is to seek evidence to support a desired view or ‘consensus,’ and then champion it. They have little interest in the more complex and messy workings of science ignoring inconvenient facts and then oversimplifying and exaggerating. I think some of them could keep the template of their recent articles that explain how this most recent factor “explains” the pause and reuse it again in the near future inserting the next explanation.
And as if on cue, just after the England et al paper was published Geophysical Research Letters produces a paper suggesting that the Atlantic Multi-decadal Oscillation is a dominant factor of oceanic influence on climate.
Plus ca change.