No Slowdown In Temperature Hiatus Research

A small sample of new research papers in scientific journals shows that the global temperature hiatus is widely accepted in the scientific community.

“There was no global hiatus,” said Hansen et al. in a review of the global temperature of 2015. Last year, of course, like the year before and this year, had global temperatures elevated by a very strong El Nino – a short-term weather event.

The so-called pause or hiatus in average annual global surface temperature has been the most talked about aspect of climate science for some years now. To those who only pay attention to the most vocal scientists, campaigners and activists the situation is now clear. The hiatus either never existed, or it is now over. For some the proof of this viewpoint is easy. To prove it one has to draw a straight line through all of the available data and say that anything else is cherry-picking the data, or hold up a particular graph on a chat show and ridicule any opposition, or seek the opinion of those selected to agree. There is however a better way to judge what is going on and that is to look at the peer-reviewed scientific literature. What questions are being asked and what research is being done away from the partisan blogs, the TV studios, the twitter put-downs and the soundbites?

Nobody would say that the Geophysical Research Letters is a fringe journal. In it Sevellec at al discuss the nature of hiatus’ in global warming saying that there has been a “recent unprecedented decade-long slowdown in surface warming.”

They write that the global surface temperature was never expected to increase monotonically with increasing radiative forcing because of decadal variations. To my mind, this is rewriting history somewhat. A decade ago there was hardly any discussion of decadal variability in the climate record and it was held that the anthropogenic signal was strong. It was only when surface temperatures did not increase by the 0.3°C per decade that some had predicted that qualifications were made. Slowly decadal variability was brought in to explain the lack of temperature rise which led to a complete change of view. Now the anthropogenic signal was being obscured by decadal climatic variability and it would be several decades before it emerged and exceeded it, as Meehl et al said recently in Nature Climate Change, “Longer-term externally forced trends in global mean surface temperatures are embedded in the background noise of internally generated multidecadal variability.”

Sevellec et al use a model and they it say demonstrates that hiatus periods are extremely unlikely using the term “rogue event.” They add that hiatus periods will vanish by 2100 and surges in global temperature, greater than that expected due to radiative forcing alone, will take over.

Shi et al in the Journal of Meteorological Research disagree. They analyse what they describe as “the so-called global warming hiatus 1998 – 2012.” They say such a hiatus period has occurred many times in the past and it is likely to be a “periodical feature” of long-term temperature change. Exactly the opposite of Sevellec et al.

Environmental Research Letters contains a paper by Checa-Garcia et al on the “contribution of greenhouse gasses to the recent slowdown in global mean temperature trends.” They say the slowdown has generated “extensive discussion.” They suggest that the hiatus is in part due to variations in ozone-destroying chemicals and the stratosphere’s response – a non CO2 effect.

Middlemas and Clement writing in the Journal of Climate say that “the causes of decadal time-scale variations are currently under debate” and propose that the hiatus is due to atmospheric air interactions with the upper ocean.

Challenging Understanding

Talking to the European Geophysical Union assembly in Vienna in April, Tao and Yunfei state that, “global temperature has not risen in the 21st century, termed a hiatus.”

They think its due to variations in the thickness of the tropopause. According to Gu et al in Climate Dynamics, “global mean surface temperature rapidly increased up to the late 1990s.” They maintain the influence of the Pacific Decadal Oscillation on this hiatus is strong.

And in Nature Geoscience Xie et al say that the earth’s energy budget for the past four decades can now be closed, albeit with a few unrealistic assumptions. In doing so they mention, “the so-called global warming hiatus since the late 1990s.” Song et al in Scientific Reports say, “the rate at which global average surface temperature has slowed down since the end of the last century.” They think it is due to a downward tendency in cloud activity which started in the early 1990s adding, “it is now accepted that a recent warming deceleration can be clearly observed.”

Yao et al in Theoretical and Applied Climatology say that the globally-averaged annual combined land and ocean surface temperature (GST) anomaly change features a slowdown in the rate of global warming in the mid-twentieth century and the beginning of the twenty-first century.

“Here, it is shown that the hiatus in the rate of global warming typically occurs when the internally generated cooling associated with the cool phase of the multi-decadal variability overcomes the secular warming from human-induced forcing.”

“We provide compelling evidence that the global warming hiatus is a natural product of the interplays between a secular warming tendency due in a large part to the buildup of anthropogenic greenhouse gas concentrations, in particular CO2 concentration, and internally generated cooling by a cool phase of a quasi-60-year oscillatory variability that is closely associated with the Atlantic multi-decadal oscillation (AMO) and the Pacific decadal oscillation (PDO).”

The hiatus is being found in new areas. An et al report that it has been detected in ice-core records from the Tibetian plateau.

The cores were taken from the Chongce glacier in 2012 and show a warming trend between 1970 – 2000 and a cooling between 2001 – 2012 which they say has contributed to the relatively stable status of the glaciers in the north western Tibetian plateau. It has also been found in neighbouring China by Xie et al reporting in the International Journal of Climatology, “As the recent global warming hiatus has attracted worldwide attention, we examined the robustness of the warming hiatus in China. Based on the results confirmed by the multiple data and trend analysis methods, we found that the annual mean temperature in China had a cooling trend during the recent global warming hiatus period, which suggested a robust warming hiatus in China.’

When looking at this small sample of peer-reviewed literature it is clear that there is acceptance of the hiatus among many in the scientific community, and much research being carried out into its nature and causes. Xie et al in Nature Climate Change say that the “recent slowdown in global warming challenged our understanding of climate dynamics and anthropogenic forcing.”

Such a body of peer-reviewed literature cannot be ignored or deleted from soundbyte debates without demonstrating a lack of understanding or interest of what is actually going on in the scientific community. Denial and ridicule of such work is disappointing, and anti-scientific.

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