The Disappearing Hiatus

This has been known behind the scenes for a while, but the publication is useful. It again demonstrates that the scientific literature is performing a very unusual function in the climate policy arena. The very clear accessible presentation of the work in this video is enormously helpful as well.

I think another thing to consider is this. This demonstrates is how very un-robust the “slowdown” is. It did not take much of a correction to eliminate the trend.

Indeed, the conclusions allude to this:

While short term trends are generally treated with a suitable level of caution by specialists in the field, they feature significantly in the public discourse on climate change.

There’s another aspect to this, though, and it may be a bigger deal than might at first be apparent. It adds up to a pretty scary situation.

That’s because the “slowdown” or “hiatus” has also had a number of alternative explanations. Decreased solar activity. Increased volcanic activity. A prevalence of cool-phase El Nino oscillations. Increase in aerosol loading from rapid and dirty Chinese industrial expansion. Heat export to deeper ocean layers.

To be sure, we are somewhat at risk of post hoc reasoning here. If there had been no sign of a “hiatus”, it is likely that less effort would have gone into explaining it! But all of these explanations appear individually to be sound, and with the possible exception of the last, likely to be reversed at any time. What that would mean is that in reality the underlying rate of warming is still accelerating. Ouch.


  1. Rahmstorf via email:

    "Not all explanation of the slowdown are additional - like ocean heat storage is the mechanism by which ENSO influences global mean temperature, not an additional thing.

    The radiative forcing discussion is highly speculative due to lack of sufficiently accurate data to nail down significant deviations in the net radiative forcing over such a short time period.

    And if after all adjustments the global warming trend shows some acceleration, this would probably get the data closer to the model-mean (rather than to a continued linear warming trend).

    But it would probably not be statistically significant, so interpreting an acceleration into 15 years of data would be as ill-founded as finding a slowdown."

    See also RealClimate

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  6. Gonna ask a dumb question, apologies in advance. Great video and great explanation over at realclimate. The impression I got, though, over the last year or more, was that most scientific conversation about this talked about ocean heat transfer. One generally heard: there's only an apparent hiatus because incoming energy is going into the oceans. I know that's just been mentioned. But at the same time, we did know, didn't we, that (a) places like the Arctic were not part of most global mean calcs and (b) they were warming much faster than average.

    So my question there: why was everyone talking about the "missing heat" going into the oceans given the obvious data holes? Or were they? Maybe I'm only picking up on mainstream, not scientific discussion.

  7. Argh, sorry, another thought: I'm also troubled by various headlines saying Global warming since 1997 more than twice as fast as previously estimated. You don't get to say "that's too short a time for drawing any conclusions about climate trends" and then use this kind of headline a little later when the data changes.

    We *knew* it wasn't a hiatus because we knew there was still an energy imbalance, the forcing wasn't magically disappearing into Narnia. Some of the posts about this paper seem to be playing to the comms agenda set by skeptics, where we feel we must counter the success of the "hiatus" meme. That meme was always scientifically inaccurate, purely because of claiming to conclude something about long-term trends with too-short a range of data. Going all "now it's twice as fast since 1997!" is trying to play skeptics at their own game, it's dangerous and will bite you in the ass later.

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  9. Michael

    You may or may not remember that I asked you about the action of latent heat of fusion in regard to melting Arctic sea ice and the Hiatus. The arctic sea ice blog has an interesting artical that refers to this possibility. Chris Reynolds on his Dosbat blog. Makes the following statement and I quote (copy and paste actually).

    As with the previous post on Arctic Amplification it is apparent that summer warming is negligible, this is due to energy going into melting ice, not raising temperatures. However the latent heat of energy melting ice, and ocean warming, is released in September to November, with later warming possibly due to thinner ice and ice growth.

    Anyway just an interesting point.


  10. I think it was because there still is a "slowdown" if not a true "pause" even if the new papers numbers are more accurate than other estimates . Or at least less acceleration than would've been expected. Chris Colose's comment # 123 at RC implies that...

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