New paper supports early-2000s warming slowdown aka ‘the pause’

Posted: February 24, 2016 by oldbrew in Analysis, climate, modelling, Natural Variation, pause

Climate scientist Ed Hawkins comments on the paper of which he is one of the co-authors. Others include Ben Santer and Michael Mann.

It has been claimed that the early-2000s global warming ‘slowdown’ or ‘hiatus’, characterized by a reduced rate of global surface warming, has been overstated, lacks sound scientific basis, or is unsupported by observations. The evidence presented in a new commentary in Nature Climate Change by Fyfe et al. contradicts these claims.

The new Fyfe et al. paper is mainly in response to Karl et al. and Lewandowsky et al., who made the following statements in their abstracts:

“These results do not support the notion of a ‘slowdown’ in the increase of global surface temperature” – Karl et al., 2015, Science

“there is no evidence that identifies the recent period as unique or particularly unusual” – Lewandowsky et al., 2016, BAMS

Firstly, climate scientists agree that global warming has not ‘stopped’ – global surface temperatures and ocean heat content have continued to increase, sea levels are still rising, and the planet is retaining ~0.5 days of the sun’s incoming energy per year.

I think there is also broad agreement that climate scientists have probably not chosen the right words (e.g. ‘hiatus’) to describe the temporary slowdown, especially when talking to the media and the public.

However, there has very clearly been a change in the rate of global surface warming. Figure 1 shows rolling 15-, 30- and 50-year trends computed for different surface and satellite global temperature datasets. There are clear fluctuations in the rate of global temperature change in the past. We also expect similar fluctuations in future – global temperatures will not increase smoothly or linearly.

Just focusing on the observations, the most recent observed 15-year trends are all positive, but lower than most previous similar trends in the past few decades. This is a clear demonstration that the rate of change has slowed since its peak.

The full post is here

  1. oldbrew says:

    Nature mag. news says:

    ‘Global warming ‘hiatus’ debate flares up again.
    Researchers now argue that slowdown in warming was real.’

    IIRC they used to argue 17 years was the limit, then a pause had to be taken seriously.
    Now it seems 20 years can go by and it doesn’t matter much.

    Meanwhile models continue to predict levels of warming far in excess of observations 😐

  2. catweazle666 says:

    Ah, just gotta love this settled science!

  3. oldbrew says:

    Some of the people who spent years trying to show the past had little ‘internal variability’ are now touting it as a reason for lack of warming this century. The logic of that is not great is it?

    They also open the door to the idea that whatever warming has occurred was mostly or mainly due to that same factor. In other words their own theory is weakened at least.

  4. Jaime says:

    More smoke and mirrors from Ed and his climate scientist colleagues. Admit something highly unusual has happened, then slowly back-pedal to a point where you can say “it’s no big deal really”. Ed says:

    “Observations should fall outside the simulated spread sporadically because of internal variability – we do not expect the observations to always match the ensemble mean. However, the recent observations are all continuously outside the ±1σ spread of the simulations for a lengthy period, which is obviously unusual. It is also not just global temperatures that have been unusual – the tropical Pacific sea surface temperatures & winds have also behaved well outside the simulated range.

    These analyses all suggest that the early-2000s were indeed ‘particularly unusual’ – so we strongly dispute Lewandowsky et al.’s statement quoted above.”

    So basically, internal variability alone is not sufficient to explain the early 2000s slowdown – which is highly unusual in the observed temperature record. I recall pointing out to Ed a paper which clearly showed that there has been in the modern slowdown – unlike other hiatus periods in the Hadcrut series – a unique and very sharp slowdown in the secular trend. He got grumpy about this and insisted the study was just a model . . . . and man-made aerosols!

    Ed goes on to say:

    “Overall, there is compelling evidence that there has been a temporary slowdown in observed global surface warming, especially when examined relative to our expectations, which can be explained by a combination of factors . . . . This has led to more widespread recognition that modulation by internal variability is large enough to produce a significantly reduced rate of surface temperature increase for a decade or even more — particularly if internal variability is augmented by the externally driven cooling caused by a succession of volcanic eruptions.

    The legacy of this new understanding will certainly outlive the recent warming slowdown.”


    So it is just internal variability, maybe augmented by a volcano or two (or three) and it’s temporary, and by the time we learn more about what’s been going on, the planet will be rapidly warming again anyway! No Ed, it’s not ‘just’ internal variability and volcanic aerosols. Something deeper has been going on. Whatever can it be? Ironically, Ed gives us the clue to answering this question earlier in his text, which he fails to expand upon, hoping perhaps that his readers will fail to notice:

    “Note that there are important issues with the radiative forcings used in CMIP5 (particularly solar & volcanic), which do not necessarily match the real world, especially after 2005”.

    He picks up on the possibility that updated volcanic forcings may explain the “highly unusual” early 2000s slowdown, but completely ignores the possibility that solar forcings may explain some or all of the observed slowdown in the underlying secular trend. Why I wonder? Perhaps because this introduces the very real possibility that, just like internal variability, solar forcings may have contributed significantly to the observed global WARMING since the 1950’s – and thereafter the significant deceleration (some might say the grinding to a halt) of global mean surface temperature rises in the 21st century. If that is the case, the Global Warming Happy Half Hour afforded by the current spike due to El Nino might end very badly for the revelers.

  5. Jaime says:

    Good comment I’ve just noticed from Nic Lewis, pointing out the paper’s misattribution of the 1950s-70s cooling to anthropogenic aerosols and suggesting that volcanic aerosols forcings have been “cherry-picked” over others to explain the current hiatus.

  6. oldbrew says:

    When everything around a theory seems ‘unusual’ – suspect the theory.

  7. oldbrew says:

    The Spectator wades in:

    ‘A new paper in a prestigious journal proves a 15-year hiatus in global warming. Why is it being ignored?’
    – by David Whitehouse

    Answer: inconvenient truth.

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