Oceans Make Climate

Discussion in 'Environmental Discussion' started by mojo, May 29, 2015.

  1. mojo

    mojo Senior Member

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    austingreen likes this.
  2. tochatihu

    tochatihu Senior Member

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    Good on you for getting to Nature (the journal) sooner than me. McCarthy's paper deserves a close look.

    doi:10.1038/nature14491

    Here is part of their abstract:

    “The Atlantic overturning circulation is declining8 and the AMO is moving to a negative phase. This may offer a brief respite from the persistent rise of global temperatures4, but in the coupled system we describe, there are compensating effects. In this case, the negative AMO is associated with a continued acceleration of sea-level rise along the northeast coast of the United States9, 10.”

    Published research, and conclusions drawn therefrom by 'others' may not always coincide. If the brief respite means continuing the most recent +0.1 degrees C/decade, instead of the earlier +0.2 degrees C/decade, it would be a gift greatly appreciated. I have not yet read what this study predicts for the future, if in fact they do predict.

    Frequent readers will know that mojo and I agree that ocean dynamics have been a big factor for climate, and the models remain unsatisfying. Perhaps we don't agree about the future, but let's just see how the next few years (or ten) go.
     
  3. tochatihu

    tochatihu Senior Member

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    Having now read McCarthy's entire paper from Nature, I have not found any assertion related to the top post. What did you find in it, mojo?
     
  4. mojo

    mojo Senior Member

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  5. tochatihu

    tochatihu Senior Member

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    Good link for phys.org

    AMO was last negative 1960-1995 (approx). First of those decades had cooling, later was warming. I have no doubt that this (and other ocean dynamics) could work against CO2 forcing. The extent of the effect seems to be unknown so far.
     
  6. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Abstract:

    Decadal variability is a notable feature of the Atlantic Ocean and the climate of the regions it influences. Prominently, this is manifested in the Atlantic Multidecadal Oscillation (AMO) in sea surface temperatures. Positive (negative) phases of the AMO coincide with warmer (colder) North Atlantic sea surface temperatures. The AMO is linked with decadal climate fluctuations, such as Indian and Sahel rainfall1, European summer precipitation2, Atlantic hurricanes3 and variations in global temperatures4. It is widely believed that ocean circulation drives the phase changes of the AMO by controlling ocean heat content5. However, there are no direct observations of ocean circulation of sufficient length to support this, leading to questions about whether the AMO is controlled from another source6. Here we provide observational evidence of the widely hypothesized link between ocean circulation and the AMO. We take a new approach, using sea level along the east coast of the United States to estimate ocean circulation on decadal timescales. We show that ocean circulation responds to the first mode of Atlantic atmospheric forcing, the North Atlantic Oscillation, through circulation changes between the subtropical and subpolar gyres—the intergyre region7. These circulation changes affect the decadal evolution of North Atlantic heat content and, consequently, the phases of the AMO. The Atlantic overturning circulation is declining8 and the AMO is moving to a negative phase. This may offer a brief respite from the persistent rise of global temperatures4, but in the coupled system we describe, there are compensating effects. In this case, the negative AMO is associated with a continued acceleration of sea-level rise along the northeast coast of the United States9, 10

    "Ocean impact on decadal Atlantic climate variability revealed by sea-level observations" Nature 521, 508–510 (28 May 2015) DOI: 10.1038/nature14491
    Using sea level on coast to estimate "AMO", I won't be buying this paper. I'll read it and share my thoughts but even the abstract has holes. No, I'd rather read an 'Argo' based paper first.

    Bob Wilson
     
  7. tochatihu

    tochatihu Senior Member

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    This publication deals with using (GPS constrained) tide gauges to detect AMO status, differently from what has been done before. A bit of the abstract (I quoted above) mentions climate consequences of AMO status.

    In media coverage, the authors are quoted on possible climate consequences, I have no problem with that; I am opposed to muzzling researchers, commentators, anybody.

    But readers here who can't be bothered to read the paper will only have the perspectives posted here. It is about a new way to detect AMO status, as Bob discerned. He found it therefore not interesting, but I do not agree. All of the 'ocean sloshes' may have affected climate, and we should broadly consider ways to assess them.

    If the authors wanted to assess AMO effects on surface T, they would certainly have cited:

    G. R. van der Werf and A. J. Dolman. Impact of the Atlantic Multidecadal Oscillation (AMO) on deriving anthropogenic warming rates from the instrumental temperature record (2014) Earth Syst. Dynam., 5, 375–382. doi:10.5194/esd-5-375-2014

    who found it to be small.

    Oceans have strongly affected climate (which might have been a good title for this thread), but AMO may not be the best candidate during the instrumental temperature record.

    Yet we don't muzzle, and published authors can say anything they want that might attract attention to their work.

    Problems could only arise if 'neutral' websites wrote only about that, and if 'affinity' websites revised the message towards 'the world will soon cool down' or something along those lines.

    To avoid any such misunderstandings, we read the paper. If questions remain, we send them to

    gerard.mccarthy AT noc.ac.uk
    (that email is slightly obfuscated here, against the bots, but y'all can figure it out)

    I hope, and hope mojo agrees, that all research should be interpreted only according to what it has shown.
     
  8. bwilson4web

    bwilson4web BMW i3 and Model 3

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    My concern about this paper is not the accuracy of the tidal gauges but the use of east coast, tidal measurements to infer Atlantic currents. Meanwhile, the Argo network of sea floating instruments plays no part in the abstract:
    [​IMG]
    If I'm going to investigate ocean currents, Argo would be the 'gold standard' augmented by others.

    A second problem is the Atlantic is important for one region, the Atlantic basins. So it is likely to have major effects in the borders (i.e., shores) than a global effect (see above Argo chart.) I am interested in regional effects but some of the boosterism claims are much larger than a region.

    This paper reminds me of the 'Atlantic Conveyer' now called: Thermohaline circulation - Wikipedia, the free encyclopedia

    Past reports were that fresh water melt would shutdown the 'Atlantic Conveyer' leading to colder temperatures in the UK and western Europe. If this paper simply shows the AMO as being part of that system leading to colder temperatures in one region, I would not be surprised . . . or enlightened. But then I used Mr. Google to see if someone might have left a copy of the paper 'in the wild.'

    Source: http://naclim.zmaw.de/fileadmin/user_upload/naclim/Archive/Dissemination/EGU-2015/McCarthy_NA_session_Mon_1145_EGU2015.pdf

    A PowerPoint summary of their approach.

    Source: http://www.aoml.noaa.gov/phod/docs/Smeed_2013.pdf

    Another paper sharing many of the same authors about AMO.

    I appreciate the importance of the AMO current for western Europe, UK, and Ireland. With the AMO shutdown, the predictions are a regional cool down. We'll see.

    In Denial 101x they pointed out simple models with current data are useful for short range predictions. But the global models are able to look at longer range trends within their limitations.

    Bob Wilson
     
    #8 bwilson4web, May 30, 2015
    Last edited: May 30, 2015
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