• New ocean temperature data help scientis

    From ScienceDaily@1:317/3 to All on Tue Sep 14 21:30:36 2021
    New ocean temperature data help scientists make their hot predictions


    Date:
    September 14, 2021
    Source:
    University of New South Wales
    Summary:
    So many climate models, so little time ... A new way of measuring
    ocean temperatures helps scientists sort the likely from unlikely
    scenarios of global warming.



    FULL STORY ========================================================================== We've heard that rising temperatures will lead to rising sea levels,
    but what many may not realise is that most of the increase in energy in
    the climate system is occurring in the ocean.


    ==========================================================================
    Now a study from UNSW Sydney and CSIRO researchers has shown that a
    relatively new ocean temperature measuring program -- the Argo system
    of profiling floats -- can help tell us which climate modelling for the
    21st century we should be paying attention to the most.

    Professor John Church from UNSW's Climate Change Research Centre in
    the School of Biological, Earth and Environmental Sciences says the
    study published today in Nature Climate Change is an attempt to narrow
    the projected range of future ocean temperature rises to the end of the
    21st century using model simulations that are most consistent with the
    Argo's findings in the years 2005 to 2019.

    "The models that projected very high absorption of heat by the ocean
    by 2100 also have unrealistically high ocean absorption over the Argo
    period of measurement," Prof. Church says.

    "Likewise, there are models with lower heat absorption in the future
    that also don't correspond to the Argo data. So we have effectively used
    the Argo observations to say, 'which of these models best agree with
    the observations and therefore constrain projections for the future?'"
    Named after the boat which Greek mythological hero Jason travelled on in
    search of the golden fleece, the Argo floats are loaded with high-tech equipment that measures ocean temperatures to depths of up to 2000 metres.



    ==========================================================================
    Each Argo float sends measurements to satellites which then beams the
    results to analysis centres around the world. There are more than 3500
    floats dispersed around the globe, with the bulk of them managed by the
    US (more than 2000) while Australia accounts for the next highest number
    of floats, numbering 317.

    Prof. Church says the Argo floats offer a new level of accuracy in
    temperature measurement. Not only are the high-tech instruments more
    reliable than in the past, but the coverage of the planet's oceans is
    so much more thorough.

    "Previously we depended on research ships making very high accuracy measurements, but only in very restricted areas. Or we would get merchant
    ships to drop expendable instruments into the water which gave better
    coverage, but with much less accurate instruments.

    "Using these approaches, there were much larger gaps in the Southern Ocean because these waters were less trafficked." The ubiquity of the Argo
    floats offers unprecedented real-time monitoring of ocean temperatures
    that will help oceanographers and climate scientists constrain their
    climate projections based on this higher resolution and accuracy of data.



    ==========================================================================
    The full story One of the takeaways from the team's analysis of the Argo
    data is that land and air temperatures only tell part of the story about
    the planet's overall heat absorption. Prof. Church says the apparent
    stability of temperatures in the early 21st century did not correspond
    with the Argo's recording of sea temperatures in the same period.

    "More than 90 per cent of the energy trapped by greenhouse gases is
    stored in the ocean and only about 1 per cent in the warming atmosphere,"
    he says.

    "In the first decade of this century, average surface temperature didn't increase that much. And it created a lot of room for climate sceptics to
    say 'what climate change?'. But throughout that period, oceans continued
    to take up heat -- and this is where the 90 per cent of the energy in
    the ocean versus the 1 per cent in the atmosphere becomes critically
    important in the total climate system.

    "The climate system was still increasing its overall heat content over
    this period." Climate forecasts It turns out that the projections
    of rising air and sea temperatures by some models in a recent set of
    modelling in the Coupled Model Intercomparison Project are warming
    too rapidly.

    The models in CMIP5, which was completed from 2010 to 2014, fits in with
    the Argo observations more closely than CMIP6, which was only recently completed.

    "Some of the 28 CMIP6 models we used were more sensitive to greenhouse
    gases for their projections," Prof. Church says.

    "Projections of climate change to the end of the century all take
    into account the effects of greenhouse gas emissions which are already responsible for much of the increased temperatures we've seen in the
    20th and early 21st centuries.

    "Even if we take strong steps now to limit emissions to the upper
    bound of the Paris Agreement target of 2oC global surface warming,
    ocean temperatures are still projected to rise five to nine times the
    observed warming by 2081-2100, with 8 to 14cm rise in sea levels from the expansion of warmed ocean waters alone." With no concerted efforts to
    rein in emissions, oceans are set to warm by 11 to 15 times the warming observed by Argo in 2005-2019, with sea levels projected to rise 17 to
    26 cm from the expansion of warmed ocean waters alone, and further rises
    from the addition of water to the ocean from glaciers and ice sheets.

    Prof. Church says the Argo data has given scientists much more solid
    figures to work with when making projections about warming. In fact,
    the likely range of the constrained projections using the Argo data is
    17 per cent narrower than the IPCC's Sixth Assessment Report.

    "While a longer Argo observational period will allow us to further
    tighten the range of projected ocean warming and sea level rise, the Argo observations and the climate model projections already highlight the need
    to urgently and very significantly mitigate our greenhouse gas emissions
    if we are to avoid dangerous impacts of ocean warming and sea level rise." ========================================================================== Story Source: Materials provided by
    University_of_New_South_Wales. Original written by Lachlan Gilbert. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Kewei Lyu, Xuebin Zhang, John A. Church. Projected ocean warming
    constrained by the ocean observational record. Nature Climate
    Change, 2021; DOI: 10.1038/s41558-021-01151-1 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2021/09/210914100056.htm

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