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Thread: Tree rings can be used to find droughts in the past

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    Default Tree rings can be used to find droughts in the past

    The premise of the article I agree with .... That there is detectable signs of drought in the rings of trees.

    But causality .... not so much so.



    ==============================================
    The secret was in the trees. Humans are making droughts worse
    Doyle Rice, USA TODAY Published 6:30 p.m. ET May 1, 2019 | Updated 9:59 a.m. ET
    May 2, 2019

    https://www.usatoday.com/story/news/...es/3643819002/


    Tree ring data can be used to find droughts as far back as 1400.
    Greenhouse gases caused by humans have been affecting global drought since
    the early 20th century.
    Lead author Kate Marvel, a climate modeler at Goddard and Columbia, said,
    “It’s mind boggling."

    The secret was in the trees.

    Looking at tree rings from ancient trees, scientists in a new study say they've
    finally found the fingerprint of human-caused global warming on drought and
    rainfall patterns worldwide from as far back as 1900.

    Amazingly, tree ring data is an accurate gauge to determine past climates: The
    rings are thinner in years when it's dry and may not grow at all in stressful
    conditions like drought.

    In fact, researchers can use tree ring data to "find" droughts as far back as
    1400, centuries before reliable weather data was available.

    According to NASA, "we now know that greenhouse gases caused by humans have been
    affecting global drought since the early 20th century."

    Climate change, aka global warming, occurs because fossil fuels such as oil, gas
    and coal are burned to power our world. This burning process releases carbon
    dioxide, methane and other greenhouse gases into our atmosphere.

    "The big thing we learned is that climate change started affecting global
    patterns of drought in the early 20th century," said study co-author Benjamin
    Cook of the NASA Goddard Institute for Space Studies and Columbia University’s
    Lamont-Doherty Earth Observatory. "We expect this pattern to keep emerging as
    climate change continues."

    This is the first study to provide historical evidence connecting
    human-generated emissions and drought at near-global scales between 1900 and
    2005.

    Lead author Kate Marvel, a climate modeler at Goddard and Columbia University,
    said, “It’s mind boggling. There is a really clear signal of the effects of
    human greenhouse gases on the hydroclimate.”

    It's also the first time researchers have identified long-term global effects on
    the water supplies for crops and cities around the Earth.

    In a warming world, some regions are expected to get drier, while others will
    get wetter. The study suggests this pattern will continue:

    All the models are projecting that you should see unprecedented drying soon, in
    a lot of places,” Marvel said.

    Many of the areas expected to dry out are centers of farming, and could become
    permanently arid. “The human consequences of this, particularly drying over
    large parts of North America and Eurasia, will likely be severe,” the study
    said.

    The study was published Wednesday in the peer-reviewed British journal Nature.
    -----------------------------------------------------------------------------------
    Article | Published: 01 May 2019
    Twentieth-century hydroclimate changes consistent with human influence

    Kate Marvel, Benjamin I. Cook, Céline J. W. Bonfils, Paul J. Durack, Jason E. Smerdon & A. Park Williams

    https://www.nature.com/articles/s41586-019-1149-8

    Naturevolume 569, pages59–65 (2019)
    Although anthropogenic climate change is expected to have caused large shifts in temperature and rainfall, the detection of human influence on global drought has been complicated by large internal variability and the brevity of observational records. Here we address these challenges using reconstructions of the Palmer drought severity index obtained with data from tree rings that span the past millennium. We show that three distinct periods are identifiable in climate models, observations and reconstructions during the twentieth century. In recent decades (1981 to present), the signal of greenhouse gas forcing is present but not yet detectable at high confidence. Observations and reconstructions differ significantly from an expected pattern of greenhouse gas forcing around mid-century (1950–1975), coinciding with a global increase in aerosol forcing. In the first half of the century (1900–1949), however, a signal of greenhouse-gas-forced change is robustly detectable. Multiple observational datasets and reconstructions using data from tree rings confirm that human activities were probably affecting the worldwide risk of droughts as early as the beginning of the twentieth century.
    Last edited by ramus; 4th May 2019 at 14:26.

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    Default Re: Tree rings can be used to find droughts in the past

    The glacial periods within the Ice Age (in which we have been sitting over a million years) are very dry and cold.
    Trees don't lie. The desiccation in major continents is a clear indication that Ice Age winter is nigh.

    Ref
    http://www.dandebat.dk/eng-klima5.htm

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