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 user 2007-07-25 at 11:35:00 am Views: 38
  • #18453

    Humans ‘affect global rainfall’

    Human-induced climate change has affected global rainfall patterns over the 20th Century, a study suggests.

    Researchers said changes to the climate had led to an increase in
    annual average rainfall in the mid-latitudes of the Northern

    But while Canada, Russia and northern Europe had become
    wetter, India and parts of Africa had become drier, the team of
    scientists added.

    The findings will be published in the scientific journal Nature on Thursday.

    Climate models have, for a number of years, suggested that human
    activity has led to changes to the distribution of rain and snow across
    the globe.

    However, the computer models have been unable to
    pinpoint the extent of our influence, partly because drying in some
    regions have cancelled out moistening in others.

    Making the link

    The scientists from Canada, Japan, the UK and US used the patterns of
    the changes in different latitude bands instead of the global average.

    While our study shows a human influence on rainfall at the global
    scale, the role of human influence in the UK flooding remains uncertain

    Dr Nathan Gillett,

    Research co-author

    They compared monthly precipitation observations from 1925-1999 to
    those generated by complex computer models to see if they could
    identify if human activity was affecting rainfall patterns.

    “We show that anthropogenic forcing has had a
    detectable influence on observed changes in average precipitation
    within latitudinal bands,” the researchers wrote in the paper.

    “These changes cannot be explained by internal climate variability or natural forcing.”

    The team estimated that human activity, such as burning fossil fuels,
    was likely to have led to a 62mm increase in the annual precipitation
    trend over the past century over land areas located 40-70 degrees
    north, which includes Canada, northern Europe and Russia.

    They also suggested the increase of greenhouse gases
    and sulphate aerosols in the atmosphere had contributed a 82mm increase
    in the southern tropics and subtropics (0-30 degrees south), and a 98mm
    decrease in precipitation in the northern tropics (0-30 degrees north).

    They added that natural factors, such as volcanic
    eruptions, had contributed to shifts in the global rainfall patterns
    but to a much lesser extent.

    One of the paper’s co-authors, Nathan Gillett of the
    Climatic Research Unit at the University of East Anglia, UK, said the
    team’s findings helped clear up any uncertainty.

    “This study shows that there has been a significant
    human effect on global rainfall patterns, with human influence causing
    a decrease in rainfall in some regions, and an increase in rainfall in

    However, Dr Gillett said it was not possible to make a
    direct link between the recent floods in the UK and human-induced
    climate change.

    “While our study shows a human influence on rainfall at
    the global scale, the role of human influence in the UK flooding
    remains uncertain.

    “Climate models generally predict that the UK will become wetter in winter and drier in summer,” he explained.

    “In the UK we have seen a trend towards more extreme rainfall in the winter but no clear trend in summer extreme rainfall.”