Global warming is amplifying our water cycle - and it's happening much
faster than we expected
Date:
February 23, 2022
Source:
University of New South Wales
Summary:
A research team has used changing patterns of salt in the ocean
to estimate that between 1970 and 2014, at least two times more
freshwater shifted from the equator to the poles than our climate
models predicted - - giving us insights about how the global water
cycle is amplifying as a whole.
FULL STORY ==========================================================================
The global water cycle -- that is, the constant movement of freshwater
between the clouds, land and the ocean -- plays an important role in
our daily lives.
This delicate system transports water from the ocean to the land,
helping to make our environment habitable and soil fertile.
==========================================================================
But rising global temperatures have been making this system more
extreme: water is moving away from dry regions towards wet regions,
causing droughts to worsen in parts of the globe, while intensifying
rainfall events and flooding in others. In other words, wet areas are
getting wetter, and dry areas are getting drier.
Up until now, changes to the cycle have been difficult to directly
observe, with around 80 per cent of global rainfall and evaporation
happening over the ocean.
But a new UNSW-led study, published today in Nature, has used changing
patterns of salt in the ocean to estimate how much ocean freshwater has
moved from the equator to the poles since 1970. The findings show that
between two and four times more freshwater has moved than climate models anticipated -- giving us insights about how the global water cycle is amplifying as a whole.
"We already knew from previous work that the global water cycle was intensifying," says lead author of the study Dr Taimoor Sohail, a
mathematician and postdoctoral research associate at UNSW Science. "We
just didn't know by how much.
"The movement of freshwater from warm to cold areas forms the lion's share
of water transport. Our findings paint a picture of the larger changes happening in the global water cycle." The team reached their findings
by analysing observations from three historical data sets covering the
period 1970-2014.
==========================================================================
But instead of focusing on direct rainfall observations -- which can
be hard to measure across the ocean -- they focused on a more unusual
aspect: how salty the water was in each ocean area.
"In warmer regions, evaporation removes fresh water from the ocean
leaving salt behind, making the ocean saltier," says co-author Jan Zika,
an associate professor in the UNSW School of Mathematics and Statistics.
"The water cycle takes that fresh water to colder regions where it falls
as rain, diluting the ocean and making it less salty." In other words,
the water cycle leaves a signature on the ocean salt pattern - - and by measuring these patterns, researchers can trace how the cycle changes
over time.
The team estimate that between 1970 and 2014, an extra 46,000-77,000
cubic kilometres of freshwater was transported from the equator to the
poles than expected -- that's around 18-30 centimetres of freshwater
from tropical and sub-tropical regions, or roughly 123 times the water
in Sydney Harbour.
========================================================================== "Changes to the water cycle can have a critical impact on infrastructure, agriculture, and biodiversity," says Dr Sohail. "It's therefore important
to understand the way the climate change is impacting the water cycle
now and into the future.
"This finding gives us an idea of how much this limb of the water cycle
is changing, and can help us improve future climate change models."
Improving future projections When Dr Sohail and the team compared their findings to 20 different climate models, they found that all the models
had underestimated the actual change in warm-cold freshwater transfer.
Dr Sohail says the findings could mean we're underestimating the impacts
of climate change on rainfall.
"Findings like ours are how we improve these models," says Dr Sohail.
"Each new generation of modelling adapts past models with real data,
finding areas that we can improve upon in future models. This is a
natural evolution in climate modelling." Scientists are now using the
sixth generation of climate modelling (called the Sixth Climate Model Intercomparison Project, or 'CMIP6'), which incorporated updates from
the fifth generation.
This newest finding is a demonstration of the scientific process at work
-- and could help improve future estimates.
"Establishing the change in warm-to-cold freshwater transport means
we can move forward and continue to make these important projections
about how climate change is likely to impact our global water cycle,"
says Dr Sohail.
"In 10 or 20 years from now, scientists can use this reference
to find out how much these patterns are further changing over time." ========================================================================== Story Source: Materials provided by
University_of_New_South_Wales. Original written by Sherry Landow. Note:
Content may be edited for style and length.
========================================================================== Journal Reference:
1. Taimoor Sohail, Jan D. Zika, Damien B. Irving, John
A. Church. Observed
poleward freshwater transport since 1970. Nature, 2022; 602 (7898):
617 DOI: 10.1038/s41586-021-04370-w ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/02/220223111230.htm
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