Climate Disruption Amplifies Atlantic Currents' Contribution to Sea Level
Rise
Saturday, 02 January 2016 00:00 By Dahr Jamail, Truthout | Report
(Photo: Rising Sea via Shutterstock)
Anthropogenic climate disruption (ACD) has progressed to a point where it
is, literally, changing one of the most important ocean circulatory currents
in the world.
In a paper recently published in the journal Geophysical Research Letters,
NASA researchers confirmed that the circulation of the Atlantic meridional
overturning circulation (AMOC) is slowing down. In 2009 and 2010 that
shifting had already been linked to a sudden and extreme five-inch sea level
rise on the East Coast.
While most people have likely never heard of the AMOC, it plays a critical
role in both global climate patterns and sea level rise along the Eastern
Seaboard of the US - and it is being changed for the worse due to our carbon
dioxide emissions.
Before we can fully comprehend the ramifications of what is happening with
this ocean current system, a basic understanding of the AMOC is in order.
"WHEN THE AMOC IS CHANGED, IT HAS SIGNIFICANT IMPACTS ON THE WEATHER IN
EUROPE, ALONG WITH OTHER PLACES."
The AMOC is a flow of warm, salty water that starts in the tropics and runs
northward into the high latitudes, where the air is much colder and extracts
heat from it. The water releases its heat to warm Europe. The water then
cools, which causes it to become denser and sink. The cold water then cycles
back southward, and the circulation continues. The AMOC keeps the United
Kingdom warmer than it typically would be, given the relatively high
latitude of the country. It also plays a role in determining sea level along
the eastern United States.
But the AMOC is receiving massive influxes of cold water from the Greenland
ice sheet, which is now melting in dramatic fashion, according to NASA.
Dr. Thomas Delworth, a research scientist at the National Oceanic and
Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, notes
the direct effect of changes in ocean circulation on weather.
"When the AMOC is changed, it has significant impacts on the weather in
Europe, along with other places," Delworth told Truthout.
One of those impacts that we are already seeing play out dramatically is sea
level rise along the United States' East Coast.
"Recent research links sea level changes to changes in the AMOC," Dr. Gerard
McCarthy, a senior research scientist with the National Oceanography Centre
in the UK, told Truthout. "So, [cities from] Atlantic City up to New York
City and Boston [are] seeing sharp sea level rises due to the overturning
circulation declining. We are seeing this now, absolutely."
McCarthy works on RAPID, a study led by the University of Arizona that
highlights the role of ocean circulation changes that cause extreme sea
level jumps along the northeastern coast of the United States. Earlier in
2014, McCarthy's work showed that a dramatic sea level jump of 128
millimeters (five inches) along this coast was directly linked to an
"unprecedented" drop in the strength of the AMOC during 2009 and 2010.
Delworth is seeing the same thing.
"When you weaken the AMOC, you increase sea level along the northeastern US
coastline," Delworth said. "You get more rapid sea level rise. So a
substantial decline [of the AMOC] over the coming decades adds to sea level
rise that is already happening. So weakening it complicates life along the
East Coast of the US."
Both Delworth and McCarthy think the AMOC will continue to weaken in the
long-term future, due to ACD impacts. The question is only, how much?
Delworth sees the rapidly melting Greenland ice sheet as a critical factor
in determining the extent to which the AMOC will weaken. This is due, in
large part, to the fact that the faster the ice sheet melts, the further the
AMOC will weaken.
More precise scientific instrumentation to measure the AMOC was only put in
place in 2004, so there have only been 11 years of data collected, and
Delworth hopes more measuring capabilities will be available in the near
future.
But even with the data collected thus far, Delworth says there is enough to
have elicited this warning: "It could be less stable than we think."
Hemispheric Implications
The AMOC is known as the "global conveyor belt" because it brings warm water
and temperatures to the eastern US and Europe, and recycles cold water from
northern latitudes back down to the tropics. In this way, it functions as a
weather regulator.
But now that ACD is altering the natural processes that impact the AMOC, the
entire weather system it regulates could begin to break down. When this
happens, Europe's weather will begin to turn dramatically colder, and will
become beset by more extreme storms, both in power and frequency.
"A SIGNIFICANT CHANGE IN THE STRENGTH OF THE AMOC WOULD ALTER WINDS,
TEMPERATURES AND PRECIPITATION PATTERNS AROUND THE GLOBE."
As noted, the portion of the AMOC disruption that is already occurring is
largely due to Greenland dumping massive amounts of cold water into the
Northern Atlantic. This fresh water from Greenland is lighter than
saltwater, so it stays on the surface, preventing saltwater from sinking,
which begins to inhibit the current, slowing it. In the long term, the
current could be shut down altogether, which would lead to dramatic shifts
in global weather patterns, including the possibility of bringing much of
Northern Europe back into an ice age.
"On the long timescales, we expect that circulation to weaken," Delworth
explained. "A prime driver of the circulation is that in the tropics the
water is less dense and warmer and lighter and piles up higher. In the
north, it is denser and sinks, so as we warm the planet, we reduce that
density contrast between the tropics and high latitudes."
Delworth said he expects to see these trends continuing in the coming
decades. Additionally, he predicts a continuation of the trend we are seeing
today of warmer waters from the tropics being pushed further north, hence
contributing further to the melting of Greenland, as a recent study shows is
already happening.
Julienne Stroeve, a senior research scientist at the National Snow and Ice
Data Center in Boulder, Colorado, told Truthout that scientists "believe
this freshwater influx could have profound impacts on the circulation of
ocean water worldwide. Ocean circulation, in turn, is a major driver for
weather patterns, both in the Arctic and around the world."
With an ongoing weakening of the AMOC, Delworth expects us to "see more
likelihood of tropical storms and increasing risk of drought in North
America."
According to Delworth, in monsoon-dependent regions stretching from Africa
to India, the changing AMOC will "move the tropical rain belts further
north, so the Sahel of Africa will see the mean rainfall decrease as those
rain belts move further north as the North Atlantic warms, while a colder
North Atlantic pushes the rain belts further south."
McCarthy expects similar impacts.
"A significant change in the strength of the AMOC would alter winds,
temperatures and precipitation patterns around the globe, with potentially
strong local effects along the east coast of the United States and the west
coast of northern European countries," he said.
Precedent for Large-Scale Changes
Climate predictions generally rely on state-of-the-art models used by the
Intergovernmental Panel on Climate Change - and the models are clear on the
future of ocean circulation.
"Pretty much universally, these models predict that the AMOC is going to be
changed as we move forward," McCarthy said. "Freshwater input by the high
Arctic is impacting it. So a large input of freshwater from Greenland as it
melts is having knock-on implications."
He added that historically, as ice sheets have retreated, as we are now
seeing in Greenland, "they have halted the current and caused ice ages."
Stroeve said that current climate models show the AMOC slowing, but not
stopping completely, during the 21st century, emphasizing that the predicted
changes are nonetheless significant.
Large-scale changes in ocean currents like the AMOC "are not unprecedented,"
she added. "About 12,000 years ago, scientists believe a massive increase in
freshwater influx from melting Arctic ice caused the AMOC to shut down
entirely, contributing to a major shift of earth's climate."
McCarthy expects that we will see "a slow decline of the AMOC," and that
North America will be "one of the main areas where the overturning
circulation impacts the weather, but over multidecadal timescales."
It is challenging to detect long-term slowdowns in the AMOC due to natural
variability and the fact that there are only 11 years of actual measurements
of its circulation, as Delworth noted.
"Over that 11-year period we have measured a decline, but don't know yet if
it's due to variability or climate change," he said.
When it comes to how fast the AMOC is slowed due to ACD impacts, time will
tell. But given the ever-increasing intensity of these impacts - and the
fact that the melting of Greenland only continues to speed up - it seems
likely the future will bring continued dramatic global changes in ocean
circulation.
Copyright, Truthout. May not be reprinted without permission.
DAHR JAMAIL
Dahr Jamail, a Truthout staff reporter, is the author of The Will to Resist:
Soldiers Who Refuse to Fight in Iraq and Afghanistan, (Haymarket Books,
2009), and Beyond the Green Zone: Dispatches From an Unembedded Journalist
in Occupied Iraq, (Haymarket Books, 2007). Jamail reported from Iraq for
more than a year, as well as from Lebanon, Syria, Jordan and Turkey over the
last ten years, and has won the Martha Gellhorn Award for Investigative
Journalism, among other awards.
His third book, The Mass Destruction of Iraq: Why It Is Happening, and Who
Is Responsible, co-written with William Rivers Pitt, is available now on
Amazon. He lives and works in Washington State.
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Climate Disruption Amplifies Atlantic Currents' Contribution to Sea Level
Rise
Saturday, 02 January 2016 00:00 By Dahr Jamail, Truthout | Report
font size Error! Hyperlink reference not valid. Error! Hyperlink
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reference not valid.
(Photo: Rising Sea via Shutterstock)
Anthropogenic climate disruption (ACD) has progressed to a point
where it is, literally, changing one of the most important ocean circulatory
currents in the world.
In a paper recently published in the journal Geophysical Research Letters,
NASA researchers confirmed that the circulation of the Atlantic meridional
overturning circulation (AMOC) is slowing down. In 2009 and 2010 that
shifting had already been linked to a sudden and extreme five-inch sea level
rise on the East Coast.
While most people have likely never heard of the AMOC, it plays a critical
role in both global climate patterns and sea level rise along the Eastern
Seaboard of the US - and it is being changed for the worse due to our carbon
dioxide emissions.
Before we can fully comprehend the ramifications of what is happening with
this ocean current system, a basic understanding of the AMOC is in order.
"When the AMOC is changed, it has significant impacts on the weather in
Europe, along with other places."
The AMOC is a flow of warm, salty water that starts in the tropics and runs
northward into the high latitudes, where the air is much colder and extracts
heat from it. The water releases its heat to warm Europe. The water then
cools, which causes it to become denser and sink. The cold water then cycles
back southward, and the circulation continues. The AMOC keeps the United
Kingdom warmer than it typically would be, given the relatively high
latitude of the country. It also plays a role in determining sea level along
the eastern United States.
But the AMOC is receiving massive influxes of cold water from the Greenland
ice sheet, which is now melting in dramatic fashion, according to NASA.
Dr. Thomas Delworth, a research scientist at the National Oceanic and
Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, notes
the direct effect of changes in ocean circulation on weather.
"When the AMOC is changed, it has significant impacts on the weather in
Europe, along with other places," Delworth told Truthout.
One of those impacts that we are already seeing play out dramatically is sea
level rise along the United States' East Coast.
"Recent research links sea level changes to changes in the AMOC," Dr. Gerard
McCarthy, a senior research scientist with the National Oceanography Centre
in the UK, told Truthout. "So, [cities from] Atlantic City up to New York
City and Boston [are] seeing sharp sea level rises due to the overturning
circulation declining. We are seeing this now, absolutely."
McCarthy works on RAPID, a study led by the University of Arizona that
highlights the role of ocean circulation changes that cause extreme sea
level jumps along the northeastern coast of the United States. Earlier in
2014, McCarthy's work showed that a dramatic sea level jump of 128
millimeters (five inches) along this coast was directly linked to an
"unprecedented" drop in the strength of the AMOC during 2009 and 2010.
Delworth is seeing the same thing.
"When you weaken the AMOC, you increase sea level along the northeastern US
coastline," Delworth said. "You get more rapid sea level rise. So a
substantial decline [of the AMOC] over the coming decades adds to sea level
rise that is already happening. So weakening it complicates life along the
East Coast of the US."
Both Delworth and McCarthy think the AMOC will continue to weaken in the
long-term future, due to ACD impacts. The question is only, how much?
Delworth sees the rapidly melting Greenland ice sheet as a critical factor
in determining the extent to which the AMOC will weaken. This is due, in
large part, to the fact that the faster the ice sheet melts, the further the
AMOC will weaken.
More precise scientific instrumentation to measure the AMOC was only put in
place in 2004, so there have only been 11 years of data collected, and
Delworth hopes more measuring capabilities will be available in the near
future.
But even with the data collected thus far, Delworth says there is enough to
have elicited this warning: "It could be less stable than we think."
Hemispheric Implications
The AMOC is known as the "global conveyor belt" because it brings warm water
and temperatures to the eastern US and Europe, and recycles cold water from
northern latitudes back down to the tropics. In this way, it functions as a
weather regulator.
But now that ACD is altering the natural processes that impact the AMOC, the
entire weather system it regulates could begin to break down. When this
happens, Europe's weather will begin to turn dramatically colder, and will
become beset by more extreme storms, both in power and frequency.
"A significant change in the strength of the AMOC would alter winds,
temperatures and precipitation patterns around the globe."
As noted, the portion of the AMOC disruption that is already occurring is
largely due to Greenland dumping massive amounts of cold water into the
Northern Atlantic. This fresh water from Greenland is lighter than
saltwater, so it stays on the surface, preventing saltwater from sinking,
which begins to inhibit the current, slowing it. In the long term, the
current could be shut down altogether, which would lead to dramatic shifts
in global weather patterns, including the possibility of bringing much of
Northern Europe back into an ice age.
"On the long timescales, we expect that circulation to weaken," Delworth
explained. "A prime driver of the circulation is that in the tropics the
water is less dense and warmer and lighter and piles up higher. In the
north, it is denser and sinks, so as we warm the planet, we reduce that
density contrast between the tropics and high latitudes."
Delworth said he expects to see these trends continuing in the coming
decades. Additionally, he predicts a continuation of the trend we are seeing
today of warmer waters from the tropics being pushed further north, hence
contributing further to the melting of Greenland, as a recent study shows is
already happening.
Julienne Stroeve, a senior research scientist at the National Snow and Ice
Data Center in Boulder, Colorado, told Truthout that scientists "believe
this freshwater influx could have profound impacts on the circulation of
ocean water worldwide. Ocean circulation, in turn, is a major driver for
weather patterns, both in the Arctic and around the world."
With an ongoing weakening of the AMOC, Delworth expects us to "see more
likelihood of tropical storms and increasing risk of drought in North
America."
According to Delworth, in monsoon-dependent regions stretching from Africa
to India, the changing AMOC will "move the tropical rain belts further
north, so the Sahel of Africa will see the mean rainfall decrease as those
rain belts move further north as the North Atlantic warms, while a colder
North Atlantic pushes the rain belts further south."
McCarthy expects similar impacts.
"A significant change in the strength of the AMOC would alter winds,
temperatures and precipitation patterns around the globe, with potentially
strong local effects along the east coast of the United States and the west
coast of northern European countries," he said.
Precedent for Large-Scale Changes
Climate predictions generally rely on state-of-the-art models used by the
Intergovernmental Panel on Climate Change - and the models are clear on the
future of ocean circulation.
"Pretty much universally, these models predict that the AMOC is going to be
changed as we move forward," McCarthy said. "Freshwater input by the high
Arctic is impacting it. So a large input of freshwater from Greenland as it
melts is having knock-on implications."
He added that historically, as ice sheets have retreated, as we are now
seeing in Greenland, "they have halted the current and caused ice ages."
Stroeve said that current climate models show the AMOC slowing, but not
stopping completely, during the 21st century, emphasizing that the predicted
changes are nonetheless significant.
Large-scale changes in ocean currents like the AMOC "are not unprecedented,"
she added. "About 12,000 years ago, scientists believe a massive increase in
freshwater influx from melting Arctic ice caused the AMOC to shut down
entirely, contributing to a major shift of earth's climate."
McCarthy expects that we will see "a slow decline of the AMOC," and that
North America will be "one of the main areas where the overturning
circulation impacts the weather, but over multidecadal timescales."
It is challenging to detect long-term slowdowns in the AMOC due to natural
variability and the fact that there are only 11 years of actual measurements
of its circulation, as Delworth noted.
"Over that 11-year period we have measured a decline, but don't know yet if
it's due to variability or climate change," he said.
When it comes to how fast the AMOC is slowed due to ACD impacts, time will
tell. But given the ever-increasing intensity of these impacts - and the
fact that the melting of Greenland only continues to speed up - it seems
likely the future will bring continued dramatic global changes in ocean
circulation.
Copyright, Truthout. May not be reprinted without permission.
Dahr Jamail
Dahr Jamail, a Truthout staff reporter, is the author of The Will to Resist:
Soldiers Who Refuse to Fight in Iraq and Afghanistan, (Haymarket Books,
2009), and Beyond the Green Zone: Dispatches From an Unembedded Journalist
in Occupied Iraq, (Haymarket Books, 2007). Jamail reported from Iraq for
more than a year, as well as from Lebanon, Syria, Jordan and Turkey over the
last ten years, and has won the Martha Gellhorn Award for Investigative
Journalism, among other awards.
His third book, The Mass Destruction of Iraq: Why It Is Happening, and Who
Is Responsible, co-written with William Rivers Pitt, is available now on
Amazon. He lives and works in Washington State.
Related Stories
There All Along: "Exceptional" Slowdown of the Gulf Stream From Greenland
Melt
By Bruce Melton, Truthout | ReportEl Niño - What It Will Bring This Year and
How It Could Change With Global Warming
By Catherine Gautier, The Conversation | News AnalysisClimate Change 2015:
The Latest Science
By Bruce Melton, Truthout | News Analysis
Show Comments
