From:
david.j.worrell@gmail.com
Antarctic melt accelerates sea level rise
http://tinyurl.com/ycauvlcn
The Union of Concerned Scientists (UCS) recently published a report called 'Underwater', which examined more closely the impact of future sea level rise on coastal cities in the US. The UCS took as their baseline that global mean sea levels would rise
about 2 meters between 2010 and the end of the century — a projection judged as being very likely in several reports published last year.
The UCS report looked at the impact on coastal communities of chronic inundation due to sea level rise — defined as a zone experiencing at least 26
floods a year. By the end of the century, the UCS analysis shows that as many as 2.4 million of today’
s residential properties and about 107,000 commercial properties, worth roughly
$1.07 trillion, would be at risk of chronic flooding.
As several million American coastal residents are forced to move inland, coastal property values collapse. The tax base of coastal towns drops catastrophically—resulting in the dramatic reduction in numerous critical social services and the total
impoverishment and eventual abandonment of many coastal communities.
In the US, Florida and New Jersey are most at risk. Over the next 30 years, roughly 64,000 homes in Florida and 62,000 in New Jersey will be at risk of chronic flooding.
These states are just the worst affected, but the whole of the eastern shoreline of the US and the coast of Atlantic Canada are all hugely at risk—particularly the low lying areas of Nova Scotia.
Only two meters?
A sea level rise of two meters in 2100 now looks like wishful thinking. Recent satellite data from NASA and the European Space Agency, show that ice losses from Antarctica are causing sea levels to rise faster today than any time in the past 25 years.
The rate of melting has risen three fold since 2012.
Sea level rise is essentially caused by two related phenomena: the melting of icesheets and glaciers, and the expansion of ocean water as it warms. It’s the melting bit which is slowly spiralling out of control.
The Greenland and Antarctic icesheets hold absolutely enormous quantities of ice. Together they lock up 99 percent of the world’s fresh water. Literally trillions of tons of ice which — if it all melted away (which it won’t) would raise sea levels
by more than 60 meters, inundate and render uninhabitable most of the islands in the Caribbean and the Pacific, and flood countless American, Canadian, and European coastal communities, driving millions of families inland in search of
higher ground.
The Antarctic is a colossal ice sheet — the largest in the world and about 9 times larger than Greenland’s. Before 2012, ice was being lost at a steady rate of about 76 billion tonnes a year. But since 2012, the amount of ice lost has jumped to
almost 220 tonnes a year. Nearly three times higher.
Most of this loss was from the huge Pine Island and Thwaites glaciers — which
are rapidly retreating due to ocean-induced melting.
More importantly, data from the GRACE satellites show that both ice sheets: Antarctica and Greenland, have undergone an accelerating rate of melting since
2009. The rest of the world’s glaciers — much smaller but still a major factor in global sea
level rise—have been melting since at least 1980.
This acceleration in sea level rise is being matched by other fundamental climate metrics. Consider atmospheric levels of carbon dioxide — the principal greenhouse gas and the major driver of increasing global warming. It’s not breaking news that
global CO2 levels continue to increase — levels are now closing in on 410 ppm: up from about 320 ppm in 1970.
But most people might not be aware that the rate of growth of CO2 concentrations is not steady: it’s increasing. The rise in atmospheric levels of CO2 is accelerating — just like the melting of the Greenland and Antarctic icesheets and the majority
of glaciers worldwide.
Although there was a slowdown in the decade from 1990 to 1999, the rate of increase picked up where it left off in the decade that followed. The current decade from 2010 looks set to continue the long term trend — although we won’t know for sure
until we get to 2020.
The take-away here is that we live on a planet where the changing climate is not business-as-usual. The fundamental geophysical factors that drive global warming, climate change, and sea level rise are accelerating.
***
A trillion dollars in lost property may be the least of our problems.
That estimate is based on a 2-meter rise. It may end up being a lot more.
And apparently, we are already seriously slowing down the North Atlantic "conveyer belt".
***
New Scientist
FEATURE 1 August 2018
Extreme heat: Why its origins could lie deep in the Atlantic
Swathes of the northern hemisphere are smashing temperature records.
Could it be because we’ve broken the ocean currents that stabilise our weather?
By Michael Marshall
http://tinyurl.com/y9mfa6sh
Excerpts:
THE northern hemisphere is roasting. Greece is battling lethal wildfires, and even the UK’s weather has been so hot and dry that record-breaking fires have
broken out in its usually damp climes. In Oman on the Arabian peninsula, thermometers registered
the hottest night on record anywhere on Earth on 28 June: the temperature never
fell below 42.6°C.
Climatologists have been quick to point out that extremes are to be expected in
a warming world. But there may be more to it than that. The ongoing European heatwave may have been made worse by a consequence of climate change rearing its head after
decades of Cassandra-like warnings. For more than a century, the oceans have been changing right under our noses, as a powerful Atlantic current has weakened. The result, it seems increasingly likely, is more extremes of both heat and cold on both sides
of the Atlantic – and the prospect of even more dramatic switches to come.
The object of concern is the Atlantic ocean conveyor belt, also known as the Atlantic meridional overturning circulation or AMOC. It is part of a global network of currents that push all the water in the oceans up and down the length, breadth and depth
of the various interconnected basins. From the tropical Atlantic off the coast of South America, warm surface water flows north towards Greenland and western Europe, bringing with it an uncharacteristically warm climate, carried by the Gulf Stream.
The water becomes saltier as it evaporates, and cools as it moves north. Both factors make it denser so that by the time it reaches the Norwegian and Greenland seas, it has sunk by 2 or 3 kilometres. From there, it makes its way back south at depth (see
map). Changes in salinity and temperature in the north Atlantic drive the entire set-up, which has caused concerns that chaos might ensue if anything changes in that region.
Atlantic conveyor belt
In 1961 oceanographer Henry Stommel showed that, in theory, these currents could exist in one of two states, with water flowing in opposite directions depending on the balance of temperature and density. At the time, this was just
a curiosity. In the
1980s, growing evidence that greenhouse gas emissions were heating up the planet caused concern that much of the Arctic’s ice would melt, including Greenland’s ice sheet. Climatologists warned that fresh water pouring into the north Atlantic would
slow the natural sinking of AMOC waters, and put a brake on one end of the conveyor belt.
Then came the finding that the Atlantic conveyor belt had stalled during the last ice age, between 110,000 and 12,000 years ago, when much of northern Eurasia and North America were covered in ice. Battalions of icebergs periodically broke off and went
marauding around the Atlantic. Spiked by fresh water, the AMOC weakened.
“Because there were similarities between what happened then and what we were predicting in the future, that caused concern that the AMOC could weaken in the
future,” says David Thornalley at University College London.
In reality, a total collapse would probably take decades or a century. The most
likely effect would be extreme sea level rise on the US eastern seaboard, extreme heat in Europe and chaotic monsoons in Africa and Asia.
In 2004, Harry Bryden of the National Oceanography Centre in Southampton, UK, and his colleagues claimed that the current had recently slowed by 30 per cent.
Using data collected on five research cruises that crossed the Atlantic between
1957 and 2004,
they found that the amount of heat being transported north had dropped significantly. A media storm ensued, but Bryden’s evidence was sparse. The main issue was that the current’s strength might vary naturally, from day to day, season to season or
decade to decade. Bryden’s study could have mistaken a temporary wobble for a
long-term decline. At the same time, climate models suggested that his slowdown
was, in fact, down to natural variability.
Nevertheless, researchers started keeping a closer eye on trends. In 2004, instruments were deployed to monitor the AMOC. One of these, the RAPID array, relies on an undersea cable running beneath the current, from Florida to the Bahamas. Because the
AMOC carries lots of salt, it contains charged ions, and their movement sets up
a voltage in the cable, which can be used to estimate the current’s strength.
Later, a second array was installed from Labrador in Canada to Scotland.
Thanks to RAPID, we now have 14 years of continuous data. “It basically showed that the AMOC has huge variability,” says Laura Jackson at the UK Met Office. Bryden himself co-authored a study of the first four years of RAPID data, showing that the
current is strongest in the northern hemisphere autumn and weakest in spring. In it he acknowledged that seasonal changes “might have accounted for a large
part of the inferred slowdown”.
This comforting conclusion was reinforced by further data. In the winter of 2009-10, the AMOC weakened by 30 per cent, but recovered the following year. The belief is that strong surface winds blowing against the current might have put the brakes on. In
this light, Jackson says, many people concluded that the original finding was “a fluke”.
Things began shifting three years ago. To get around the variability problem, researchers sought data spanning even longer timescales. Stefan Rahmstorf at the Potsdam Institute for Climate Impact Research in Germany and his colleagues
looked at how sea
surface temperatures varied worldwide from 1901 to 2013. Mostly, they found a warming trend, but in the north Atlantic, a blob-shaped region had cooled, particularly since 1970. Tellingly, climate models suggest that such a cool spot is a sign of a weak
AMOC.
Just months after Rahmstorf’s study was published in March 2015, Europe was hit by a scorching summer that broke a number of temperature records. The following year, Aurélie Duchez of the National Oceanography Centre in Southampton, UK, showed it was
linked to the cold spot in the north Atlantic. In the past, similar heatwaves were more likely if the cold spot was more intense. We now have evidence that this mechanism has operated for millennia.
It seems the AMOC moderates Europe’s weather, reducing both winter storms and
summer heatwaves. Losing it unleashes both. A related possibility is that the recent spate of extremely cold winters and snowstorms in the eastern US might be linked to the
current’s weakening. The idea is that the cold patch in the north Atlantic affects the jet streams over North America, unleashing blizzard after blizzard.
Back in Rahmstorf’s team, there was another significant finding. Michael Mann
of Penn State University had previously estimated how surface temperatures had changed since AD 900, using records contained in tree rings, marine sediments, ice cores and
corals. In that data, the team found no previous signs of a north Atlantic cool
spot. They concluded that the AMOC slowdown since 1970 was “an unprecedented event in the past millennium”.
“When that came out it was quite controversial,” says Jackson. Some questioned whether the cold blob might simply have been caused by something else.
That looks increasingly unlikely. For one thing, it turns out that the older climate models – the ones that had suggested the AMOC was stable during the 20th century – were probably biased towards producing a stable current. For example, Wei Liu of
the Scripps Institution of Oceanography in California showed last year that the
models don’t capture how salt moves around the oceans. When this issue was resolved, the simulated AMOC became more prone to collapse. Better models have shown that the
current can be pushed into an “off” state by fresh water – coming from a melting Arctic, for instance – and will then stay off for more than 400 years.
[Uh oh... if we mess up and turn it off it could stay off for 400 years...]
Earlier this year, three studies offered critical evidence that a slowdown is already underway. The first was led by Marilena Oltmanns at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany. She and her colleagues focused on the Irminger Sea
south of Greenland from 2002 to 2014. They found it to be unusually warm and low in salt for several summers, particularly 2010 – exactly the conditions that would weaken the AMOC. What’s more, the winters that followed were so mild that the water
never cooled enough to sink properly. More often than not, a quarter of the fresh water was still there as spring broke, suggesting the convection current wasn’t working as it should.
Then in April, Rahmstorf returned to the fray, armed with better evidence that the north Atlantic cool blob really was a signature of a weak current. His team
also reconstructed how the current had changed from 1870 to 2016, and showed that it had
weakened by 15 percent since the middle of the 20th century and, after a brief recovery in the 1990s, had been declining steadily throughout the 21st century.
Finally, Thornalley and his colleagues examined Rahmstorf’s claim that the weakening was bigger than anything in the past 1000 years. They focused on one part of the current: the deep western boundary current or DWBC, which carries the cold waters back
south.
[continued in next message]
--- SoupGate-Win32 v1.05
* Origin: www.darkrealms.ca (1:229/2)
