[Vision2020] PNAS 2-22-16: Study Reveals Stunning Acceleration of Sea Level Rise, Potential 4 ft., This Century

Ted Moffett starbliss at gmail.com
Thu Feb 25 19:40:30 PST 2016

Article just published in the Proceedings of the National Academy of
Sciences is at second link below, with an article from Climate Central
about this article lower down.  The 4 ft. sea level rise
potential by the end of this century is mentioned in the Climate Central
article, based on a business as usual scenario, with the global economy
continuing to be primarily fossil fuel powered.  And for long term time
scales, sea level rise from anthropogenic global warming could continue for
centuries, as the first reference below indicates.  Global warming has the
potential to remain a major problem for many generations in the future:

Sea level rise over the next 2000 years
Posted on 17/07/2013
Bethan Davies <http://www.antarcticglaciers.org/author/bethan/>

A new paper by Levermann et al. in PNAS
<http://www.pnas.org/content/early/2013/07/10/1219414110>uses the record of
past rates of sea level rise from palaeo archives and numerical computer
models to understand how much sea level rise we can expect per degree of
warming in the future. These data suggest that we can expect a global sea
level rise of *2.3 m per 1°C of warming within the next 2000 years*: well
within societal timeframes. A 2°C of warming would result in a global sea
level rise of 4.8 m within 2000 years. This would inundate many coastal
cities in Europe alone, and cause untold economic and societal damage.

"Temperature-driven global sea-level variability in the Common Era"



Study Reveals Stunning Acceleration of Sea Level Rise


*Published:* February 22nd, 2016

By John Upton

The oceans have heaved up and down as world temperatures have waxed and
waned, but as new research tracking the past 2,800 years shows, never
during that time did the seas rise as sharply or as suddenly as has been
the case during the last century.

The new study, the culmination of a decade of work by three teams of
farflung scientists, has charted what they called an “acceleration” in sea
level rise that’s triggering and worsening flooding in coastlines around
the world.

The findings also warn of much worse to come.

The scientists reported in a paper published Monday
<http://www.pnas.org/cgi/doi/10.1073/pnas.1517056113> in Proceedings of the
National Academy of Sciences that they have greater than 95 percent
certainty that at least half of more than 5 inches of sea level rise they
detected during the 20th century was directly caused by global warming.


“During the past millennia, sea level has never risen nearly as fast as
during the last century,” said Stefan Rahmstorf
<http://www.pik-potsdam.de/~stefan/>, a physics professor at Potsdam
University in Germany, one of 10 authors of the paper. “That was to be
expected, since global warming inevitably leads to rising seas.”

By trapping heat, rising concentrations of atmospheric pollution are
causing glaciers and ice sheets to melt into seas, lifting high tides ever

Globally, average temperatures have risen about 1°C
<http://www.climatecentral.org/news/the-world-is-halfway-to-2c-19663> (nearly
2°F) since the 1800s. Last year was the hottest recorded
easily surpassing the mark set one year earlier
<http://www.climatecentral.org/news/record-2014-hottest-year-18502>. The
expansion of warming ocean water was blamed in a recent study
about half of sea level rise during the past decade.

Changes in sea level vary around the world and over time, because of the
effects of ocean cycles, volcanic eruptions and other phenomenon. But the
hastening pace of sea level rise is being caused by climate change.

“The new sea level data confirm once again just how unusual the age of
modern global warming, due to our greenhouse gas emissions, is,” Rahmstorf
said. “They also demonstrate that one of the most dangerous impacts of
global warming, namely rising seas, is well underway.”

Were it not for the effects of global warming, the researchers concluded
that sea levels might actually have fallen during the 20th century. At the
very least, they would have risen far less than was actually the case.

A report published by Climate Central on Monday, the result of an analysis
based in part on the findings in Monday’s paper, concluded that climate
change was to blame for three quarters of the coastal floods recorded in
the U.S. from 2005 to 2014, mostly high tide floods. That was up from less
than half of floods in the 1950s.

“I think this is really a first placing of human fingerprints on coastal
floods, and thousands of them,” said Ben Strauss
<https://www.climatecentral.org/what-we-do/people/ben_strauss>, vice
president for sea level and climate impacts at Climate Central. Strauss led
the analysis, which also involved government and academic researchers.

Governments and communities have been slow to respond to the crisis of
rising seas, though efforts to adapt to the changes underway are now being
planned around the world.

“There’s a definite recognition among people who weren’t talking about sea
level rise 5 years ago that it’s something to be concerned about,” said Laura
Tam <http://www.spur.org/about/staff/laura-tam>, a policy director at SPUR,
which is an urban planning think-tank based in San Francisco. “And
something that needs to be planned for.”

A high-profile effort to track long-term changes in sea levels was based on
analysis of sediment layers at a single location in North Carolina. Published
in 2011 <http://www.pnas.org/content/108/27/11017.abstract>, that study
produced a chart of sea levels that bounced up and down over time, changing
with global temperatures, and then ticked sharply upward as
industrialization triggered global warming.

“North Carolina basically showed us that this could be done,” said Andrew
Kemp <http://eos.tufts.edu/people/kemp.htm>, a sea level scientist at
Tuft’s University. He was a co-author of both Monday’s paper and the paper
published in 2011.

Monday’s paper combined the data from North Carolina with similar analyses
from 23 other locations around the world plus data from tide gauges.

Rob DeConto <http://www.geo.umass.edu/faculty/deconto/Site/Home.html>, a
professor at UMass Amherst who researches prehistoric climates, and who was
not involved with the study, described the report as a “nice job” that
“used a lot more data than anybody else has used in a study like this.”
RELATED *The Human Fingerprints on Coastal Floods
*Images Show Impact of Sea Level Rise on Global Icons
*What Does U.S. Look Like With 10 Feet of Sea Level Rise?

The analysis goes further than explaining historical sea level rise. It
includes worrying projections for the future.

By extending their findings to future scenarios, the scientists showed that
the amount of land that could be inundated in the coming years will depend
heavily on whether humanity succeeds in slashing pollution from fuel
burning, deforestation and farming.

The Paris Agreement negotiated in December
to do just that, with nations agreeing to take voluntary steps to reduce
the amount of pollution they release after 2020. It could take decades,
though, before that untested approach is revealed to have been a success, a
failure, or something in between.

Even If humans quickly stop polluting the atmosphere, potentially keeping a
global temperature rise to well below 2°C (3.8°F) compared with
preindustrial times — a major goal of the Paris climate agreement — seas
may still rise by an additional 9 inches to 2 feet this century, the study
concluded. That would trigger serious flooding in some areas, and worsen it
in others.

Under the worst-case scenario investigated, if pollution continues
unabated, and if seas respond to ongoing warming by rising at the fastest
rates considered likely, sea levels could rise more than 4 feet this
century alone, wiping out coastal infrastructure and driving communities


The problem would be made far worse if the Antarctic or Greenland ice
sheets collapse — something that’s difficult to forecast.

Their projections for future sea level rise were similar to those published
in 2013 <https://www.ipcc.ch/report/ar5/wg1/> by scientists convened by the
United Nations, following the Intergovernmental Panel on Climate Change’s most
recent assessment
climate science.

They also closely matched projections that were coincidentally published in
a separate paper <http://www.pnas.org/cgi/doi/10.1073/pnas.1500515113> in
the same journal on Monday.

The similarity of the other papers’ projections “strengthens the
confidence” in the findings, said Robert Kopp <http://www.bobkopp.net/>, a
Rutgers University climate scientist who led the analysis.

The convergence of the findings in Monday’s papers was a “nice result,”
said Matthias Mengel <http://www.pik-potsdam.de/~mengel/>, a researcher at
at Potsdam University who coauthored the other sea level rise study
released Monday. He led a team of sea level scientists who took a different
approach than Kopp’s team to projecting future sea levels.

Mengel’s team projected future sea levels by combining the results of
models that anticipate changes to icebergs, ice sheets and ocean expansion
in the years ahead, and used those findings to predict sea levels.

For years, different approaches to projecting future sea level rise have
arrived at different results, but the gap has recently been closing, which
Mengel described as “a really good sign for sea level science” — even if
it’s ominous news for humanity.


Vision2020 Post: Ted Moffett
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