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Evidenced-based Sea Level Rise Projections Remain Low
From Paul C. "Chip" Knappenberger and Patrick J. Michaels of Cato.
"When it comes right down to it, the biggest potential threat from a
warming climate is a large and rapid sea level rise. Everything else
that a changing climate may bring we’ve seen before (or at least the
likes of it), recovered from, and are better off for it (i.e., gained
experience, learned lessons, developed new technologies, etc.). In fact,
the more often extreme weather occurs, the more adaptive is our
response (see for example,
decreasing mortality in heat waves). So in that sense, climate change
may hasten our adaptive response and reduce our overall vulnerability to
it.
A large and rapid sea level rise is a bit of a different story—although perhaps not entirely so.
While we do have a large amount of infrastructure (e.g., big cities) in low-lying coastal regions, it is completely wrong to show them underwater in the future—a typical
device used by climate activists. What will happen is that we will act
to protect the most valued portions of that infrastructure, as shown in a
recent report from leading experts (including from the U.S. Environmental Protection Agency) on sea level rise and response.
But, while targeted action will save our big cities, there is still a
lot of real estate that will be lost if sea level rises a large
amount in a short amount of time (say, by more than a meter [a little
more than 3 feet] by the end of the 21st century).
We therefore keep a vigilant eye on sea level rise research. And what
we’ve concluded is that sea level rise by the year 2100 is very likely
to be quite modest, say about 15 inches—an amount that should allay
concerns of a catastrophe. We’ve detailed literature in support of our
conclusions here, there, and elsewhere.
This week, a new paper has come to our attention that further supports our synthesis.
In the journal Quaternary Science Reviews, researchers
Nicolás Young and Jason Briner summarized the extant scientific
literature on the size of the ice sheet covering Greenland during warm
periods in the recent geologic past, with a special emphasis on the
middle Holocene—a multi-millennial period centered some 3,000–4,000
years ago during which the temperatures across Greenland were about
1°–3°C higher than the 20th century average. They note this is similar to conditions projected to occur there by about the year 2100.
What Young and Briner found was that the size of the Greenland ice
sheet—especially the best observed portions covering the west and
southwestern parts of Greenland—during the mid-Holocene was smaller than
it is today—but not by a whole lot. They wrote:
[W]e suggest that despite some degree of inland retreat,
the West and Southwest [Greenland ice sheet] margin remained relatively
stable and close to its current position through the Holocene thermal
maximum.
The implication is that despite a period of warmer-than-present
temperatures in Greenland lasting some 2,000 years, the ice sheet did
not shrink to such an extent as to result in a whole lot of sea level
rise. This is good news as to what to expect from future warming—the
Greenland ice sheet seems pretty stable in the face of rising
temperatures.
This is consistent with the remarkable findings of Dorthe
Dahl-Jensen’s research team concerning the warmest era in the last 1.5
million years or so—the first 6,000 years of the last interglacial
period, known as the Eemian. It began 128,000 years ago.
The ratio of two different isotopes of oxygen (18O/16O)
in air trapped in ice provides an accurate measure of local
temperature, and because snow compacts every year, it’s fairly
straightforward to count backward, year-by-year, as one drills down
through the Greenland icecap. Up until Dahl-Jensen’s report, no one had
gotten completely through the Eemian. And, up until then, it was
thought that temperatures in those 6,000 years were some 2°–4°C warmer
than in the current era.
(Greenland’s temperatures were pretty flat
during the 20th century.) Dahl-Jensen’s work shows that
Greenland was an astounding 8° +/– 4° warmer! Over that 6,000 years,
Greenland lost approximately a quarter of its ice, contributing to 2
meters of sea-level rise.
Young and Briner, along with Dahl-Jensen, provide strong evidence
that Greenland’s ice will be disturbed very little by what humans are
likely to do to the atmosphere. Let’s use the top-end of Young and
Briner’s warming by 2100 (3°C) and jack it up to 5° for the next hundred
years. Then, let’s make the plausible assumption that we haven’t a clue
about society’s energy structure 200 years from now, so we’ll stop
things there and let the warming damp back to 20th century
levels in 500 years. The integrated heat applied to Greenland (we’ll
provide gory details on request) works out to 1,500 degree-years. What
Young and Briner found was that the Holocene maximum provided, on
average, 4,000 degree-years (2,000 years multiplied by 2°), over twice
what humans can contribute. And Dahl-Jensen showed it took a whopping
36,000 degree-years to melt only a quarter of the ice there, 24 times what we can do. In other words, we can’t change the climate enough to ever cause a massive sea level rise from melting Greenland’s ice.
Young and Briner also find that the models tend to overdo the
mid-Holocene ice sheet retreat. Examining a leading ice sheet model
(described by Lecavalier and colleagues), Young and Briner conclude:
The modeled minimum ice sheet in Lecavalier et al. (2014)
at 4 [thousand years ago] equates to a 0.16 [meter] sea-level
contribution, but considering minimal inland retreat of the ice margin
based on geological reconstructions, we suggest that this value may be a
maximum estimate of the [Greenland ice sheet] contribution to sea level
in the middle Holocene.
Lecavalier’s estimate of 0.16 meters equates to 6.3 inches—which
Young and Briner think should represent the worst-case result of 2,000
years of projected end-of-the-century temperatures across Greenland.
This also comports well with the estimates from the United Nations
Intergovernmental Panel on Climate Change (IPCC), which, in its Fifth Assessment Report,
projected the sea level rise from Greenland as being between 0.07 and
0.21 meters (2.8 to 8.3 inches) with a median value of 0.12 meters (4.7
inches) even under its highest greenhouse gas emission scenario.
Like we said, our view that future sea level rise will be modest is
now firmly established by the scientific literature, contrary to
nonscientific alarmist claims."
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