Guest “For once it’s not worse than previously thought” by David Middleton
But it’s still catastrophic… Because models…
Some Past Sea Levels May Not Have Been as High as Thought, Says Study of Rising and Sinking Landmasses
But Even Reduced Estimates, If Applied to Today, Would Be Catastrophic
BY KEVIN KRAJICK | AUGUST 9, 2021
One of the current mysteries of climate science surrounds the widely accepted evidence that during the planet’s most recent past natural warm period, about 128,000 to 117,000 years ago, global sea levels peaked as high as 6 to 9 meters (20 or 30 feet) higher than today. And, during that so-called last interglacial, temperatures were just 1or 2 degrees C (1.8 to 3.6 F) warmer than those of preindustrial times—marks we may surpass by century’s end, if not sooner. Such a deluge could have been produced only by collapses of the Greenland and/or Antarctic ice sheets. If that happens now, it will drown much of the human world. Yet, at least so far, models of future sea level rise generally hover around a meter or so within the next 100 years. What are we missing, and how much should it scare us?
In a new study, a team at Columbia University’s Lamont-Doherty Earth Observatory believes they have an answer: They say that researchers examining signs of past sea levels along various coasts may have failed to accurately correct for long-term ups and downs of the land itself. Based on newly sophisticated measurements made across the Bahamas along with new methods of analyzing data, the researchers produced lower—though still daunting—estimates for the last interglacial. They say seas peaked at least 1.2 meters (4 feet) higher than today—roughly in line with most current models for the next 100 years of so.
They combined these findings with hundreds of different models of how glacial isostatic rebound could have traveled through the Earth, and converted the calculations into global sea levels. This produced the new, lower estimates.
This is unmitigted horst schist:
They say seas peaked at least 1.2 meters (4 feet) higher than today—roughly in line with most current models for the next 100 years of so.
Sea level reconstructions over the past 100-200 years show sea level rising at 1.6-1.9 mm/yr.
Total sea level rise over that period of time is about the length of an Estwing rock pick
J14 starts 60 years earlier than CW11, capturing the falling sea level at the end of neoglaciation and the Little Ice Age. We can see that J14 and CW11 match up pretty well from 1880-1930 and then again from about 1993 onward; but they are very different from 1930-1993. J14 exhibits an acceleration to 3.2 mm/yr from 1929-1963 and then a deceleration to less than 1 mm/yr from 1963-1993, after which it accelerates back to about 3.2 mm/yr.
Jevrejeva et al., 2008 (J08) and Jevrejeva et al., 2014 (J14) indicate that the acceleration, to the extent there is one, started 150-200 years ago, consistent with the end of neoglaciation and that a quasi-periodic fluctuation (~60-yr cycle) is present. Church & White, 2006 (CW06) and Church & White, 2011 (CW11) also note the 19th Century acceleration; but also assert a more recent acceleration, presumably due to anthropogenic global warming. This SLR acceleration is, at worst, innocuous.
If this acceleration was maintained through the 21st century, sea level in 2100 would be 310 ± 30 mm higher than in 1990, overlapping with the central range of projections in the Intergovernmental Panel on Climate Change Third Assessment Report (IPCC TAR) [Church et al., 2001].
310 mm from 1990-2100 is less than 3 mm/yr… Not much of an acceleration and a far cry from being 1.2 m and “roughly in line with most current models for the next 100 years of so.”
Short of Doctor Evil suddenly melting the Greenland ice sheet with a “space laser,” it would be physically impossible for sea level to rise another 1.2 m over “the next 100 years of so.”
For sea level to rise by 850 mm by the end of this century, it would have to accelerate to a rate of ~20 mm/yr from 2081-2100. This is nearly twice the rate of the Holocene Transgression.
Sea level rose by about 100 m during the Holocene Trangression.
That catastrophic sea level rise, including the Meltwater Pulse 1A boogieman, occurred at a time when Earth had a lot more ice to melt than it does now.
Fun with sea level
Here’s J14 plotted at the same vertical scale as the Statue of Liberty…
Church, J. A., and White, N. J. ( 2006). “A 20th century acceleration in global sea‐level rise”. Geophys. Res. Lett., 33, L01602, doi:10.1029/2005GL024826.
Church, J.A., White, N.J., 2011. “Sea-level rise from the late 19th to the early 21st Century”. Surv. Geophys. https://ift.tt/2VIqk8M.
Jevrejeva, S., J. C. Moore, A. Grinsted, and P. L. Woodworth (2008). “Recent global sea level acceleration started over 200 years ago?”. Geophys. Res. Lett., 35, L08715, doi:10.1029/2008GL033611.
Jevrejeva, S. , J.C. Moore, A. Grinsted, A.P. Matthews, G. Spada. 2014. “Trends and acceleration in global and regional sea levels since 1807”. Global and Planetary Change. %vol 113, 10.1016/j.gloplacha.2013.12.004 https://ift.tt/2Xf756b
Siddall M, Rohling EJ, Almogi-Labin A, Hemleben C, Meischner D, Scmelzer I, Smeed DA (2003). “Sea-level fluctuations during the last glacial cycle”. Nature 423:853–858
via Watts Up With That?
August 10, 2021 at 04:55PM