Climate Denial Crock of the Week

One of the boggling images that was included in James Hansen’s recent dire warning on climate change and sea level rise, were pictures of gigantic boulders, that may have been moved to high ground during violent storms in the Eemian period, a warm spell like the one we are moving into, some 120,000 years ago.

For the Eemian, the cause of the warming was orbital, a change in the Earth’s orientation to the sun. In our time, scientists understand well that those orbital forcings are actually bringing a very slight cooling effect for the last several thousand years, until the human-caused spike in greenhouse gases spiked planetary temperature in the last century.

Part of the warning from Dr. Hansen is that in a warm period, additional heat in the atmosphere may fuel monster storms, and that paleo-artifacts like these boulders are indicators that such storms were features in a world much like the one we are headed for in coming decades.

Washington Post:

In the model employed by Hansen and his coauthors, this cooling and freshening of the oceans eventually leads to a shutdown of the oceans’ circulation, and warm waters trapped at depth below a cold fresh surface layer in the Antarctic region, continually eating away at ice sheets from below. It also triggers a globe with ever-warming tropics but cold poles — leading to a large contrast in temperatures between the mid-latitudes and the polar regions.

A larger temperature contrast between the tropics and the poles, the researchers posit, would then strengthen winter storms or so-called extratropical cyclones, which draw their energy from such contrasts. The study therefore contemplates more powerful storms. It notes research suggesting that in the Eemian period, the last time the world saw major sea level rise of as much as 5 to 9 meters (between 16 and 30 feet), gigantic waves apparently moved huge boulders from the seafloor to the top of hills in the Bahamas.

“During this last warm interglacial, not much warmer than the present, [the world saw] not only a higher than present average sea level, but ultimately a significantly higher sea level that required the melting and or collapse of probably both Greenland and West Antarctica, along with basically this great oceanic disturbance,” says Paul Hearty, a geologist at the University of North Carolina, Wilmington who is one of Hansen’s co-authors on the new paper, and conducted the research on the Bahama boulders. “There were storms, and a lot of more catastrophic type events associated with this big climate shift.”

James Hansen for Earth Institute, Columbia University:

In plain English, the boulders are old rock of “hammer-ringing” hardness. They sit on younger softer (“punky”) Eemian-era substrate. The boulders are limestone formed on the floor of the North Atlantic Ocean at least 300-400 thousand years ago.

The boulders had to be placed there (on the cliff facing the North Atlantic) in the late Eemian or immediately thereafter before sea level had fallen much from its high Eemian level. It required powerful long-period waves from the Northeast to scour the ocean floor and lift the boulders. The boulders are all located at the apex of a narrowing horseshoe-shaped embayment; ocean waves funneled into this embayment generate huge surge and splash as they reach the cliffs.

One might have guessed that the boulders were deposited by a tsunami, but accompanying (V-shaped) “chevron” ridges and run-up deposits suggest otherwise. The chevron ridges and run-up deposits are located along the 900 kilometer eastern front of the Bahamian Islands at places most susceptible to ocean incursion. The power of the storms is indicated by the fact that the chevrons extend as much as several kilometers inland and the run-up deposits on hills immediately adjacent to the chevrons reach heights as great as 30-40 m above today’s sea level.

The suggestion in (former New York Times writer Andrew) Revkin’s comment on our paper that the boulders were instead remnants of erosion is dismissed readily. The “simple drawing…explaining boulder formation through chemical weathering” can be dismissed by going to Eleuthera and examining the boulders. One of them is shown in Fig. 1.

Appearance might be enough, but there is ample scientific evidence. The boulders are much older than the substrate on which they rest. Also the orientation of the original bedding planes of the boulders (i.e., the horizontal level at the time the limestone was formed from carbonate sediments on the ocean floor) can readily be discerned. The bedding planes are at a variety of angles, as expected for boulders tossed from the ocean.

An important characteristic of the chevrons is imbedding of lesser younger chevrons within those that penetrated furthest inland. This is an expected result of storms while sea level was falling, as Earth moved into the post-Eemian ice age. If, instead, the imbedded chevrons were caused by a tsunami, a series of tsunamis would be required.