Massive storms and Western Atlantic sea level rise resulted from slightly warmer temperatures and moderate CO2 concentrations over a hundred thousand years ago

Geologic evidence is the forerunner of ominous prospects for a warming Earth, October 12, 2017, Science Daily

While strong seasonal hurricanes have devastated many of the Caribbean and Bahamian islands this year, geologic studies on several of these islands illustrate that more extreme conditions existed in the past. A new analysis shows that the limestone islands of the Bahamas and Bermuda experienced climate changes that were even more extreme than historical events.

The image on the left shows eolian (lower) and runup bedding (upper) exposed in a roadcut on Old Land Road on Great Exuma Island (road elevation +23 meters). On the right are thick beds with fenestral porosity, or ‘beach bubbles,’ showing that massive waves ran up over older dunes exposed in a roadcut on Suzy Turn Road along the Atlantic Ocean east side of Providenciales, Turks and Caicos Islands, BWI. Credit: Marine Geology

While strong seasonal hurricanes have devastated many of the Caribbean and Bahamian islands this year, geologic studies on several of these islands illustrate that more extreme conditions existed in the past. A new analysis published in Marine Geology shows that the limestone islands of the Bahamas and Bermuda experienced climate changes that were even more extreme than historical events. In the interest of our future world, scientists must seek to understand the complexities of linked natural events and field observations that are revealed in the geologic record of past warmer climates.

In Bermuda and the Bahamas, the geology of the last interglacial (LIG; approximately 120,000 years ago) is exquisitely preserved in nearly pure carbonate sedimentary rocks. A record of superstorms and changing sea levels is exposed in subtidal, beach, storm, and dune deposits on multiple islands. Extensive studies by the authors over the past decades on these islands have documented stratigraphic, sedimentologic, and geomorphic evidence of major oceanic and climatic disruptions at the close of the last interglacial.

Dr. Paul J. Hearty, a retired Associate Professor at the University of North Carolina at Wilmington, and Dr. Blair. R. Tormey, a Coastal Research Scientist at Western Carolina University conducted an invited review of published findings. It demonstrates that during a global climate transition in the late last interglacial, also known as marine isotope substage 5e (MIS 5e), abrupt multi-meter sea-level changes occurred. Concurrently, coastlines of the Bahamas and Bermuda were impacted by massive storms generated in the North Atlantic Ocean, resulting in a unique trilogy of wave-transported deposits: megaboulders, chevron-shaped, storm-beach ridges, and runup deposits on high dune ridges.

While perhaps more mundane than the megaboulders (found only locally on Eleuthera), the sedimentological structures found within chevron ridge and runup deposits across islands throughout the Bahamas and Bermuda point to frequent and repeated inundation by powerful storm waves, in some locations leaving storm deposits tens of meters above sea level.

During the last interglacial, sea levels were about 3-9 meters higher than they are now. The geologic evidence indicates that the higher sea-levels were accompanied by intense “superstorms,” which deposited giant wave-transported boulders at the top of cliffed coastlines, formed chevron-shaped, storm beach ridges in lowland areas, and left wave runup deposits on older dunes more than 30 meters above sea level. These events occurred at a time of only slightly warmer global climate and CO2 (about 275 ppm) was much lower than today.

The authors emphasize “the LIG record reveals that strong climate forcing is not required to yield major impacts on the ocean and ice caps.” In our industrial world, rapidly increasing atmospheric CO2 has surpassed 400 ppm, levels not achieved since the Pliocene era about 3 million years ago, while global temperature has increased nearly 1 °C since the 1870s. Today, ice sheets are melting, sea level is rising, oceans are warming, and weather events are becoming more extreme.

Drs. Hearty and Tormey conclude that with the greatly increased anthropogenic CO2 forcing at rates unmatched in nature, except perhaps during global extinction events, dramatic change is certain. They caution that, “Our global society is producing a climate system that is racing forward out of humanity’s control into an uncertain future. If we seek to understand the non-anthropogenic events of the last interglaciation, some of the consequences of our unchecked forward speed may come more clearly into focus…a message from the past; a glimpse into the future.”

P.J. Hearty, B.R. Tormey. Sea-level change and superstorms; geologic evidence from the last interglacial (MIS 5e) in the Bahamas and Bermuda offers ominous prospects for a warming EarthMarine Geology, 2017; 390: 347 DOI: 10.1016/j.margeo.2017.05.009

Elsevier. “Geologic evidence is the forerunner of ominous prospects for a warming Earth: Slightly warmer temperatures and moderate CO2 concentrations over a hundred thousand years ago led to dramatic superstorms and sea-level rise in the western Atlantic Ocean.” ScienceDaily. ScienceDaily, 12 October 2017. <www.sciencedaily.com/releases/2017/10/171012114839.htm

Hurricane-related financial loss could increase more than 70 percent by 2100 if oceans warm at the worst-case-scenario rate predicted by the Intergovernmental Panel on Climate Change, according to a new study. The study used a combination of hurricane modeling and information in FEMA’s HAZUS database to reach its conclusions.

If oceans warm at a rate predicted by the Intergovernmental Panel on Climate Change, the United Nation-sponsored group that assesses climate change research and issues periodic reports, expected financial losses caused by hurricanes could increase more than 70 percent by 2100, according to a study just published in the journal Sustainable and Resilient Infrastructure.

The finding is based on the panel’s most severe potential climate change — and resulting increased sea surface temperature — scenario and is predicted at an 80 percent confidence level.

The results of the study, which focused on 13 coastal counties in South Carolina located within 50 miles of the coastline, including the most populous county, Charleston, are drawn from a model simulating hurricane size, intensity, track and landfall locations under two scenarios: if ocean temperatures remain unchanged from 2005 to 2100 and if they warm at a rate predicted by the IPCC’s worst-case scenario.

Under the 2005 climate scenario, the study estimates that the expected loss in the region due to a severe hurricane — one with a 2 percent chance of occurring in 50 years — would be $7 billion. Under the warming oceans scenario, the intensity and size of the hurricane at the same risk level is likely to be much greater, and the expected loss figure climbs to $12 billion.

The model drew on hurricane data for the last 150 years gathered by the National Oceanic and Atmospheric Administration, then created simulated hurricanes under the two scenarios over 100,000 years and estimated the damage from every storm that made landfall in the study area.

Researchers then overlaid information from the Federal Emergency Management Agency’s HAZUS database, a zip-code-by-zip-code inventory of building types and occupancy. HAZUS sets out loss estimates according to wind speed for costs of repair, replacement, content and inventory, as well as costs resulting from loss of use, such rental income loss, business interruption and daily production output loss.

The researchers did not find that warming oceans will lead to more frequent hurricanes, only that warmer seas will lead to higher wind speeds and storms that are greater in size and therefore cover a larger area.

The losses are calculated based only on wind and wind-driven rain and do not include the large financial impacts of storm surge or flooding.

“The study shows that a significant increase in damage and loss is likely to occur in coastal Carolina, and by implication other coastal communities, as a result of climate change,” said one of the authors of the paper, David Rosowky, a civil engineer at the University of Vermont and the university’s provost.

“To be prepared, we need to build, design, zone, renovate and retrofit structures in vulnerable communities to accommodate that future,” he said.

The study was based on the IPPC’s Fifth Assessment, issued in 2013 and 2014. The worst-case ocean warming scenario the loss study is based on was not anticipated or included in the prior report, published in 2007.

“That suggests that these scenarios are evolving,” Rosowsky said. “What is today’s worst case scenario will likely become more probable in the IPCC’s future reports if little action is taken to slow the effects of climate change.”

The increasing severity of hurricanes will also affect hurricane modeling, Rosowsky said, and consequent predictions of damage and financial loss. In a postscript to the paper, which will also be published as a chapter in a forthcoming book, Rosowsky cites the three catastrophic storms of the current hurricane season, Harvey, Irma and Maria, as examples of events so severe they will shift the assumptions about the likelihood that such severe hurricanes will occur in the future.

Yue Wang, David V. Rosowsky. Hazard-based regional loss estimation considering hurricane intensity, size and sea surface temperature changeSustainable and Resilient Infrastructure, 2017; 1 DOI: 10.1080/23789689.2017.1364564

University of Vermont. “Warming seas could lead to 70 percent increase in hurricane-related financial loss.” ScienceDaily. ScienceDaily, 12 October 2017. <www.sciencedaily.com/releases/2017/10/171012151803.htm