Did climate change contribute to the sudden collapse of the twelve story condominium last week in Surfside, Florida? That question was being asked almost immediately as part of the pressing question as to the cause. In my interviews with NBC-TV Channel 6 and the Huff Post I made clear that we should let the forensic engineering investigations do their methodical work. That will largely have to await conclusion of the search and recovery operation, which is presently paramount. The full assessment will require the careful removal of the collapsed building to see the foundation.
We don’t want to pre-judge or jump to any conclusions as there are huge lessons and liabilities at stake for many potential parties. In addition to culpability there is concern for other buildings that may have similar risks. Still we can reasonably define potential contributors from climate change that should be considered –– and eliminate some that have been suggested:
Beach erosion is a major concern in this area just north of the famous Miami Beach that some have suggested as a factor. Judging by the photos however, I see no evidence that coastal erosion is involved in this situation.
Subsidence has been reported at that location. This occurs when the underlying rock or sediment layers compact or settle and could cause structural columns to be unsupported. Proper engineering of the foundation should prevent this from happening. In places like South Florida where limestone is the substrate, sinkholes can develop over time, with devastating effect. These are caverns that occur when the rock is chemically dissolved by natural ground water or pollutants. There is some concern that rising sea level may be increasing sinkholes, which can affect subsidence even some distance away.
Salt water increased by rising sea level. A particular effect of salt water on the structure of buildings comes from its interaction with the steel used to reinforce concrete. The steel “re-bar” is the rod with a ridged surface that can be seen at almost any construction site. A thin rusting layer on the steel from fresh water is quite acceptable. When the steel rod is exposed to highly corrosive salt water there can be big problems. Hairline cracks in concrete may not be a structural problem. But if saltwater wicks its way into the concrete and gets to the steel re-bar, significant damage can occur. As you can see on rusted steel in cars for example, the rusted steel expands as it blisters. That can cause the concrete to delaminate. “Spalling” is the proper term. When this happens the concrete loses its structural strength. If this happened in critical structural columns or walls it could have been a significant factor in the building’s collapse.
In the warm tropical conditions of South Florida spalling can be a significant problem. Global sea level is rising and accelerating. Annually the global average rate is still only about a quarter of an inch, but the effect is cumulative, like a drip filling a bucket. In the last thirty years, the rate has tripled. Since that building was built forty years ago, sea level has risen several inches. The high water levels are most noticeable during peak high tide, the “king tides” that are now a phenomenon in most coastal communities. It is certainly possible that salt water creeping higher and higher has added to the spalling concrete and may have contributed to this disaster. The investigation should answer that.
In the coming years and decades this problem will surely get even worse as the ice sheets on Greenland and Antarctica continue to melt in a warming world, raising global sea level higher and higher. This should encourage us all to support efforts to slow the warming, which largely results from carbon dioxide emissions from burning fossil fuels. Even with that effort however, we need to design and build to be more flood resistant during king tides, heavy rainfall, and coastal storms. We also need to start adapting to a higher base sea level which will be more noticeable in the coming decades.
Author of Moving to Higher Ground: Rising Sea Level and the Path Forward (The Science Bookshelf 2021)