A friend recently asked me, "so, are you bullish on Miami yet, or are you still worried about the water?" And my response was that I love Miami, but that I do think about the risk of climate change.

Then today, another friend sent me this study by scientists at the University of Miami showing that 35 buildings along the Miami Beach to Sunny Isles Beach coastline experienced some degree of subsidence between 2016 to 2023. In other words, they sunk into the ground a little.

Here's how they measured this:

The study published December 13, 2024, in the open-access journal Earth and Space Science, of the American Geophysical Union, employed a satellite-based technique known as Interferometric Synthetic Aperture Radar (InSAR). By combining 222 SAR images from the European Sentinel-1 satellites, the research team created a surface displacement time series. The technique utilizes "persistent radar scatterers" as reference points for measurement. These scatterers include fixed elements on a structure such as building balconies, rooftop air conditioning units, and boardwalks, which reflect the radar signal back to the satellite antenna. Satellites flying at 700 kilometers above Earth can measure millimeter-scale displacements.

Now, some degree of subsidence is normal. But apparently, not this much:

“The discovery of the extent of subsidence hotspots along the South Florida coastline was unexpected,” said Farzaneh Aziz Zanjani, the study’s lead author, a former post-doctoral researcher and alumna of the Rosenstiel School. “The study underscores the need for ongoing monitoring and a deeper understanding of the long-term implications for these structures.”

So yeah, I'm still worried about the water. It's something I would need to get a lot smarter on in order to feel comfortable.

This is a fascinating little experiment:

From Oct. 12, 2020 to Jan. 3, 2021, Redfin ran an experiment on 17.5 million of its users across the US. As prospective homebuyers entered the site, Redfin assigned them randomly to either a group that was shown flood-risk information on each property or a group that was not.

The flood-risk scores came from First Street Foundation, a climate and technology nonprofit that works to make climate hazards more transparent to the public. In June 2020, First Street published the first public maps that revealed flood risk for every home and property in the contiguous US. 

First Street scores properties on a scale of 1 to 10 based on the likelihood that they will flood in the next 30 years (which is assumed to be a typical mortgage term). A score of 1 means the property has "minimal" risk and a score between 9-10 is considered "extreme" risk.

So what happens once you start showing people flood-risk information? They, not surprisingly, start systematically looking for safer properties. After one week of users being exposed to this new information, prospective buyers who were previously looking at "extreme" homes started looking at homes that were about 7% safer.

After 9 weeks, these same "extreme" home buyers were looking at properties that were about 25% less risky. And for some buyers, in particular those working with a Redfin agent or partner, their flood-risk tolerance dropped by over 50%. (Embedded in this data might be a sales pitch for working with a knowledgeable Redfin agent or partner).

Also interesting is the fact that below "severe" flood risk (a score between 7-8), there was very little change in behavior. "Major" flood risk, it would seem, isn't all that concerning to most buyers. It needs to be "severe". Nevertheless, it is noteworthy that people will in fact make behavioral changes when presented with clear climate-risk data.

This recent paper by Miyuki Hino (University of North Carolina) and Marshall Burke (Stanford) makes the case that US homes situated within floodplains are currently overvalued by a total of $34 billion. And that's because the associated risks are not being properly accounted for in the value of these homes.

The problem, it would seem, comes down to information. Because the discount for flood risk was found to be higher (1) for commercial buyers (presumably because they're more sophisticated and/or have better access to information) and (2) in states where sellers must disclose flood risk (Louisiana is probably the most stringent about this).

This feels a bit like one of those realtor commercials that tries to scare you into using one. But it does appear to demonstrate just how opaque the market can be and how information asymmetries potentially distort asset prices. Perhaps most importantly, I wonder when climate risk will get fully valued.