Natural Variability in South Florida Sea Level Rise

Sea level rise (SLR) in South Florida is a major concern of research because of its impacts on coastal communities. Whether it be economic, ecological, or agricultural, its threats have been felt through nuisance flooding and contamination of freshwater resources, especially in the Florida Coastal Everglades. While the dominant signal over the past century has been a steady increase in SLR associated with anthropogenic warming, we find that South Florida SLR is also well correlated with natural modes of variability in the ocean and atmosphere such as the Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO). Locally, SLR is expected to be driven by natural climate variability, with the Gulf Stream ocean current playing a significant role. To study this, we ran correlations and other statistical analyses, particularly looking at possible factors affecting sea surface height in Key West. We found that the rate of SLR in Key West is accelerating and has been increasing 7.48mm/yr since 2010, which is much higher than the global average. For the last 50 years, the NAO and AMO are 2 modes of climate variability that have shown strong correlations to sea level changes in Key West. Notably, the AMO pattern we obtained from the spatial correlation of sea surface temperature to Key West sea level is tied to a weaker Gulf Stream flow and AMOC. This follows from the accumulation of ocean water resulting from less transport. However, it was found that certain modes of climate variability are present over some time frames, yet absent during other windows of time; suggesting that the relative influence on South Florida’s SLR due to these modes may change over time. To identify these changes, we performed a running correlation analysis using a moving 20-year window on the indices that describe the oscillatory behavior of several leading modes of variability known to influence South Florida’s climate. It became evident that the NAO was well correlated with Key West sea surface height over the period from 1948 to 1980 and again over the period from 2005 to 2017. This positive NAO pattern is associated with an overall stronger surface wind circulation which corresponds with the path of the Gulf Stream. For the PDO, the correlation analysis suggests that there is little concurrent correlation with Key West sea surface height until the period 2005 to 2017, which indicates that it might just be coincidental. Over the coming year these results will be applied to further study the role of the Atlantic Meridional Overturning Circulation (AMOC) in driving the AMO, and to better understand the relationships found between sea level in Key West and its regional drivers.