“It is important to recognize that we have a “new normal,” whereby the environment in which all storms form is simply different than it was just a few decades ago. Global climate change has contributed to the higher sea surface and sub-surface ocean temperatures, a warmer and moister atmosphere above the ocean, higher water levels around the globe, and perhaps more precipitation in storms.”
Two new papers have recently been published examining the link between global warming and hurricane intensity. In both cases, the scientists have found evidence that the most intense hurricanes are already occurring more often as a result of human-caused global warming. However, their predictions about future hurricane changes differ somewhat.
Hurricane Storm Surges
Last year, Tamino examined Grinsted et al. (2012), which demonstrated that the most extreme storm surge events can mainly be attributed to large landfalling hurricanes, and that those events are strongly linked to hurricane damage. The study also found that there have been twice as many
Katrina-magnitude storm surge events in globally warm years as compared to cold years. In a new paper, Grinsted et al. (2013) constructed a storm surge index beginning in 1923 from six long tide gauge records in the southeastern USA. The idea is that surges in sea level recorded at tide gauge stations can tell us about strong hurricane events. Consistent with their 2012 results, the authors found:
“The strong winds and intense low pressure associated with tropical cyclones generate storm surges. These storm surges are the most harmful aspect of tropical cyclones in the current climate, and wherever tropical cyclones prevail they are the primary cause of storm surges.”
They compared their storm surge index to changes in global surface temperature, to temperatures in the Main Development Region (MDR; a part of the Atlantic Ocean where most hurricanes form), and to MDR warming relative to the tropical mean temperatures (rMDR).
Figure 1: (A) Average surge index over the cyclone season. (B) Observed frequency of surge events with surge index greater than 10 units per year (surge index > 10 units). (C) Global average temperature, MDR temperature, and rMDR temperature anomaly. Inset shows locations along the US coast of the six tide gauges used in the surge index.They found that averaged sea surface temperatures over the MDR are the best predictor of Atlantic cyclone activity, followed by global average surface temperature, with MDR warming relative to the tropics being the worst predictor of hurricane activity.
Grinsted et al. then used the relationships between hurricane storm surges and global and MDR temperatures to predict how storm surges will change in the future. They used the Representative Concentrations Pathway (RCP) 4.5 scenario, which represents a future in which we slowly reduce human greenhouse gas emissions such that they peak around the year 2040. In this scenario, there is approximately 2.4°C global surface warming over the 21st century. (Shown in Figure 2)
