We have often discussed the observed patterns of Atlantic tropical cyclone activity and what may lie behind them, and we generally have concluded, based upon both our analysis of the data, along with a thorough review of the scientific literature, that identifying a statistically significant and robust human signal in the observed history of Atlantic basin tropical cyclones, whether over the past 100+ years, or in recent decades, is untenable.
We have largely come to this conclusion as the observed increases in hurricane activity in recent decades far exceeds that generally projected by climate models run with observed changes in anthropogenic emissions, and there is ample (and growing) evidence that the Atlantic hurricane record is characterized by multi-decadal oscillations that are tied to multi-decadal oscillations in ocean circulation, atmospheric circulations, and patterns of sea surface temperature variability. That these multi-decadal oscillations can be traced backward in time for at least several centuries, is strong indication that they are a natural part of the earth’s climate system, rather than being primarily driven by human alterations of the earth’s atmosphere.
This conclusion has important implications for the future, as it suggests that as the sign and strength of the natural cycles controlling hurricane behavior wax and wane, so to will the future activity of Atlantic tropical cyclones, both in frequency and intensity. The contrary conclusion—that anthropogenic “global warming” is largely controlling the activity of Atlantic tropical cyclone activity—portends, conversely, an ever stormier future.
While we have tried to present clear evidence that the scientific tide seems to be turning in the direction of a predominately “natural” origin of past, present, and future, Atlantic tropical cyclone variability, there are still many prominent groups, including the U.S. Climate Change Science Program (CCSP) and the U.S. Environmental Protection Agency (EPA) that choose to rely on out-dated findings to support their claims of a significant anthropogenic impact on current and future Atlantic hurricane activity in their current draft versions of climate change summary documents. As public reviewers of these documents, we have continually stressed that their conclusions are ill-founded and out-of-date and must be amended and modified to reflect the current state of scientific knowledge on this topic. We hope that they will choose to do so in when the final versions of these documents are released.
As further support to our contentions concerning the underlying influences on Atlantic tropical cyclone behavior, hurricane researchers Gabriel Vecchi, Kyle Swanson, and Brian Soden published a ‘Perspectives’ piece in this week’s Science magazine which summarizes their view of the subject.
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