Previous Faculty Information Suggests Atlantic Hurricanes Are No Extra Frequent Than In The Previous – Watts Up With That?

by Bob Yirka, Phys.org

Researchers from several institutions in the United States have found that the increase in hurricanes that have formed in the Atlantic in recent years is not related to global warming. Instead, they suggest in their article published in Nature Communications that it simply reflect the natural variable weather patterns.

Over the past few decades, scientists studying satellite data have found that the number of hurricanes forming in the Atlantic has increased. Many in the field have suggested that this was due to the effects of global warming. A warming ocean would of course lead to more active atmospheric activity. The problem with this thinking, according to the researchers in this new effort, is that satellite data only dates back to 1972. Prior to that date, hurricane frequency data was usually obtained from eyewitness accounts that omitted many hurricanes that never touched land. In this new study, researchers drew on the old record books to learn more about the frequency of hurricanes in front of satellites.

The ancient data dates back to 1851 and comes from records kept by workers of the National Oceanic and Atmospheric Administration. The workers had collected data from eyewitnesses on the east coast, along the Gulf of Mexico, islands in the Atlantic, and fishermen venturing out to sea. The researchers then calculated the ratio of hurricanes that never landed in modern times to those that did and worked backwards using modern data along with mathematical techniques to estimate the number of hurricanes by 1860 that were never recorded . They then plotted these numbers on a timeline.

abstract

Atlantic hurricanes pose a great threat to life and property and are an issue of great scientific interest. Historical changes in observational practice have limited the usefulness of keeping records of the frequency of major hurricanes in the Atlantic on a scale of several centuries. In order to evaluate past frequency changes, we have developed a homogenization method for the frequency of Atlantic hurricanes and large hurricanes from 1851 to 2019. We note that the recorded increases in Atlantic hurricanes and the incidence of major hurricanes at the century level, and the associated decrease in the hurricane impact fraction in the United States, are consistent with changes in observation practices and are unlikely to be a true climate trend. After homogenization, increases in basin-wide hurricane and major hurricane activity since the 1970s are not part of an increase at the century level, but rather a recovery from a deep minimum in the 1960s to 1980s. We suspect that internal (e.g., multidecadal) climate variability and the aerosol-induced reduction in major hurricane frequency in the mid to late 20th century have likely masked the century-scale greenhouse gas warming contributions to the frequency of major hurricanes in the North Atlantic.

introduction

Tropical cyclones (TCs) are of great scientific interest and pose a major threat to human life and property around the world1,2,3. Of particular interest are multidecadal changes in the TC frequency that result from a combination of intrinsic variability in the weather and climate system and the response to natural and anthropogenic climate forcings4,5,6,14,15,16,17,18,19, 20,21,22,23,24,25. Although the North Atlantic Basin (NA) is a small contributor to global TC incidence, Atlantic hurricanes (HUs) have been the subject of extensive research, both because of the long-term trajectory and frequency records for this basin, as well as their impact on landing. It is practical and customary to consider Saffir-Simpson Categories 3-5 (maximum sustained winds greater than 50 ms-1) HUs separate from total frequency and refer to them as major hurricanes or MHs. Historically, MHs accounted for ~ 80% of hurricane-related damage in the United States of America (US), although they accounted for only 34% of TC events in the US1.

Globally, models and theoretical arguments suggest that in a warming world the peak HU intensity and rate of intensification should increase, so there is a tendency that the proportion of HU that has high Saffir-Simpson categories (3rd, 4th or 5th) should increase ), in models rises in response to increases in CO2, but the model forecasts with regard to changes in the frequency of MHs in individual catchment areas (e.g. NA) are more mixed6,20,21,22,25,26,27,28,29 , 30. Homogenized satellite-based TC intensity observations since the early 1980s show an increase in the proportion of MH in total TCs in both the NA and worldwide14, and since the 1980s there has also been a documented increase in the proportion of global and NA HU that a rapid intensification 15. Theoretical arguments, model studies and observational analyzes indicate that the overall incidence of TCs and their intensity in the tropics and especially for Atlantic HUs vary differently and can show clear connections to climate factors14,15,25,26,27,28, 29.30, 31.32. There is considerable dispersion in model projections of the 21st century response of both the overall NA HU frequency and the response of the frequency of the most intense NA HUs6,20,21,22,25,26,27,28,29,30. The relationship between the recently recorded, multi-decade changes in NA-HU activity and the HU projections of 21st or non-greenhouse gas forcing16,17,18,19,20,21,22,23.

Has the number of the strongest hurricanes in the North Atlantic changed by a century? Analysis of longer records (ie, dating back to the 19th century) of NA-HU and MH frequencies provide an additional lens by which to interpret both recent changes in HU activity and projections of future hurricane activity. The North Atlantic Hurricane Database Version 2 (HURDAT2; Ref. 33) provides records of NA HU activity dating back to 1851 – a record of nearly 170 years of HU activity. HURDAT2 can be used to study secular changes in aggregated statistics of NA-HU activity, e.g. . The US HU strike record we use includes storms for which either hurricane force or vmax ≥ 33 ms-1 or strong hurricane force or vmax ≥ 50 ms-1 winds from the Atlantic or Gulf of Mexico impacted the continental US this record includes storms, where the center did not go ashore.

Due to changed observation practices, there are serious inhomogeneities in this database, which make it difficult to assess long-term changes7,8,9,10,11,12,13. In particular, the monitoring capacity has increased significantly in the last 170 years, so that the probability that an HU will be observed is much higher today than at the beginning of the recording10; the recorded increase in Atlantic TC and HU frequencies in HURDAT2 since the late 19th century is consistent with the effects of known changes in observational practice7,8,9,10,11,12. Estimates of the frequency of major hurricanes can also be influenced by changing observation systems13.

We show here that the recorded increases in NA-HU and MH frequency and the ratio of MH to HU can be understood as a result of previous changes in the NA samples. We build on the methodology and expand the results from Ref. 10 to develop a homogenized record of the catchment-wide NA HU and MH frequency from 1851 to 2019 (see section Methods), this homogenized record shows that the increase in NA HU – and MH frequency is not a continuation of changes on a century scale since the 1970s, but a recovery from a deep minimum in the late 20th century.

This blog post that we covered last month seems to anticipate that paper.