Longer period of record reveals increases in storm intensity
Researchers from NOAA and the Cooperative Institute for Meteorological Satellite Studies have greater confidence that warming surface temperatures and increasing tropical cyclone intensity appear to go hand-in-hand.
A new study in the Proceedings of the National Academy of Sciences (PNAS) indicates a significant global increase in hurricane intensity over a four-decade period, showing the emergence of more significant findings than previous work.
Stronger Links: Hurricanes and Global Warming
Theory and climate models have consistently connected warming trends on Earth to tropical cyclone intensity. To strengthen the case, Jim Kossin of NCEI widened the lens. He scrutinized nearly four decades of homogenized enhanced infrared satellite data, adding about 10 years of data to previous work. The data measured many features of a hurricane, such as cloudtop temperature above the eyewall. The analysis carried over techniques that addressed heterogeneities, or differences, in the data that are caused by advances in technology over time.
In light of concern about hurricane planning and adaptation, Kossin and colleagues wanted better confidence in projections that storm intensity may be greater under future warming. New algorithms by NCEI indicate future years could be among the warmest, and according to a statistical analysis, the year 2020 is very likely to rank among the five warmest years on record. Also, hurricanes rank as the costliest U.S. weather and climate disaster.
Because of the longer data period studied, statistically significant global trends were identified. The longer analysis of geostationary satellite imagery from 1979–2017 produced more definitive results than prior analysis of 1982–2009 data. The work supported the link between warming and hurricane intensity more strongly than before.
Trends emerged in the proportion of major tropical cyclones—defined as Saffir-Simpson Category 3–5 storms with winds equal to or greater than 96 knots (111 mph)—compared to all categories of hurricanes (1–5). Over the 39-year period of study, 1979–2017, about 225,000 intensity estimates were available for about 4,000 individual tropical cyclones worldwide. Between the first and last halves of the study period, Kossin found a “clear shift toward greater intensity that manifests as increased probabilities of [a storm] exceeding major hurricane intensity.”
Results determined that the probability of a hurricane having wind speeds with major strength increased by approximately 15 percent between the early and latter halves of the record. This corresponded to a statistically significant rate of increase of approximately 8 percent per decade. A time series of the proportion of all hurricanes exceeding major hurricane strength exhibited a similar increasing trend of approximately 6 percent per decade.
The researchers categorized the data by location to account for regional variability. The North Atlantic, along the hurricane-prone U.S. eastern seaboard, showed high exceedance rates. “The greatest changes are found in the North Atlantic where the probability of major hurricane exceedance increases by 49 percent per decade, significant at greater than the 99 percent confidence level,” the authors stated.
However, regional variability in the North Atlantic, due to conditions such as the Atlantic meridional overturning circulation (AMOC), complicated a complete understanding of the trend. Additionally, the amplitude and significance of the trends among individual ocean basins varied considerably, according to the study.
Reference: Kossin, James P., K. R. Knapp, T. L. Olander, and C. S. Velden. "Global increase in major tropical cyclone exceedance probability over the past four decades." PNAS.org. N.p., 2020. Web. 18 May 2020. doi.org/10.1073/pnas.1920849117