Cyclone Chapala was captured early Monday morning by NOAA’s Aqua satellite.
NOAA
Tropical cyclones can cause devastating and deadly damage in East and Southeast Asian countries. But accurately tracking changes in the frequency and intensity of typhoons is challenging, partly because data on these storms hasn’t always been consistently tracked, and partly because there’s just a lot of variability in the number of storms making landfall.
In a recent issue of Natural Geosciences, new cluster- and bias-corrected analyzes of storm data show that the intensity and frequency of these dangerous storms have increased significantly. This increase is most likely due to the warming of the oceans associated with climate change.
The authors of this article focused on typhoons that affect East Asia, limiting the analysis to the Northwest Pacific. They used a regional cluster analysis to examine the storm data, grouping the cyclones based on the part of the ocean where they formed and their movement patterns. This clustered analysis allowed the researchers to organize the inconsistent data so that they could draw conclusions despite the variability of the data.
The analysis found that the frequency of typhoons making landfall has increased by 12 to 15 percent over the past 37 years. In addition to the increase in typhoon frequency, there has been a marked and significant increase in Category 4 or Category 5 storms, which are the most dangerous and deadly. This doesn’t mean that the number of storms increased, just that more of the storms that made landfall were strong enough to be called typhoons.
Having seen this increase in dangerous storms, the authors examined changes in sea surface temperature, which can fuel energy in storms. They hypothesized that there is a link between the increase in storm intensity and human-induced warming of the ocean. When they looked at the four clusters of storm data separately, they saw that the two clusters of storms that form in regions of more pronounced ocean warming saw stronger increases in both frequency and intensity.
Storms that form off the coast of East Asia and Southeast Asia have a large and robust increase in both frequency and duration, while the rate of change for storms that form in open waters far from shore is more modest. These data also seem to show that the increase in severe tropical cyclones is related to locally amplified warming of the ocean adjacent to East Asia and Southeast Asia.
When changes in storm frequency and intensity over time were compared to changes in ocean surface temperature over time, the authors found that the intensity curve for storms closely matched the warming curve for oceanic temperatures. The authors suggest that this increase in storm intensity may be because a warmer ocean reduces the negative feedback otherwise caused by the typhoon mixing the surface with cooler upper ocean waters.
The exact role of climate change in storm power is controversial. While sustained warming will almost certainly affect future storms, it is often difficult to pinpoint a clear effect in past data, especially since weather events such as storms have an inherent degree of randomness.
Having analyzed data from several tropical cyclone datasets, the authors are confident in the robustness of their findings. Despite inconsistencies, the data all led to the same conclusions. This relationship between ocean surface temperatures and increases in typhoon intensity is likely to provide important information that researchers can incorporate into climate and weather models, hopefully helping prepare for and anticipate severe weather.
Natural Geosciences2016. DOI: 10.1038/NGEO2792 (About DOIs).