The world’s most powerful storms leave an imprint on on forests long after their howling winds fade. And based on those imprints, scientists have confirmed a bizarre trend is afoot. Tropical cyclones in the world’s most active cyclone basin have been migrating north, putting people who might be ill-equipped to handle them in harm’s way.
Scientists have seen tropical cyclones migrating poleward since the advent of satellite records. However, that relatively short period of record extending back to 1980s leaves a question of whether it’s a blip or a trend. That’s a particularly important question in the northwest Pacific, which is home to the strongest storms on Earth as well as huge population centers in China, Taiwan, Japan, South Korea, and southern Siberia in the northern half of the cyclone basin.
The only way to get that answer is to get more data, and luckily, nature has a trick up its sleeve. Researchers mined the data recorded in tree rings and forest canopies as a proxy for cyclone activity in the northwest Pacific. Their results, released Monday in the Proceedings in the National Academy of Sciences, provide a nearly 100-year snapshot of storm tracks in the basin.
The scientists gathered tree cores along a more than 800-mile transect from south to north along the East China Sea and Sea of Japan. The number of rings in those cores revealed the tree’s age. But more importantly, the spacing of the rings revealed when the trees has experienced a canopy disturbance where extra sunlight suddenly resulted in a sudden growth spurt.
One of the only things likely to cause that kind of disturbance is a tropical cyclone, allowing the researchers to build a proxy database for cyclone activity. The findings show that canopy disturbances have becoming significantly more common at the northern end of the study’s sampling sites. There hasn’t been any change in trends at the southern end of the study.
There are, of course, a lot of factors that can cause cyclones tracks to shift. El Niño can play a role in any given year, while longer term climate oscillations like the Pacific Decadal Oscillation can have a more lasting influence. But the trend in the new study is also likely tied to climate change, which is warming the oceans and essentially stretching the tropics further poleward.
“[T]he expansion of the tropics leads to increased sea surface temperatures at higher latitudes, where they trigger tropical cyclone genesis and hence poleward migration of tropical cyclone activity,” Jan Altman, a researcher at the Institute of Botany, Czech Academy of Sciences who led the new study, told Earther.
In addition to shifting tracks, climate change could also be influencing a trend toward more intense landfalling cyclones on the northwest Pacific. Neither is a good trend, but especially the northward shift, which means that people who aren’t used to dealing with cyclones could be forced to deal with their impacts. Governments and NGOs in those areas may have fewer resources to respond, increasing the odds of blowing up a catastrophe into a humanitarian disaster.
The techniques could have applications in other cyclones basins as well. While Atlantic basin hurricane activity is pretty well-documented in the U.S., doing an analysis like this in data-poor countries in the Caribbean could be a huge boon. Previous work looking at stalagmite data in Belize has shown a shift toward more north and east landfalling cyclones in the basin. Using tree rings could further refine scientists’ understanding of the changes, which could also improve modeling of what the future holds.
“There are recent studies, one from Virginia and one from Gulf of Mexico region that show that tree-rings can capture cyclone activity already, so I imagine you will see a lot more of these studies going forward,” Nicole Davi, a tree ring expert at William Patterson University, told Earther.