Earth’s seasons are no longer predictable, study finds Humans reshaping the planet’s climatic rhythms

The planet’s seasons are far less fixed than once believed. In fact, some regions experience seasonal timing that differs dramatically from areas just a short distance away. This irregularity may have shaped evolutionary changes in ecosystems—and now, human-driven shifts could create even greater consequences in the future.

Earth has “hot spots that are seasonally ‘asynchronous’ with surrounding areas,” according to a study published in Nature. These are regions where the “timing of seasonal cycles can be out of sync between nearby locations,” said Drew Terasaki Hart, an ecologist and study author, to The Conversation. “These differences in timing can have surprising ecological, evolutionary and even economic consequences.”

Traditionally, our understanding of seasons comes from phenology—“the timing of natural events, like when trees flower or animals migrate, simply by watching.” This works well in places with distinct winters, such as Europe and North America, but “can struggle in the tropics and in arid regions,” Hart noted. To fill these gaps, researchers turned to satellite data, uncovering seasonal anomalies that would otherwise go unnoticed.

One example lies in Earth’s Mediterranean climate zones, which include California, Chile, South Africa, southern Australia, and the Mediterranean basin. These areas experience a “double peak” seasonal pattern because “forest growth cycles tend to peak roughly two months later than other ecosystems,” said Hart. They also “show stark differences in the timing of plant growth from their neighbouring drylands, where summer precipitation is more common.”

Previously, this phenomenon had only been documented in California. Another case is the American Southwest, where cities “just about 100 miles [160 kilometres] apart can show very different annual rhythms because one area leans on summer monsoon rains while another splits rain between winter and summer,” according to Earth.com.

Season of change

Asynchronous seasons likely played a major role in biodiversity and evolution. Many of these regions host unique ecosystems, the study noted. “Because seasonal cycles of plant growth can be out of sync between nearby places, the seasonal availability of resources may be out of sync too,” Hart explained. “This would affect the seasonal reproductive cycles of many species.” These mismatched cycles can drive genetic diversity.

But the story doesn’t end with nature—humans are also reshaping the rhythms of the planet. A study cited in the article and published in Progress in Environmental Geography argues that human activity is creating entirely new seasonal patterns. There has been a rise in “syncopated” seasons—“places where things are still technically on beat, just in weird and unpredictable ways,” said Vice. Think “heat waves where there should be rain or snowstorms in April.”

Other regions are now experiencing “arrhythmic” seasons, which lack any discernible pattern: “Springs come too early. Summers won’t end. Winters barely exist.” These disruptions can lead to extreme weather and wreak havoc on agriculture.

Unstable seasons are a direct result of climate change. The “scale and rapidity of changes to our planet’s biogeochemical cycles profoundly impact the sociopolitically interpreted (re)definitions of seasonal rhythms.” Or as Vice put it: “There used to be four seasons. Now we have melting ones, burning ones, polluted ones and plastic ones.”

By Nazrin Sadigova