Earth's seasons are out of whack

The planet's seasons are not as immutable as previously thought. Turns out there are parts of the world that have different seasonal timing than those regions even just a short distance away. This irregularity may have led to evolutionary changes in various ecosystems. Now, humans are also adding to the seasonal alterations, which could create fresh future consequences.

Time warp

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

Our current understanding of seasons comes from phenology, which is when people study the "timing of natural events, like when trees flower or animals migrate, simply by watching," said Orbital Today. The method "works well in much of Europe, North America and other high-latitude places with strong winters" but can "struggle in the tropics and in arid regions," said Hart. The study wanted to expand on seasonal observations using satellite data. This allowed scientists to identify irregularities in seasonal patterns that may not have been otherwise observed.

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One of those examples was in Earth's Mediterranean climate regions, characterized by mild, wet winters and hot, dry summers. This includes regions like California, Chile, South Africa, southern Australia and the Mediterranean. These areas have 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 neighboring drylands, where summer precipitation is more common." This phenomenon had only previously been documented in California. Another example is the American Southwest, where cities "just about 100 miles apart can show very different annual rhythms because one area leans on summer monsoon rains while another splits rain between winter and summer," said Earth.com.

Season of change

Disjointed seasons have likely had a significant effect on biodiversity and evolution. Many of these seasonally asynchronous regions have singular biodiversity, according to the study. "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," said Hart. "This would affect the seasonal reproductive cycles of many species." Varying reproductive cycles could give way to genetically diverse species.

While seasons are not straightforward, per the study's findings, humans may also be influencing the shift. A study published in the journal Progress in Environmental Geography suggests that the planet is developing new seasons because of human activity. There has been a rise in "syncopated" seasons, which are "places where things are still technically on beat, just in weird and unpredictable ways," said Vice. This includes "heat waves where there should be rain or snowstorms in April." Some regions have been having "arrhythmic" seasons, which have no pattern to them. "Springs come too early. Summers won't end. Winters barely exist." This lack of consistency can lead to extreme weather events and disturb agriculture.

Unpredictable seasons are a 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," said the Progress in Environmental Geography study. "There used to be four seasons," said Vice. "Now we have melting ones, burning ones, polluted ones and plastic ones."