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The Lasting Damage of Sudden Heat Waves Is Highly Unpredictable

While melting sea ice will happen gradually, sudden heat waves can throw ecosystems lethal wild cards.

It's well known that gradual increases in global temperatures will likely bring melting Arctic ice that floods major coastal cities. But recent research suggests that sudden heat waves can cause just as serious disasters—with the power to destroy ecosystems—in even less time.

Since the seventies just under two million acres of white spruce in Alaska's Kenai Penninsula have been infested by beetles. One major outbreak in the 1990's destroyed 38 million trees, the most killed by an insect infestation in American history.

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Scientists now believe that warmer temperatures in the Arctic, where climate change is helping to melt ice twice as fast as the national average, allowed the beetles to mature faster, reproduce more, and stay alive through the winter.

No one predicted the population explosion. It was an unforeseen consequence of rising temperatures, and its effects are still being felt: the hectares of dead trees have even been blamed for feeding huge wildfires in the region this year.

A new study published in the journal Global Change Biology, confirms that certain species like the spruce beetle can unexpectedly thrive under extreme temperature changes caused by global warming, and then rapidly morph its ecosystem.

The researchers, mostly out of the University of Exeter in England, examined species of aphid that co-exist in relatively equal numbers under normal conditions, and exposed them to a series of extreme temperature events. The point of the project was to determine how climate change dictates which species prevail in any given ecosystem.

The results show that even in brief extreme heat events, certain aphid species can mass reproduce over others—vastly changing their surroundings in very short order.

"Previous studies have largely focused on how changes in mean temperature affect populations and community structure while neglecting changes in extreme high temperatures," researchers noted in the study. "Importantly, even small changes in average temperature can dramatically increase the frequency and magnitude of extreme high temperature events."

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Because past experiments on the effect of temperature in natural communities raised the thermostat just a few degrees at a time, the researchers tested large spikes in temperature with short exposure times.

After choosing three species of aphid that feed on the same variety of wheat, Sitobion avenae, Schizaphis graminum, and Rhopalosiphum padi, they simulated a series of heat waves in climate-controlled growth chambers.

The researchers chose a maximum temperature of 38°C and allowed it to be reached up to once per day—conditions based on climate change models that predict future heat waves temperature and frequency.

The researchers also conducted experiments outside the lab isolating patches of naturally grown wheat and jacked up the temperatures on entire fields to observe the effect on natural aphid populations.

Aphids aren't just a garden pest: they're a major agricultural menace, causing the loss of millions of bushels of wheat, barley, and soybeans every year. Plus, they spread a variety of viruses between crops, much like mosquitos do with humans.

Aphid giving birth.

They also thrive in hot and dry temperatures global warming brings about. CBC is already reporting a dramatic increase in the aphid populations in Edmonton, Alberta. Mosquitoes on the other hand—a species that thrives when they endure wet and cold springs—are on the wane in the city as western heat waves persist.

In the laboratory and in the field, the researchers noticed a similar population spike in one species of aphid. Despite living in harmony with its neighbours at normal temperatures, Rhopalosiphum padi had a significant advantage once the simulated heat waves began.

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Not unlike their northern beetle counterparts, the newly dominant aphids grew up faster, lived longer, reproduced more, and had healthier offspring.

After seeing this stark contrast in success between species, researchers consulted historical records. They found the same heat-happy species they identified in their work enjoying significant upticks in population during years with heat waves, regardless of the average annual temperature.

The value of the study lies in highlighting two major issues facing climate change adaptation: existing ecosystems will be disturbed in significant and unpredictable ways as climates heat up, especially when destructive pests like aphids can unexpectedly surge in population.

Humans are already feeling the consequences of extreme temperature events. The undeniable increase in temperature over the past decade hasn't yet swallowed any cities, but heat waves cause deaths every year, and their recent increase has been concretely attributed to global warming.

Recently released reports on climate change also stress the need for humans to adapt to their ecosystems, but acknowledge that, especially when it comes to complex ecosystems, it can be incredibly difficult to predict what to prepare for when small disruptions cause unforeseen damages.

Ultimately the aphid study shows, similarly, that sudden increases in temperature could set off extreme events that select unpredictable new winners and losers in natural communities.

In other words, while nature is good at balancing out ecosystems on its own over time, humans will scramble to adapt: meaning random forest fires and heat waves might become the norm, while the beetles and aphids live long and prosper.