Can we use Raleigh to predict effects of climate change? NC State researchers think so.

Gloomy scale insects look like bumps on this Raleigh maple tree.  A 2-degree temperature difference can mean 200 times as many of these pests, according to N.C. State University researchers.
Gloomy scale insects look like bumps on this Raleigh maple tree. A 2-degree temperature difference can mean 200 times as many of these pests, according to N.C. State University researchers. University of Florida

When you think of a science lab, you might think of beakers, lab coats, microscopes and petri dishes. But when N.C. State University professor Steven Frank thinks of a place to study science, he walks out the front door.

Frank and his co-authors recently published a review paper that explores using cities as experimental labs to help us understand and prepare for climate change.

“The problem if you’re studying climate change is that you only have one planet,” said Marc Johnson, a professor at the University of Toronto who was not involved with the study. “You want multiple climates where you can warm up some and compare the warm planets to the cool planets.

“But a lot of the environmental factors that are changing in cities are the same things that are changing in our planet. We can use cities as large-scale experiments to understand this process.”

Raleigh is hot
This heatmap from August 2007 shows how Raleigh and other urban areas are warmer than more rural areas. Eleanor Lahr and Steve Frank

The urban ‘heat island’ effect

Cities run warmer than rural areas. Unlike the ground in forests, our streets, sidewalks and buildings form impervious surfaces, which means that water can’t go through them.

Concrete and brick absorb the sun’s heat during the day, which is why walking barefoot on the street is less comfortable than on grass. These impervious surfaces release the heat back into the air once the sun is down. This means that city days and nights are hotter than in surrounding areas. That’s called the urban “heat island” effect.

Animals and plants change to deal with the hotter climate. For instance, a 2013 study out of Frank’s lab compared pests on trees in different parts of Raleigh. A temperature difference of 2 degrees resulted in 200 times as many gloomy scale insects sucking the nutrients out of oak trees, Frank said.

“When the scales get warmer, they survive the winter and produce two to three times more babies, so the population builds up much faster,” Frank said. “It’s important because 2 degrees is the amount of change we expect globally in the next 50 to 100 years.”

If a 2-degree temperature difference led to 200 times as many insects in Raleigh, then global warming of 2 degrees could lead to 200 times as many insects everywhere.

But don’t panic yet, because this logic doesn’t work directly — Raleigh isn’t exactly a warmer, paved version of the rest of the world.

Because of cars, cities contain more carbon dioxide than the rest of the planet. Since we sluice water along impervious surfaces to different places instead of absorbing it into the ground, we disrupt the water cycle. Differences such as air quality and pollution might be changing creature behavior, not warmer climes. The paper tries to untangle city effects from warming effects.

“We have to figure out for which species can cities help us predict the effects of climate change, and for which species is it too different?” Frank said. “We think it’s a pretty good prediction for plants and small insects that can’t move from where they are. Either they’ll become more abundant if warming helps them, or they’ll die if it hurts them.”

City living—not for everyone

When we say that plants and animals adapt to city living, we mean populations instead of individuals. Some ants could be born with higher tolerance for heat, and thus scuttle across those pavements for more food. Over time, those ant groups thrive while more sensitive ant groups flounder and die off.

“We used to think evolution was like Darwin’s finches, something that happens over thousands and millions of years,” said Emily Meineke, who led the oak tree study and is now a postdoc at Harvard. “But with rapid global change and urbanization, we find plants and animals evolving very quickly, over the course of a few generations.”

The review lists and analyzes dozens of papers like the oak tree study. From flowers that bloom earlier to lizards with longer legs, living beings react to cohabitation with humans.

“Cities can represent pros and cons for species,” said conservation biologist Phoebe Barnard of the University of Washington. “They have so many stressors like domestic cats, windows, cars, higher rates of infectious diseases and higher rates of developmental abnormalities. It’s remarkable how well many species have adapted to cities.”

Added Johnson, the Toronto professor, “There’s a group of species that love these areas. Cockroaches, rats, bedbugs, house mice, starlings — these are species that only live with humans.”

The importance of studying cities

Cities are “the fastest growing ecosystem on the planet,” Johnson said. As of 2008, over half the world’s population lives in cities. According to the U.S. census, cities hold 80.7 percent of Americans.

“Despite the fact that most of us live in cities and there is no natural analog of this ecosystem, we have a very poor understanding of how they are influencing life around us,” Johnson said. “It’s kind of scary.”

The researchers hope that this review paper leads to more research on how species adapt to urban areas and where conservationists should focus their future efforts.

“We have to understand urbanization and how it may predict which species survive the next 300 to 500 years of this dizzying environmental change,” Barnard, the conservation biologist, said. “I want to try to help as many species as possible through this, but it takes a triage approach.”

“That’s might be like somebody standing up in a crowded party and shouting doomsday, but like medical triage we have to engage in conservation triage.”

Moving science from the lab bench to the local park can help us engage with science and topics such as climate change and global warming, said Susana Wadgymar, professor at Davidson College, which is outside Charlotte. For instance, next time you see an oak tree, you can look for the hard bumps of gloomy scales peppering its trunk.

“[Other studies] are like watching a documentary; it’s interesting but is it happening in your backyard? Probably not,” Wadgymar said. “Research in urban centers might hit home because you can apply those findings to what’s going on around you.”

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