Warming Trends: Where Have All the Walruses Gone? Plus, a Maple Mystery, ‘Cool’ Islands and the Climate of Manhattan

SCIENCE

ISO: Walrus Counters 

Researchers are recruiting 500,000 citizen scientists to help count walruses, which face massive challenges as the climate changes. 

The World Wildlife Fund and the British Antarctic Survey have gathered 600,000 satellite images from the range of the Atlantic and Laptev walrus populations, and each image needs to be reviewed to see if walruses are present. Once the images have been narrowed down, scientists need help count the number of the Arctic marine mammals gathering on shores in the High North. 

Walruses prefer to live on sea ice where they can easily access the ocean for clams and snails. But climate change has reduced the sea ice extent, forcing walruses to congregate on land. But the 2,000-pound animals are easily spooked, which can lead to deadly stampedes and presents a challenge for researchers on the ground trying to study walruses.

So instead, they are using satellite images collected by the company Maxar to count the number of walruses in all 600,000 of the 650-foot-by-650-foot frames the company captured in its photos from space in the summers of 2020 and 2021. This data will help establish a baseline for researchers to monitor how climate change affects these populations moving forward, said Peter Fretwell, a scientist at the British Antarctic Survey. 

“This is not just playing, this is actually making real science,” he said. “We need to know about walrus and how they’re being impacted.”

Citizen scientists who participate go through quick training to learn how to identify images with walruses in them, which can be tricky, as rusty barrels and vegetation can be mistaken for groups of walruses. Participants go through images and mark the ones that have walruses in them. Each photo is viewed by several different volunteers to increase the confidence about whether or not it has walruses, which is why such a large number of citizen scientists are helping with the count. Once the images with walruses have been narrowed down, citizen scientists will shift to counting the number of individuals.

“This really engages lots of people and really enthuses them,” Fretwell said. “We can give them some message about about the walrus and and enthuse them about walrus, but also about climate change and polar regions which are changing really rapidly.”

SCIENCE

A Bigleaf Maple Mystery, Solved by Studying Tree Rings

An iconic tree native to Washington state has been dying at rapid rates for the last decade. For a long time, scientists didn’t know why. Now, they have evidence that a hotter, drier climate is to blame. 

The bigleaf maple tree, known for its absurdly large leaves that can reach over a foot across, is one of the few deciduous trees native to the Pacific Northwest. In 2011, the Washington Department of Natural Resources began documenting reports of dead bigleaf maple. Researchers spent years looking for an insect or a pathogen that was killing the trees, with no evidence that an infestation or infection was to blame.

Then, researchers at the University of Washington and the Department of Natural Resources cored trees—drilling pencil-sized samples from their trunks that allow scientists to study the tree’s rings without cutting it down. They saw that tree growth was lower, signaling stress in the trees, in the hot and dry years that have been common recently. 

Nearly a quarter of the trees surveyed showed signs of decline. The researchers found that the tree’s declines were associated with these hot and dry years, especially for those located near roadsides or urban areas where they would experience even more stress. This stress leads to weakened immune systems in the trees, leaving them vulnerable to diseases, the researchers said in a recent study.

“They can tolerate a fair amount of disturbance but at some point trees are dying,” said study co-author Patrick Tobin, an associate professor of disturbance ecology at the University of Washington. “And that’s exactly what we saw as a result of the climate record in recent years. They were already at the brink and they were basically just pushed over the cliff, so to speak.”

As the climate warms, Tobin said it may be necessary to start watering our trees in urban environments, just like we water the tomatoes in our gardens.

“This may be the world we live in now,” he said.

SCIENCE

The ‘Cool Island’ Effect

New research shows that large-scale solar parks experience a “cool island” effect, with air temperatures in the area surrounding the parks reduced by up to 2.3 degrees Celsius.

This is the opposite effect experienced by urban “heat islands,” where dark surfaces like buildings and roads absorb heat and warm local temperatures relative to the surrounding environment. 

Scientists from Lancaster University in the U.K., Ludong University in China and the University of California Davis in the U.S. conducted the research using satellite imagery at two solar parks: the 850-megawatt Longyangxia solar park in China and the 300-megawatt Stateline solar park in California. 

The researchers are not sure exactly why solar parks experience the cool island effect, but believe it is in part due to solar panels intercepting the sun’s rays and shading the land, leading to cooler land temperatures that affect air temperatures up to nearly half a mile away from the edge of the solar park.

This could potentially have a negative impact on ecosystems, where just a few degrees of cooling can put some species over a tipping point where they can no longer survive. 

“A couple of degrees could make the difference between there being frost or no frost, or have relatively little impact,” said Alona Armstrong, a lecturer at Lancaster University who is co-lead author of the research. “The consequences will depend on how sensitive the ecological processes are to temperature changes and how close the temperature is to any thresholds. So the implications will be quite site dependent.”

On the other hand, as the climate changes, there could be positive impacts from a local cooling effect to counteract warming temperatures, Armstrong said. “It depends on what you want from that land, but also what ecosystem it is and what other disturbances there are,” she said.

More research is needed to understand the mechanisms driving the cool island effect, Armstrong said, and to investigate how cooler temperatures may affect ecosystems, which could inform where to locate future solar parks. 

SCIENCE

‘Is This Street Now Cooler Than it Was?’

A truck loaded up with scientific sensor equipment will soon putter around Manhattan, collecting small-scale climate data throughout the highly variable urban environment. 

This allows researchers at the U.S. Department of Energy’s Brookhaven National Laboratory who developed the mobile observatory to collect data on temperature, precipitation, cloud cover and wind in multiple locations throughout the city without installing permanent sensors. 

“Things are so heterogeneous throughout the different parts of the city,” said Katia Lamer, a research associate in Brookhaven’s Environmental and Climate Sciences Department. “Some neighborhoods have trees, some don’t, some neighborhoods have skyscrapers, some have shorter buildings. All this variability impacts the city’s atmospheric conditions and microclimate.”

The sensors can measure how air flows around buildings, which Lamer said is important for understanding how air pollutants move and mix in the city’s atmosphere. Plus, she said, warming temperatures will change how this air moves and who is affected. 

The mobile observatory will also allow researchers to monitor the effectiveness of different climate mitigation measures, such as planting more trees and painting streets white to reduce local temperatures. 

“We can come back, take measurements and start asking ourselves: Is this street now cooler than it was? Is this climate resilience strategy effective or not?’” Lamer said.