A 2020 study in Nature Communications used satellite data to estimate Arctic vegetation over time, sampling thousands of sites across Alaska, Canada and western Eurasia. The researchers found that between 1985 and 2016, about 38% of the sites showed greening.
“Not everywhere in the Arctic is green,” says Logan Berner, a terrestrial ecologist with the University of Alaska Southeast, who led the study. “But there’s enough greening that if you look at the average greenness of the Arctic over time, it’s going up.”
According to Berner, who grew up in southern Alaska, this consistent increase in average greenness tracks strongly with an increase in summer temperatures.
Changes in our water
“People have coined the term that lakes are sentinels in the landscape,” says David Butman, a professor at the University of Washington who focuses on biogeochemistry and satellite remote sensing. Lakes react quickly to changes in the environment, so measuring lake color through satellite monitoring can help quantify those changes.
Butman worked on a 2021 study in Proceedings of the National Academy of Sciences of the United States of America (PNAS) that measured green wavelengths in more than 400,000 lakes in the boreal Arctic zone in North America. Researchers found that green values declined by 15% between 1984 and 2019, meaning that, to the naked eye, these lakes got significantly darker.
Thawing permafrost is a possible reason. As it thaws, soil can mix with lake water, making it darker. The researchers found that the greatest declines happened in warmer and wetter regions.
The darker a lake gets, the more heat it can store, according to Butman. “You can imagine, you know, a black car and a hot day,” he says. The darker a lake is, the longer it stays warm after the summer, disrupting the natural timings of processes like fish life cycles and algae production. When soil or other outside material sinks to the bottom of a lake, microbes consume oxygen to break it down, leading to the production of methane, a potent planet-heating gas.
On a global scale, many lakes fall within the green-blue color spectrum. Bright blue lakes, often depicted in illustrations, are rarer than green lakes.
In 2022, scientists Xiao Yang and Catherine O’Reilly led a study in Geophysical Research Letters that analyzed the color of more than 85,000 lakes. They found that blue lakes are generally found in northern places with cooler summers and are covered in ice in the winter, such as Moraine Lake in Canada or Lake Baikal in Russia.
The birds and the bees
Many animals have appearances that blend in with their surroundings for survival. When those surroundings start to shift, animals such as the snowshoe hare begin to stand out. The snowshoe hare’s white winter fur sticks out with less snow on the ground, leaving it more vulnerable to predators.
Researchers haven’t found evidence that hares are adapting the timing of their molts to align with their changing winter. But some insects have already changed coloring. North American male dragonflies, for instance, have adapted to warmer climates by losing color on their wings, according to a study in PNAS.
Losing some of the heat-absorbing color can help the dragonflies stay cooler, but the males also lose color that helps attract females. And researchers predict this will continue to be the case in the future as the climate continues to warm. An even tinier example is a specific kind of bee.
Sevan Suni is an associate professor at the University of San Francisco who studies interactions between plants and pollinators. She has been going to Costa Rica for the last 15 years to study a group of bees commonly known as orchid bees.
These bees are the sole pollinators for about 200 species of orchids in Central and South America. Their bodies look almost jewel-like, with shiny iridescent shells.
Year after year, Suni noticed that one species of bee, the champion’s orchid bee, seemed to shift color from blue-green to orange-red. She and others discovered that, in hotter areas, the number of orange-red bees has increased over time while the number of blue-green bees has decreased.
