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Greenland Becoming Darker | Earth Wise

July 5, 2021 By EarthWise Leave a Comment

According to research published by Dartmouth University, a weather pattern that pushes snowfall away from parts of Greenland’s ice sheet is causing the continent to become darker and warmer.

Reducing the amount of fresh, lighter-colored snow exposes older, darker snow on the surface of Greenland’s ice sheets. Fresh snow is the brightest and whitest. The reflectivity of snow decreases fairly quickly as it ages. This decrease in albedo – or reflectivity – allows the ice sheet to absorb more heat and therefore melt more quickly.

The research attributes the decrease in snowfall in Greenland to a phenomenon called atmospheric blocking in which persistent high-pressure systems hover over the ice sheet for up to weeks at a time. Such systems have increased over Greenland since the mid-1990s. They push snowstorms to the north, hold warmer air over Western Greenland, and reduce light-blocking cloud cover.

All of this contributes to Greenland melting faster and faster. According to research cited in the study, the Greenland ice sheet has warmed by nearly 5 degrees Fahrenheit since 1982. Overall, Greenland is experiencing the greatest melt and runoff rates in the last 450 years, at the minimum, and quite likely the greatest rates in the last 7,000 years.

The Greenland ice sheet is the second largest ice body in the world, after the Antarctic ice sheet. It is 1,800 miles long and about 700 miles wide at its greatest width. Its thickness is between 1.2 and 1.9 miles. If the entire sheet were to melt, it would lead to a global sea level rise of 24 feet. So, the darkening of Greenland is a source of great concern.

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Greenland Becoming Darker, Warmer as Snow Changes

Photo, posted April 3, 2012, courtesy of Francesco Paroni Sterbini via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Not All Trees Cool The Planet | Earth Wise

March 24, 2021 By EarthWise Leave a Comment

A new study from Clark University has found that deforestation does not always contribute to planetary warming, as is generally assumed. The researchers have found that there can be places where removing trees actually cools the planet.

Forests soak up carbon dioxide from the air and store it in the trees themselves and in the soil. This process is important for slowing the accumulation of greenhouse gases in the atmosphere.

The new research focuses on a different effect that forests have on climate. They are darker than other surfaces, which causes them to absorb more sunlight and retain heat. This is known as the albedo effect.

In most places, the absorption of carbon outweighs the albedo effect and forests help cool the planet. But there are some locations, including the Intermountain and Rocky Mountain West, where more forest actually leads to a hotter planet when both processes are taken into account. State-of-the-art satellite remote sensing allowed the researchers to quantify the effects of forest loss in the United States.

The upshot of this research is that large-scale tree-planting initiatives, such as Canada’s 2Billion Trees Initiative and the Nature Conservancy’s Plant a Billion Trees campaign need to make sure to put the right trees in the right places.

Every year, about a million acres of forest are being converted to non-forest across the lower 48 states as a result of suburban and exurban expansion and development. It is important to take into account the albedo effect in trying to replace the climate-cooling capabilities of these disappearing forests by planting more trees.

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Clark geographer Christopher Williams: More trees do not always create a cooler planet

Photo, posted June 5, 2017, courtesy of Todd Petrie via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Cooling Cities With White Roofs

April 16, 2018 By EarthWise Leave a Comment

The phenomenon of urban heat islands has been well known since the 19th century. The materials from which city buildings and roads are made reflect much less solar radiation and absorb more of it than the vegetation they have replaced. The absorbed energy is then radiated in the form of heat into the surrounding air making cities warmer.