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Planting huge numbers of trees is often proposed as a way to reduce the severity of climate change. Studies have looked at the potential for Earth‘s ecosystems to support large additional areas of forest and have found that it would be possible to have at least 25% more forested area than we do now. This in turn could capture large amounts of carbon and substantially reduce the amount in the atmosphere.

A recent study by researchers at Clark University in Massachusetts and The Nature Conservancy mapped the climate impact of tree planting across the globe, identifying where it would be most and also least beneficial. The study, published in Nature Communications, found that trees planted in arid, desert regions or in snowy places like the Arctic would, on balance, worsen warming rather than reduce it.

Trees take up carbon dioxide from the atmosphere, which helps to keep warming in check. But trees with dark, green leaves also absorb heat from sunlight. Snow and desert sand, on the other hand, are light-colored and reflect more sunlight back into space. For this reason, trees planted in snowy areas or in the desert will absorb more sunlight than their surroundings. This can negate the climate benefits of soaking up carbon dioxide.

Previous studies only looked at how much carbon dioxide would be removed by planting trees in order to determine how much warming would be prevented. The new study finds that it matters where the trees are planted.

Fortunately, the new study also shows that tree planting projects that are currently underway or that are in the pipeline are largely concentrated in regions where they will indeed help slow global warming.

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This Map Shows Where Planting Trees Would Make Climate Change Worse

Photo, posted April 5, 2022, courtesy of UC Davis Arboretum and Public Garden via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

The rising seas represent a threat to coastal cities across the globe. Increasing that threat is the fact that most global cities are slowly sinking as the earth beneath them settles and groundwater is removed. Another factor that has seldom been considered is that in major metropolises, the weight of large, concrete-and-steel skyscrapers may be hastening the sinking.

A new study by the U.S. Geological Survey published in the journal Earth’s Future estimated the weight of every building in New York City – 1.085 million of them – which they determined to add up to 1.68 trillion pounds – and estimated the downward force of those structures across the city.

The study found that buildings have a greater effect in areas that are rich in clay compared with those areas where sand or bedrock predominate. The softer the soil, the more compression there is from buildings. It wasn’t a mistake to build large buildings in New York, but it is important to understand that doing so pushes down the ground more and more.

The study determined that New York is sinking by around 1 to 2 millimeters each year, although some areas are sinking much faster. The researchers say that cities must plan for future sinking, which will exacerbate the impact of rising seas. Sea levels are rising 1 to 2 millimeter each year, so the subsidence caused by the weight of buildings is equivalent to moving a year ahead in time with regard to rising ocean levels. This is not a cause for immediate panic, but it is important to understand that this ongoing process only increases the risk of inundation from flooding.

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New York City Sinking Under Weight of Skyscrapers

Photo, posted January 29, 2016, courtesy of Always Shooting via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Where not to plant trees

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New York Is Sinking | Earth Wise

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