Planet Caught Up in Carbon Catch-22

Because of global warming, northern forests like this one near Quebec City, Canada, will release more carbon than they absorb, mainly due to increased rates of carbon loss during warmer autumns, according to a new study.

Photo: Marc Andre Giasson

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A climate change catch-22 may be causing carbon sink capacities to cancel themselves out in different seasons. According to a new study by the Global Carbon Project published today in the journal Nature, the longer growing season is reducing the amount of carbon stored in northern forests.

The plant life on Earth acts like a giant set of seasonal lungs, breathing in carbon and exhaling it. Trees and other flora typically hold in more than they exhale over time, so scientists refer to them as "carbon sinks."

Though warmer spring weather encourages carbon-absorbing flora, balmy autumns increase soil decomposition, which drastically reduces carbon uptake. Scientists believe the loss of carbon to the atmosphere in autumn is significant enough to cancel out the extra carbon taken up by northern forest ecosystems in the spring.

Following this vicious carbon cycle, the ability of northern forests to sequester carbon will only diminish as the growing season continues to grow longer and warmer in both the spring and autumn.

The study undermines the hope that forests might absorb and hold more carbon in a warmer world, thereby offsetting some of the greenhouse gas emissions fueling climate change.

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