May 6, 2010 | A study that includes NCAR scientists suggests that plant leaves emit far less methane when exposed to sunlight than according to previous research. The research, published in New Phytologist on April 28, estimates that foliage is the source of less than 1% of Earth’s methane emissions. 

The research is especially significant for allaying fears that forestry and agriculture contribute to climate change, as methane is a potent greenhouse gas that is 23 times more effective than carbon dioxide at trapping heat in the atmosphere. Plants act as a carbon sink, storing carbon dioxide in their leaves, bark, and wood. According to the study's authors, this ability to store carbon far outweighs the small amounts of methane that plants generate.

To carry out the study, scientists from the UK’s University of Edinburgh created artificial leaves made from plant pectin (structures contained in the primary cell walls of plants), exposed the leaves to ultraviolet lamps, and measured the methane produced. Then they teamed with NCAR’s Julia Lee-Taylor and Sasha Madronich to combine these laboratory results with satellite data showing Earth’s leaf coverage, atmospheric ozone, cloud cover, temperature, and solar ultraviolet radiation, enabling them to calculate the amount of methane produced by all the planet’s foliage. This amount is much lower, by factors of 10 to 100, than previous estimates.

The authors caution that recent studies have shown that pectin is not the only molecular source of plant methane emissions driven by ultraviolet radiation. To confirm the contribution of foliage to the global methane budget, further study is needed.

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