Tuesday, December 5, 2023

New study points to reduced warming effect of methane

Neal Wallace
The scientists say despite their findings, methane remains a potent contributor to global warming, and efforts to reduce methane emissions are still required.
Methane’s shortwave absorbance affects clouds in different layers of the atmosphere which induces cooling.
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A new study has found the interaction between methane and the atmosphere reduces the overall warming effect of the greenhouse gas by up to 60%.

A report by researchers in Nature Geoscience says that although greenhouse gases absorb long-wave radiation in the atmosphere, methane also absorbs short-wave radiation reducing its warming effect.

They found that methane absorbs short-wave radiation, which comes directly from the sun and counteracts its surface warming effect.

“Using targeted climate model simulations, we have shown that methane short wave absorption and the associated adjustments act to reduce its ERF (effective radiative forcing) by about 20% and mute its warming and wetting effects in coupled simulations by up to 30% and 60%, respectively.”

Methane’s shortwave absorbance affects clouds in different layers of the atmosphere which induces cooling.

“An even larger impact occurs for precipitation as methane short-wave absorption offsets about 60% of the precipitation increase relative to its long-wave radiative effects,” Nature Geoscience reports.

This process aids the reflection of incoming short-wave radiation and its impact on high-level clouds, enhances outgoing long-wave radiation.

“The cloud responses, in turn, are related to the profile of atmospheric solar heating and corresponding changes in temperature and relative humidity.” 

The scientists say despite their findings, methane remains a potent contributor to global warming, and efforts to reduce methane emissions are still required.

Globally the atmospheric concentration of methane has increased by about a factor of 2.4 since preindustrial times, the report states, from about 0.75 to 1.8 parts per million by volume.

Methane is a potent greenhouse gas with the report noting its global warming potential is 27.9 times that of carbon dioxide on a 100 year time horizon, but with a relatively short lifetime of about 10 years.

NZ methane emissions account for about 43% of its greenhouse gas emissions, with most coming from ruminant animals.

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