Study finds methane cools even as it heats

Most climate models do not yet account for a new UC Riverside discovery: methane traps a great deal of heat in Earth’s atmosphere, but also creates cooling clouds that offset 30% of the heat.

Greenhouse gases like methane create a kind of blanket in the atmosphere, trapping heat from Earth’s surface, called longwave energy, and preventing it from radiating out into space. This makes the planet hotter.

In addition to absorbing longwave energy, it turns out methane also absorbs incoming energy from the sun, known as shortwave energy.

This effect is detailed in the journal Nature Geoscience, alongside a second finding that the research team did not fully expect. Though methane generally increases the amount of precipitation, accounting for the absorption of shortwave energy suppresses that increase by 60%.

Annual mean near-surface air temperature response to methane, decomposed into (a) longwave and shortwave effects; (b) longwave effects only; and (c) shortwave effects only.

Both types of energy — longwave (from Earth) and shortwave (from sun) — escape from the atmosphere more than they are absorbed into it. The atmosphere needs compensation for the escaped energy, which it gets from heat created as water vapor condenses into rain, snow, sleet, or hail.

Methane changes this equation. By holding on to energy from the sun, methane is introducing heat the atmosphere no longer needs to get from precipitation.

Additionally, methane shortwave absorption decreases the amount of solar radiation reaching Earth’s surface. This in turn reduces the amount of water that evaporates. Generally, precipitation and evaporation are equal, so a decrease in evaporation leads to a decrease in precipitation.

The research team discovered these findings by creating detailed computer models simulating both longwave and shortwave methane effects. Going forward, they would like to conduct additional experiments to learn how different concentrations of methane would impact the climate.

Scientific interest in methane has increased in recent years as levels of emissions have increased. Much comes from industrial sources, as well as from agricultural activities and landfill. Methane emissions are also likely to increase as frozen ground underlying the Arctic begins to thaw.

Tags: Atmosphere, Earth, Greenhouse gases, Methane, UC Riverside