New findings on methane

New findings on methane

This will be a piece of research the NZ government will want to bury as deep as they possibly can.

Methane may not warm the Earth quite as much as previously thought

The gas absorbs both longwave and shortwave radiation, with competing effects on climate

Methane is a greenhouse gas with dual personalities. It heats Earth’s atmosphere 28 times as potently as carbon dioxide, gram for gram. But its absorption of the sun’s radiation high in the atmosphere also alters cloud patterns — casting a bit of shadow on its warming effect.

So rather than adding even more thermal energy to the atmosphere, as previously thought, methane’s solar absorption sets off a cascade of events that reduces its overall warming effect by about 30 percent, researchers report March 16 in Nature Geoscience.

“These are really interesting and important results,” says Rachael Byrom, a climate scientist at the CICERO Center for International Climate Research in Oslo who wasn’t involved in the new study. Nonetheless, she says, “methane still remains a really key gas that we need to target in emissions reductions.”

Humans are responsible for most of the methane entering the atmosphere, where it worsens global warming. Concentrations of the potent greenhouse gas have risen about 162 percent since preindustrial times, according to the U.S. National Oceanic and Atmospheric Administration.

The largest sources of anthropogenic methane include fossil fuel uselivestock, rice farming, landfills and biomass burning (SN: 9/29/22; SN: 7/14/20). Scientists fear that as warming triggers thaw of permafrost in the Arctic regions, this could also lead to increased methane emissions, as microbes in the soil consume dead plant material and release the gas (SN: 9/25/19).

Greenhouse gases like methane exert their strongest effects by absorbing infrared “longwave” radiation emitted from the planet’s surface. Earth emits this longwave radiation when it is struck by “shortwave” radiation coming directly from the sun. Most studies of greenhouse gases focus on longwave absorption.

But scientists are learning that greenhouse gases, including methane, also absorb some of the sun’s shortwave radiation. Recent estimates suggested that methane might contribute up to 15 percent more thermal energy to the atmosphere than previously thought, due to this additional shortwave absorption.

However, the new study reveals that methane’s shortwave absorption has the opposite effect. This finding is based on a detailed analysis of the gas’s absorption at various wavelengths.

The result is “counterintuitive,” says climate scientist Robert Allen of the University of California, Riverside. It happens because of the way that methane’s shortwave absorbance affects clouds in different layers of the atmosphere, Allen and colleagues’ simulations suggest.

When methane absorbs shortwave radiation in the middle and upper troposphere, above about three kilometers, it further warms the air — leading to fewer clouds in that upper layer. And because methane absorbs shortwave radiation high up, less of that radiation penetrates down to the lower troposphere. This actually cools the lower troposphere, leading to more clouds in that layer.

These thicker low-level clouds reflect more of the sun’s shortwave radiation back out to space — meaning that less of this solar radiation reaches Earth’s surface, to be converted into longwave radiation.

Meanwhile, upper-level clouds, in addition to greenhouse gases, are known to absorb longwave radiation. So fewer of these clouds means that less of the longwave radiation emitted by Earth is captured in the atmosphere — and more of it escapes to space without contributing to climate change.

With methane’s shortwave absorption, “you expect warming of the climate system,” Allen says. “But these cloud adjustments actually overwhelm the heating due to absorption, leading to a cooling effect.”

Allen and his colleagues conducted the study using a computational model of Earth’s climate. When they took the traditional approach — considering only methane’s longwave absorbance — they estimated that the gas has caused 0.2 degrees Celsius of warming since preindustrial times, out of 1.06 degrees C total warming. But when they also included shortwave absorbance, methane’s contribution to warming fell to about 0.16 degrees C.

In addition to warming the planet, methane is also thought to increase global precipitation, due to greater evaporation of water with higher temperatures. But the researchers found that inclusion of shortwave absorbance also reduced methane’s precipitation effect, from a predicted 0.3 percent increase in precipitation (based on longwave absorbance alone), down to an increase of about 0.18 percent.

An illustration of the sun, Earth and the Earth's atmosphere. The image shows rays from the sun, white arrows, hitting the Earth's atmosphere while the forces of carbon dioxide, methane and water vapor are shown in orange arrows.
Greenhouse gases such as carbon dioxide (CO2), methane (CH4) and water vapor (H2O) exert their strongest warming effects (orange arrows) by absorbing longwave infrared radiation (darker orange arrows) emitted by Earth as it is struck by shortwave radiation (light yellow arrows) from the sun. But the gases can also directly absorb shortwave radiation from the sun, modifying methane’s climate effects in surprising ways, a study finds.A LOOSE NECKTIE/WIKIMEDIA COMMONS (CC BY-SA 4.0)

It will be important to include methane’s shortwave effects in future climate projections, says Daniel Feldman, an atmospheric scientist at the Lawrence Berkeley National Laboratory in California, who was not involved in the study. But he thinks that more work needs to be done to clarify those effects.

The new study analyzed methane’s shortwave impact using only one comprehensive model that included both the atmosphere and ocean, he says. “I would just like to see that sort of analysis done across multiple models,” increasing confidence in the results.

4 thoughts on “New findings on methane

  1. Hello H2O, mixed with nano-particles, to create larger clouds/water droplets before rain.

    Where I live, a complete haze-over 2 day’s ago, with forecasted rain. But none fell. Then the next day it rained. All day, big droplets. 15 years ago it “Spit” or “drizzled” with fog, for days/a week. Not anymore. 1-2 days of pouring rain and then a dry spell for a week or two. The “Climate Changed!” (Ha)

    Clouds always make it warmer.
    In the Canadian Winter. An overcast night is always warmer than a clear night.
    The clouds hold the heat in.
    Interesting info about Methane and it’s reaction with Sunlight in the layers of the atmosphere. I thought it had properties like CO2, X10. Over a time-span. Apparently not!

    Compounding factors, with altering results, depending on “the science.”
    Very interesting indeed. Maybe I’m a nerd.

  2. Looks like we are about to find out:

    Vast amounts of ocean heat are moving toward the Arctic this year. With further melting of sea ice and thawing of permafrost, the Arctic Ocean can be expected to receive more and more heat over the next few years, i.e. more heat from direct sunlight, more heat from rivers, more heat from heatwaves and more ocean heat from the Atlantic Ocean and the Pacific Ocean.

    1. The arctic is already mostly slush in the Summer.
      Anything under “green” is slushy/broken, weak, thin ice. The Summer hasn’t even started. This is a Danish Projection. Satellite photos have shown, the multi-year arctic ice is basically gone already, in Aug-Sept.
      Are you From Brunswick in Germany, Canada or is there another Brunswick?
      I love geography.

      In school, over a decade ago. I spent my spare time in class, making detailed maps of imaginary places. With Cities, Roads, power stations, railway’s, fjord’s, mountain ranges, volcanos, rivers, lakes, borders, national colours.
      Imaginary war’s… One time a teacher gave me 5% extra on a test. Because I covered the blank backside, with a fake map and all that stuff. It was already an A. 80%+ correct.
      I think they just liked my imagination and were promoting it.

      1. I actually still doodle maps for fun.
        They’re not nearly as detailed as they used to be.
        I had some glowing reviews, on the accuracy of my costal border creation/duplication during high-school.
        For art, I made a map of Canada/The USA. With states/provinces, rivers/lakes. And major mountain’s/Elevated ground. (Leading to a river)
        The Canadian northern islands are jagged with no straight lines!
        100% A+ !

        OK, Thanks. Take care all. God Bless you!

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