Greenhouse Gases: The Earth's Own Tanning Oil

Global warming is often a term that scares some people, but a new study is giving scientists a better conceptual understanding of its affect on the planet, possibly putting minds at ease. As humans pump carbon dioxide into the air, adding to the greenhouse gas effect, over time it acts as the Earth's own version of tanning oil, rather than covering it in a warm blanket like previous research suggested.

Published in the journal Proceedings of the National Academy of Sciences, the study may change the story of global warming, but unfortunately the ending is the same.

"This is a neat study in that it changes the way we think about the climate system," lead author Aaron Donohoe, a postdoctoral researcher at MIT, said in a statement. "We looked at processes that are well captured in the models, but the conceptual understanding of how they work hasn't been fleshed out before."

When carbon dioxide (CO2) first builds up in the atmosphere, it does indeed act as a blanket, trapping long-wave infrared energy emitted by the Earth's surface. But as the Earth gradually heats up under this blanket, hotter objects release more long-wave radiation that eventually cancels out the warming effect.

So once things balance out after about a decade, what keeps things heating up? Researchers from the University of Washington determined that it's shortwave radiation - the high-energy rays coming directly from the Sun.

Scientists normally shy away from shortwave radiation because clouds can reflect this visible light back to space, and clouds are an unpredictable factor when it comes to climate change.

Nonetheless, researchers behind this latest study explored the matter further. They compare its effects to that of melting ice. Melting ice creates darker surfaces that can absorb more heat, and the more melting the more heat it can absorb. Likewise, warmer air holds more water vapor, causing it to absorb solar radiation that might otherwise bounce back off clouds, ice or snow.

So overall, those effects are like putting tanning oil on the planet, letting it absorb more of the Sun's incoming rays.

"While greenhouse gases trap one type of radiation, it's the other type - visible, shortwave radiation - that is really sustaining global warming over the long term," explained co-author Kyle Armour.

The findings can help people better understand global warming and how it works, as well as allow scientists to more accurately detect climate change in satellite data, which can measure shortwave radiation.