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Why understanding something smaller than a pinprick (an aerosol particle) is the key to something as big as a planet (global climate)

February 23, 2011 Leave a comment

UPDATE MARCH 4: Sadly, Glory launched this morning but did not reach orbit because the payload faring did not separate. The faring protects and encloses the satellite during launch and initial ascent. With this extra weight onboard, the launch system was unable to reach orbit and landed in the ocean. Condolences to the mission team that spent years designing and building the ill-fated Glory spacecraft.


mosaic of images and art associated with glory mission

To learn anything, you first need to know what you don’t know. Let’s call them the “known unknowns.”

In climate science, one of the thorniest known unknowns is the impact of aerosols, microscopic particles that drift in the atmosphere absorbing and reflecting energy, and tweaking clouds. My colleague Adam Voiland — Goddard Space Flight Center’s chronicler of all things aerosol — explained it this way in one of his many fine web features and press releases on the topic:

“The particles can directly influence climate by reflecting or absorbing the sun’s radiation. In broad terms, this means bright-colored or translucent aerosols, such as sulfates and sea salt aerosols, tend to reflect radiation back towards space and cause cooling. In contrast, darker aerosols, such as black carbon and other types of carbonaceous particles, can absorb significant amounts of light and contribute to atmospheric warming.”



The Glory mission, which is scheduled to go into orbit this week, will attempt a much better understanding of aerosols and — climatologists hope — lead to needed improvements in the computer simulations that predict where earth’s climate is heading in the coming decades.

But for my part, the Glory mission actually takes me back a decade or so, to the mid-1990s when I worked for a now-defunct science magazine called Earth. The UN’s Intergovernmental Panel on Climate Change (IPCC) had, in 1995, published its Second Assessment Report. Using a newfangled thingie called the World Wide Web, science reporters eagerly poured over the IPCC report’s many hundreds of pages, trying to make sense of it all.

One issue that stood out was — you guessed it — the role of aerosols in global climate change. Here’s what the panel authors said on page 525 of a portion of the IPCC report, Working Group I: The Science of Climate Change.

“Atmospheric aerosols (Chapter 2) also play an important role in the Earth’s radiative budget. There are fairly reliable estimates of the amount of sulphur burned but these do not translate directly into number density of aerosols, for which the size, hygroscopic and optical properties, as well as their vertical, horizontal and temporal distributions, have not been well observed.”



Allow me to translate: It’s saying that we know how much sulfur-containing fuels we burn (coal, for example), which produces sulfate particles that have a cooling effect on climate; but that doesn’t tell us how much of this aerosol is produced, how much energy it reflects, and where it is.

And on page 526, the report tells us why we should care about aerosols, from a practical point of view:

Thus, at present the uncertainty in aerosol radiative forcing is the largest source of uncertainty in the total radiative forcing of climate over the past industrial period. Since aerosols are very patchy in their distribution, they could create significant regional climate changes regardless of their effect on globally averaged forcing.



{If you have a lot of time on your hands or need something very heavy to hold doors open, download and print Working Group I: The Science of Climate Change by clicking HERE.}

So here is the punchline for this week: Glory will provide data needed to help resolve uncertainties about aerosols and climate. The hope is that computer models will be able to make better predictions of where Earth’s climate is heading.

If you want to learn more, here is a series of recent videos about the Glory mission. And don’t miss this and this web feature about Glory, by Adam Voiland.






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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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