Life in the Volcano

Efforts to measure the amount of climate-changing CO2 humans are pumping into the atmosphere reached a major milestone recently. NASA was able to launch, and then bring to life, a very clever satellite named OCO-2 (the Orbiting Climate Observatory 2) that can see the CO2 in the atmosphere and measure its concentration. Mission scientists have just begun to announce some of their preliminary findings.

OCO-2 satellite
The OCO-2 satellite, on orbit since 2014, detects CO2 concentration in the atmosphere beneath.

The advent of OCO-2 is a grand feat for two reasons: The first, an unfortunate prologue to this story, is that a previous attempt to launch such a mission didn’t quite make it. The first probe, called simply OCO, was launched atop a rocket out of Vandenburg Air Force Base in California back in 2009, but a glitch caused the protective cover enclosing the satellite to stay stuck in place. Too heavy to make orbit, the whole mess plunged unceremoniously into some lonely stretch of the Pacific near Antarctica. Parts of it by now may well have created a very expensive and sad artificial reef deep on the ocean floor.

No doubt after some frustrated tears were shed, the scientist and engineers on the project picked themselves up, rebuilt a near carbon(!)-copy of the probe, and tried again. In the wee hours of July 2, 2014, the mission team and scientists everywhere again held their breath for several long minutes as the second attempt pushed off from the launch pad. This time it worked, and without much fuss OCO-2 reached its proper orbit (with several friends), opened its solar panels, and began to look around.

Diagram of A-Train of earth-observing satellites
The “A-Train” (Afternoon flyover) of earth-observing satellites, including OCO-2.

The other reason to get excited that OCO-2 is working is that the data being sent back by the craft is itself nearly a marvel. It turns out a seemingly trivial thing like measuring atmospheric CO2 concentrations from orbit is extremely hard. The instruments on OCO-2 work by looking for wavelengths of light that CO2 absorbs very well. Absorbing radiation is a trick CO2 does quite well, albeit not in any wavelengths we can see – for instance, its ability to absorb infrared light emitted from the earth (often thought of as “heat”) is the reason why human emission of CO2 is the main contributor to increased temperature and general climate havoc in the modern globe. OCO-2 infers the CO2 concentration by measuring the amount of light that “isn’t there” in a few key parts of the spectrum of sunlight bounced off the earth, gobbled up by the CO2 in the atmosphere. However, the ground and oceans and other gases in the atmosphere are also very good at absorbing light on their own, leaving little light remaining in a few narrow bands for OCO-2 to intercept and interpret. Measuring CO2 concentrations this way is like trying to figure out who among a crowd is wearing a slightly darker shade of blue deep — when everyone is standing around in the woods under a half moon. To compensate, OCO-2 has to take its measurements over relatively large footprint areas of about 1 by 2 km (something less than a square mile), and is confined to doing its work only within widely spaced orbital tracks.

Even with the constraints inherent in the mission, the probe is already beginning to serve its scientific purpose, and the first test and demonstration results just started hitting scientific publications in the past few months. I got to hear about some of those results at the most recent meeting of the American Geophysical Union this December in New Orleans.

In a recent paper in Nature (and nice presentation at AGU) Dr. Florian Schwandner of NASA’s Jet Propulsion Laboratory and his collaborators showed that OCO-2 could detect two key processes of interest to the mission planners, and the scientific community at large.

For one, OCO-2 can see the CO2 belched by erupting volcanoes. The molten rock cast skyward by volcanoes contains dissolved CO2 from deep within the earth that boils out on reaching the surface, leaving a plume of high-concentration CO2 that quickly dissipates downwind. OCO-2’s instruments were lucky enough to pass right over the currently erupting Mount Yasuur on remote Tanna Island in the Pacific, and sensitive enough to detect the distinct tail of CO2 wagging behind. Their measurements let them predict that this volcano was emitting something in the neighborhood of 42 thousand metric tonnes of CO2 per day – comparable to the output of one reasonably large coal-burning power plant.

An erupting volcano
Volcanoes — now measurable from orbit!

Offering even more giddy possibility for scientists like me who study urban carbon emissions, OCO-2 also passes directly over a few major cities like Los Angeles. There the CO2 being emitted by all the cars and industries and power plants in the L.A. basin are much easier to see from space than a volcanic eruption. A view of CO2 measured by OCO-2  show deep red pixels indicating high CO2 concentration over downtown and Orange County, shading to lower-concentration greens as one passes over the San Gabriel’s and into the thinly populated Antelope Valley beyond. The instruments even appear to be able to measure slight changes in CO2 concentration with seasonal changes as plants green up and weather patterns change.

OCO-2 passes over the Los Angeles basin.
OCO-2’s path over the L.A. basin, carbon dioxide concentration in parts per million (ppm).

What makes these preliminary results exciting for me is the prospect that tools like OCO-2 may give us a whole new means of monitoring ongoing CO2 emissions from our cities — and with that knowledge, the ability to tackle the job of reducing them. A common refrain in the world of climate mitigation is, “You can’t regulate what you can’t measure”. With instruments like OCO-2, our ability to measure our impact just made a significant jump.

And these results also underline a perhaps easily missed message about the scale of our impacts on the planet: A natural force as powerful as a volcanic eruption would seem to dwarf any planetary commotion mere human beings could possibly conjure up. Yet watching these giant plumes of CO2 rising from the surface, one couldn’t help but think the truly enormous volcanoes on Earth are our cities. From space, most of us seem to go about our lives inside the rims of volcanoes – ones we ourselves have made.

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