When it comes to global warming and climate change, discussion of carbon and greenhouse gases is inevitable. But a commentary in the brand new open access journal Earth’s Futuresuggests that pride of place in any examination ought instead go to albedo.
You know, the measure of how much sunlight different materials reflect. Loyal readers may recall a few pieces we ran in 2009 looking both at how different Earth surfaces affect albedo—fresh snow reflects roughly 80 percent of sunlight, old snow 60 percent, grass 20 percent, and forests 10—and how by painting the top of cityscapes white we might be able to offset some of the warmth caused by carbon emissions. And white roofs do help a bit, as both our writers and former Energy Secretary Steven Chu have noted.
In the new piece by Harvard’s Russell Seitz, he argues that humans don’t even known how much albedo is present on Earth, and that any measure is transient given annual changes in greenery and sea ice and longer term changes in urban footprints and cultivated land. These “known unknowns” matter because “albedo, not atmospheric chemistry, determines the first decimal place of the Earth’s temperature.” He writes that the uncertainty in estimates of the albedo’s “radiative forcing” is by itself “several times larger than total greenhouse gas forcing.” (Radiative forcing is the difference between the energy the Earth receives from the sun and what it bounces back into space.)
As noted, humans have been monkeying with albedo for their entire history, tearing down forests, putting up cities, creating reservoirs, generating soot, and helping sea ice to melt. It’s not a one-way street to inferno—some simulations find that cutting down every forest in the world could cool the planet.
But that’s on land. Water covers 7/10ths of the planet, and liquid water reflects very little sunlight. As Seitz has said elsewhere, “The deep oceans absorb 93 percent or more of the sunlight falling straight into them. That’s literally as dark as an asphalt parking lot.” That adds a lot of warmth to the equation—an all-water world would have an average temperature of 90 degrees Fahrenheit.
It is ironic that while acutely aware of black asphalts’ capacity to soak up solar heat, few urban planners realize how absorbing water’s features can be. Dark as a parking lot, the pond in Central Park undoes the cooling eﬀect of the white roofs that overlook it by adding up to a gigawatt to the city’s peak summer heat load.
But the oceans aren’t just water—marine life, in particular plankton, can come and go in great patches that affect albedo. And there are clouds and waves and other variables sloshing around:
While we have anecdotal accounts of outliers from white squalls and amaranthine reefs to Homer’s wine-dark sea, nobody really knows the color of the ocean or the depth of the clouds scudding over it. All we have are averages of averages concealing another layer of unknowns.
Seitz has an interesting bio, being both a skilled material scientist and geophysicist who also has worked in international affairs. And he’s a got a dog in the albedo fight. For a couple of years he’s been talking about creating trillions of tiny bubbles—not Don Ho-size tiny bubbles, but truly microscopic ones—to brighten the ocean. These “hydrosols”—they’ve been called “clouds turned inside out”—in theory would reduce water’s albedo and thereby slow warming. (Here’s a technical explanation that includes the nice line, “The low energy cost of microbubbles suggests a new approach to solar radiation management in water conservation and geoengineering: Don’t dim the Sun; Brighten the water.”) Seitz is now chief scientist for Microbubbles LLC, which is trying to monetize this bit of geoengineering in part by showing how “bright water” could reduce local evaporation of valuable fresh surface water inland.
Fiddling with the ocean’s albedo isn’t a brand new idea for geoengineering our way out of climate change without undue sacrifice. As our solar energy guru John Perlin noted in 2009:
Some people have suggested grandiose schemes using the albedo as their weapon. One scheme envisions sending off large white planks throughout our oceans and allowing them to float where they will. Others suggest anchoring huge artificial white-painted islands in the seas. An even bolder scheme has come up — the launch of huge white umbrellas, as large as football fields, to shade the earth.
Besides appearing far-fetched and expensive, it's tough to predict what adverse effects such large-scale interventions might bring.
A related point is made in a new paper by Axel Kleidon and Maik Renner in the journal Earth System Dynamics. They argue that combating global warming is more complex that just tweaking the heat-in/heat-out equation, especially when you start considering the effect of existing heat on the water cycle. While effect of heat and precipitation can be understood, "An important implication of our results is that geoengineering approaches to reduce global warming are unlikely to succeed in restoring the original climatic conditions."
Seitz is presenting his bubbles, inserted into the top layer of water using compressed air, as more of a way to conserve water or affect the temperature on a local or regional scale. Writing in Environment magazine last year, Robert Olson raised the stakes a magnitude and described microbubbles (and a few other technologies) as "soft geoengineering," He defined soft geoengineering as “interventions that are local, are scalable, are reversible, pose few environmental risks, and have multiple benefits.” Whether tiny bubbles are truly benign remains to be seen, and Seitz’s roadshow includes a section on risks. Nonetheless, he suggests the biggest risk lies in ignoring our own albedo footprint.