a citizen’s journal by Thomas Nephew

Earth’s albedo falling

Posted by Thomas Nephew on May 11th, 2005

NASA’s Earth Observatory explains:

…white shows areas where Earth reflected the highest percentage of shortwave solar radiation. Dark blue shows areas where Earth reflected the lowest percentage of shortwave solar radiation. Notice how the highest albedo values are in regions where Earth is mostly covered by snow and ice, or clouds, or both. The lowest albedo values occur in forest-covered landscapes or open ocean.

…A drop of as little as 0.01 in Earth’s albedo would have a major warming influence on climate—roughly equal to the effect of doubling the amount of carbon dioxide in the atmosphere, which would cause Earth to retain an additional 3.4 watts of energy for every square meter of surface area.

In the May 6, 2005, issue of the journal Science, the CERES Science Team reported Earth’s shortwave albedo has been steadily declining since the Terra CERES instrument began making the measurement in February 2000. Over the 4-year span (2000 through 2004), the CERES instrument measured an albedo decrease of 0.0015, which equals an extra half a watt of energy per square meter retained in the Earth system.

Do the bonehead climatologist math — .01/(.0015/4)= 27 years to “double CO2 effect” if this continues — and you may feel like “so what? Who cares what happens in 27 years?” But wait! That’s not all! The whole thing accelerates, too: more warmth retained melts more ice reflecting sunlight, meaning more dark surfaces to absorb heat, meaning more warmth retained.

In the first article of Elizabeth Kolbert’s recent “The Climate of Man” three part series in the New Yorker (I, II, III), ocean scientist Donald Perovich discusses albedo in similar terms:

“Not only is the albedo of the snow-covered ice high; it’s the highest of anything we find on earth,” he went on. “And not only is the albedo of water low; it’s pretty much as low as anything you can find on earth. So what you’re doing is you’re replacing the best reflector with the worst reflector.” The more open water that’s exposed, the more solar energy goes into heating the ocean. The result is a positive feedback, similar to the one between thawing permafrost and carbon releases, only more direct. This so-called ice-albedo feedback is believed to be a major reason that the Arctic is warming so rapidly.

“As we melt that ice back, we can put more heat into the system, which means we can melt the ice back even more, which means we can put more heat into it, and, you see, it just kind of builds on itself,” Perovich said. “It takes a small nudge to the climate system and amplifies it into a big change.”

It seems to me more and more like we have only a few choices: we can either start slowing down global warming now, slam on the brakes later, or hit the wall shortly after that.

One Response to “Earth’s albedo falling”

  1. » Blog Archive » Arctic ice cap loss accelerates Says:

    […] “Barcelona” points out, since ice reflects sunlight and open water absorbs it, this isn’t just a symptom of global warming, but a cause of it as well — the process is self-accelerating. Speaking with Elizabeth Kolbert for her 2005 New Yorker […]

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