The Week In Doom: Plankton Edition (Plus, A Reply To Megan McArdle)

by Bradford Plumer | July 30, 2010

Let's see, what unnerving bit of geoscience is going to drop on our laps this week? Michael O'Hare points to a grim new study in Nature about phytoplankton. Yep, that should do the trick. These microscopic organisms live in the ocean and account for half of the organic matter created on the planet. They're gobbled up by larger plankton, which, in turn, underpin the marine food web. Fish and whales depend on them for survival. And that means we do, too.

And it turns out that the number of phytoplankton has been declining steadily for the past half century—down about 40 percent since 1950. Fair warning: Satellite data only goes back about 30 years, so it's hard to tell if this drop is just a coincidence or part of some long-term trend. But what's troubling is that phytoplankton seem to be dwindling most rapidly in the parts of the ocean that are warming up, which would suggest that climate change could be responsible. And if this is part of a long-term trend, that's worrisome. A major disruption to the ocean food chain would not be good news. Here's the BBC:

"Phytoplankton... produce half of the oxygen we breathe, draw down surface CO2, and ultimately support all of our fisheries," said Boris Worm, another member of the Dalhousie team. "An ocean with less phytoplankton will function differently."

The question is: how differently? If the planet continues to warm in line with projections of computer models of climate, the overall decline in phytoplankton might be expected to continue. But, said, Daniel Boyce, that was not certain. "It's tempting to say there will be further declines, but on the other hand there could be other drivers of change, so I don't think that saying 'temperature rise brings a phytoplankton decline' is the end of the picture," he said.

Those caveats are worth heeding. But one potential worry here is that this could function as a climate feedback mechanism. The ocean absorbs about 40 percent of the carbon-dioxide that humans emit. Phytoplankton either turn that CO2 into oxygen or else they die and bury some of it deep down on the ocean floor. But as the supply of phytoplankton plummets, they'll absorb less and less CO2. Indeed, there's evidence that the ocean is already becoming less effective in its ability to act as a carbon sink. And if that happens, more carbon-dioxide lingers in the air, trapping heat on the planet, there's more global warming, ocean temperatures rise, and more phytoplankton could die. Repeat until gloomy.

Over at The Atlantic, Megan McArdle is a little more sanguine about this study. For one, she notes, it's only a single paper. True enough. And even with this one paper, we still don't know if there's a long-term trend here. More broadly, though, her warnings against ecological doom-mongering seem misplaced to me: "One of the things that drives me batty about environmentalists and journalists writing about climate change is the insistence that every single side effect will be negative," she writes. "This is not really very likely."

She's partly right. Not every side effect will be negative. Just this week, The New York Times ran a piece about how marmots will thrive in a hotter world. So, three cheers for marmots. But the bad news tends to far outweigh the good. As the IPCC concluded in 2007, "Costs and benefits of climate change for industry, settlement and society will vary widely by location and scale. In the aggregate, however, net effects will tend to be more negative the larger the change in climate." No one's ignoring the upsides. They're just focused on the larger downsides. For instance, McArdle suggests that more CO2 in the air will boost plant growth, which in turn will help suck more carbon out of the air and ameliorate things somewhat. It might surprise her to learn that scientists are perfectly well aware of that fact. But recent modeling suggests that this effect will likely be offset by other plant-related factors—like changes in evaporation—and the net result will be more warming, not less.

One main point to note here is that, on the whole, global warming will be neutral for this round little rock adrift in the ether that we like to call Earth. You could even say this is an exciting time for Mother Nature. Big changes are afoot. Some species will thrive and many others will die. Evolution will proceed apace. There will still be some forms of life around even if the planet heats up by 5°C or 10°C. As McArdle rightly notes, there have been periods in the past, millions of years ago, when carbon concentrations in the atmosphere were even higher than today, and, to quote Jurassic Park, life found a way.

The problem here is for one very particular life form: people. As I wrote in this TNR piece on planetary boundaries, we big-brained hominids have enjoyed a relatively stable climate for the past 10,000 years—a geological period dubbed the Holocene. Sea levels have been kept in check. Temperatures have fluctuated around a narrow band. And that relative predictability has enabled us to stay rooted in one location, to set up farms and cities, to plan for the future. We've adapted very well to the planet we have, and we've grown quite used to it. Most of our infrastructure has been built under the impression that the planet will basically look the same tomorrow as it did yesterday. That means that wrenching shifts in our ecosystem run the risk of being extremely painful—in the same way a big disruption to our financial system was extremely painful.

The second problem is that we just don't know what's in store. By belching up millions of tons of greenhouse gases into the atmosphere, we're running a massive science experiment on the planet, one that can't really be reversed. Maybe this phytoplankton stuff is just a blip. Or maybe it's part of an ominous trend that's going to rearrange the face of the oceans as we know it—oceans we've come to rely on for our survival. That doesn't strike me as a gamble worth taking.

(Flickr photo credit: willapalens)

Source URL: