Global warming has recently been subjected to a media blitz, thanks both to the international climate conference in Copenhagen, and the controversy surrounding the online publication of filched e-mails between a number of leading climate scientists.
Lost in the clamor were two new reports, which, in their separate ways, serve to illustrate a gap that has grown up between the physics and politics of climate change. Even as polls indicate slackening concern among Americans about global warming, evidence shows that the greenhouse effect is rapidly intensifying.
The studies in question suggest the enormity of the change the planet is beginning to undergo, but they also demonstrate, by their anonymity, how difficult it seems to be for climate change to capture the public imagination.
In the last decade of climate research, the rate of global warming has consistently matched or outpaced the "worst-case" projections produced by leading climate models. And yet no matter how many studies are published revealing alarming new data, public opinion on the matter seems still to be determined by politics instead of physics.
It is worth remembering, in this light, that while we can negotiate with each other about climate change and what to do - or not do — about it, we cannot negotiate with the climate itself.
The first study was published in the journal Science in late November. Conducted by Japanese and Canadian researchers, and it concerns a seemingly obscure problem: the well-being of shellfish in the Arctic Sea. As early as 1999, scientists warned that one consequence of climate change could be the acidification of ocean water. The ocean absorbs gases from the atmosphere, and close to half of all the carbon dioxide humans have emitted since the beginning of the 19th century has been soaked up by the sea.
In 1999, Ken Caldeira, a well-known climate scientist at Stanford University, found that clogging the atmosphere with carbon dioxide will eventually alter the pH of seawater — a process he termed ocean acidification. He also warned that as the climate change accelerates, the ocean will become undersaturated with aragonite — the form of calcium carbonate that shellfish use to form their shells.
When Caldeira conducted his study in 1999, he projected that it would take three centuries for ocean acidification to threaten shellfish with extinction.
Caldeira published the first part of the study, in Nature, with the subheading "The coming centuries may see more ocean acidification than the past 300 million years."
Caldeira's projection, it now seems, was optimistic — a recurring phenomenon in climate modeling. The new Science study drastically shortens his time frame. The researchers project that the Southern Ocean will become undersaturated with aragonite by 2030, and the North Pacific by 2100. Arctic surface waters will become undersaturated within a decade. Moreover, they found that aragonite saturation has already decreased in the top 50 meters of the Canada Basin, due not only to increased atmospheric CO2 levels, but also sea-ice melt.
The fate of shellfish in the Canada Basin may seem obscure. But shellfish — beginning with pteropods but including everything from mussels to clams — help form the basis of the ocean food chain. If they can't form shells due to consequences of global warming, fish can't eat them, seals and polar bears can't eat the fish, and an enormous ecological catastrophe ensues. "It puts the entire [Arctic] food chain at risk," Fiona McLaughlin, one of the researchers, told Reuters.
The Science study is interesting in part because it shows that sea-ice melt is a major cause of aragonite undersaturation.
"Sea ice is so pure it has very few of these (carbonate) ions. It means that when we are melting this ice, which by its nature is more acidic, we are making surface waters more acidic," McLaughlin said. According to the study, ocean acidification — a phenomenon whose strange and alarming nature is evoked by its very name — won't begin in the Southern Ocean until 2030.
But that projection may have to be sped up. Less than two weeks after the Science study was published, an ominous new report concerning the stability of Antarctic ice upended a widely held assumption in the scientific community.
Antarctica is divided into two ice sheets — one on the western side of the continent, the other on the east. Scientists have known for some time that the western sheet is melting. When Al Gore showed film of glaciers crashing into the sea in the documentary An Inconvenient Truth, the footage came from the west Antarctic coast. At the time, the frozen continent was losing as much as 36 cubic miles of ice per year, a trend unambiguously linked to global warming.
As Gore pointed out, if the West Antarctic ice sheet were to disappear completely, it would cause the ocean to rise and cover much of the world's low-lying land, including large parts of the Eastern seaboard.
But while scientists were certain that the West Antarctic sheet was melting, it was generally assumed that its eastern counterpart was stable or even gaining mass. The region is so cold that it seemed insulated against all but the most drastic warming.
So it came as a shock when, on Dec. 1, the journal Nature Geoscience published evidence showing that the East Antarctic sheet is also melting. Studying data collected by a NASA satellite, researchers at the University of Austin, in Texas, discovered that the sheet has been losing mass for at least the last three years. The data, they found, "indicates that as a whole, Antarctica may soon be contributing significantly more to global sea-level rise."
The most recent report from the U.N. body tasked with tracking climate change, the Intergovernmental Panel on Climate Change, projected that by the end of this century ice melt will cause the seas to rise by a maximum of just under 2 feet. That report was released in 2007. A week after the Nature Geoscience data was released, a study by European researchers, published in the Proceedings of the National Academy of Sciences, projected that sea levels may increase by more than 6 feet by 2100.
A 6-foot sea level rise would, models show, submerge more than 22,000 square miles of U.S. land on the Atlantic and Gulf coasts. Most of Florida and Louisiana would become uninhabitable, and large parts of Manhattan would disappear. Worldwide, more than 100 million people — nearly a third of the total population of the United States — would be displaced.
It is also worth noting that the complete disappearance of the West Antarctic ice sheet is frequently used as an example of a "worst-case" scenario, to illustrate how bad global warming could become on a multiple-century time scale. Its melting would cause the seas to rise by 20 feet. The full melting of the East Antarctic ice sheet, by contrast, would cause them to rise by 200 feet — a nearly unimaginable prospect.
As the studies above show, climate change is already reconfiguring the natural world. How extensive that reconfiguration ends up being — and how much suffering results in consequence — depends on whether politicians across the world can agree to take strong action to reduce greenhouse gas emissions. Their success, in turn, will to a large extent depend on the answer to a simple question: When will the gap between the politics and the physics of climate change close?
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