What The Past Can Tell Us About A Future “Super-Greenhouse” World

Fifty-six million years ago, enough carbon leaked into the atmosphere to alter the climate and acidify the ocean. The same thing is happening now, much faster. But this time, we know what’s going to happen, and it isn’t pretty.



Even the most extreme natural global warming episode of
the last 65 million years can’t hold a candle to what we’re doing to the
atmosphere now. If a new study of layered rock deposits from the Norwegian Arctic is correct, then we’re releasing carbon dioxide 10
times faster than at any other time since the dinosaurs died out.

The Paleocene-Eocene
Thermal Maximum (PETM), is one of the
best geo-historical examples of what a future super-greenhouse could be
like. It happened about 56 million years ago, and although
nobody knows exactly what triggered it, numerous studies show that
carbon emissions were the main culprits–perhaps arising from various
coal seams, limy organic ocean muds, and frozen methane ices. This,
of course, was long before people appeared on Earth, so we had nothing
to do with it. Instead, undersea volcanism might instead have started it by immolating carbon-rich marine deposits.

What did the PETM do to the planet and its inhabitants? Carbon
dioxide concentrations jumped as much as five times higher than those
in our present atmosphere, adding at least 10°F to climates that were
already much warmer than today and probably finishing off what little
ice and snow may have whitened the polar regions in winter. The
greenhouse gas surplus lingered for 150,000 to 200,000 years, and turned
the deepest parts of the oceans into stagnant, acidified dead zones.

As unpleasant as being
suffocated to death by the carbonic acid bath must have been
for many deep-sea denizens, the PETM wasn’t the great mass
extinction or ecological “disaster” that some media accounts describe it as.Most
of the extinctions occurred among a relatively narrow range of
organisms–including tiny ocean-dwelling amoebae–but
in shallower waters and on land, most species pulled through.

No polar bears
survived the PETM, but that’s not because of warming; it’s because the
hot spell happened so far back in time that bears hadn’t even evolved
yet. In fact, none of our modern mammals existed back
then, and a tour of the Earth of 56 million years ago would reveal a
fantastical menagerie that included hoofed, carnivorous “wolf-sheep” and
our earliest, lemur-like primate ancestors scampering freely among
universally warm latitudes and continents. Dawn redwood forests ringed the shorelines of the ice-free Arctic Ocean, and lush beech woods covered Antarctica. Deep
ocean life suffered the most because the huge slug of carbon dioxide
acidified the bottom waters (much as we see beginning to happen today),
and greenhouse warming may also have slowed or stopped the sinking of
well-oxygenated polar waters to the sea floor.

These facts are well
known to geo-historians, but this latest study adds a new wrinkle to the
PETM story by comparing it explicitly to what’s going on today. So what, if anything, is the value of such a finding to us here and now? The article posits one
lesson: Although many species survived the rapid onset of the PETM
greenhouse, it doesn’t mean that modern biodiversity isn’t threatened by
today’s gas buildup–because this time it’s happening much faster than


Still, some
relatively recent natural climatic changes have actually been just as
abrupt as our present warming; perhaps that’s why the paper focuses on
CO2 buildups rather than temperature. Furthermore, we simply don’t know how adaptable most species on Earth are–we haven’t even cataloged all of them yet. And regardless of how the pace of that earlier event compares with our own, today’s species didn’t live through it anyway.

The most compelling lesson is that yet another independent, peer-reviewed
exploration of the past has shown that a super-greenhouse is not just
the delusional fantasy of enviro-doomsayers. Scott Wing, a
top PETM expert with the Smithsonian Institution, thinks that this kind
of study is especially important because it clearly shows that adding
lots of CO2 to the atmosphere does warm the planet and
make the oceans more acidic. “People can be as skeptical as they want
about global warming resulting from human carbon emissions,” he told me
recently, “but the geological fact is that this kind of thing really has
happened before.”

This latest addition to the PETM story offers us a warning. For
the first time, billions of people and swarms of powerful machines are
unearthing and igniting fossil carbon deposits on a planetary scale. This means that even the best paleo
studies can’t fully inform us about what lies ahead, and we’re
essentially driving ourselves and our planet into the future with our
eyes half closed.

But I suppose we knew that already, didn’t we?

[Image by Flickr user echobase_2000]

Curt Stager is an ecologist, paleoclimatologist, and science journalist with a Ph.D. in biology and geology from Duke University. His new book is DEEP FUTURE: The Next 100,000 Years of Life on Earth (St. Martin’s Press, March 2011).




About the author

Curt Stager is an ecologist, paleoclimatologist, and science journalist with a Ph.D. in biology and geology from Duke University (1985)