Here Comes the Heat

In icy depths and on windswept peaks, scientists discover a secret:
55 million years ago the world got hot—very hot.
The culprit? Then, as now,
a rapid infusion of carbon causing abrupt and extreme climate change.
Moving from the laboratory to the field, picking up the dirt,
big brains give us straight talk about heat . . .

and cyclones, and conveyor belts, and methane burps on the ocean floor,
and the uncontrolled experiment that is planet earth.

It is 24°C at the North Pole. It rains copiously, and the Arctic Ocean feels like a warm bath. The rest of the planet is sweltering. The sea is acidic; ocean currents have stopped or shifted course. As many as half of the single-celled benthic foraminifera, a key part of life on the ocean floor, have been wiped out. Some parts of the world are experiencing extreme flooding, ferocious storms, and frequent cyclones. It is too hot even for tropical jungles, and three-quarters of the Colombian and Venezuelan rainforest has died. It is a global crisis, affecting every part of the land, the air, the ocean, and everything that lives on or in them.

This may sound like something out of a Hollywood disaster movie, but actually these cataclysmic events took place 55 million years ago. During a unique moment in geological history called the Paleocene-Eocene Thermal Maximum (petm), a period lasting roughly 150,000 years between the Paleocene and Eocene eras, the earth got hot—very hot. Nobody is exactly sure what the world was like during the petm or what triggered the warming, but the Hollywood script would benefit from any one of the reigning theories: explosive volcanic activity or a major underwater landslide; changing sea-circulation patterns warming the intermediate ocean waters; or, possibly, a giant asteroid plowing into the earth. Any of these could have unleashed methane hydrates from the ocean floor, which, in turn, would have introduced a massive amount of carbon into the atmosphere, severely disturbing the natural carbon cycle. Fossil remains from the petm are allowing scientists to piece together a picture of that distant world, and there appear to be haunting similarities with our own.

Scientists consider the remains of the petm, which were first discovered fifteen years ago, to be the Rosetta Stone of global climate change, the nearest parallel in the fossil record to what is happening to the planet right now. “It is as close as we can get to an analog,” says Peter Wilf, a geologist at Penn State University. Then as now, tremendous amounts of carbon were rapidly introduced into the atmosphere, and the petm fossil record reveals what lived and what died, where things happened and over what period of time. Scientists can also use it to determine how life on earth responded. This all occurred 10 million years after the extinction of the dinosaurs, when mammals were starting their long rule, but many millions of years before the first human saw light.

As analogues go, it’s an alarming one. It’s not just that the petm carries the stigma of intense global climate change or that the warnings derived from research into the period are eerily consistent with those sounded by former US vice-president Al Gore, British economist Sir Nicholas Stern, and much of the scientific community. The petm also suggests something else: the effects of increased carbon in the atmosphere could be much more dramatic than first expected. In fact, the petm indicates that the catastrophic effects on the planet’s biosphere of a massive rise in carbon levels could come into play in our lifetimes—long before any major steps can be taken to avert the problem. “We are running an uncontrolled experiment,” says Wilf. “I think we’re really, really in for it. The potential for societal breakdown is enormous.”

This is why I am climbing the Pyrenees in northern Spain on a rainy morning. I’ve listened to four days of papers, both esoteric and frightening, on the petm and now I want to put my hands on it, bear witness to what it means. This is the field-trip portion of an extraordinary international conference, Climate and Biota of the Early Paleogene, held every few years for paleontologists and climate scientists studying this piece of history. In June, two of the conference’s superstars, paleoecologists Henk Brinkhuis and Appy Sluijs from the University of Utrecht, scored the cover story in Nature (along with a number of colleagues) based on analysis of sediments from the petm, which were obtained during an Arctic drilling expedition. The samples from the Arctic core demonstrate that the petm was a time of “widespread, extreme climatic warming . . . associated with massive atmospheric greenhouse gas input.” Sea-surface temperatures near the North Pole, for instance, increased from about 18°C to 23°C. Many of the other papers presented in the auditorium in Bilbao also deal with the disturbing effects of the increase in greenhouse gases during the petm, and many are destined for the same fate as that of Brinkhuis and Sluijs. These studies are a preview of the unsettling science headlines to come.

Carbon is present in the atmosphere in two stable isotopes: heavy and light. When an uncharacteristically large amount of carbon is released, the balance of heavy and light isotopes on the planet changes, and that change is captured in the geological record. Paleontologists investigating the petm see a stunning spike in the light isotope of carbon, an indication that 55 million years ago a tremendous burst of carbon entered the atmosphere—an amount greater than what would have resulted from the incineration of every living thing on land and in the sea.