Daniel Schrag

Schrag discussed the causes, risks, and myths of climate change on December 6 in Snyder Auditorium as part of the Dean’s Distinguished Lecture series. The lectures aim to share the latest science and spark synergies between HSPH faculty and colleagues, said Dean Barry Bloom in his introductory remarks.

Fifty million years ago, palm trees grew in Wyoming, tropical crocodiles lurked in Greenland, and a pine forest covered Antarctica. "This is where we’re heading," Schrag said. "The question is how long will it take until Earth looks like this–1,000 years or 10,000 years."

Some sort of rapid event turned up the heat several degrees about 55 million years ago, although the cause is a matter of scientific debate. Some have proposed that a massive release of methane, another greenhouse gas, caused the abrupt warming, but Schrag believes the culprit was carbon dioxide and that the event is an analogue for future climate change. One of Schrag’s graduate students is exploring whether vast inland seaways that covered Africa and North America dried out and triggered bacteria in the muck to release double or triple the amount of carbon dioxide.

One troubling lesson from this ancient analogue is that modern climate models fall short of recreating the full temperature increase, known as the Paleocene-Eocene Thermal Maximum. "The real world is more sensitive than the models we’re using," Schrag said. "So we think something is missing from the models–maybe a type of cloud or feedback that increases the warming."

The mysterious physics of water, in the form of ice and clouds, accounts for the major uncertainties of climate modeling. Carbon dioxide and other greenhouse gases both absorb the sun’s infrared radiation and radiate the heat back out to space. "Water makes things really difficult," Schrag said. "As temperatures increase, there is more water vapor in the atmosphere. Water is a big amplifier."

Scientists know more about carbon dioxide. The gas plays a key role as a planetary thermostat. Early in the life of the planet, the sun was less luminous and gave less warmth to the earth than today. To compensate, levels of carbon dioxide were high, trapping available heat, scientists believe. As the sun became more luminous, levels of carbon dioxide decreased. The thermostat has worked for millions of years by a surprisingly simple chemical reaction, Schrag said. Silicate rock on the ground reacts with carbon dioxide and water. The products wash out to sea and precipitate as calcium carbonate at the bottom of the ocean. Below the water, the seafloor and its calcium carbonate eventually sink deep into the earth, creating volcanoes that burp the carbon dioxide back out.

The industrial age seems to have changed the equation. The carbon dioxide levels have climbed in lockstep with the increased burning of fossil fuels. The atmospheric levels exceed 300 parts per million (ppm) for the first time in millions of years and are projected to keep climbing. "Even if we do incredible things to stabilize the carbon dioxide emissions now, we will still be at around 500 ppm by the years 2040 or 2060," Schrag said. "We are performing an experiment on a planetary scale no one has done for millions of years. No one knows where we’re going, but there are likely to be plenty of surprises."

The business-as-usual scenario in the climate models predicts carbon dioxide levels of 900 ppm by the end of the century. The United States now emits one-quarter of the carbon dioxide, but developing countries are likely to catch up, especially by burning cheap and plentiful coal. "Developing new technology to get energy from coal without releasing carbon dioxide to the atmosphere must be a priority for current research," Schrag said.

Controlling climate change is a huge technical challenge, but it may be possible to sequester carbon dioxide underground, in the ocean, or in sediments beneath the sea floor, Schrag said. In response to a question, he said that massive tree-planting efforts could sequester as much as 1 billion tons of carbon dioxide a year, but people will be producing 25 billion tons a year by the end of the century.

"It’s valuable, but it’s not the first-order solution," he said. And worse, as the frozen arctic tundra thaws, bacteria there may send up another 5 billion tons a year.

"All countries will be affected by droughts, storms, and rising sea levels," Schrag said. But the effects of climate change on human health are likely to be greatest in developing countries that do not have the resources to adapt to disruptions in the air and water quality and food supply.

In this country, the political wake-up call to initiate a sustained response that can survive 30 years of politics and economics is likely to take the form of an extreme event, such as a deadly heat wave, an unprecedented flood, or a major increase in tornados and hurricanes. Ironically, weather is so chaotic that it is impossible to say that one particular storm is associated with climate change, Schrag said.

--CCM