Past may tell future

UCI researchers are trying to pry climate secrets out of trees, sky and ocean by tracking the global movement of carbon.

By Pat Brennan

October 21, 2002

Carbon is famous when it takes a form that can make people rich: diamonds and oil. But carbon is also essential to life on Earth, an element vital to our bodies as well as the stability of our oceans and atmosphere.

For researchers at University of California, Irvine, carbon is the focus of new, groundbreaking research that seeks to answer one of civilization's most pressing questions: How fast is the planet heating up?

The answers could help the world better prepare for the effects of global warming.

"We know human-caused changes are outstripping whatever happened in the past," said Susan Trumbore, UCI Earth System Science professor, one of three researchers in charge of the project. "If we can predict how emissions change, we can predict how the atmosphere will change."

The warming is mostly due to the buildup of one kind of carbon-carbon dioxide-in the Earth's atmosphere, along with other greenhouse gases, climate scientists agree.

When fed information about the carbon dioxide buildup, computer models of climate now pump out hazy predictions of rising sea levels and dwindling glaciers-enough to suggest to many scientists and activists that a crisis is coming. The predictions are not precise enough, however, to pin down where, when and how.

The key is the planet's carbon cycle, the life-giving exchange of gases among the atmosphere, oceans, and land. Researchers need to know exactly where carbon dioxide goes and how long it stays there.

Accelerator will help reveal mysteries

By using a $1.5 million particle accelerator, now being fine-tuned in a basement laboratory, UCI researchers plan to unlock the secrets held in coral, tree trunks, dead leaves and ocean water, where carbon dioxide is bound up and stored.

These bits of matter, once blasted into vapor inside the accelerator to release their carbon constituents, should reveal the footprints of carbon dioxide around the planet: where it goes, how long it stays and how much storage capacity exists in plants and oceans.

The more carbon that can be locked up in deep ocean currents or tree trunks, the slower the planetary warming will be, Trumbore said. But to learn the details of this cycle of carbon storage and release, scientists must know how long carbon dioxide resides in plants, soil, oceans and air.

Only complex instruments such as UCI's accelerator can measure the carbon atoms in these bits and pieces precisely enough to reveal details of their past, which will help researchers gauge the future.

And no one has yet taken such measurements in detail. UCI's accelerator, paid for with a $2 million grant from the W. M. Keck Foundation, is the first in the nation dedicated almost exclusively to carbon research.

Determining the severity of warming

The research is essential to resolve debates among climate scientists about how quickly the warming will take place in the next few decades and how severe it will be.

Right now, it appears that the increase in carbon dioxide is bringing an explosion of growth in the world's forests. Much of it is welcome: The East Coast, where most forests were logged to oblivion over a century ago, now has a thicker covering of trees than it did at the time of the Civil War.

But the picture isn't all rosy. In some places such as Texas, trees may be replacing rare native grasslands, wiping out one habitat type in favor of another.

A bigger question: Can forests and plants keep absorbing more and more carbon dioxide, perhaps turning Earth into a thick, greenhouse jungle? Or will they reach a point of saturation, causing atmospheric carbon dioxide to increase its alarming buildup?"

"We know CO2 is missing in the atmosphere," Trumbore said. "We know we're burning fossil fuels and that half of the CO2 we're putting in the atmosphere stays there. Where is the other half going?"

Carbon can be used as a "clock"

Carbon comes in a variety of forms: as carbon dioxide gas in the air, as dissolved carbon in ocean water, as the hard stuff-calcium carbonate-that ocean-dwelling creatures make their shells out of.

It also comes in different forms at the atomic level. And that allows carbon to be used as a "clock" that tells the age of a sample and, by extension, how long it has been locked up in, say, a tree or a core of ocean sediment.

A rare type of carbon, carbon-14, is absorded by living plants and animals, becoming part of their tissues as they grow. It is usually created by high-energy cosmic rays that strike nitrogen in the atmosphere.

When the organisms die, the absorption of carbon-14 stops, and the carbon-14 starts to decay back into nitrogen. By measuring how much carbon-14 has decreased in a tissue sample, scientists can tell how long the tissue has been dead and when the carbon in it was first locked up.

The atomic bomb tests of the 1950s and 1960s released abnormally large amounts of carbon-14 into the atmosphere, so scientists can use that carbon "spike" to precisely date specimens within the past 40 years. Older samples show far less carbon-14. These can de dated on scales of centuries and millenniums. So the scientists can see short-term trends-1963 to present-as well as long-term trends going back hundreds or thousands of years.

CO2 levels closely track temperature

Such studies by other researchers have already revealed the Earth's atmosphere is hitting its highest level of carbon dioxide in 420,000 years. Levels closely track temperature: During ice ages, carbon dioxide levels have been low.

The planet is now in a period of accelerated warming, with a 30 percent increase in carbon dioxide concentrations in the atmosphere over the past 150 years- a trend that began about the same time industrialization became widespread in Europe and North America.

And while many researchers still debate whether the planet's rising temperature and carbon dioxide levels bear the stamp of human influence, Trumbore says she has no doubt.

"A big piece of evidence is that fossil fuels have no carbon-14," Trumbore said.

So if fossil fuel-burning is adding large amounts of carbon dioxide to the atmosphere, scientists should see an overall drop in atmospheric carbon-14. And that is exactly what they are seeing, she said. "That is kind of a smoking gun," she said.

Oceanographer Ellen Druffel, meanwhile, will use the accelerator to peer back in time at an important climatic event: El Nino.

Traditional measurements provide only about 100 years' worth of El Nino records. But by measuring carbon levels inside corals, Druffel expects to see back several centuries.

Pinning down the El Nino cycle more precisely will reveal important clues about changes in the Pacific Ocean.

"El Nino really does affect climate worldwide," Druffel said. "We're finding out more about this every day - what the global connections are."