Our climate has been changing constantly since Earth began—long before human beings were around to study it. And although climate change isn’t new, the study of how human activity affects climate is a modern-day quest of the highest priority.

For more than 100 years, scientists have monitored the Earth’s surface air temperature through a global network of land-based weather stations and readings taken across the oceans. These data show it has risen more than one degree Centigrade since the late 1800s. Scientists also know that human activities—primarily the burning of fossil fuels—have increased the greenhouse gas content of the Earth’s atmosphere significantly over the same period. These gases, such as carbon dioxide, build up in the atmosphere and prevent the sun’s warmth from radiating back out into space.

At the University of Miami, researchers in a wide range of fields—including physics, chemistry, biology, geology, meteorology, oceanography, and even sociology—are working to understand the impacts of global climate change on various regions of the world. Last year the Intergovernmental Panel on Climate Change (IPCC) released its Fourth Assessment Report, concluding that global warming is “unequivocal” and the likelihood that human activity is its primary cause is greater than 90 percent. UM scientists contributed to the assessments of the IPCC, a group that includes more than 2,000 experts from 154 countries.

Much climate change research has fo­cus­ed on high latitudes—areas like the Arctic, the North Atlantic, and Greenland, where sea surface temperatures are rising and ice sheets are melting faster than the projected rate. One of the greatest contributions UM scientists are making is in the area of tropical climate change.

“It’s a big world, and if we’re looking at just one small region, we’re really missing the big picture,” says Amy Clement, associate professor of meteorological and physical oceanography and contributor to the 2007 IPCC report.

The first step in exploring climate change is finding out what the Earth and its climate were like in prehistoric times. Clues come from fossilized skeletons of tiny plants and animals found in sediment cores, frozen ice, tree rings, and other artifacts.

“There’s no question that global warming is real,” says Larry Peterson, associate dean of academic affairs and professor of marine geology and geophysics at the Rosenstiel School of Marine and Atmospheric Science, who has a joint appointment in the Department of Geological Sciences in the College of Arts and Sciences. “Our instrumental record of temperature change goes back to 1860. What happened before 1860? That’s where a lot of the debate is.”

Peterson is working in the Cariaco Basin, an area of the tropics off the northern coast of Venezuela. Sediments there are de­posit­ed without oxygen, so they remain intact. “It’s probably one of the premier paleoclimate records other than ice cores,” he says.

In his well-lit laboratory at the Rosenstiel School, Peterson holds a nondescript, meter-long tube with the delicate care of a father for a small child. Its contents, covered in plastic wrap, resemble densely packed mud but hold what Peterson hopes will teach him how climate change in the tropics relates to the abrupt temperature changes that have been recorded in high-latitude ice cores.

For years, environmentalists have warned that one of the consequences of global warming would be an upsurge in the most violent hurricanes, the kind that thrive over warm water. But several factors besides ocean temperature, such as atmospheric winds, also come into play. Using a combination of computer models and observational data, Brian Soden, associate professor of meteorology and physical oceanography in the Rosenstiel School, studies how tropical cyclones might respond to global warming. In a study published in the journal Nature last year, Soden and Gabriel Vecchi of the NOAA Geophysical Fluid Dynamics Laboratory concluded that global warming is likely to have little effect on Atlantic hurricane activity.

“We know the oceans are getting warmer as a result of human activities, primarily the burning of fossil fuels,” Soden says. “While other studies have linked this warming to an increase in hurricane intensity, our study is the first to identify other changes in the environment that could counteract these effects. The environmental changes we found do not suggest a strong increase in Atlantic hurricane activity during the 21st century.”

The warming of ocean surface water can have far-flung effects on climate because the ocean surface and the atmosphere exchange heat and moisture. During El Niño conditions, for example, trade winds relax and enable warmer water to extend across the tropical Pacific. The result of an El Niño event may be drought in southern Africa and wet conditions in the southeastern United States. Together, El Niño and its cool-ocean counterpart, La Niña, are a main source of year-to-year variation in weather and climate around the world. One of Soden’s observations: In response to global warming, the tropics tend to slowly drift toward a more El Niño-like state.

Soden’s colleague Clement ap­proach­ed the same question but found different results. Her models suggest global warming would cause the Pacific to move toward a La Niña state. The two published a study on their contrasting theories about the tropical Pacific’s response to global warming.

“We thought it was an important research question that needed to be resolved,” Clement says. “So when we sat down together to try to understand the differences between our results, we realized we were both right in part.”

Climate researchers also focus on salt in the oceans, which plays an important role in the movement of heat. As warm water from the tropics moves through the mid-latitudes, its salinity gradually increases because of evaporation. The saltier, denser water sinks and contributes to a current of denser water far below the surface that spreads heat and salinity throughout the globe. This global conveyor belt, known as the thermohaline circulation, helps regulate climate. Scientists have used computer models to study the conveyor belt as it was 21,000 years ago, when thick sheets of ice covered big chunks of the planet. The results show a different thermohaline circulation pattern then, with water from the Antarctic penetrating farther to the North Atlantic.

Another issue of concern to scientists is whether global warming will change this conveyor, as melting ice adds fresh water to the conveyor source regions. Rana Fine, Rosenstiel School professor of marine and atmospheric chemistry, uses the inventory of chlorofluorocarbons (CFCs) in the oceans to determine how fast water masses form in this conveyor belt and the rate at which they circulate. Added to the atmosphere starting in the 1940s as refrigerants and aerosol spray propellants, CFCs are greenhouse gases that contribute to the destruction of the ozone layer. A small amount of CFCs has dissolved in the oceans, where they are inert. But they reveal both how old different waters in the ocean are and the yielding rate for important processes. Water 4,000 meters down in the North Atlantic is far younger than it would be somewhere in the North Pacific, for example.

“The conveyor belt moves so much heat, fresh water, carbon dioxide,” says Fine, who has found no change in the conveyor thus far. “It’s so important to the Earth’s climate system that you really don’t want to see it slow down.”

Using state-of-the-art scientific findings on climate change is a key focus for UM scientists, such as Kenneth Broad, UM associate professor of marine affairs and policy in the Abess Center for Ecosystem Science and Policy as well as codirector of the Center for Research on Environmental Decisions, based at Columbia University.

“Climate models are impressive in their ability to capture trends on large regional scales,” Broad explains. “But there is considerable uncertainty in predictions on smaller spatial scales and in the timing of specific impacts. This poses a challenge for local political acceptability of preemptive actions. Some impacts are more certain—such as sea level rise and melting glaciers—but are serious enough in terms of threats to our economy and way of life around the world that it would be negligent to not act proactively.”

Broad’s insights are based on his studies of the relationship between climate and perception, use and misuse of scientific information, and decision-making under uncertainty.

“Most people do not feel they are directly affected by a few degrees of warming or ice melting in faraway regions,” he says. “In Florida the general public and politicians rarely make the connection between sea level rise and salt water intrusion tainting our underground fresh water supply and loss of biodiversity, or the economic impact of increased beach erosion on tourism, or shifts in disease vectors due to temperature and precipitation changes.

“Most people are worried about immediate problems—the mortgage crisis or the war in Iraq—and tend to psychologically discount problems they may have to face years down the road. We must begin to shape policies that provide incentives both for reducing greenhouse gases and for preparing for the inevitable impacts.”

ALEXANDRA RAVINET is a freelance writer in North Bay Village, Florida.