Changes in temperature, salinity, currents mean ripple effects elsewhere

When the wind starts to blow and the rain starts to fall, most people don’t blame the oceans for their plight.

But the waters that cover more than 70 percent of Earth’s surface are intimately linked to the planet’s climate.

“Many people think climate is the weather. In fact, the ocean is the largest driver of climate,” said Fei Chai, an oceanographer with the Climate Change Institute at the University of Maine.

In the real world, the oceans and the atmosphere lack the distinct boundary lines depicted in textbooks. Water, carbon dioxide, oxygen and other molecules constantly travel back and forth between the air and the sea.

Most coastal residents understand how the oceans help to moderate temperature by warming or cooling breezes that pass over the water en route to land.

The oceans play a similar role on a global scale. The sea can absorb or release a tremendous amount of heat, slowing the impact of a climate shift.

The oceans also hold a great deal of carbon dioxide, one of the most abundant greenhouse gases. Carbon is present in all living things – including plankton and the calcium carbonate structure of clams and corals – which will eventually decompose, creating more carbon dioxide.

“A cooler ocean tends to hold carbon dioxide – like a can of Coke,” Chai explained. “When you have warmer water, the CO2 starts bubbling out of the water into the air.

This is just one of the many climate phenomena that concern scientists, like Chai, who produce models predicting what might happen if the climate changes. For example, high levels of CO2 in the atmosphere could warm the oceans, prompting the release of still more CO2 and spurring further warming.

And as Hurricane Katrina so aptly demonstrated, warm oceans also can trigger more immediate effects. Monster storms will happen occasionally in any climate, but warmer water has the potential to breed more ferocious hurricanes.

The ocean currents that bring monsoons to India, El Ninos to Peru, and nor’easters to Maine are also at the whims of global climate. Currents are put in motion by cold water sinking to the sea bottom in the polar regions because it becomes more dense and holds more salt as it loses its heat to the air. The cold water moves downhill along the sea bottom toward the equator, where it warms and returns to the surface. Prevailing winds then drive the warm surface water back toward the poles. The result is continual motion throughout the oceans.

This system was dubbed “the great conveyor belt” by climatologist Wallace Broecker of the Lamont-Doherty Earth Observatory at Columbia University, because it drives much of the world’s weather. Scientists cite changes in the circulation pattern as a major factor in past ice ages. The system has been relatively stable for the past 200-300 years, after likely playing a role in the cold phase known as the Little Ice Age between the 14th and 19th centuries.

But if Earth becomes too warm, millions of gallons of fresh water from melting polar glaciers and icebergs could pour into the sea, interfering with the temperature and salt balance, or thermohaline, that maintains the currents.

“The ocean transports a lot of heat from the western side of the Atlantic to the eastern side,” Chai said.

Without this conveyor belt, the Gulf Stream, which carries warm water to the United States and Western Europe, could weaken or change path.

Broecker and some other scientists believe they have evidence from ice cores that suggests that this system has changed in the past, bringing ice and snow to the temperate regions. The disaster movie “The Day After Tomorrow” was based on Broecker’s theory – albeit in a dramatically exaggerated form that depicted the start of a new ice age in Manhattan over a period of a few days.

To better understand, and predict, the behavior of these systems, scientists have deployed a small army of buoys and free-swimming rovers to monitor the high seas, transmitting their data by satellite.

Chai uses this and historical climate data to create complex models on a supercomputer with the capability of 256 high-powered PCs, showing how the oceans change over time, their warm and cold currents strengthening and dissipating.

Internationally, the goal is someday to have thousands of live data collectors, drifting in all of the world’s oceans, searching for the signals that the climate is beginning to change.