Earth is the only planet that we know about with such an abundance of water; Nature provides humanity with an incredibly valuable resource in the world's oceans

Robert Costanza is a different kind of economist. He and his colleagues call themselves "ecological economists." They factor in the value of Nature when calculating the worth of goods, production, and national wealth.

In 1997, Dr. Costanza and others created a bit of a stir when they published an article in the science journal Nature in which they estimated the annual value of the biosphere to be $33 trillion U.S. This figure is greater than all the annual Gross Domestic Product of the world's economies combined.

The ecological economists estimated the value of the oceans to be $21 trillion, while the land was worth $12 trillion. The actual figures are debatable; only best-guess estimates. The really interesting aspect is that the oceans were given almost twice the value of the land.

That shouldn't be surprising; 71 percent of the planet is covered by water. But, when all is said and done, it is just water. However, the world's oceans are far more than that. They are:

* The basic source for the hydrologic cycle that makes life on Earth possible;

* A global thermostat that regulates entire climates;

* The cleaning agent that absorbs carbon dioxide and generates oxygen;

* A primary source of animal protein (fish) for one billion people;

* The superhighway that carries most globalized trade; and,

* The playground for tens of millions.

There are some more specific numbers that go along with those assets.

The oceans are Nature's solar-driven water pump. About 430,000 cubic kilometres of water evaporate from the oceans every year. Of this, around 110,000 cubic kilometres fall on Earth's land surface as precipitation. That's a lot of water; the flow over Niagara Falls is one cubic kilometre every 46.27 hours. This water makes the growing of crops possible. The run-off then refills lakes and rivers before flowing back to the ocean to refuel the hydrologic cycle.

The ocean is also the engine that drives the world's climate. Water absorbs and holds vast amounts of solar energy, which is then released slowly. This has the effect of changing climates almost everywhere by moderating extremes of heat and cold.

Oceans absorb and store carbon dioxide from the atmosphere. Because this invisible gas is one of the main agents of climate change, the ocean is an important sink that helps to modify human impacts on global climate.