Sulu archipelago, Philippines

More than 6,000 of the 7,100 Philippine Islands are uninhabited, like this islet in the Sulu Archipelago, a set of 500 islands that separate the Celebes and the Sulu seas. Their extraordinary biodiversity is under threat, not from distant industrial sites but from the effects of global pollution. These islands, which barely rise above the surface of the water, are among the first potential victims of global warming and are certain to disappear when the sea level rises. The oceans, which maintain our planet's equilibrium, play a major role in our climate, storing up heat from warmer times and releasing it later, transporting it in its currents, providing the water for rain-bearing clouds through evaporation, and trapping and absorbing carbon dioxide. This vast mass of water is inhabited by fauna whose diversity is scarcely imaginable and which, through the food chain - from plankton through fish to the marine mammals - plays an enormously important role in human subsistence.