BBC: Some extraordinary phenomena have taken place in recent times; Hurricane Katrina, the heat wave of 2003, polar bears swimming in search of ice and vast swarms of insects enveloping an African village. But are these isolated incidents or are they omens of a greater global change?

Sir David discovers that the world is warming at an unprecedented rate, and finds out why this is now far beyond any normal allowance for cyclical fluctuation. But are humans to blame? These changes are already in motion whatever we do now, but Sir David believes that we may be able to act to prevent a catastrophe.

People around the world are having to adapt their way of life as the climate changes; the Inuit in the Arctic whose hunting is now limited, the Pacific island inhabitants forced to move as their homes disappear beneath the waves, and the Siberian homes slowly sinking into the permafrost. Sir David investigates some of the possible scenarios for the future, including rising sealevels, insect plagues and an increase in diseases.