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? David Attenborough 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 Attenborough believes that we may be able to act to prevent a catastrophe.