George Monbiot explains how whales can change an entire ecosystem through a process known as a trophic cascade. Trophic cascades are ecological processes which start at the top of the food chain and tumble all the way down to the bottom.

This video is a follow-up to the original segment on the impact of wolves being reintroduced to Yellowstone National Park after 70 years.

When whales were at their historic populations, before their numbers were reduced, it seems that whales might have been responsible for removing tens of millions of tonnes of carbon from the atmosphere every year. Whales change the climate. The return of the great whales, if they are allowed to recover, could be seen as a benign form of geo-engineering. It could undo some of the damage we have done, both to the living systems of the sea, and to the atmosphere.