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"SURVIVING THE CENTURY"

The inaugural Carl Sagan Memorial Lecture
Cornell University, 8 May 2017
It’s a great honour to give this Carl Sagan lecture. The ideas he stood for need proclaiming louder than ever today. We need an optimistic vision of life’s destiny --- in this world, and perhaps far beyond it. We need to think globally, we need to think rationally, we need to think long-term. Carl’s influence was immense, through his science and – most of all, through his eloquence and global outreach.
In this talk I’ll try to address some themes that would have engaged him..

We’ve been familiar with this image [Earthrise] for nearly 50 years –it’s iconic for environmentalists. .

But suppose some hypothetical aliens had been watching the Earth for its entire history, what would they have seen? Over nearly all that immense time, 4.5 billion years, things would have changed very gradually. The continents drifted; the ice cover waxed and waned; successive species emerged, evolved and became extinct.

But in just a tiny sliver of Earth's history - the last one millionth part, a few thousand years - the patterns of vegetation altered much faster than before. This signalled the start of agriculture. Changes in land-use accelerated as human populations rose.

Then came even faster changes. The carbon dioxide in the atmosphere began to rise anomalously fast. The planet became an intense emitter of radio waves. And something else unprecedented happened: small projectiles launched from the planet's surface escaped the biosphere completely. Some were propelled into orbits around the Earth; some journeyed to the Moon and planets.

If they understood astrophysics, the aliens could confidently predict that our biosphere would face doom in a few billion years when the Sun flares up and dies. But could they have predicted this unprecedented runaway fever -- less than half way through the Earth's life?

And what might they see if they watched for another century? Will this spasm be followed by silence? Or will stability ensue? And will more projectiles leave the Earth to establish oases of life elsewhere?

These are the questions I'll speculate about

Some years ago I wrote a book which I entitled 'Our Final Century ?' My publisher deleted the question-mark. The American publishers changed the title to 'Our Final

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