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Our Final Hour: A Scientist's Warning: How Terror, Error, and Environmental Disaster Threaten Humankind's Future in this Century—on Earth and Beyond

by Martin Rees, 2003, Basic Books, 228 p., ISBN 0-465-06862-6, US$25.00 list price.

Sir Martin Rees is Royal Society Professor at Cambridge University and England's Astronomer Royal. He is the author of Just Six Numbers, Before the Beginning, Gravity's Fatal Attraction, and Our Cosmic Habitat written for general readership.

If you like to worry—or think you should—then this book is for you. Sir Martin plainly describes a host of threats to civilization. The 21st century might well be our last unless we, as a species, take bold steps to define our values and decide how we want to go forward. He judges that the odds are no better than 50:50 than humankind will survive to the end of the century. "I hope to stimulate discussion on how to guard (as far as is feasible) against the worst risks, while deploying new knowledge optimally for human benefit."

Among his long list of threats are these:

Natural and engineered viruses. Self-replicating nano-machines would be a special case that could turn the biosphere into "gray goo."
Experiments gone awry. With high-energy physics, we might tear the fabric of space itself. Or a chain reaction might start that "erodes everything on Earth."
Thermonuclear threat. We lived under this threat for the latter half of the 20th century. Rees is concerned that small disaffected groups, even individuals, have the potential to inflict great harm. Rees hopes to loose a $1000 bet: By 2020 an instance of bioerror or bioterror will have killed a million people.
Meteorites. We might well detect near-space objects on a course that might intersect the Earth's orbit. If discovered with sufficient time, there might me ways to divert the meteor and avoid collision. 10-km sized rocks hit the earth on average every 50-100 million years.
Superintelligent machines. These could be the last invention humans ever make, and they might take over. A more positive view would have human brains gradually augmented with cyber extensions. Eventually, we might desire to engineer our successors.
Depletion of Earth's resources. Population threatens the ability of the environment to process our waste. Rees makes a strong case for renewable energy.

Rees isn't the first to sound the alarm. He gives high praise to the young H.G. Wells who presented a 1902 lecture "Discovery of the Future" at the Royal Institution in London. Wells identified these risks: "something from space, or pestilence, or some great disease of the atmosphere, some trailing cometary poison, some great emanation of vapour from the interior of the Earth, or new animals to prey on us, or some drug or wrecking madness in the mind of man." Late in life, Wells was additionally concerned with cyber risks and human pressure on the environment.

The odds of various risks are presented throughout, though with less precision (in expression) than I prefer.

Among the many illustrations in the book is this version of a "doomsday argument" (pp. 136-7):

Approximately 60 billion people have ever lived, and approximately 10% of those are alive today. The dead outnumber the living by a factor of ten. Consider two scenarios for humankind's future:

Pessimistic: Our species dies out within one or two centuries (or survives with only a small population).
Optimistic: Humanity lives for many millennia with at least the present population, so trillions of people will be born in the future.

Suppose these ultimate numbers of people to live are represented by two identical-appearing urns: The "Pessimistic" urn contains 10 tickets numbered 1-10. The "Optimistic" urn contains 1000 tickets numbered 1-1000. Each digit represents 10 billion people who will sometime live on Earth. You pick an urn at random and draw a ticket, number 6. Because this is such a low number, you are approximately 100 times more likely to have drawn from the Pessimistic urn. The number 6 represents the 60 billion people who have lived on Earth. Our known place in the birth roll suggests that our species' future will more likely be very short rather than very long.

The argument is attributed to astrophysicist Brandon Carter. He holds that conditions in the universe must be very special for life and intelligence to emerge.

The central message is to emphasize our responsibility for stewardship: for the Earth and for humanity. There are many threats that one can worry about. Cost-effective actions are available for some of these risks, and I'm hopeful that decision analysis will help us steer a path.

This is a well-written, engaging book. Despite the grim topic, I think all persons interested in risk will enjoy reading this book.

—John Schuyler, March 2005.