Ward outlines the critical role of plate tectonics as Earth's thermostat, describing how the weathering of granite removes carbon dioxide from the atmosphere and prevents a runaway greenhouse effect like the one that destroyed Venus. He discusses the galactic habitable zone, noting that Earth's position far from the dangerous center of the Milky Way protects it from gamma ray bursts and heavy asteroid bombardment that would sterilize closer worlds.
The conversation shifts to abrupt climate change, with Ward warning that a 10-year thermohaline circulation collapse could devastate European agriculture and trigger wars over food. He reveals he has read the script for The Day After Tomorrow and critiques its compressed timeline. Ward also challenges SETI's optimism, recounting his debates with Seth Shostak and suggesting that the search for extraterrestrial intelligence may be premature given threats facing Earth.
Key Moments
Refuting Carl Sagan: Ward says microbial life is probably common but Rare Earth was written largely as a back slap to Carl Sagan, whose estimate of more than a million intelligent species in the Milky Way Ward considers far too generous given current evidence.
Ten mass extinctions from warming: As a paleontologist of mass extinctions, Ward says scientists now identify about ten extinction events caused directly by global warming - not just the dinosaur-killing asteroid - and that the Earth's atypical 10,000-year period of climate calm is about to end.
Europe goes to war over food: Ward predicts the thermohaline shutdown will plunge Europe to Labrador-like winters; 500 million Europeans, no longer self-sufficient in food but heavily armed, will likely invade Tunisia or other grain-growing regions, potentially triggering global war within a decade.
Galactic habitable zone: Ward explains that proximity to the galactic center exposes planets to constant comet bombardment and gamma-ray bursts; Earth's far-out location is why we've had only one major impact event in 500 million years - making galactic real estate a key filter on complex life.
Jill Tarter wants me dead: Ward jokes that SETI's Jill Tarter - the real-life inspiration for Jodie Foster's Ellie in Contact - would like to see him killed by a Sherman tank because Rare Earth is the most dangerous threat to SETI's premise.