With tipping points and extreme global warming looming, the key to understanding our climate future lies in our distant past With rising emissions, we are on track to cause rapid global warming with devastating con- sequences. But how bad could climate change get and what might it do to planet Earth and humanity? Runaway Climate explores the causes of the Paleocene Eocene Thermal Maximum (PETM) rapid climate-heating episode, its dramatic impact on life on Earth, and lessons for our climate future. Fifty-six million years ago our planet experienced a period of intense warming known as the PETM, resulting in a rapid global temperature increase of about 7°C. Triggered by natural geological processes over millennia and magnified by strong climate feedback loops, the PETM lasted for about 180,000 years and drastically altered life on Earth. Yet in only a few short decades we've pumped similar amounts of greenhouse gasses into the atmosphere, making the PETM an unsettlingly apt analogy for our current predicament. This deeply cautionary tale explores: The runaway feedbacks that pushed the PETM's climate past the tipping point Subsequent cascades of environmental devastation—from plant and animal migrations to ocean acidification, extreme weather, and mass extinctions A sobering vision of life on hothouse Earth—a hostile world of desertification, sea-level rise, climate refugees, and agricultural collapse The urgent need for decisive individual and collective actions to slash carbon emissions, stabilize the climate, and undertake a rapid transition to a cleaner and healthier future. Scientifically rigorous, yet accessible to a wide audience, Runaway Climate is essential reading for every- one committed to understanding and taking action on the climate emergency.