"Civilization has only a 50-50 chance of making it to the 22nd century"

Personally I wouldn't even give civilization 50-50 odds, but I'm glad that someone with authority, Sir Martin Rees, Britain's Astronomer Royal, is speaking out about it. He went as far as to publish a popular book about it called Our Final Hour.

He saw some of the likely pullers of the linch pin as:
* out-of-control technology: biotechnology and nanobots. You only have to really screw up once.
* strangelet: Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) could produce particles called strangelets, which grow by consuming nearby ordinary matter and basically eat the planet. The odds of this were put at one-in-50-million, which is about the odds of winning the lottery. Again, you only have to really screw up once.
* environmental disaster/destruction: my guess is parts of the biosphere might still be functional in the even of a global disaster, however you have to be very lucky/rich to live which is the ultimate form of class warfare.