I met James Hansen several decades ago, and remember him all the back to  1988 when he first testified in Congress .  This was six years after I had left the U. S. Senate, a time period when global warming was an issue of importance only to a very few scientists.  I am on his mailing list, and this morning received his views on  The Venus Syndrome and Runaway Climate . Paper starts with: Mars, Venus and Earth   are the Goldilocks planets – too cold, too hot, and just right. These planets reveal how a planet’s surface temperature depends on atmospheric gases as well as the planet’s distance from the Sun. The physics is energy balance: a planet sends back to space, as (infrared) heat radiation, the energy in sunlight that it absorbs. Absorbed solar energy depends simply on the Sun’s irradiance, ⁱ   the planet’s distance from the Sun, and the fraction of incident sunlight that the planet absorbs (the remainder being reflected). The surface temperature is then ...