Saturday, July 08, 2017

Venus if You Won't

Stephen Hawking recently suggested that Trump's policies could produce a Venusian style runaway greenhouse on Earth. This produced scathing critiques from the wise and the less wise, including the Stoat and the Lumonator. Just how confident can we be that Hawking is wrong? I'm pretty confident, but not quite so confident as the w and the lw, mentioned above. Let's review some pertinent facts:

First, because Venus is closer to the Sun than Earth, it receives about 1.88 times as much solar radiation as Earth does, but the story doesn't stop there. Venus is also much shinier than Earth, with an albedo of 0.76, more than twice that of Earth (0.37) and consequently absorbs less solar radiation than Earth does (about 91% of what we do). Also, recall that the Venusian greenhouse started when the Sun was a lot cooler than it is now, quite possibly when Venus received less solar radiation than Earth does today.

Of course the chemistry of the Venusian atmosphere is much different than that of Earth, but much of that difference is due to the runaway greenhouse. For example, the enormous concentration of CO2 in the Venusian atmosphere is due to the fact that without oceans, the carbon that winds up in carbonate rocks on Earth winds up in the atmosphere, and the oceans likely disappeared due to photodissociation of water in the upper atmosphere and loss of the hydrogen to space.

My estimate: critics 0.95, Hawking 0.05. But do your own math.