I guess the big alarmist news at the moment is that Stephen Hawking has been quoted as saying:
Trump’s action could push the Earth over the brink, to become like Venus, with a temperature of two hundred and fifty degrees, and raining sulphuric acid.
Well, this is simply not true. As this Climate Feedback says:
It is not possible for Earth’s climate to become as extreme as Venus’ climate in the foreseeable future. And even extreme global warming would not be linked to sulfuric acid precipitation, which occurs on Venus because of volcanic emissions of sulfur gas.
As Chris Colose mentions in the Climate Feedback article, it is theoretically possible to make modern Earth hot enough such that the upper atmosphere becomes quite wet and conducive to substantial water loss to space. However, even this would not be a Venus-like runaway and it is also extremely unlikely (probably, virtually impossible).
On Twitter, Robert Grumbine made the point that a Venus-like runaway is far less likely than something like an extinction-level asteroid strike, and we don’t exactly go around worrying about something like that (we do, however, commit some resources to keeping track of asteroids).
As Ken Caldeira also pointed out, unrestrained fossil fuel burning likely leads to nasty climates, but not as nasty as Venus. I think this is a key point; we don’t need to invoke extremely unlikely (virtually impossible) catastrophic scenarios in order to argue that continuing to pump CO2 into the atmosphere might be a really bad idea.
So, one of the obvious problems with what Hawking has said is that it is simply wrong. The other is that this is an important issue and we really should be discussing the real consequences of continuing to emit CO2 into the atmosphere, not having to deal with high-profile people making alarmist claims. Of course, in the grand scheme of things, this is probably just another blip along the ever complicated climate communication highway, but it would be nice if people who should know better didn’t keep scoring these kind of own goals.
Stoat on Hawking radiation.