Global warming: have we lost already?

Imagine that we spot a dino-killer coming our way, 10km of space rock due to impact in 80 years.

I think that would concentrate our minds.

So how does a 10km meteor compare to this view of our climate future? (emphases mine)

Too late? Why scientists say we should expect the worst of global warming | Environment | The Guardian

At a high-level academic conference on global warming at Exeter University this summer, climate scientist Kevin Anderson stood before his expert audience ...

.... Anderson, an expert at the Tyndall Centre for Climate Change Research at Manchester University ... pointed out that carbon emissions since 2000 have risen much faster than anyone thought possible, driven mainly by the coal-fuelled economic boom in the developing world...

.... he said it was "improbable" that levels could now be restricted to 650 parts per million (ppm).

The CO2 level is currently over 380ppm, up from 280ppm at the time of the industrial revolution, and it rises by more than 2ppm each year. The government's official position is that the world should aim to cap this rise at 450ppm.

The science is fuzzy, but experts say that could offer an even-money chance of limiting the eventual temperature rise above pre-industrial times to 2C ...

At 650ppm, the same fuzzy science says the world would face a catastrophic 4C average rise. And even that bleak future, Anderson said, could only be achieved if rich countries adopted "draconian emission reductions within a decade". Only an unprecedented "planned economic recession" might be enough. The current financial woes would not come close.

... Many scientists, politicians and campaigners privately admit that 2C is a lost cause. Ask for projections around the dinner table after a few bottles of wine and more vote for 650ppm than 450ppm as the more likely outcome.

Bob Watson, chief scientist at the Environment Department and a former head of the IPCC, warned this year that the world needed to prepare for a 4C rise, which would wipe out hundreds of species, bring extreme food and water shortages in vulnerable countries and cause floods that would displace hundreds of millions of people. Warming would be much more severe towards the poles, which could accelerate melting of the Greenland and West Antarctic ice sheets...

... Garnaut, a professorial fellow in economics at Melbourne University, said: "Achieving the objective of 450ppm would require tighter constraints on emissions than now seem likely in the period to 2020 ... The only alternative would be to impose even tighter constraints on developing countries from 2013...

.... Earlier this year, Jim Hansen, senior climate scientist with Nasa, published a paper that said the world's carbon targets needed to be urgently revised because of the risk of feedbacks in the climate system. He used reconstructions of the Earth's past climate to show that a target of 350ppm, significantly below where we are today, is needed to "preserve a planet similar to that on which civilisation developed and to which life on Earth is adapted". Hansen has suggested a joint review by Britain's Royal Society and the US National Academy of Sciences of all research findings since the IPCC report...

There's not necessarily a lot that's new in this review, more a collection of bad news since the IPCC report. The situation is particularly confusing now because while many believe the island nations are doomed, it's thought that open declaration would sabotage agreements that would benefit everyone else.

It makes sense. If you live on an island nation, you may not have much interest in supporting a 550 ppm target since you'll be under water anyway (or live elsewhere). You might push for 400 ppm, though that would require onerous changes in China, and thus we'd have no agreement at all.

So how does 600 ppm, maybe with permafrost and ocean methane release feedback, compare to a 10km meteor impact?

I think the hot earth is preferable, but I'd like to hear from an authority I trust.