[Lynbarry]

The problem with this is that once we've reached a "perilous level of global warming", it is quite possible that there is no way back.

The 2 degrees target seems to be already out of reach and everything beyond that gets closer and closer to being unpredictable. Of course no one knows what exactly will happen anyway. But as an example: If the arctic permafrost starts to melt methane gets released into the atmosphere which further accelerates everything [1].

I would not hope on some not-yet-existing or not-yet-usable technologies to fix everything we're messing up now. The "eventually" when finally everyone stops using fossil fuels because other kinds of energy are cheaper might be just too late.

[1] http://grist.org/climate-change/2011-12-05-the-brutal-logic-...

[netcan]

This is where geo-engineering can come in. I think climate scientist will be much more comfortable discussing it if it seems we are on track for fixing the underlying causes.

There are bunch of different ideas, most of them involve directly interacting with global temperature by reflecting energy back to space. Injecting sulphur dioxide into the atmosphere for example, mimics how some volcanic eruptions cause temporary cooling. Another is massive scale cloud seeding over the oceans.

One of the scariest things about these ideas is how cheap could be are. What happens if Canada decides it would really prefer a milder winter and sprays the hydro dioxide up there like a bunch of unruly mounties? Then they cut it out and Uzbekistan do the same.

[_jal]

Purely my (possibly terribly misinformed) opinion, but geo engineering (used here to mean the bundle of blue-sky proposals to manipulate the climate intentionally after we've completely screwed it up unintentionally) is a red herring and, at best, a high-risk hail-mary.

It is a red herring: in discussing climate change, it is brought up primarily as a reason not to worry about doing anything now, we'll fix it in post. The sheer number of otherwise smart, educated people who blithely assume that attempting to modulate a huge chaotic system we don't fully understand and can't model is a tribute to optimism and not much else. Add to that the fact that we only have one atmosphere on which to practice, and, well, I'm not optimistic.

And that is before we get in to the (alluded to by the parent post) public choice questions on an global scale, something that history demonstrates is, politely, extremely difficult, extremely slow, mostly toothless and prone to cheating. To pick one example, we, as a species, cannot agree that leaving explosive objects scattered around to randomly maim and kill is, on balance, a bad idea.

If, in 100 or whatever years, the options are go extinct slowly or pump tons of reflective gas into the upper atmosphere and see what happens, well, I'd vote to go for broke, too. But that is all the "geo-engineering" approach is at this point.

[rbanffy]

> And that is before we get in to the (alluded to by the parent post) public choice questions on an global scale, something that history demonstrates is, politely, extremely difficult, extremely slow,

If we could agree on global-scale engineering projects to manipulate the climate, we'd probably be able to agree on reducing dependence on fossil fuels...

[dreamcompiler]

Many types of geo-engineering could in theory work to cool the planet. But none of the proposals I'm aware of will decrease the CO2 in the atmosphere. Without fixing that, we'll still have ocean acidification, which will dramatically change how the oceans support life. It's possible that most forms of seafood we know today will become extinct. http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidificati...

[netcan]

Yup, all the more reasons to keep our coastal cities out of it.

[vixen99]

So on which climate sensitivity estimate are you basing your comment, and why are you choosing it in preference to others?

A compilation of at least 30 published studies based upon satellite and ocean observations demonstrate climate sensitivity to a doubling of CO2 levels after all feedbacks is only about 0.5 C, which is ~7 times less than the 3.2C claimed by the IPCC AR5 modelled mean estimate.

[gherkin0]

> The problem with this is that once we've reached a "perilous level of global warming", it is quite possible that there is no way back.

IIRC, there have been significant periods in prehistory where there were no ice caps, and technically we're currently in the middle of an ice age [1]. That's not to say that the effects of global warming won't cause severe stresses on our current ecosystems and civilization, but it's an overstatement to say "there's no way back."

[1] https://en.wikipedia.org/wiki/Quaternary_glaciation

[mikeash]

There's always an implied "in a timescale that's meaningful for human civilization" in these things.

Of course the Earth can eventually recover, but if it takes a million years it might as well be never for the purposes of this discussion.