Assume that GHG emissions, land use changes that have affected albedo, solar output changes, celestial cycles and things we don't yet grok have been increasingly warming the earth and may in future warm it to an extent we would rather not endure for any number of reasons.

What are the sensible responses people can make? A variety of hacks have been studied:

"To really stop climate change in its tracks, you have to go to virtually zero emissions in the next two decades.

"So the question is, is there a silver bullet that can help us to limit the amount of climate change?"

Some such "silver bullets" aim to scrub carbon dioxide (CO2) out of the atmosphere, some to cool Earth directly by veiling it; others are yet more radical.

While most are confined to computer models or scribbling on the backs of envelopes, a few have been tried cautiously. . .

Consider the notion of shading the planet with mirrors. The US National Academy of Sciences found that 55,000 orbiting mirrors would reflect enough sunlight to counter about half the doubling of carbon dioxide.

But each mirror must be 100 sq km; any larger and you would need a manufacturing plant on the Moon, says Dr MacCracken. The price tag of space-based fixes makes them prohibitive - for now.

By contrast, the "human-volcano" approach is on terra firma and less costly. Inspired by studies of the Mt Pinatubo eruption of 1991 and the cooling effect of its sulphur plume, one proposal suggests that naval guns shoot sulphur pellets into the air to increase Earth's albedo, or reflectivity. . .

A few years ago, Dr Caldeira set out to disprove an idea put forward by Livermore physicists Lowell Wood and Edward Teller to cool the Earth with a sheet of superfine reflective mesh - similar in concept to orbiting mirrors.

In a computer model, Dr Caldeira and colleague Bala Govindasamy simulated the effects of diminished solar radiation.

"We were originally trying to show that this is a bad idea, that there would be residual regional and global climate effects," explains Dr Caldeira.

"Much to our chagrin, it worked really well."

Last year there was some discussion in Free Fire Zone about a couple of space based shielding schemes. The best one, by Oliver Morton, was to locate a smallish shield at L1.

For space shielding, you don't want to put the things round the equator, which will mess up meridional heat flow and still leave you with any polar melting you were going to get anyway; you want to put them at the L1 point, where they shield the whole planet equally, and design them so that they can autonomously use the light pressure for station holding. That makes their negative forcing as similar as it can be to GHG forcing (though the fit is far from perfect -- sun shields don't cool you at night).

Sequestration was also discussed. The complexities weren't dismissed, but it seemed to me that the attitude was that humans will one day master such technologies - or else perish. Planets and stars change and we can either accept the challenge or hide under the bed and hope the monsters go away, that things stay constant and no celestial events occur. I'm not inclined to rely on hope.

The exact opposite attitude cripples a large segment of the paleo-environmental community, including those scientists infected with those reactionary ideas.

While humans have a long history of wanting to control weather and climate - cloud seeding is an example - this incarnation of geoengineering is such a hot potato that scientists cannot even agree whether it should be discussed publicly.

"The knowledge that we maybe could engineer our way out of climate problems inevitably lessens the political will to begin reducing carbon dioxide emissions," observes David Keith from the University of Calgary in Canada. . .

Ken Caldeira agrees that geoengineering is, for the moment, a tempting but illusory quick fix to an intricate system; a much less problematic solution, he says, would be to change our lifestyles by reducing energy consumption and CO2 emissions.

"I think the Earth's system is so complicated that our interfering with it is very likely to screw things up and very unlikely to improve things," he says. "And this is the only planet we have."

Amazing. One "scientist" thinks we should conceal knowledge of technologies that could reverse climate change because it would be harder to sell political fixes that wouldn't actually fix anything. Another thinks it would be easier to "change our lifestyles by reducing energy consumption and CO2 emissions". He's apparently been out of contact with humanity since he was weaned and has no clue what the world is up to these days or even what human beings are like.

However difficult it may be to implement technological fixes for atmospheric change it will be far, far easier than trying to change society. However much things squirm around in physical reality when you intervene in a system, they are placid and constant compared to what happens when you tinker with social systems. It seems to me that political activists, politicians and many scientists fail to demonstrate the minimal maturity required to make useful techno-social decisions. They seem to believe in magic, perhaps as a consequence of taking their own sophomoric musings seriously, like people who play "planning games" and forget that reality is nothing like their simplistic model systems.

Update:

On the other hand . . .

"Today's technology base is insufficient to provide clean and plentiful energy for 9 billion people," the authors write. "To satisfy tomorrow's energy needs, it will not be enough simply to apply current best practices. Instead, new technologies, especially carbon capture and sequestration at large industrial plants, will need to be brought to maturity."

Primary energy use worldwide is currently about 14 trillion watts each year and rising. This equates to 2.2 kilowatts (kW) per person globally and results in the release of nearly 25 billion tons of carbon dioxide into the atmosphere. Residents of the U.S., however, use 11 kW per person, 85 percent of which comes from burning fossil fuels, a process that contributes to the rising level of carbon dioxide in the Earth's atmosphere.

"Technology in general and energy at its base ultimately define the carrying capacity of the Earth for humans," says Lackner, director of the Center for Sustainable Energy at the Earth Institute. . .

Lackner and Sachs, however, see vast room for progress in meeting the world's growing energy needs without threatening to destabilize the Earth's climate. In particular, they identify carbon capture and sequestration as an important part of any future plan to address the problem. Given the best available projections for energy use, economic growth and atmospheric dynamics, they find that a carbon capture and sequestration system could help keep carbon dioxide levels from reaching 500 ppm by 2050 at a cost of between 0.1 and 0.3 percent of gross world product.

Other large-scale solutions they identify include solar energy, clean coal technology and nuclear power, though they identify problems with each that must be resolved.The authors also see widespread use of hybrid engines as another readily deployable technology to help reduce carbon dioxide emissions. All together, a program to keep the Earth's carbon dioxide levels in check could cost less than 1 percent of projected gross world product as of 2050.

I'm not endorsing Sachs or EPI - they both have pretty dodgy reputations - but it is interesting to read this on the same day as the weepy beeb article that dismisses technological solutions.