[thedoc (OP)]

What do aeroplanes, airships, rockets, guns and gas pipes have in common?  They could all help to cool the Earth by delivering millions of tonnes of global warming-busting aerosols into the Earth’s stratosphere.

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[CliffordK]

It just seems to be counter-productive to fly airplanes and use extra fuel specifically to make high clouds.  And, I would think there would have to be a lot of flights, for a fairly short-term effect.

Is there any way to work this in with commercial jet traffic?  What are the effects of northerly intercontinental flights (summer vs winter?)

The development and deployment cost of some kind of a space mirror would be very high, but once up there, it could last for essentially as long as one wanted it.  And, if designed right, one might be able to heat one part of the planet and cool another part of the planet.  Or, perhaps capture energy for some other use.

[damocles]

Heat one part of the planet and cool another, CliffordK? I doubt that that would "capture energy". Much more likely that it would provide the driving force for super storms on a scale way beyond anything we have yet seen!

Yes this strategy would provide energy, but energy that would surely be expressed in rogue, untameable ways!

If we are planning to produce a lot more stratospheric aerosol, we are also planning a lot more ozone depletion. The chemistry that produces the Antarctic Ozone Hole is largely catalyzed by the surfaces of particles in stratospheric aerosols. At mid latitudes and tropical latitudes, the chemistry would be a little different, but it would still amount to significant ozone depletion.

Lethal UV radiation can be blocked out by the effectiveness of scattering of short wavelength radiation by aerosol, but even so we would need to think very carefully about lowering our ozone shield!

[CliffordK]

Much of the recent ozone depletion seems to be related to polar winter weather.  I.E.  When the sun doesn't shine, in a place where few humans are living. 

Much of the ozone hole fills back in every summer when one gets the solar exposure.

Yet, I agree that any geoengineering could have unintended consequences. 

Targeted artificial warming the poles in the winter may in fact reduce the temperature differences, and reduce storms.  However, it would depend if one chose to just warm the land masses, or warm both the land and water.

[damocles]

Much of the recent ozone depletion seems to be related to polar winter weather.  I.E.  When the sun doesn't shine, in a place where few humans are living. 

Much of the ozone hole fills back in every summer when one gets the solar exposure.

Yet, I agree that any geoengineering could have unintended consequences. 

Targeted artificial warming the poles in the winter may in fact reduce the temperature differences, and reduce storms.  However, it would depend if one chose to just warm the land masses, or warm both the land and water.

The ozone story is rather more subtle than that CliffordK. The chemistry that leads to the Antarctic phenomenon, and a similar less developed phenomenon in the North, involves aerosol, and visible sunlight. It occurs not in the winter, but in the spring, with returning sunshine after the polar night. And aerosol plays a very important part.

The stratosphere is a very dry place. Only in the Antarctic winter does it get cold enough to saturate with water vapour, and form ice aerosol. Nitric acid aerosol also forms at those temperatures. September and October are the peak months for ozone depletion. Not before September because there is no sunlight, and not after mid to late November because all of the clouds evaporate in the warmer sunshine.

Aerosol that is thrown into the stratosphere by certain types of volcano does not evaporate -- it consists largely of non-volatile sulfates. It also provides surfaces for the critical ozone-depleting reactions to occur, although the detail of the chemistry is different because of the absence of a long winter darkness to pre-process the chemicals, and the different chemical nature of the sulfate particles.

We can tell when there is volcanic aerosol in the stratosphere: if you look in the region of the sky near the sun on a clear day (and assuming no local smog or raised dust), it will have quite a pink tinge, that fades into the normal light blue as one's eye wanders to the sky further from the sun. The last time that I remember this happening in the Southern hemisphere was about 20 years ago when there were significant major eruptions of Pinatubo in the Philippines and of a major volcano in Chile within a few months of each other.

There has been a lot of work done on the chemistry of stratospheric ozone in the presence of sulfate aerosol -- I am not fully in touch with the latest modelling and evidence. however it is almost certainly the case that (1) there is some ozone depletion involved, and (2) that scattering of solar UV light at high altitude by a stratospheric aerosol more than compensates in reducing the amount of UV that penetrates to the Earth's surface.

[yor_on]

Sure we can, a major atomic war should do it, and decrease population world wide too. It won't be a pretty sight though, and the aftermath will be hard to live with.