Hi Oliver,

I'm glad you raised the ozone issue, because ozone depletion is probably 
the most important thing to minimise with stratospheric sulphate 
geoengineering.  There are two things to do: (i) deploy the aerosol in 
spring such that most of it will have disappeared by the following 
winter, when its effect on ozone is greatest [1] [2]; and (ii) be more 
aggressive in preventing CFCs and other ozone depleting products get 
into the atmosphere.  At present the ozone depletion in the Arctic is 
reducing steadily, but not nearly as fast as it could be with more 
aggressive action.  (I don't know about the Antarctic.)

BTW, the aerosol serves to mask out UV, which is the main problem 
arising from ozone depletion.  This would help to compensate for ozone 
depletion it causes.  It might actually bring a net benefit in UV reduction.

There is very bad news from the Arctic, where the sea ice is showing 
ominous signs that we could have a record retreat this summer.

Cheers,

John

[1] The chemical process which results in ozone depletion occurs below a 
certain temperature.

[2] Deployment of aerosol in the Arctic lower stratosphere means that 
circulation tends to bring the aerosol down into the troposphere faster 
than it would deployed at lower latitudes.   This means that the effect 
of the aerosol can be shut off quickly if necessary, for example if 
there were another Pinatubo-like volcanic eruption putting its own 
sulphate aerosol into the stratosphere.  It so happens that initial 
deployment of the aerosol technique will probably start in the Arctic 
lower stratosphere, focussed on saving the Arctic sea ice - which is in 
such a critical state.

---

On 17/02/2011 13:19, Oliver Tickell wrote:
> The main risk with sulphate dispersal is ozone loss, not acid rain.
>
> Acid rain easily dealt with - anyone introducing high level sulphate 
> should reduce low level sulphate emissions by at least that amount, 
> producing a new benefit. For example by financing new and additional 
> reductions from shipping, power stations etc.
>
> Oliver Tickell.
>
> On 17/02/2011 11:11, John Nissen wrote:
>>
>> Hi Brian, Torsten,
>>
>> It's amazing how scared people are of geoengineering with stratospheric
>> sulphate aerosol, when we've been putting so much sulphate aerosol into
>> the troposphere. There is similar reflection of sunlight at either level
>> in the atmosphere, but the aerosol in the troposphere typically gets
>> washed out in a few weeks, whereas the aerosol in the stratosphere lasts
>> for a few years, as we observed from Mt Pinatubo eruption in 1992 (which
>> produced 0.5 C cooling over two years). So you need only a small
>> fraction (a few per cent) of aerosol in stratosphere to produce the same
>> dimming effect.
>>
>> Because of the relatively small quantities needed in the stratosphere,
>> the danger from acid rain is negligible. This has even been agreed by
>> Alan Robock, who is well known for his anti-geoengineering stance.
>>
>> Our human irrationality over "cleaning the atmosphere" was drawn to my
>> attention by James Lovelock, in his book "Gaia's revenge". He points out
>> how reducing pollution, and thus removing the sulphate aerosol from
>> atmosphere, has unmasked global warming which is potentially
>> catastrophic. One can see from the record of glacier ice mass loss [1],
>> that there has been a sudden increase in rate around the late 80s, which
>> cannot be explained by any sudden increase in CO2 level in the
>> atmosphere. This could be explained by the reduction of sulphate
>> aerosols around that time, or alternatively by some kind of positive
>> feedback cutting in. Either way the scientific community has not reacted
>> to this in a rational way - to seek some method _other than emissions
>> reduction_ to counter global warming. Instead the scientific community
>> has dug an even deeper hole for themselves, and put emissions reduction
>> as the _only_ way to save the planet - rejecting geoengineering as a
>> short term action. I even heard, with my own ears, Sir David King
>> (former chief scientific adviser to the government) say, at a House of
>> Commons event, that geoengineering wouldn't be needed for thirty or
>> forty years, if ever [2]. How can one expect environmentalists to
>> support geoengineering when the top scientists are saying things like
>> that? It makes me really angry.
>>
>> The trouble is that climate scientists have dug such a big hole for
>> themselves, that they cannot get out. It seems that any event which
>> indicates the _immediate dangers_ of our situation on this planet causes
>> them to dig harder, and downplay the danger. How often is the
>> extraordinarily rapid retreat of Arctic sea ice mentioned, though the
>> Arctic heating is like a burning fuse for the methane time bomb and
>> Greenland ice sheet collapse. The fact that we have an emergency is
>> ignored. It is criminal - no worse - genocidal. It is also incredibly
>> stupid.
>>
>> John
>>
>> [1] http://raonline.ch/pages/edu/pdf/WorldGlaciersData0305.pdf
>>
>> [2] What is he doing here but to discredit geoengineering?
>> http://www.oxfordgeoengineering.org/about.php
>>
>> ---
>>
>> On 16/02/2011 14:25, Brian Orr wrote:
>>> Well that more or less wraps that up ........except "global dimming"
>>> sounds a lot more user-friendly than
>>> "Solar Radiation Management". Just adjust the blinds a little and the
>>> room will soon get quite comfortable!"
>>>
>>> So all we have to do is to persuade our political leaders to swing our
>>> industry and life-styles towards producing
>>> enough dimming and cutting back on the stuff that's causing the
>>> problem and over the course of the next 50 years
>>> or so we'll get Mother Earth back on her feet again.
>>>
>>> Whose going to be first to explain the need to our political leaders?
>>>
>>> Brian Orr
>>>
>>> On 16 Feb 2011, at 12:12, Torsten Mark Kowal wrote:
>>>
>>>> Forumers:
>>>>
>>>> I agree with Jon Nissen's deep worry that key Earth Systems are
>>>> already spiralling out of control. We can see NASA's images and
>>>> diagnosis here -
>>>> http://earthobservatory.nasa.gov/IOTD/view.php?id=49132 and that of
>>>> NSIDC http://nsidc.org/arcticseaicenews These observations are
>>>> extremely alarming.
>>>>
>>>> However, I am sorry to add to this bleak picture, but I think the
>>>> arguments so far have neglected to account for the fact that humanity
>>>> is, of course, already engaged in massive geo-engineering.
>>>>
>>>> Our species is already involved in immense negative forcing of global
>>>> climate through /human-produced aerosols/ that are found in the Asian
>>>> Brown Cloud, due to China/India/SE Asia etc. fossil-fuel burning;
>>>> desertification; and other sources of tropospheric particles, such as
>>>> African, Asian and Latin American forest burning.
>>>>
>>>> These are the drivers of the _global dimming phenomenon_. You can see
>>>> this first covered by the media in the original Horizon 2005
>>>> documentary on /Global Dimming /
>>>> http://video.google.com/videoplay?docid=-4488155708142678419#docid=-5512125026951860045, 
>>>>
>>>> which, while perhaps over-the-top in ringing alarm bells, does
>>>> describe a phenomenon that is as yet little discussed.
>>>>
>>>> I don't know how many on this list are aware of the issue, but
>>>> science clearly finds that these mixtures of aerosol particles
>>>> suspended in the atmosphere (coming from deserts and the burning of
>>>> fossil fuels and forests) is - for the time being - "holding in
>>>> check" part of the GHG-induced warming our species has already
>>>> committed the planet to.
>>>>
>>>> While the effects of aerosols are very complex, NASA's James Hansen
>>>> has stated that today's evidence shows that the aerosol load could be
>>>> causing from -1 to -2 w/m2 of radiative forcing reduction, due to
>>>> increased reflectivity of clouds and atmosphere that these aerosols
>>>> cause, thus offsetting global warming.
>>>>
>>>> This could be a lot more than shown in AR4's "SPM2" Figure from 2007.
>>>>
>>>> Once humankind begins to clean these up (to reduce carbon emissions
>>>> from dirty sources, so as to achieve cleaner air locally), then the
>>>> reductions in total global radiative forcing will lead to the release
>>>> of significant further global climate change, in the decades that
>>>> follow the clean-up.
>>>>
>>>> The further hidden commitment to warming will come into play would be
>>>> in addition to the approximate 0.8 degree centigrade 'global warming
>>>> commitment' that is coming our way over the next three decades -
>>>> whatever humanity does about our GHG emissions - due to the delay in
>>>> the responses of the Earth's systems to the planet's energy imbalance
>>>> from current radiative forcing. [See Global and Regional Climate
>>>> Change: Underlying Science and Emerging Riddles
>>>> http://mitworld.mit.edu/video/589 ]
>>>>
>>>> This is a very significant trap that humankind faces - we clean up
>>>> China, India, eastern Europe etc; we reduce desertification and
>>>> deforestation - but then we also immediately stop benefiting from the
>>>> geo-engineering we have already caused, via these vast emissions of
>>>> reflective aerosol particles.
>>>>
>>>> In effect our species has made a pact with our climate - the
>>>> longer-term, diffuse impacts of our continued carbon pollution are
>>>> for now offset by that same pollution - due to the regional dimming
>>>> resulting from the aerosols that this carbon burning also liberates.
>>>>
>>>> This is explained in the attached paper, just published in
>>>> Geophysical Research Letters - */Climate commitment in an uncertain
>>>> world/* by K. C. Armour and G. H. Roe; reported in "Nature" here -
>>>> http://www.nature.com/nclimate/2011/110215/full/nclimate1044.html?WT.ec_id=NCLIMATE-20110215 
>>>>
>>>>
>>>>
>>>> /Climate commitment|the warming that would still occur given no
>>>> further human inuence|is a fundamental metric for both science and
>>>> policy. It informs us of the minimum climate change we face and,
>>>> moreover, depends only on our knowledge of the natural climate
>>>> system. Studies of the climate commitment due to CO2 show that global
>>>> temperature would remain near current levels, or even decrease
>>>> slightly, in the millennium following the cessation of emissions.
>>>> However, this result overlooks the important role of the non-CO2
>>>> greenhouse gases and aerosols.
>>>>
>>>> This paper shows that global energetics require an immediate and
>>>> significant warming following the cessation of emissions as aerosols
>>>> are quickly washed from the atmosphere, and the large uncertainty in
>>>> current aerosol radiative forcing implies a large uncertainty in the
>>>> climate commitment.
>>>>
>>>> Fundamental constraints preclude Earth returning to pre-industrial
>>>> temperatures for the indefinite future. These same constraints mean
>>>> that observations are currently unable to eliminate the possibility
>>>> that we are already beyond the point where the ultimate warming will
>>>> exceed dangerous levels.
>>>>
>>>> /Just like the courtier Damocles asking to try out King Dionysius's
>>>> magnificent lifestyle, the human species is fortunate only for a
>>>> short time. We know that while Damocles sat down in the king's throne
>>>> surrounded by every luxury, Dionysius had arranged that a huge sword
>>>> should hang above the throne, held by the handle only by a single
>>>> hair of a horse's tail. Damocles begged the tyrant that he be allowed
>>>> to depart, because he no longer wanted to be so "fortunate". So,
>>>> prophetically, "The value of the sword is not that it falls, but
>>>> rather, that it hangs." It may appear to be enviable to wear a crown
>>>> of power and to have access to all resources, but there are threats ­
>>>> at all times ­ to the one who wears the crown.
>>>>
>>>> I have a strong sense of foreboding engendered by this terribly
>>>> precarious situation, of visible and close peril. The onset of this
>>>> long-playing tragedy is for now delayed, but only by the delicate
>>>> trigger of humanity's procrastination in reducing the dirty load of
>>>> carbon-related aerosols.
>>>>
>>>> Mark Kowal
>>>>
>>>> <ArmourRoe_committed_draft.pdf>
>>>
>