Re: [HPAC] Re: Albedo

[John Nissen]

Hi Robert,

Because L1 wobbles as the moon circles the Earth, it may be difficult to get the desired cooling effect from space mirrors.  And anyway the main cooling will be around the equator, whereas we have a priority on cooling the poles, because of tipping processes nearing a point of no return.

The temptation of space mirrors will be to postpone SAI, and then it will be too late to prevent tipping-point catastrophe.  However space mirrors would be worth developing as a possible technique to take over from SAI in two or three decades perhaps.

Gernod was asked whether SAI could be weaponised, and he thought not, because the SAI provides a fairly even cooling between latitude of injection and pole due to Brewer-Dobson circulation in the stratosphere.

BTW, I think ships should use bunker oil when away from the coast, to help restore a lot of albedo which seems to have been lost recently; though ideally the sulphur extracted in purification should go into the stratosphere as SO2 to produce even greater cooling!

Cheers, John

On Fri, Apr 17, 2026 at 12:34 AM Robert Chris <robert...@gmail.com> wrote:

Oops! I hit Send too soon.

I meant to add that mirrors in space might fit the notion of an international albedo accord much more neatly than attempts to engage with large numbers of technologies that are perceived to be marginal in their impact and/or potentially too risky.

It becomes a unified global Moonshot approach with a clear objective and very well defined operational focus.  The big problem will be decisions around who controls the thermostat; but that applies in all albedo options.

Regards

RobertC

On 17/04/2026 00:30, Robert Chris wrote:

Following our discussion a few minutes ago, I've just done a back of the envelope calculation that shows that to deliver a negative forcing of -1Wm^-2, 2.4% of Earth's land surface (an area about the size of India) would need to treated.  This assumes s starting albedo of 0.2 and an increase to 0.8 which is the albedo of pristine snow.

I think we can assume that painting surfaces white or covering them in reflective material is not going to be a plausible way to provide a worthwhile amount of global cooling.  That said, it could provide really worthwhile amounts of local cooling in tropical climates.

It should also be noted that outside of the tropics, painting building roofs white would increase the demand for heating in winter months.  It would also require considerable maintenance everywhere to keep the surfaces clean and fully reflective.  The cost profile is not attractive.

Mirrors at L1 (a spot between Earth and Sun that's about 1 million miles from Earth), crazy at that might seem at first glance, it could well turn out to be by far the most cost-effective option.  Search on 'mirror in space Lagrange L1' and lots of options emerge.

Regards

RobertC

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[Robert Chris]

Hi John

As regards L1 wobbling, that's what research is for.  I very much doubt that there are engineering challenges associated with space mirrors that can't be overcome with well-resourced research.  I see your concerns as research questions not as reasons to not proceed.

I'm amused by the notion that space mirrors will be a moral hazard for SAI in the same way that SAI is a MH for emissions reduction.  I have written extensively about this in this group.  MH is nonsense.  It is an imagined problem for which there is zero empirical evidence.  Moreover, if it ever did emerge as a real problem, it could immediately be stopped by policymakers applying regulations to do so.  If they didn't do that for fear of backlash  from vested interests, it would be the policymakers' timidity that would be the problem not the MH.

As to space mirrors being developed as a successor to SAI, what if SAI never happens at sufficient scale and speed?  I think it's very plausible that SAI will not be deployed at the scale and speed necessary to avoid COCAWKI (the collapse of civilisation as we know it).  However much we think it MUST happen, there are many others for whom it MUST NEVER happen, and even more who aren't that interested either way.  My crystal balls are not sufficiently reliable to predict the future role of SAI, so I think it prudent to assume that it might not deliver its potential and we'll need something else.  Why not space mirrors? 

It isn't either/or.  It's both/and.

I also think that COCAWKI is plausible, indeed probably rapidly becoming most likely.  Contemplating COCAWKI requires a different mindset.  Almost no one is yet focussing on that.  Perhaps a few preppers are.  And Jem Bendell!

Regards

RobertC

[Paul Gambill]

IMO, from talking with the Planetary Sunshade Foundation folks, I really like the sunshade/space mirror concept. It is far more elegant than SAI, and while it introduces different types of risks, I like that it can offer reflection without many of the downsides of aerosol deployment. Unfortunately I think most of the SRM research field has viewed a sunshade concept as more sci-fi than even their own work, so it hasn't gotten a lot of attention. There is a conference coming up next month in the UK about this.

If in the proverbial napkin diagram SAI is the temporary intervention to peak shave, then with a sunshade it could go like this recursively:

1. Begin SAI
2. A sunshade isn't plausible until the second half of the 21st century, so once it starts getting deployed, then you can wind down SAI
3. Then wind down the sunshade as albedo normalizes and GHG levels are restored to pre-industrial levels

With a sunshade, we might need SAI for only a few decades, instead of potentially centuries. But that's as far as my knowledge goes on this, and I am looking forward to learning more at that workshop!

Paul

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Paul Gambill

Inevitable & Obvious

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[Paul Klinkman]

I'm primarily with the "rehydrate the earth" advocates.  Their video has a drawing that shows updrafts transferring latent heat from the forests up to the stratosphere, putting it above at least half of the earth's greenhouse blanket, and from there the heat radiates more quickly into space.  Also, the clouds help.  

In the Arctic I advocate restoration of polar ice packs and some coating of land masses with ice or snow in spring.  These are alternative tools for changing polar albedo, and they at least need to be examined for development, for ramping up.  Beyond that you might have an argument for SAI, particularly in the Antarctic because the sulfur asthma problem is pre-solved for you.  Almost nobody lives down there.

Yours in Hope,

Paul Klinkman