# Are orbital sun shades to reverse climate change realistic?

#### arusse02

I'm referring to proposals that suggest putting large reflective surfaces at the L1 Lagrange point.

I've also been thinking of something like capturing a nearby asteroid and turning it into an artificial ring at the equator or dumping lots of small infrared reflecting particles or releasing sulfur gasses in leo.

How cost effective and realistic are these methods? How much would you need to actually impact climate change? Are there any other possible space based solutions?

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#### phinds

Gold Member
How cost effective and realistic are these methods? How much would you need to actually impact climate change? Are there any other possible space based solutions?
What research have you done on this so far? What have you found out?

#### etudiant

Gold Member
Back in the 1980s, when NASA still did research on far out issues, they sponsored a series of seminars on 'Radiant Energy Conversion in Space'.
The idea was that solar cells would be much more durable in space, no day/night cycle, no rain or sleet or snow, no wind or structural stresses. That leads to massive solar arrays, eventually perhaps hundreds of square miles, with power transmission emerging as a serious issue.
Even so, compared to the millions of square miles of earth surface, a rounding error impact, unlikely to reverse any global phenomena.
Imho, the more promising option is to fertilize the southern ocean. It seems iron is a missing trace element there for plankton growth, as demonstrated with smaller scale iron seeding experiments generating massive algae blooms. As one researcher said subsequently: ' Give me a tanker full of iron sulfate and I'll give you an ice age'.

#### essenmein

How much would you need to actually impact climate change? Are there any other possible space based solutions?
Not space based, but Krakatoa eruption reduced global temps by about 1.2C, this had equiv yield of about 200Mt, so one solution to climate change is a limited but decent nuclear exchange. Gives results quickly too!

Probably not the type of thing people are looking for though.

#### anorlunda

Mentor
@arusse02 asked about shades to block some solar energy from reaching earth. At least that's what the title says.

@etudiant replied with an idea to use space solar panels tho bring more solar energy to earth.

You can not be further apart.

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#### anorlunda

Mentor
I'm referring to proposals that suggest putting large reflective surfaces at the L1 Lagrange point.
Can you provide a link to one such proposal complete with numbers? It's hard to comment if we don't know what it is.

#### russ_watters

Mentor
How cost effective and realistic are these methods? How much would you need to actually impact climate change? Are there any other possible space based solutions?
It would probably get you in the right order of magnitude if you calculate the mass of enough mylar balloons to block 1% of the sunlight reaching Earth and multiply by perhaps $5000 / kg to get them where they need to be. #### phinds Science Advisor Gold Member It would probably get you in the right order of magnitude if you calculate the mass of enough mylar balloons to block 1% of the sunlight reaching Earth and multiply by perhaps$5000 / kg to get them where they need to be.
Just for grins, I did a VERY rough calculation based on that assumption. Here are my notes:

Earth radius = 4000 miles x 5000 feet/mile = 2E7 feet
area (simplifying assumption is that the sun is pointing at a flat disk)
= pi * (2E7 feet)^2 = 1.25E15 sqft x 1% => 1.25E13 sqft to cover

16" Mylar balloon, simplified as a 16" square => (16/12)^2 sqft = 1.77 sqft

Amazon has 16" balloons at about 1/4oz each

1.25E13 x 1 balloon/1.77sqft => 7E12 balloons x (1/4)OZ / balloon * 1lb/16oz

=> 1.1E11 lbs x $5K/Kg x .45Kg/lb =>$2.48E14

Those figures assume the $5K/Kg includes the cost of the balloons (or Mylar sail or whatever) So, that's about$240,000,000,000,000 per sail

The GDP of the USA is $19.4 trillion / year =$19,000,000,000,000

240,000,000,000,000 ($/sail) / 19,000,000,000,000 ($/year) => 12.6 years per sail

So the cost is the entire output of the USA for 12.6 years

If you have the entire Earth chipping in it would be the entire output of the Earth for about 3 years.

Doesn't really seem very practical.

#### mfb

Mentor
Let's repeat this with a more sensible unit system, and sheets instead of balloons. The area of Earth is pi*(6370 km)2, covering 1% needs ~3*(637 km)2 ~ 1.5*1012 m2.
A 2 micrometer sheet (solar sails use that) with roughly the density of water needs 0.002 kg/m2. Multiply: 3*109 kg.
Multiply again: 1.5*1013 \$ or 15 trillion USD. Deployed over 20 years this is 1% of the gross world product.

No one would use existing rockets for that, of course. We would use a few billions to develop proper, reusable rockets to cut launch prices, or maybe even tens of billions to deploy a megastructure like a StarTram or an orbital ring. That would cut further launch costs massively.