Giant, remotely alterable mirror in space

[woolyhead 15]

You are correct about the argument re:CO2, but it acts on short wave radiation. If it acted on long wave radiation then it would stop the suns heat from entering the atmosphere in the first place.

What it actually does though is stop heat that is re radiated from the ground in the infra red from leaving.

 

It gets colder as you ascend because air pressure drops. It's nothing to do with the greenhouse affect though.

 

---------- Post added 10-10-2013 at 20:37 ----------

 

Obelix: you're obviously feeling more like doing maths tonight than me.

 

What area of mirror would we require to float/place on the equator to achieve the desired 2k drop?

 

3.14x(8000)x(8000)/4 sq miles is the area of the earth's surface facing the sun. Based on the method of proportionality with degrees K the mirror must intercept 1 percent of the total incident energy, so it needs an area of 1/100 of the above, ie 502400 sq miles. This is a diameter of 708 miles approx (ignoring the pi and the 4). I'm not saying this is all there is to solving the global warming problem, however.

 

---------- Post added 11-10-2013 at 12:56 ----------

 

Photosynthesis is constrained by energy, not CO2 availabilty...

 

Something that size in low earth orbit is going to be subject to massive tidal forces if it twitches just a little bit out of orbit. At 172 miles up there is a massive amount of drag as well which means it'll need constant boosting.

 

Assume something of 140 miles across is casting a shadow on an area 8000 miles across. The difference in size is the square of the diameters so 19600:64000000 that's about 1:3300. That's the total amount of energy you intercept, but it's only in the way of the sun for at most half the time in it's orbit so it's 1:6600 of the incident energy captured... that's going to be a 20th of a degree K assuming it's a linear relation.

 

I agree about the tidal forces. The diameter of a shadow depends on four things, distance, dia of the mirror in orbit and the size of the source and the beam angle, so the equation becomes more complicated. I think the angles subtended by the sun and by the mirror as seen from earth come in to this. I was obviously wrong about the necessary mirror dia and orbit height, so what values do they need to be at. What do you think? Your suggestion that the shadow is only as big as the mirror can't be right, surely? That would imply that the angle subtended didn't come into it. I now realise that several mirrors in orbit would require less enormous mirrors. By the way, this question that I asked Sheffield Forum has found its way into Google's "Giant mirrors in space to reduce global warming" page. Is it normal for Sheffield Forum to allow this?

Edited October 11, 2013 by woolyhead

[Cyclone 10]

I suspect that we can treat the sun as a point source for the purposes of this calculation.

 

---------- Post added 11-10-2013 at 13:10 ----------

 

Pi r^2/4... how is that the effective surface area exposed to the sun? Is that even what you were trying for, as r is 6371 and you used 8000, and then you gave answer in sqr miles???

 

I work out a surface area of 127.5 million sqr kilometres. 1% of that is 12 million sqr kilometres...

 

The circumference around the equator (ignoring equatorial bulge) is 12000pi roughly.

 

So that's a mirror entirely encircling the earth, 30 miles wide. Assuming we couldn't pave over a large strip of quite a few countries it might have to spread to be 60 miles wide and only cover about half the equator.

[fake 10]

 

---------- Post added 10-10-2013 at 18:39 ----------

 

 

I tried looking up this web page and was told "we haven't got this."

 

---------- Post added 10-10-2013 at 18:52 ----------

 

 

 

Seems like the URL is faulty in some way.

 

Click on "Search for "Znamya (space mirror" in existing articles."

 

Then click on the first link.

[Obelix 11]

Either a bigger mirror or several of them spaced round the earth in orbit would be needed. I'm yet not sure about what diameter and distance they need to be at. What do you think?

 

It's an utter none starter and we'd be better off burning much less carbon, building a fleet of liquid salt gen 4 reactors burning thorium and moving to electric vehicles. It'd cost less and be of more utility.

[woolyhead 15]

It would take years to build (would have to be shipped up piece by piece like the ISS was) and would cost a fortune, it would need to be the largest man made structure to date to be effective!

 

The radius of the earth is approx 3958.75587 miles - it would need to be AT LEAST 1/2 this size (so approx 2000 miles) to be effective, to the point of being able to reflect the sunlight to specific places on the earth..

 

If it was 1/2 the dia of the earth, ie 1/4 its area, the amount of cooling it would create would be far too much, assuming nearly all the earth's heat comes form the sun and keeps us alive. The absolute temperature created by the sun on earth is, say 30 C, which is 300 deg K. To reduce this by 1/4 would mean a new temperature of 3/4 of 300, ie 225 K, or -48 C. We'd freeze!

[dosxuk 10]

The absolute temperature created by the sun on earth is, say 30 C

 

And this is where your idea starts to fall apart.

 

It's not been 30°C at any point in the day here.

[Cyclone 10]

And this is where your idea starts to fall apart.

 

It's not been 30°C at any point in the day here.

 

It's an average over the entire surface of the globe (facing the sun).

I suspect it's actually about 20 degree's lower than that, but why quibble, it only makes a tiny difference to the % change needed.

[andysm 17]

What about setting off lots of big bombs to put lots of dust into the atmosphere, then we would get a mini nuclear winter but without the radiation.

 

---------- Post added 13-10-2013 at 10:59 ----------

 

Or just spray paint the deserts with brilliant white paint to reflect the sun away from the earth.

 

---------- Post added 13-10-2013 at 11:00 ----------

 

Billions of white ping-pong balls in the oceans may do the same thing.

 

---------- Post added 13-10-2013 at 11:05 ----------

 

What about a vast world-wide breeding programme for cabbage-white butterflies.

 

---------- Post added 13-10-2013 at 11:10 ----------

 

Actually we don't really need to reduce the temperature of the whole earth, just the polar ice-caps to encourage the ice caps to grow. So we need 2 big mirrors to cover north and south poles.

[woolyhead 15]

pay for and What about the political aspects of this. I mean politicians aren't exactly falling over themselves to implement any powerful global heat-reduction schemes are they. Just reducing the UK's carbon footprint hardly does the job when so many other big countries including America don't want to know. Poorer or less affluent countries can't afford to do very much unless they make their people suffer as a result. The arguments will go on and on until it's too late to prevent thermal runaway. The only practical way to get global temperature stability and controlled reduction is for the rich countries to pay for and build the space mirror. They could earn the money as time goes by, year by year, as the work progresses.

Edited May 3, 2019 by woolyhead

[swarfendor437 14]

So, when is a topic Computer and Tech Chat and not a 'General Disccussion' topic on Global warming?

[woolyhead 15]

On ‎08‎/‎10‎/‎2013 at 20:16, probedb said:

What next? Are you going suggest a giant toupee to cover up the holes in the ozone layer?

So what's your solution to the global warming problem?

On ‎03‎/‎05‎/‎2019 at 23:55, swarfendor437 said:

So, when is a topic Computer and Tech Chat and not a 'General Disccussion' topic on Global warming?

When it's technical, and we chat about it, it's tech chat. Because  I reckon the term Computer and Tech Chat means Computer Chat and also Tech Chat. Two subjects. Is that wrong?  And how to control global warming is technical, isn't it? Why must a topic only be eligible for only one category or the other and not both? But if you want, you have my agreement  to delete my offering based on erroneous categorisation. Or transfer it to Global Warming. 

Edited May 10, 2019 by woolyhead

[Cyclone 10]

I'd assumed that this was "tech" like what NAS should I buy, or what is the best wireless speaker.  Not science fiction like can I build a 300 sqr mile mirror in orbit, or what kind of atomic screwdriver will work best to adjust the quantum fluctuation in my shield frequencies.