Paint your roof white to reduce global warming

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Discussion Overview

The discussion centers around the proposal to paint roofs, roads, and pavements white to enhance their reflectivity and potentially mitigate global warming. Participants explore the implications of this idea, including its effectiveness, environmental impact, and the nuances of the claims made by Professor Chu regarding carbon emissions reductions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants express skepticism about the significance of the proposed effects on global warming, questioning the validity of the claims made by Professor Chu.
  • There is a suggestion that using concrete instead of asphalt for roads might be a more effective solution, though concerns about CO2 emissions from concrete processing are raised.
  • One participant discusses the potential benefits of white roofs in reducing energy consumption for cooling buildings, highlighting the importance of albedo and its impact on the heat island effect.
  • A participant proposes a rough calculation comparing the carbon offset from painting roofs white to the emissions from cars, suggesting that a significant number of roofs would be needed to achieve a comparable effect.
  • Some participants note the ambiguity in Chu's statement about the equivalence of carbon savings, questioning whether it refers to a direct comparison of time or energy savings.
  • There are multiple references to the need for clarification on the claims made by Chu, with some participants suggesting he may have misspoken or miscalculated.

Areas of Agreement / Disagreement

Participants generally do not reach a consensus on the effectiveness of the proposal or the accuracy of Chu's claims. There are competing views regarding the significance of the initiative and the methods suggested for implementation.

Contextual Notes

Participants express uncertainty about the calculations and assumptions involved in estimating the impact of painting roofs white. There are also unresolved questions about the environmental costs associated with different materials used for road construction.

Who May Find This Useful

This discussion may be of interest to those studying environmental science, urban planning, climate change mitigation strategies, and the effects of urban heat islands.

  • #61
Interesting discussion on solar panels. I would like to know what is required to convert the energy from the panel to 230v at 50hz to enable household appliances to be operated.
Can you store the energy? How is it synchronised with the town mains when you are providing them power? I guess this is way off topic. Is there a thread on solar panels?

Regards Richard
 
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  • #62
Richard111 said:
Interesting discussion on solar panels. I would like to know what is required to convert the energy from the panel to 230v at 50hz to enable household appliances to be operated.
A simple box of electronics

Can you store the energy?
Not efficently, some people off grid have banks of batteries but it's large and expensive

How is it synchronised with the town mains when you are providing them power?
A rather more complicated and expensive box of electronics.

This might be interesting.

https://www.youtube.com/watch?v=IELITZ2VSvk
 
  • #63
Richard111 said:
Interesting discussion on solar panels. I would like to know what is required to convert the energy from the panel to 230v at 50hz to enable household appliances to be operated.
Can you store the energy? How is it synchronised with the town mains when you are providing them power? I guess this is way off topic. Is there a thread on solar panels?

Regards Richard

Many areas do or will offer net metering. This allows you to effectively use the grid for your energy storage. When you produce more power than you use, you supply power to the grid and your meter runs backwards. When you need energy back, the meter runs forwards again. Rather than limiting the contributions to the grid and the value of the energy that you produce, as was done in the past, you simply see the net metered value on your electric bill or credit.

Wrt the issue of white roofs vs solar panels, obviously the cost is the definitive factor. Many people simply cannot afford to spend $30K-50K on solar panels. Whitewash is cheap.
 
  • #64
Richard111 said:
Interesting discussion on solar panels. I would like to know what is required to convert the energy from the panel to 230v at 50hz to enable household appliances to be operated.
Google 'inverters'
...How is it synchronised with the town mains when you are providing them power?
As mgb_phys that requires a more sophisticated inverter system, a switch between you and the town mains, and it _must_ be setup by a registered electrician.
 
  • #65
mgb_phys said:
Not efficiently, some people off grid have banks of batteries but it's large and expensive
Battery storage is efficient, the only significant loss is the DC/AC conversion (if needed) and that is small (~10%). It expensive as you say, unless used as emergency/backup power only (lead acid) where the cycle life is small.
 
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  • #66
Thank you mgb_phys, Ivan and mheslep for your response. I had to skip the U-tube tutorial as my "broadband" is too slow. I googled "inverters" and found I do not know enough to define my requirements.

This year my electricity charges have gone up 40% and the prediction is a further 25% rise by about December. As a pensioner this is not sustainable.

During winter I heat my house with LNG and find there is no problem keeping cool in summer as I live in Milford Haven.

The household appliance that works the hardest is the kettle. I find we boil at least four kettle fulls a day. I checked and note that the kettle filled to the max mark holds 1.5 litres of water and takes 3 minutes 20 seconds to boil and draws a steady 10 amps while switched on.

By using timer switches all appliances that use to remain on standby are now completely disconnected from 11pm to 7am. This, among other measures, has reduced my weekly consumption from about 70 units to 60 units. I will need to reduce my consumption by about a further 20% just to keep my monthly payments constant.

So, painting my roof white will bring no benefit whatever, and will cost for the paint, and the payback time of any sort of solar panel system that would ensure I enjoy my tea over just the summer months will be beyond my expected lifetime.

The only cost effective system for me is to install a multifuel stove. This will provide heating and cooking facilities.

We are returning to the conditions I lived under as a child during the war. Even the bath water was heated in large pans on the cast iron stove.

I am not impressed with this brave new world.
 
  • #67
mheslep said:
Battery storage is efficient, the only significant loss is the DC/AC conversion (if needed) and that is small (~10%). It expensive as you say, unless used as emergency/backup power only (lead acid) where the cycle life is small.

Lead-acid batteries are listed as being 75% - 85% efficient.
http://wiki.xtronics.com/index.php/Sealed_Lead_Acid_Battery_Applications

In practice, efficiency is governed in large part by Peukert's Law - high rates of discharge mean less efficiency.
 
  • #68
Why not cover large uninhabited areas of the Earth by aluminium foil? Aluminium foil of thickness 0.01 mm covering 1000 by 1000 km only contains 27 million tonnes of aluminium. The price of the bauxite needed to manufacture the aluminium is only about $80 billion.
 
  • #69
a quick explanation of why white paint works to cool the planet

1 around 50 percent of sunlight is visible light

2 around 50 percent of sunlight is heat (infra red - i will call it heat for the moment)

3 visible light is a frequency of light NOT absorbed by the atmosphere

4 some HEAT (infra red) from the sun IS absorbed by the atmosphere directly (greenhouse gasses which makes the atmosphere warmer).

5 HEAT from the sun also warms the surface of the planet and this HEAT is then radiated back into the atmosphere again being absorbed by greenhouse gasses.

6 visible light is poorly absorbed by the atmosphere, some of it gets reflected back by the atmosphere (white clouds).

7 the visible light that doesn't get reflected back by the atmosphere is either reflected by the surface (eg a snow field) or absorbed by the surface (an asphalt carpark/ road). this absorbed light heats the dark surface. this heat is then radiated into the atmosphere and is absorbed by greenhouses gasses making the atmosphere warmer.

8 by painting your roof white and other surface you reflect around 50 percent of the visible energy from the sun, a significant amount of this is reflected back into space WITHOUT heating the atmosphere.

9 by painting enough roofs you make buildings cooler and cool the atmosphere. air conditioning works easier to cool houses because they are cooler, perhaps you wouldn't even need air conditioning?

if you are thinking of using white paint to cool your roof you will need a special white insulative paint that both reflects the visible frequencies of light and stops infra red frequencies from heating your roof.


white roof keep buildings cooler because less energy is absorbed by the building, with insulation even less energy makes its way into the building. the white roof reflects energy that would have otherwise heated the air above the roof and would have made the neighbourhood temperature hotter.

i remember seeing an article some time ago, an area in spain covered in white roofed greenhouses recorded slightly lower air temperatures than anywhere else in spain. if you still don't think white roofs do much, think about this, imagine if you painted all surfaces black in a city, can you imagine just how hot it would be on the streets - it might not be possible to walk the streets. the poles are not just cooleer because of the sun being at a shallower angle, the white sends a massive chunk of energy away from the area making it much cooler.
 
  • #70
Count Iblis said:
Why not cover large uninhabited areas of the Earth by aluminium foil? Aluminium foil of thickness 0.01 mm covering 1000 by 1000 km only contains 27 million tonnes of aluminium. The price of the bauxite needed to manufacture the aluminium is only about $80 billion.

Sure ! My dream. But then, by folding this Al foil into parabolic troughs and turning it into CSP plants, why not ?
 
  • #71
People who address issues of long-term climate variability by cherry-picking yearly data should be called to task. Many places in the US experienced record heat and drought and others got drowned and buried in cloud-cover for weeks. Invoking short-term variations to "disprove" long-term trends is intellectually suspect.
 
  • #72
turbo-1 said:
Invoking short-term variations to "disprove" long-term trends is intellectually suspect.
And the same is true if you replace "disprove" with "prove".
 
  • #73
Hurkyl said:
And the same is true if you replace "disprove" with "prove".
You're right. Can you see where the climate-change nay-sayers might have a weakness, using logical arguments?
 
  • #74
turbo-1 said:
You're right. Can you see where the climate-change nay-sayers might have a weakness, using logical arguments?
:confused: I don't understand the question -- too vague.



It looks to me like Ivan was saying "Hey look -- record high temperatures. See? Global warming!" to which mhsleep retorted "That's not a valid argument. Look -- record lows too! :-p"

Of course, we have no idea what Ivan and mhsleep actually meant with their two comments -- neither offer any explanation, and Ivan's doesn't obviously relate to anything over the past page or so. (mhsleep's is presumably a direct reply to whatever he thought Ivan meant)

We're supposed to have guidelines against merely posting a link and/or a quote without any further comment...
 
  • #75
HurkylI said:
t looks to me like Ivan was saying "Hey look -- record high temperatures. See? Global warming!" to which mhsleep retorted "That's not a valid argument. Look -- record lows too! :-p"
Yes that is what I meant, and how I meant it.

Hurkyl said:
We're supposed to have guidelines against merely posting a link and/or a quote without any further comment...
Yes you are right of course, deleted post.
 
  • #76
Ivan Seeking said:
This is another approach being tested for feasibility.http://wattsupwiththat.com/2008/09/07/newest-geo-engineering-plan-is-salt-water-daffy/

Ah, yes, I had seen that elsewhere. It sounds pretty problematic to me. As I understand it, it would increase albedo of *existing cloud cover*, but that's already pretty high, so I don't know how much you can win. On the other hand, cloud cover works both ways (as "greenhouse" and as albedo) so it is not clear who wins (you also reflect back more efficiently IR radiation). Finally, you increase, at least locally, the vapor pressure of water, which is a strong greenhouse gas (although I reckon that this is not a big problem given the short duration of the water cycle).

So to me it is not obvious *what* it could do, and moreover, *what way* it would work (more or less warming) ?
 
  • #77
Skyhunter said:
The biggest carbon offset from painting your roof white is a reduction in energy expended for cooling. A lot of energy is used to heat and cool buildings. Living roofs are even better, they provide insulation, evaporative cooling, particulate scrubbing, and an environment for butterflys and other native fauna.

Yeah, this is a great idea and has a huge range of environmental benifits.

I think it is worth the fire risk and bad karma of not cleaning my gutters, but only for the environmental payoffs of course! :P
 
  • #78
Ivan Seeking said:
http://www.timesonline.co.uk/tol/news/environment/article6366639.ece

That should read that it would yield the same benefit as removing all of the cars for 11 years...

https://www.youtube.com/watch?v=pLlxjYACa5U

If the results would be that significant, why not paint the center and edges of roads white - everything except the tire tracks?

We already have the painting equipment - just need to modify a bit. I'm sure there's some loose change in the stimulus Bill that could be diverted.
 
  • #79
I bought a white metal roof and it helps a lot in summer. It also helps to use a fan to "sample and hold" the cool night air around 4 AM. Add that to digging 10 feet down for a basement and migrating there for the summer and the result is about three days worth of air conditioning for the whole summer in West Virginia.

In winter the trombe wall helps warm the South side. I use about a fourth of the gas that others burn for heat. Electricity is normally 250 KWH/month.
 
  • #80
My car is white, i must say, its the best 'color' ever.
 
  • #81
I guess we will know if this will work when the polar ice caps melt. All that ice has a large albedo.
 
  • #82
bassplayer142 said:
I guess we will know if this will work when the polar ice caps melt. All that ice has a large albedo.

It's difficult to say. The total projected effect (there's not much reason to doubt it) comes down to 1 extra year delay. It comes down to offsetting the effect of the emissions of about 1 year. Even if there's 50% error on it, it will mean that it comes down to offsetting the effect between 6 months and 1 year and a half.
 
  • #83
Has anyone explained why we can't just paint the roads white - except for the tire track lines?