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This strategy, to get rid of some sunlight, doesn't fix our problem with CO2. In fact, it's likely to make the problem worse. Our planet has two primary natur

This strategy, to get rid of some sunlight, doesn't fix our problem with CO2. In fact, it's likely to make the problem worse. Our planet has two primary natural methods for lowering atmospheric CO2. One, natural weathering, is not impacted with this strategy. The other, plantlife, is absolutely affected. If you were to take 10% of sunlight away from Earth, then it logically follows that plants would get 10% less sunlight to convert CO2 into starches and H2O into oxygen. The resource you're trying to constrain, in the name of fighting effects of rising CO2 levels, is the very resource you need in order to fight rising CO2 levels. Sure, blocking or deflecting some light might lower Earth's temperatures temporarily, but you'd exacerbate CO2 levels semi-permanently. We, as a community, need to come to the realization that our CO2 problem is not strictly a temperature problem.

taberiand 9y ago
There isn't going to be one single solution, but reducing incoming sunlight by a small percentage (1-2%) could be a cost effective part of a multi-layer approach.
koverstreet 9y ago
Amount of sunlight is not the limiting factor on plant growth in most places. In fact, it's often the opposite - plants shut down respiration during midday to limit water loss because it's too hot.
- mchannon 9y ago
  I imagine "most places" refers to most places on land, which is less than 20% of the range of where plants grow. Ocean-based plantlife is the workhorse on this planet, and I would argue that the lion's share is absolutely constrained by available sunlight. Further, there's a substantial difference between "respiration" and absorption of sunlight. Pineapple plants, for instance, only "breathe" at night.
  - tlb 9y ago
    Plant life in the oceans is mainly limited by minerals, especially iron. That's why the oceans aren't green and slimy. Dumping iron powder in will usually cause an algae bloom, which eventually die and take the carbon they fixed to the bottom, so seeding the oceans with iron is a potential way of reducing CO2 in the atmosphere. Of course, like any large-scale meddling, there will be collateral damage.
    - 6502nerdface 9y ago
      > will usually cause an algae bloom, which eventually die and take the carbon they fixed to the bottom It works so well that this could even be how the current "icehouse earth" conditions got started in the first place. The Azolla bloom of 49 ma dropped atmospheric CO2 levels from 3500ppm to 650ppm in less than 1 my, and CO2 has been in that lower range ever since. https://en.m.wikipedia.org/wiki/Azolla_event https://en.m.wikipedia.org/wiki/Azolla_event
  - jws 9y ago
    A quick, non-biologist's googling suggests that nitrate and ammonium are the limiting factors for most oceanic algae. I recall there being experiments for areas are iron limited, so they spread iron sulfate and created algae blooms. I suppose intuitively, if you scoop up a bucket of ocean water, it is not green. If light were the limiting factor you would expect the water to contain lots of light absorbing algae. This does happen in nutrient rich waters, like the sewage lagoons and creeks I grew up near.
hwillis 9y ago
Every idea for geoengineering as a solution to climate change is insane. They're either nonsense, like solar chimneys, or they're like this one: way worse than the problem currently is, and WAY worse than not emitting CO2 would be. Take atmospheric sulfate aerosols[1], which I often see touted as the solution, usually by conspiracy theorists. The kind of people who think "big green energy" is money play, and this simple solution is being hidden for some grand reason. "Atmospheric sulfate aerosols" means spraying sulfuric acid into the air. It's all the joy of this solution with the added bonus of primarily blocking visible light, destroying the ozone layer, and scattering light so that solar panels and plant life don't work as well. Oh yeah, and SPRAYING ACID INTO THE AIR. Intentional acid rain, forever. It's an incredibly foolish, destructive idea that people with zero drive to do basic research support vocally. The cheapest, easiest and safest way to fight climate change is to stop emitting CO2. It would be so incredibly easy to stop 80% of anthropogenic emissions. These geoengineering plans are worse in every way. [1]: https://en.wikipedia.org/wiki/Stratospheric_sulfur_aerosols https://en.wikipedia.org/wiki/Stratospheric_sulfur_aerosols
- microcolonel 9y ago
  > It would be so incredibly easy I don't think it's as easy as you think it is to cut emissions by that much, and it certainly wouldn't be humane. Biological sequestration is closer to a real solution, since it is analogous to how the hydrocarbons we're burning were created in the first place. It might be easier to irrigate the Sahara and flood it with Salicornia and salt mangrove than to stop China from burning coal.
  - hwillis 9y ago
    >I don't think it's as easy as you think it is to cut emissions by that much, and it certainly wouldn't be humane. No, seriously, it really is that easy. The average cost of a new car in the US is $30k, the model 3 is 35k. Every single passenger road vehicle could be replaced with an electric car for ~$1 trillion. It would cost even less to upgrade the grid to full battery-backed solar power and replace gas heating with electric. Over ten years thats 200 billion annually to eliminate 85% of the co2 released by the US and 50% of the methane. In terms of threats to the country that barely registers as spending. The iraq war was 10+ trillion dollars, we shipped 12 billion in $100 bills on pallets and lost it. Renewable energy is near price parity to fossil fuels, even if you adopt it stupidly it still isnt that expensive. You make china stop burning coal by buying them solar panels. Nobody says no to free electricity.
tonmoy 9y ago
What's the point of lowering CO2? Isn't the only reason to try to lower CO2 is because it is acting as a GHG?
- roywiggins 9y ago
  Ocean acidification, for one https://en.wikipedia.org/wiki/Ocean_acidification https://en.wikipedia.org/wiki/Ocean_acidification
- thescriptkiddie 9y ago
  https://en.wikipedia.org/wiki/Ocean_acidification https://en.wikipedia.org/wiki/Ocean_acidification
fleitz 9y ago
Sunlight is not the bottleneck for plant growth, CO2 and temperature are.
ridgeguy 9y ago
Maybe the diffractive elements the paper proposes could deflect wavelengths not used by plants. This would reduce total insolation on Earth but leave photosynthesis and CO2 absorption untouched.
TTPrograms 9y ago
You could definitely reflect ex. infrared without affecting photosynthesis. I think your response is a little quick to brush off these ideas. There are many possible venues for geoengineering that could have fantastic benefits, even beyond affecting climate change. Brushing them off as ideas akin to "playing god" is both unprincipled and potentially harmful to both mankind and the planet.
BurningFrog 9y ago
> Sure, blocking or deflecting some light might lower Earth's temperatures temporarily, but you'd exacerbate CO2 levels semi-permanently. This hurts to read. Blocking sunlight "might" not lower temperatures. It is absolutely certain. It's a very basic fact that sunlight is what heats our planet.
- khazhoux 9y ago
  I think you're misreading. The uncertainty of "might" refers to the plan actually occurring, not to the temperature lowering. You can read this sentence as: "Sure, you might block or deflect some light and that will lower Earth's temperatures..."
idlewords 9y ago
You can't assume that a reduction in sunlight reaching the top of the atmosphere means a reduction in total sunlight reaching plants on the earth's surface, because of complex feedback effects involving cloud cover. Moreover, as multiple posts in this thread point out, sunlight is not the limiting factor in plant growth.
perilunar 9y ago
> If you were to take 10% of sunlight away from Earth No one is talking about 10%. Article mentions 1.8%.
jk2323 9y ago
Look, even as a scientist it is incredible hard for me to have a solid opinion on the CO2 influence. (Is it causing warming? Is warming a good or bad thing? etc.). But climate change is the rule in earth history, not the exception. But I kindly ask you to have a look at this link: https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fer...
dexen 9y ago
>The other, plantlife, is absolutely affected. Astute observation, but the problem is easily fixable. Plants use particular wavelengths of light (IIRC mostly from the visual spectrum) for photosynthesis. If the proposed spacecrafts were to block mostly UV and infrared, letting most of visible spectrum through, it'd do plants no harm at all. The relevant technology is already available and widely used. For example typical car's windshield consists of two or more layers of special UV/infrared absorbing foil sandwiched between glass panes for structural support. In case of a spacecraft, all you'd have to do is spin the fuselage at low RPM to keep the foil extended. EDIT: my only contention with any sun-blocking spacecrafts is that they'd have to be carefully engineered to prevent use as a weapon for attacking ground & orbital targets with focused beams of light.
- andai 9y ago
  Re: holy shit has that idea ever been explored? Giant lens / mirror array in space?
UnpossibleJim 9y ago
That beings said (though, I am CERTAINLY no proponent of this idea), were we to make this geostable "sunshade" out of some sort of solar power generation device (since all of this is ridiculous conjecture, I don't have to think about the logistics) it could cool the (already) elevated global temperatures while reducing green house gas emissions. Though, that would create it's own long term issues to be solved, but all of these fanciful odeas tend towards band-aids, instead of solutions =) still, fun thought experiments
ozfive 9y ago
This one for one ratio that you mention of blocking the sun out would not logically follow. Any plant life losing sunlight that does any significant amount of carbon absorption would die. Where are they planning to throw some shade Antarctica?

taberiand 9y ago

There isn't going to be one single solution, but reducing incoming sunlight by a small percentage (1-2%) could be a cost effective part of a multi-layer approach.

koverstreet 9y ago

Amount of sunlight is not the limiting factor on plant growth in most places. In fact, it's often the opposite - plants shut down respiration during midday to limit water loss because it's too hot.

mchannon 9y ago
I imagine "most places" refers to most places on land, which is less than 20% of the range of where plants grow. Ocean-based plantlife is the workhorse on this planet, and I would argue that the lion's share is absolutely constrained by available sunlight. Further, there's a substantial difference between "respiration" and absorption of sunlight. Pineapple plants, for instance, only "breathe" at night.
- tlb 9y ago
  Plant life in the oceans is mainly limited by minerals, especially iron. That's why the oceans aren't green and slimy. Dumping iron powder in will usually cause an algae bloom, which eventually die and take the carbon they fixed to the bottom, so seeding the oceans with iron is a potential way of reducing CO2 in the atmosphere. Of course, like any large-scale meddling, there will be collateral damage.
  - 6502nerdface 9y ago
    > will usually cause an algae bloom, which eventually die and take the carbon they fixed to the bottom It works so well that this could even be how the current "icehouse earth" conditions got started in the first place. The Azolla bloom of 49 ma dropped atmospheric CO2 levels from 3500ppm to 650ppm in less than 1 my, and CO2 has been in that lower range ever since. https://en.m.wikipedia.org/wiki/Azolla_event https://en.m.wikipedia.org/wiki/Azolla_event
- jws 9y ago
  A quick, non-biologist's googling suggests that nitrate and ammonium are the limiting factors for most oceanic algae. I recall there being experiments for areas are iron limited, so they spread iron sulfate and created algae blooms. I suppose intuitively, if you scoop up a bucket of ocean water, it is not green. If light were the limiting factor you would expect the water to contain lots of light absorbing algae. This does happen in nutrient rich waters, like the sewage lagoons and creeks I grew up near.

hwillis 9y ago

Every idea for geoengineering as a solution to climate change is insane. They're either nonsense, like solar chimneys, or they're like this one: way worse than the problem currently is, and WAY worse than not emitting CO2 would be. Take atmospheric sulfate aerosols[1], which I often see touted as the solution, usually by conspiracy theorists. The kind of people who think "big green energy" is money play, and this simple solution is being hidden for some grand reason. "Atmospheric sulfate aerosols" means spraying sulfuric acid into the air. It's all the joy of this solution with the added bonus of primarily blocking visible light, destroying the ozone layer, and scattering light so that solar panels and plant life don't work as well. Oh yeah, and SPRAYING ACID INTO THE AIR. Intentional acid rain, forever. It's an incredibly foolish, destructive idea that people with zero drive to do basic research support vocally. The cheapest, easiest and safest way to fight climate change is to stop emitting CO2. It would be so incredibly easy to stop 80% of anthropogenic emissions. These geoengineering plans are worse in every way. [1]: https://en.wikipedia.org/wiki/Stratospheric_sulfur_aerosols https://en.wikipedia.org/wiki/Stratospheric_sulfur_aerosols

microcolonel 9y ago
> It would be so incredibly easy I don't think it's as easy as you think it is to cut emissions by that much, and it certainly wouldn't be humane. Biological sequestration is closer to a real solution, since it is analogous to how the hydrocarbons we're burning were created in the first place. It might be easier to irrigate the Sahara and flood it with Salicornia and salt mangrove than to stop China from burning coal.
- hwillis 9y ago
  >I don't think it's as easy as you think it is to cut emissions by that much, and it certainly wouldn't be humane. No, seriously, it really is that easy. The average cost of a new car in the US is $30k, the model 3 is 35k. Every single passenger road vehicle could be replaced with an electric car for ~$1 trillion. It would cost even less to upgrade the grid to full battery-backed solar power and replace gas heating with electric. Over ten years thats 200 billion annually to eliminate 85% of the co2 released by the US and 50% of the methane. In terms of threats to the country that barely registers as spending. The iraq war was 10+ trillion dollars, we shipped 12 billion in $100 bills on pallets and lost it. Renewable energy is near price parity to fossil fuels, even if you adopt it stupidly it still isnt that expensive. You make china stop burning coal by buying them solar panels. Nobody says no to free electricity.

tonmoy 9y ago

What's the point of lowering CO2? Isn't the only reason to try to lower CO2 is because it is acting as a GHG?

roywiggins 9y ago
Ocean acidification, for one https://en.wikipedia.org/wiki/Ocean_acidification https://en.wikipedia.org/wiki/Ocean_acidification
thescriptkiddie 9y ago
https://en.wikipedia.org/wiki/Ocean_acidification https://en.wikipedia.org/wiki/Ocean_acidification

fleitz 9y ago

Sunlight is not the bottleneck for plant growth, CO2 and temperature are.

ridgeguy 9y ago

Maybe the diffractive elements the paper proposes could deflect wavelengths not used by plants. This would reduce total insolation on Earth but leave photosynthesis and CO2 absorption untouched.

TTPrograms 9y ago

You could definitely reflect ex. infrared without affecting photosynthesis. I think your response is a little quick to brush off these ideas. There are many possible venues for geoengineering that could have fantastic benefits, even beyond affecting climate change. Brushing them off as ideas akin to "playing god" is both unprincipled and potentially harmful to both mankind and the planet.

BurningFrog 9y ago

> Sure, blocking or deflecting some light might lower Earth's temperatures temporarily, but you'd exacerbate CO2 levels semi-permanently. This hurts to read. Blocking sunlight "might" not lower temperatures. It is absolutely certain. It's a very basic fact that sunlight is what heats our planet.

khazhoux 9y ago
I think you're misreading. The uncertainty of "might" refers to the plan actually occurring, not to the temperature lowering. You can read this sentence as: "Sure, you might block or deflect some light and that will lower Earth's temperatures..."

idlewords 9y ago

You can't assume that a reduction in sunlight reaching the top of the atmosphere means a reduction in total sunlight reaching plants on the earth's surface, because of complex feedback effects involving cloud cover. Moreover, as multiple posts in this thread point out, sunlight is not the limiting factor in plant growth.

perilunar 9y ago

> If you were to take 10% of sunlight away from Earth No one is talking about 10%. Article mentions 1.8%.

jk2323 9y ago

Look, even as a scientist it is incredible hard for me to have a solid opinion on the CO2 influence. (Is it causing warming? Is warming a good or bad thing? etc.). But climate change is the rule in earth history, not the exception. But I kindly ask you to have a look at this link: https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fer...

dexen 9y ago

>The other, plantlife, is absolutely affected. Astute observation, but the problem is easily fixable. Plants use particular wavelengths of light (IIRC mostly from the visual spectrum) for photosynthesis. If the proposed spacecrafts were to block mostly UV and infrared, letting most of visible spectrum through, it'd do plants no harm at all. The relevant technology is already available and widely used. For example typical car's windshield consists of two or more layers of special UV/infrared absorbing foil sandwiched between glass panes for structural support. In case of a spacecraft, all you'd have to do is spin the fuselage at low RPM to keep the foil extended. EDIT: my only contention with any sun-blocking spacecrafts is that they'd have to be carefully engineered to prevent use as a weapon for attacking ground & orbital targets with focused beams of light.

andai 9y ago
Re: holy shit has that idea ever been explored? Giant lens / mirror array in space?

UnpossibleJim 9y ago

That beings said (though, I am CERTAINLY no proponent of this idea), were we to make this geostable "sunshade" out of some sort of solar power generation device (since all of this is ridiculous conjecture, I don't have to think about the logistics) it could cool the (already) elevated global temperatures while reducing green house gas emissions. Though, that would create it's own long term issues to be solved, but all of these fanciful odeas tend towards band-aids, instead of solutions =) still, fun thought experiments

ozfive 9y ago

This one for one ratio that you mention of blocking the sun out would not logically follow. Any plant life losing sunlight that does any significant amount of carbon absorption would die. Where are they planning to throw some shade Antarctica?