What do new materials mean for battling climate change
Getting the Oceans back to average
According to the climate.gov website, the world’s oceans have a surplus of 120 sextillion joules (12*10^22) or 120 billion trillion joules of excess energy. For reference it takes about 35,273 joules to bring a cup of water from room temperature to 80 °C aka a cup of hot tea*. In layman’s term’s our ocean’s have enough surplus energy to make over 3.4 quintillion cups of tea (a quintillion is a billion billion). Our question for today is, how might new materials and technology help us get rid of all of that surplus energy? (fi you just want an answer you can skip to the bold text near the bottom)
Broadly speaking there are two ways you can help to reduce how much heat energy is in something.
Source: Wikipedia (the square should roughly show what 1 million square kilometers would look like overlayed on the Earth.)
One way is to help move the heat energy away from that thing you want to cool, using a fan on a hot day would be an example. The other way is to reduce how much energy you are adding to something, like turning down a burner when your pot is starting to boil over. On the human scale it can be relatively easy help move away heat energy or reduce how much heat energy is being absorbed by the thing you are trying to keep from overheating. When you start talking about planets, it gets a bit more complicated
(ok so its at this point I am going to start talking about things that I’m like 66% confident that I’m on the right track, that being said if you know literally anything about climate modeling and something needs correcting please let me know and I’ll update accordingly)
On a planetary scale, one way to reduce how much heat is being created on a planet is to change how much light energy is absorbed and converted into heat energy. This is called the albedo, which uses a scale of 0 to 1 to describe how reflective the material is. An albedo of zero means that the material will absorb all the light energy that hits it and converts that energy into something else, usually heat. Having an albedo of 1 means that if you were to aim sunlight at the material all that energy would be reflected away. Seawater has a very low albedo of about 0.06, meaning over 90% of the sun’s energy that hits seawater is absorbed. On the other end of the spectrum is ocean ice with an albedo of 0.5-0.7 meaning less than half of the sun’s energy hitting the snow is absorbed.
The other way to help cool things off is helping heat to leave the confines of our atmosphere. Until recently the only way to help heat escape the Earth was to reduce the quantities of greenhouse gases in the atmosphere, lowering greenhouse gases makes it easier for heat to leave. While our civilization should work to help return greenhouse gas levels back to pre-industrial levels it is worth investigating other ways to move that heat energy away.
New innovations in material sciences have allowed researchers to create Passive Daytime Radiative Cooling (PDRC) materials. These PDRCs do two things, reflect as much sunlight as possible while at the same time emitting thermal energy in a frequency that greenhouse gases are unable to block. As a result, PDRCs can be cooler than the world around them. Objects coated in PDRCs can be 5-10°C (9-18°F) cooler than surrounding air, as they are able to send heat energy off into the vacuum of space. Because PDRCs are still in their infancy the volume of published research is still relatively narrow, this article will outline how PDRCs might be used to cool the oceans.
Before more writing, some variables
2016 Global Ocean Average Temperature 14.84°C (58.69°F)
20th Century Global Ocean Average Temperature 13.9°C (57°F)(
PDRC Albedo 0.95+/-0.03 (a range is being used to allow for subsequent variability
PDRC heat loss rate 127 Watts/m2 (this is the best-case scenario)
The average square meter of planet Earth absorbs about 240 Watts/m2 (I think this is 24/7 corrections welcome) (340 watts reach the earth about 1/3 is reflected back leaving us with the 240 watts
Average Planetary Albedo 0.3
Albedo of Seawater 0.06
Calculated average energy absorption of ocean water: 320 watts/m^2
(340 Watts/m^2*(1-0.06)=319.6w/m^2)
Area of the world’s oceans 361.8 million square kilometers
If we were to cover part of the Earth’s ocean with PDRCs we would be able to attack the heat energy imbalance on two fronts, reducing how much of the sun’s energy that gets converted into heat energy and helping the heat that’s already here sneak through our atmosphere’s green house effect.
For this article we are going to imagine that humanity has rallied its resources together to modify 1 million square kilometers (about the area of Texas and California combined) of “average” ocean. Our “average” ocean is assumed to receive 340 watts of solar energy every second 24 hours a day (obviously this doesn’t occur in the real world, but this is a value used by NASA’s Earth observatory for global average solar gain). First we must calculate how much energy this swath of ocean would absorb from sunlight naturally.
1) 340 watts/m^2*(1-0.06)*# of seconds in a year* 1,000,000 km^2*(1,000,000 m^2/km^2)
= 1.01 sextillion Joules (1.01*10^22)
Next we would want to look at how much less energy per year the region would absorb if the local albedo was higher
a) 0.3 = 2.57*10^21 fewer Joules/year
b) 0.5 = 4.72*10^21 fewer Joules/year
c) 0.7 = 6.86*10^21 fewer Joules/year
d) 0.96 = 9.65*10^21 fewer Joules/year
Knowing the energy reduction, while lazily assuming the global energy balance has gone back to the 20th century average, we can estimate how long it would take for the ocean’s energy to get back to historic norms.
a) [albedo = 0.3] 1.2*10^23 Joules / 2.57*10^21 Joules/year =46.6 years
b) [albedo = 0.5] 1.2*10^23 Joules / 4.72*10^21 Joules/year =25.4 years
c) [albedo = 0.7] 1.2*10^23 Joules / 6.86*10^21 Joules/year =17.5 years
d) [albedo = 0.96] 1.2*10^23 Joules / 9.65*10^21 Joules/year =12.4 years
From this, we can see that if humans were just able to raise the albedo of the ocean region to that of snow, the ocean energy surplus could be eliminated in under 20 years.
Next, we would want to model how black body cooling might improve performance. For the black body cooling, we are going to assume a constant rate of heat transfer. Technically black body cooling rates are dependent on the temperature of the object that they are cooling, with colder objects losing heat energy more slowly than warmer objects, but we’re going to be lazy to save time.
N watts/m^2*# of seconds in a year* 1,000,000 km^2*(1,000,000 m^2/km^2) =
1) PDRC @ 5 watts/m^2 = 1.58*10^20 Joules per year
2) PDRC @ 10 watts/m^2 = 3.15*10^20 Joules per year
3) PDRC @ 25 watts/m^2 = 7.88*10^20 Joules per year
4) PDRC @ 50 watts/m^2 = 1.58*10^21 Joules per year
5) PDRC @ 120 watts/m^2 = 3.78*10^21 Joules per year
Best case cooling scenario
[albedo = 0.96 thermal emissivity 120W/m^2] 1.2*10^23 Joules /( 9.65*10^21 Joules/year + 378*10^21 Joules/year) = 8.93 years
You might notice that even the most effective PDRC is only about 50% more effective than simply raising the albedo to the planetary average, let alone getting the region to have the albedo of ice. That means that under a best-case scenario where the black body emitter is able to consistently provide 120 watts/m^2 of cooling, you might be able to reduce the cooldown time by 3.3 years.
This improvement of cooling time sounds tempting, the faster we can help the ocean all the better, or even if we don’t decrease the cooldown time we might reduce our area requirements. What these estimations don’t account for is the cost of implementing this idea. While researchers are hard at work trying to reduce the cost of creating PDRCs the would still add to the cost of making this white coating and there is a chance that the environment might take an even larger hit when humans put the effort into making their massive PDRC blanket.
TLDR If humans were to cover 1 million square kilometers of the ocean in PDRCs, the best-case scenario would require almost a decade to help reduce the current heat surplus already there. 8.93 years using advanced PDRCs or 17.5 years just covering the water in long-lasting ice.
Some additional thoughts.
Man modeling this stuff is complicated, I know I probably made some errors, this was more to get ballpark figures, not to be hyper-precise, but if any assumptions are absolutely incorrect or if there is an easier way to model this stuff please let me know in the comments.
While the numbers I used were based on the global average value for how much energy a given square meter of the Earth receives from the sun, a better model would try to account for the latitude the reflective region was added to. If you could deploy the floating cooling blanket closer to the equator, it’s reasonable to assume that you could reflect more energy, and as the water in that region is hotter that the PDRC would be more likely to be emitting more heat energy. Moving the blanket closer to the poles would provide an opportunity for some positive feed back loops, where cooler water would make ice formation easier and that ice could compliment the floating blanket.
One way to deploy this massive cooling surface area could be to deploy something like shade balls, where they float along reflecting away heat. Best case scenario for floating reflective balls would be about 90% coverage. That means the effective albedo of the region covered would need to account for that spacing.
Personally I think where PDRCs might be helpful in large scale geoengineering projects is to help make ice production more energy-efficient. As I mentioned earlier blackbody cooling is dependent on temperature, the hotter the thing being cooled, the more heat energy that can be lost. Imagine floating ice factories creating seed ice using renewable energy to power their pumps and PDRCs to maximize cooling efficiency. This vision has no answer to who will pay for this crazy idea, but it is worth noting that Johannesburg South Africa is looking to tow massive chunks of ice to their city to ensure they have sufficient water.
I hope this was interesting, questions and comments are welcome.
*this temperature was chosen as it is closer to the upper bound of temperatures for safe hot beverages https://www.ncbi.nlm.nih.gov/pubmed/18226454. The heat energy of the tea was taken using the difference in total heat energy contained in water at 80 degrees C vs 20 degrees C