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In the TV show Futurama, an in-show infomercial mentions that Earthicans started dropping giant ice cubes in the ocean to slow down global warming. Now, Futurama is a show where science is a mixed bag: Futurama has a number of scientist consultants, but they also often send science to the back of the bus if it means having better jokes.
How feasible would this solution be in a more realistic setting?
If you drop an ice cube into a room temperature drink, the drink will be slightly colder for a little while. But what happens then? Answer: the drink warms up again until it has the same temperature as its surroundings.
What happens when these melt? Does the drink stay cold? No, it does not. (Image source)
The issue with global warming is not that we are accumulating heat in such a way that if we can just manage to make a one-time dump/soak of heat, then we will be all right. It is not as if we are sitting on a warm rock that must just be cooled off a bit and then things are fine.
Four things to keep in mind for further discussion:
The heat that we gain is more or less constant, save for geographically local variations. This does not vary to any great degree. The amount of incoming heat is for all intents and purposes the same over the time-spans that we care about.
That we lose heat proportional to the fourth power of the temperature means that the temperature on the surface of the Earth will be very stable. Because if the surface cools, it radiates a lot less heat, and this is then balanced by the incoming heat, and will warm up the surface again. Conversely if the surface warm up it will quickly radiate a lot more heat. The incoming heat will not be enough to compensate for that which is radiated out, so the surface cools. So this is a sort of self-regulating mechanism.
The factor that messes it up for us is the atmosphere. The atmosphere is like a big blanket for the Earth. Some of the heat that is radiated away from the surface does not disappear into space but is instead reflected back to the surface again, the so called "greenhouse effect". This means an increase of the incoming heat.
Now if this reflection is constant, or changes only very slowly, the balance between incoming and outgoing remains constant and the temperature does not change very fast. We can adapt to any slow change. This is the way it has been throughout most of civilized history.
But if the greenhouse effect becomes more pronounced, and this happens fairly quickly, then more heat is being reflected back to the surface, and this upsets the balance. It is like swapping a thin blanket for a thicker one. Now we have more incoming heat than before, and this is not balanced by the outgoing heat. This means that the surface will warm up; its temperature will rise until there is balance between incoming and outgoing again.
Dumping some ice onto the planet will not help. While it is true that this will soak up some heat it is a very transient effect and will only cool the surface for a short while. The cooling caused by the ice soaking up heat upsets the balance between incoming and outgoing. Now there is a big difference between them, because the now cooler surface radiates a lot less heat. So the laws of thermodynamics will quickly restore the balance.
There is only one way that we can stop global warming and that is to make sure that more heat is dumped into space again. This we would do by thinning out the "blanket" that is greenhouse gasses (GHG), chiefly carbondioxide but also methane and some other GHG. We would thin it out by halting the emissions of these gasses into the atmosphere, and then let natural processes take their course, by which already existing such gasses are either broken down or integrated into sold matter, such as plant life.
Some suggest we can prevent also some heat from reaching us, with so so called Climate Engineering, but those plans are... eh... "unsure cards" to put it mildly
Halley's mass is 2.2×1015 kg.
A cubic kilometer of water has a mass※1 of 1 × 1012 kg
Oceans hold 1.35 × 10 9 cubic kilometers, which gives us 1.35 21 kg of water.
So, the mass of the Halley is half a millionth of the ocean. If it is 200 C colder than Earth oceans (say −180° C for the comet, 20° C for the ocean) when dropped, the calculus of how much would it cool the ocean is approximately as follows:
SpecificHeatice-180to0 = 180 K × 0.513※2 cal/K = 92.34 cal
Enthalpyice = 79.72 cal
SpecificHeatwater0to20= 20 K × 1 cal/K = 20 cal
TotalSpecificHeat = 92.34 cal + 79.72 cal + 20 cal = 192.16 cal
All of the above values are per gram. This gives the approx. value of cooling as※3
EnergyChange = 192.16 cal/g * 2.2*1018 g = 4.22 × 1020 cal.
Which, with a specific heat of 1 cal per gram of water gives a temperature change of
TemperatureChange = 4.22 × 1020 cal × 1 K·g/cal / 1.35 × 1024 g = 3,125 × 10−4 K = 3,125 × 10−4 C = 0.0003125 C of variation.
Comets usually have ice of it, but not only water ice. If we see the Halley's composition, it shows things like CO and CO2 ice. So, while you may get some to reduce the heat by dropping it, you also get to release greenhouse gases to the atmosphera, somewhat reducing the effect.
Comets are moving at astronomical speeds, and slowing their mass will release energy as a lot of heat.
Even if we somehow "stop" the Halley comet to allow for it to slowly fail into the ocean, it will still have gravitatory energy. Maybe it would be not enough to cook a steak, but it would still heat the falling water and the air around it considerably, reducing (if not negating completely) any possible gain due to the comet temperature.
In order to drop it, the comet will have to get into our orbit. That means that the Sun will be warming it from some time, reducing the temperature differential.
Despite the popular image of an icy rock, when a comet approachs the sun it begins to melt and evaporate (in fact, that is what the whole "tail" of the comet is, gas and particles projected away from the comet).
Obviously, the "hotter" a comet is, the less effect we will get by dropping it on the sea.
※2 Specific heat of ice seems to be 2,108 J/kg·K, or 0,513 calories
※3 Since the mass of the comet is nine orders of magnitude lower than the mass of the oceans, I would not change that value.
To me, it's the same as if you'd said:
Stopping global warming by leaving the fridge open.
So, maybe we should just be a bit more careful with this earth of ours.
@SJuan76 's answer is incomplete. He did the math to show the small cooling effect of, but didn't show the heating effect. I shamelessly copied his cooling numbers, and added heating numbers to compare.
Halley's mass is $2.2\times10^{15} \text{kg}$.
A cubic kilometer of water has a mass of $1\times10^{12} \text{kg}$
Oceans hold $1.35\times10^{9}$ cubic kilometers, which gives us $1.35\times10^{21} \text{kg}$ of water.
So, the mass of the Halley is half a millionth of the ocean. If it is 200 C colder than Earth oceans when dropped, it would cool the ocean only by 4/10,000 C.
Comets have both kinetic energy and potential energy as they fall to earth. The Kinetic energy will be at least as much as the orbital energy of LEO. The Potential energy is equivalent to mass times gravity times height. However, since gravity is not constant coming from LEO, the gravity times height portion is actually an integral $$\int_{surface}^{orbit} g(h) dh,$$ where $g(h)$ is force of gravity as a function of height. This function is $$ \frac{GM}{r^2}$$ where $GM = 3.98\times10^{14} \frac{\text{m}^3}{\text{s}^2}$. The radius or height of LEO is $6.671\times10^{6} \text{m}$ and the surface of earth is $6.371\times10^{6} \text{m}$.
Given the mass of the comet as $2.2\times10^{15} \text{kg}$, the potential enery equation: $$2.2\times10^{15}\int_{6.371\times10^{6}}^{6.671\times10^{6}} \frac{3.98\times10^{14}}{h^2} dh.$$ I solve that to be $1.2\times10^{22} \text{J}$.
How much energy is that? Given a mass of the ocean of $1.4\times10^{21}$ kg and a specific heat of 3850 J/kg*C, the heating due to potential energy is 22/10,000, or more than five times the cooling effect.
So basically, just dropping a comet from dead stationary in orbit, without any kinetic energy, will release potential energy many times more than the anticipated cooling effect.
This approach is not only infeasible, thermodynamics says it wouldn't work at all.
Though many of the previous responses are correct, there's a simpler answer that's been missed, though @Alexander von Wernherr came close:
To me, it's the same as if you'd said:
Stopping global warming by leaving the fridge open.
- Ice needs to be produced. This requires large quantities of energy for freezing water, which requires more and more power plants.
Irrespective of the potentially negative environmental impacts of building more powerplants and burning more fuels to freeze water into ice, cooling, refrigeration, and freezing do not result in a decrease in the overall energy of the system. Your kitchen fridge works by pulling thermal energy out of the air inside the fridge, and dumping that thermal energy into the air outside the fridge. So leaving the fridge open doesn't cool your kitchen (the system) at all (and refrigerators aren't perfectly efficient, so they actually create some waste heat).
Even someone figured out a way to freeze massive amounts of water and deliver the ice to the ocean in a perfectly efficient way, their setup must do something with all the thermal energy they've taken out of the now-frozen ice! That may mean heating other, separate water, or simply exhausting hot air, etc, but the overall temperature of the Earth does not decrease.
Clever idea with the comets though; if they didn't heat the atmosphere on entry, enough of them could temporarily cool the earth, because they are a heat sink that is exogenous to the system.
If we drop enough ice to rise ocean level sufficiently (say 60 feet = 20 m), lots of prime ocean-front land will get flooded. Factories, cities, farms, nuclear power plants. Raised oceans will also lift glaciers in Antarctic and Greenland from the bedrock, and add all those cubic miles of the frozen water will slide to the oceans, rising the ocean level on some 200 more feet within months, flooding yet more cities and arable land.
Displacement of the population from flooded areas will result in wars for territory, water, arable lands. Inevitable changes of the climate will decrease productivity of agriculture, increasing the pressure for wars even more. Destroyed factories will decrease productivity, increasing the intensity of wars for remaining resources even more. Which (together with cancellation of many humanitarian projects keeping big chunks of Africa alive) will led to huge migration out from most affected territories, starvation.
More fortunate countries will close to any migrants. Illegal immigration might become capital offense resulting in summary execution on the spot.
All that fighting, starvation and killings will decrease population substantially and will slow down global warming a little bit. Not much, because positive feedback will increase global warming: all that missing ice in Antarctic and Arctic does not reflect sun's energy back to space but keeps warming Earth. And thawed permafrost releases even more carbon to air, and also methane, which is even more potent greenhouse gas than CO2. Which leads to the final frontier: melting Methane clathrates frozen at the bottom of the oceans: clathrate gun hypothesis
In fact, we don't even need to add any additional ice. There is enough ice already melting that above scenario is plausible in 100 years.
Also, it does not have to be ice. Rocks (or anything that can displace water) will do. For extra bonus damage to civilization, drop those chunks of ice or rocks strategically (in mouths of bays, don't waste them in the middle of the oceans), causing most possible damage to coastal cities by tsunami. Drowning millions of people, destroying all that production capacity and drenching arable land in salt water will put some dent to production of greenhouse gases, and will nudge civilization bit farther towards the collapse, for the final solution of the greenhouse problem.
You can play with increasing ocean level and flooding some areas on this map: http://geology.com/sea-level-rise/ - lots of fun to be had! https://coast.noaa.gov/digitalcoast/tools/slr has more detailed maps (check flooding in your neighborhood) but max flooding is only 6 feet (geology.com goes up to 60 meters). Good enough for next 50 years, but we need MORE! :-)
If you want to extend the effect, dump large ice cubes into the ocean - less surface area means more not-melted time.
For all those who aren't computer scientists, $O(...)$ notation represents asymptotic pace;
$O(1) = 3$
$O(n) = 6x+6$
$O(n^2) = 8x^2+350x+5$
*per cube. Really, they don't melt at $O(n)$ pace per $cm^3$ of ice, but $O(n)$ pace per $cm^2$ of surface area. The surface area of a $O(n)\space cm^3$ cube can be informally approximated to $O(\frac{1}{n})\space cm^2$.
$h$ - heat in ocean
$i$ - heat coming in per second
We take freshwater and freeze it, dumping the heat into the ocean.
$h$ goes up by $W$ every time we put 1 cube in. $i$ goes down by $G$ for $H$ seconds every time we put 1 cube in.
We just need $G*H > W$.
And don't forget that in reality $H$ is not constant, it goes down per the size of the cube.
$Find\space cube\space size \space s \space such \space that\space G*h(s) > W.$
As if it wasn't obvious enough,
O(n) linear, and the output is O(n^2) exponential.
$\endgroup$
Dec 11, 2016 at 18:43
One of the biggest problems with global warming is that it has an accelerating effect due to the melting of the ice caps. Since light colors reflect light while dark colors absorb it, decreasing the albedo ("whiteness") of the planet overall (melting the ice caps, for instance) will cause the temperature to rise faster. The converse is also true: making the planet whiter can decrease global temperatures. Since ice is white, artificially putting ice back onto the ice caps can counteract global warming.
Of course, there are practical issues with this:
Yes, black holes can be cool
To begin with, we will have to add a mere $2.8\times10^{16}$ kg of ice per year. Based on SJuan's estimate of $1.35\times 10^{21}$ kg for the mass of the ocean, this is just $2.07 \times 10^{-5}$ times the total mass of the ocean. Of course with the green house gasses still building up and increasing gravitational force from all the melting ice increasing atmospheric pressure (and thus temperature), we simply add more and more ice each time.
For the purposes of this calculation we presume that to cool the ocean we need the same mass of ice relative to the growing mass of the ocean each time. One solar mass is ($2 × 10^{30}$ kg), so the time before the earth's ocean is as massive as the sun is $\frac{log{1.99 \times 10^{30}} - \log{1.35\times 10^{21}}}{\log{1.0000207}}$ or 1.02 million years. At about this point the earth will converge to a black hole with a nice cool temperature round $10^{-8}$ kelvin - thus solving the problem once and for all.
It won't solve the global warming,
Because , to make those ice cubes , you have to cool water , to do that you have to reduce the thermal energy of the water and that thermal energy will add to the environment, so when you give back the ice cubes to the environment, it absorbs thermal energy which it output when making if the ice cubes , so the temperature will stay the same , in fact it can go up since the ice making process is not 100% energy efficient
About comets
This is not possible as well. Because when comets come in the direction of earth it gets heated up due to air friction. Even most of the metal comets get vaporized even before they hit the ground. In ice cubes case , all of the ice cubes will be heated water or steam when they hit the ground. This will make the global temperature go up.
Mmm! what if a massive(earth size) ice comet fell down ?
Yes. Theoretically this can solve the global warming. 100% for sure . But Hitting this size of mass on the sea can make huge tsunamis and scariest part is the earth can be shifted from the orbit , even it can leave the solar system. Which will make it an ice planet. Eventually a dead planet. (Didn't even have to talk about what happens when it starts to melt)
To get rid of heat, you need to move the heat energy from the hot area to a cold sink. The heat energy the Earth is receiving is eventually radiated away to the cold and darkness of interstellar space, but since the Earth is an extremely complex and chaotic system (actually a series of systems like the atmosphere, the hydrosphere, the lithosphere and the ecosphere) there are no simple ways to map the various pathways heat energy arrives from the sun and departs.
What this really means is the heat energy in the ocean will only be temporarily diverted into melting the ice, but how it will affect the overall heat balance is not going to be predictable in any real or coherent way. A super volcano event like Tambora caused the "year without summer" by filling the upper atmosphere with aerosols, for example, but the resulting increase in smowcover or icepack did not start a global cooling chain reaction. Indeed, the only way we know for certain to cause such events as the "Little Ice Age" involve a reduction in the Sun's output, such as the Maunder Minimum between the 1400's and the late 1700's, or the current apparent reduction in solar activity which is happening now.
Warming periods are less predictable or explainable, the warm weather enjoyed by the Roman Empire or during the European Warm Period don't have an evident cause that we can point to, for example.
If the goal is to cool the Earth, the necessary thing to do is change the heat balance. Since the "cold sink" is already at an unvarying 3K, the place to interrupt the heat flow is to block the Sun with an orbital sunshade, perhaps at the Earth Sun L1 point or having millions of small mirrors orbiting the Earth (Injecting aerosols into the upper atmosphere, while known to work. would not be a quickly or easily removable as needed).
All the other answers deal with physics and thermodynamics and ignore the root of all evil - Money.
There may be an issue of ownership - Halley would surely have a word to say about reuse of his comet, were he still alive.
Since he's not alive, ownership will pass to his descendants, who have to be located and queried. Given that Edmond Halley was English there will be a reasonably-sized Compulsory Purchase payment due to Halley's estate
Refer to https://en.wikipedia.org/wiki/Compulsory_purchase_in_England_and_Wales
In short - complex finances could kill this faster than the consensus that it won't help anyway.
Build a really big orbital beanstalk.
Catch ice. Raise (warmish) water and lower near-0-K ice, trading their KE with minimal friction.
Build large glaciers from this ice, increasing albedo of Earth.
This both lowers the current temperature of Earth, and makes it reflect more light. Between the two, at huge scales, you could actually cool the Earth.
The fact that the icebergs melt is unimportant, because you are refreshing them at whatever rate required.
Obviously painting the entire oceans white (covering them in ice) would be sufficient to outdo modest global warming.
The energy required to do this is all in orbit. And as we lift as much water as we lower water, the process is mostly a closed system; you can even bag the water you raise up before you freeze it in orbit to reduce sublimation losses. You basically are building a giant refrigerator plus coating the planet in mirrors.
At the scale of Futurama tech insanity, this is mild. At any reasonable scale, it isn't.
After read the SJuan76 and kingledion you can notice that it's almost impossible get colder the planet using comets. A comet has very low water compared to the entire oceans so the change of temperature they do is impercetible.
Also, you can't cold directly the planet making ice because to cold an object you have to warm another (transfer heat). Maybe you could transform thermal energy into electricity but that can't be done at planetary scale.
But....
Before continue I have to say:
Do you have read about the Albedo? Well, you should do.
Albedo (/ælˈbiːdoʊ/) is a measure for reflectance or optical brightness (Latin albedo, "whiteness") of a surface. It is dimensionless and measured on a scale from zero (corresponding to a black body that absorbs all incident radiation) to one (corresponding to a white body that reflects all incident radiation).
Each material has and albedo value:
With this we can know that some materials reflect better the light of the sun (heat) and it escape of the Earth.
I've found some values over the Internet. I'm not sure which of them is more precise so I'll use all of them:
$$\begin{array}{|c|c|} \hline \ \text{Sustance} & \text{Albedo} \\ \hline \ \text{Ocean} & \text{%}5 - 10\text{%} \\ \hline \ \text{Open Ocean} & 6\text{%} \\ \hline \ \text{Melting Snow} & 40\text{%} \\ \hline \ \text{Oceanic Ice} & 50\text{%} - 70\text{%} \\ \hline \ \text{Atartica Snow} & 80\text{%} \\ \hline \ \text{Fresh Snow} & 80\text{%} - 86\text{%} \\ \hline \ \text{Freshly Fallen Snow} & 90\text{%} \\ \hline \end{array}$$
Firt we have to know the actual heat that it's absorbed by oceans, and the amount that it's reflected.
$$\frac{\text{Ocean surface}}{\text{Earth surface}} = \text{% of ocean surface}$$ $$\frac{361,000,000 \text{ km²}}{510,072,000 \text{ km²}} = 70.77 \text{%}$$
So the $70.77 \text{%}$ of the Earth surface is cover by water.
We know that solar constant of light in the atmosphere is $1,366 \text{W/m²}$ but at the surface only reach $1,025 \text{W/m²}$ (I won't count clouds).
So:
$$361,000,000 \text{ km²} \times 1,025 \text{ W/m²} = 370,025,000,000,000 \text{ Watts} = 370.025 \text{ TW}$$
If we substract the values of the albedo (that power * albedo value) with the total energy we can know how much energy is absorbed and how much is reflected:
$$\begin{array}{|c|r|r|r|} \hline \ \text{Sustance} & \text{Albedo} & \text{Reflected} & \text{Absorbed (Heat)} \\ \hline \ \text{Ocean} & 5\text{%} & 18,501.25\text{ GW} & 351,523.75\text{ GW} \\ \hline \ \text{""}& 10\text{%} & 37,002.50\text{ GW} & 347,823.50\text{ GW} \\ \hline \ \text{Open Ocean} & 6\text{%} & 22,201.50\text{ GW} & 347,823.50\text{ GW} \\ \hline \ \text{Melting Snow} & 40\text{%} & 148,010.00\text{ GW} & 222,015.00\text{ GW} \\ \hline \ \text{Oceanic Ice} & 50\text{%} & 185,012.50\text{ GW} & 185,012.50\text{ GW} \\ \hline \ \text{""} & 70\text{%} & 259,017.50\text{ GW} & 111,007.50\text{ GW} \\ \hline \ \text{Atartica Snow} & 80\text{%} & 296,020.00\text{ GW} & 74,005.00\text{ GW} \\ \hline \ \text{Fresh Snow} & 80\text{%} & 296,020.00\text{ GW} & 74,005.00\text{ GW} \\ \hline \ \text{""} & 86\text{%} & 318,221.50\text{ GW} & 51,803.50\text{ GW} \\ \hline \ \text{Freshly Fallen Snow} & 90\text{%} & 333,022.50\text{ GW} & 37.002,50\text{ GW} \\ \hline \end{array}$$
Water is about $70.77 \text{%}$ of the surface of Earth, now is your mission determine if changing the albedo of that surface (turn water into ice or snow) would reduce Significantly the heat of Earth. I think yes.
I am not sure but I think human contamination increase the amount of energy aborbed by $+0.2 \text{ W/m²}$, with a range $+0.1\text{ W/m²}$ to $+0.4 \text{ W/m²}$.
So human contribute with $102,014.4\text{ GW}$, with a range of $51,007.2 \text{ GW}$ to $20,402.88 \text{ GW}$. If you freeze the oceans the new albedo gain would counter-act our actual contamination.
It depends on the ice composition, amount, and where you release it
Current theory is that the previous ice ages were caused by large amounts of glacial ice being dumped into the Mid Atlantic Current, shutting it off sporadically and preventing the equatorial oceanic heat transfer to Europe and Canada (the main reason England is so rainy and warmer than its latitude should indicate is this effect).
Dumping a large amount of freshwater ice into the region occupied by the Mid Atlantic Current could replicate this effect.
link: http://www.sciencemag.org/news/2016/06/crippled-atlantic-currents-triggered-ice-age-climate-change
The time period would probably be shorter than normal, due the the same effects others have described, since we have too much heat trapping gas in the atmosphere.
Another interesting tidbit is that historically the southern hemisphere cools when the northern hemisphere gets warmer, and vice versa. Right now the ice sheets in Antarctica are actually growing (link: https://www.nasa.gov/feature/goddard/nasa-study-mass-gains-of-antarctic-ice-sheet-greater-than-losses) and this is one of the main talking points for global warming skeptics due to this historical pattern.
Edit: Wow this thread got necroed from last year, didn't even notice.
Entropy will mess that all up. While the ice could lower the temp. barely, eventually the ice will melt, causing higher sea levels. Plus, think of it as percentages. In school if you get something lower than a hundred, your average grade will never be exactly %100 percent ever again until it's reset (but you can't reset the temperature). So then, once its water, you cant change it back. If then you take the water and put it in your freezer, the freezer outputs heat through its back, causing equal yet opposite heat. Entropy is inevitable, so there isn't much of a solution.
To put things in perspective, the volume ratio of water ice on Earth to ocean is approximately 1/43,750,000. If all the ice on Earth melted (which it may yet do), it is the same as placing 1 gallon of ice into a lake containing 43.75 MILLION gallons of water. Can you picture it? Now imagine you had a thermometer in one end of the lake, and it read 80o F. Just how much do you think that thermometer would change, if you dumped one single gallon of ice into the lake anywhere away from the thermometer? Can you imagine it? THAT non-change is what will happen to ocean temperature if all the ice on Earth melts ... nothing! Ocean temperatures worldwide will not change more than a tiny, tiny fraction of 1 degree! Then, they will warm right back up ... probably within weeks. Sadly, the only way to stop this catastrophe is to STOP burning fossil fuels.
