# The polar ice caps are melting. Can I replace them with icebergs made of pykrete?

Pretend I'm writing a story about a world exactly like our own. Real world physics, no magic, modern technology.

Suddenly an eccentric world leader comes up with the idea to replace the melting glaciers in Earth's polar regions with glaciers/icebergs made of pykrete, which has a higher melting point, in a mad/genius attempt to help save the polar bears and other arctic life.

Ignoring the political issues involved, would this be a viable solution or would it have disasterous consequences?

Clarification: The world leader is not attempting to replace the entire north/south pole with pykrete, just the parts that melt due to Earth's rising average temperature. He's mad/genius, not completely stupid.

This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

• Pykrete doesn't have a lower melting point at all, it just takes longer to melt completely than an equivalent volume of pure ice at a given temperature. – Ash Jun 4 '18 at 15:29
• Does this assume that you already have that much pykrete? It sounds like you're going to need a lot of sawdust, which means you need a lot of wood, which is similarly not good for the environment. – HDE 226868 Jun 4 '18 at 15:33
• @HDE226868 Growing a lot of wood is a carbon-sink and locking it away in icebergs is carbon-sequestration... except for the slight problem that this won't actually accomplish anything, it is brilliant! – pluckedkiwi Jun 4 '18 at 15:39
• @pluckedkiwi You'd have to use pre-existing wood if you wanted to accomplish this on any short enough timescale. That means deforestation to some extent. – HDE 226868 Jun 4 '18 at 15:40
• @HDE226868 tree-farms are the majority source of bulk wood anyway - it would drive up the price of other wood products for a little bit, but shouldn't need anything new. Though now I'm wondering just how much sawdust is produced all over the world. Throw in everything down to wood chips from mulching downed trees and brush clearing, and you might not even have that much of an effect on global wood-byproduct supply. You're not going to need to replace all the glaciers and sea ice in one quick go anyway - I suspect the ability to form the pykrete icebergs would be the bigger bottleneck. – pluckedkiwi Jun 4 '18 at 15:49

No. The logistical issues have already been covered but even if you solved that it wouldn't help.

1. The Pykrete would still melt, it has low thermal conductivity so it melts slowly but if the exterior temperature is above freezing then it will still melt. There is no need for equations here. The speed is greater than zero so as the temperature rises the pykrete will melt eventually.

2. Pykrete is not white. It's a short of muddy-brown color. This would cause it to absorb far more heat from sunlight than the white ice or snow does - and actually cause the area to warm faster than it would otherwise.

Essentially you are creating an artificial Ice Albedo feedback situation. Sea Ice has an Albedo of between 0.5 and 0.7, reflecting away between 50% and 70% of the incoming energy from the sun. As per this study fresh snow has an albedo of around 0.83 and ice around 0.38.

Unfortunately I cannot find a figure for the albedo of pykrete but from the color alone you can see that it will be lower than that of pure ice, allowing it to absorb more energy. Trees and bare soil for example have an albedo of around 0.15 which seems reasonable as a starting point for a model. Even if you are generous to Pykrete and take a figure somewhere between ice (0.38) and bare soil (0.15) you're absorbing 3 times as much energy as snow does, and still substantially more energy than ice.

• Also, this seems useful but it's too much for me to digest now. – Mołot Jun 5 '18 at 10:57
• @Mołot Yep, found ice figures and filled them in. Good figures for wood/wood chipping seem hard to find though. I did find a random forum post listing 0.13 as the albedo for rough/old wood but no source for that claim and it was in a post about modelling so could well be about what "looks right" as opposed to scientifically accurate. – Tim B Jun 5 '18 at 11:02
• After much consideration I'm accepting this answer. Although the other answers have very good maths and all conclude that replacing the entire polar ice caps with Pykrete isn't possible (even though I thought the question made it clear that the king wasn't trying to replace all the ice), the exact question was "would this be a viable solution or would it have disasterous consequences?" and I think this answers that better by proving that the pykrete would melt faster than the ice, and thus wouldn't be a suitable substitute. The mad king will be sad to know he's just mad and not a genius. – Pharap Jun 8 '18 at 2:04

The polar ice caps are estimated to contain between 27 and 32 million cubic kilometer of ice. Let's round this up to 30 million cubic kilometer.

To make pykerete, we would need to blend it with sawdust, so that water is 86% and sawdust 14%. Let's also round up ice density to 1000 $kg/m^3$ and wood density to 700 $kg/m^3$

The volume of sawdust required is...

$$30 \times 10^6 km^3 of \ ice \times \frac{14 \text{% sawdust by mass}}{86 \text{% ice by mass}} \times \frac{1000 kg/m^3 \text{ ice}}{700 kg/m^3 \text{ sawdust}} = 7 \times 10^6 km^3 of sawdust$$

According to this estimate there are $3 \times 10^{12}$ trees on Earth. Assuming an average volume of 1 cubic meter of wood per tree, it turns out we don't have enough trees to make all that sawdust.

So we would end up with no trees, lees oxygen in the atmosphere and a destroyed global climate.

• Just a note, the percentages start as mass fraction not volume ah? I can't quite follow your math so you may have factored that in already. Those are some really small trees too. – Ash Jun 4 '18 at 16:10
• @Ash, 1000 and 700 account for the densities. – L.Dutch Jun 4 '18 at 16:27
• Are you trying to replace all ice on Earth in a single year? More reasonably all one would need do is match production to the current rate of loss, and of that only of sea ice (if the goal is polar bear survival - glacier mass isn't relevant). – pluckedkiwi Jun 4 '18 at 16:58
• You might want to factor in "trees grow" into your answer. – Yakk Jun 4 '18 at 17:32
• Your math is pretty dubious, even assuming you meant to calculate volume of sawdust and not mass. – cms Jun 4 '18 at 21:16

The current winter max ice cover in the Arctic Ocean is roughly 20,000km$^{3}$ to replace that with Pykrete you'd need around 2800 gigatons of sawdust or similar filler material and 20,000 gigatons of fresh water to produce that much Pykrete.

Pykrete still melts at 0°C, it just melts slower than the same volume of pure ice, so the end result is that you're dumping fresh water and wood chips into the Arctic Ocean. The added carbon from the wood could be disastrous in terms of anthropogenic warming based on Carbon Dioxide and Methane releases. The fact that the sawdust melted out of the Pykrete would cover the surface and prevent light from getting into the water is a two edged sword, it will reduce the ocean albedo compared to open water but it will also choke the surface disrupting the phytoplankton blooming cycles that form the basis of the oceanic food chain and a large source of global oxygen.

I've ignored any replacement of permanent ice like the Greenland Ice Sheet due to the logistically impossibility of emplacing material in such locations.

• The CO2 in the sawdust would have been taken out of the atmosphere during tree growth. – Yakk Jun 4 '18 at 17:32
• @Yakk Except it already was so Carbon that should be in trees is now in the atmosphere. – Ash Jun 4 '18 at 17:38
• trees grow back. Unless you clear-cut and prevent the trees from regrowing, you can sustainably convert atmospheric carbon to sawdust that way. – Yakk Jun 4 '18 at 19:54
• @Yakk I refer you to L.Dutch's answer indicating that a global clear-cut is exactly what this enterprise would require. – Ash Jun 5 '18 at 11:20

I can't stand idle and watch bad math go unchecked ;-). I will present the correct figures for how much wood this would require first, then append the equation of how to calculate at the end.

### Global wood production

Firstly, how much wood does the globe consume annually? According to this link, it was close to: $$R_w = 4\times 10^9 \; \text{m}^3\text{/yr}$$
As of 2008. I believe this includes all construction and firewood. We will use a round value for the density of wood as $\rho_w = 700 \; \text{kg/m}^3$ and convert this into a mass: $$R_w = 2.8 \times 10^{12} \; \text{kg/yr}$$

### Replacing all polar ice with Pykrete

I didn't know what Pykrete was before this question, but a quick google search suggests it is a mixture of 86% ice and 14% wood pulp / sawdust by weight. If one wishes to replace all 30 million cubic kilometers of polar ice with and equivalent amount of Pyrkete, you would need $$M_w = 3.6 \times 10^{18} \text{kg}$$ of wood. This is roughly six orders of magnitude, or 1 million times more wood than is produced annually.

### Replacing just the net yearly ice loss

According to NASA global polar ice is decreasing at a rate of: $$R_I = 5 \times 10^4 \; \text{km}^2 \text{/yr}$$

I wasn't able to find an estimate of how many cubic meters this is, but if we assume an approximate average of 100m of height (it doesn't really matter, as you will see), then the rate of volume of ice loss is: $$R_I = 5 \times 10^{12} \; \text{m}^3\text{/yr}$$

To produce this much Pykrete a year you would need: $$M_w = 6.1 \times 10^{14} \text{kg}$$ per year, or 219 times the current world yearly wood consumption.

### Why Pykrete

Besides the infeasible scales we are discussing, I saw no indication online that Pykrete would give any advantage to ice loss; Pykrete is structurally similar to concrete at temperatures around $-15 \text{C}$.

### Appendix: Calculate the mass of wood for a given volume of Pykrete:

The fact that Pykrete is 14% wood by total weight can be expressed as: $$M_w = 0.14 M_p$$ Where $M_p$ is the total mass of Pykrete. This total mass is of course the mass of both ice and wood combined: $M_p = M_w + M_i$. Substituting this and rearranging gives: $$0.86 M_w = 0.14 M_i$$ The mass of ice $M_i$ can be calculated as $M_i = \rho_i V_i$ where $\rho_i$ is the density of ice. The Volume of ice can be substituted for the total volume of Pykrete minus the total volume of wood: $V_i = V_p - V_w$: $$0.86 M_w = 0.14 \rho_i ( V_p - V_w )$$ And finally the volume of wood is related to the mass of wood: $V_w = M_w / \rho_w$ where $\rho_w$ is the density of wood. Therefore: $$0.86 M_w = 0.14 \rho_i ( V_p - M_w / \rho_w )$$ Some algebra is now required to solve for $M_w$. It simplifies to:

$$M_w = \frac{0.14 \rho_i \rho_w}{0.86\rho_w + 0.14\rho_w} V_p$$

Which is the required amount of wood as a function of the desired volume of Pykrete.

I'm not sure this is an answer, but it's too long for a comment.

How do you expect to freeze the pykrete?

If you simply expect to dump all this material (stated by other answers) and it freeze on it's own, you are adding to the problem of rising temperatures. Even if the water and wood mixture freezes, it has raised the surrounding temperature to do so. A single ton of this material probably wouldn't make that much of a temperature difference, but at the amounts you are talking about, you're likely to cause more problems.

The Second Law of Thermodynamics tells us:

https://www.bluffton.edu/homepages/facstaff/bergerd/NSC_111/thermo6.html
2. When heat is transferred from one body to another, the temperatures equalize. As the temperature of the heat source falls, that of the heat sink rises.

So, as the water and wood mass loses temperature (heat source), the temperature of the surrounding ice (heat sink) rises. Of course, this doesn't account for latent heat, but it's still heat transfer.

Cooling/freezing materials in a mechanical way, such as using a refrigeration unit, simply moves the heat from one material and radiates it in another location. Needing to freeze X,XXX number of tons of water and wood will raise the temperature of another location by a considerable amount.

The First Law of Thermodynamics tells us:

http://wikieducator.org/Thermodynamics/Energy
The internal energy of a system is constant unless changed by doing work or by heating

So, we would have to move the heat out of the "system" of the poles and move it someplace else. Unfortunately, on a scale this large, the Earth's atmosphere likely becomes the new "system". Unless we radiate the heat directly into space, we're simply robbing Peter to pay Paul.

To do any of this freezing in a man-made way would take massive refrigeration units that would cause more heat production and greenhouse gasses, causing more issues with the heating of the poles. Even if we could physically build them, the cost would be astronomical, probably on the order of the GDP of some medium sized countries.

And if would could still manage that, why not go ahead and just freeze salt water? It freezes at about 28 degrees F (https://oceanservice.noaa.gov/facts/oceanfreeze.html) and we'd have to get the ice to be considerably colder than that to stay frozen for any significant amount of time to make the effort worth doing.

According to an article I just found, the ice is also melting from the bottom:

https://www.theguardian.com/environment/climate-consensus-97-per-cent/2018/may/09/global-warming-is-melting-antarctic-ice-from-below
With global warming, both of the poles are warming quite quickly, and this warming is causing ice to melt in both regions. When we think of ice melting, we may think of it melting from above, as the ice is heated from the air, from sunlight, or from infrared energy from the atmosphere. But in truth, a lot of the melting comes from below. For instance, in the Antarctic, the ice shelves extend from the land out over the water. The bottom of the ice shelf is exposed to the ocean. If the ocean warms up, it can melt the underside of the shelf and cause it to thin or break off into the ocean.

The research paper the article references: