climate policy

Will hydrogen make air travel sustainable?

pnrj current events, futurism, public policy , , , , , , ,

Apr 9 JDN 2460042

Air travel is currently one of the most carbon-intensive activities anyone can engage in. Per passenger kilometer, airplanes emit about 8 times as much carbon as ships, 4 times as much as trains, and 1.5 times as much as cars. Living in a relatively eco-friendly city without a car and eating a vegetarian diet, I produce much less carbon than most First World citizens—except when I fly across the Atlantic a couple of times a year.

Until quite recently, most climate scientists believed that this was basically unavoidable, that simply sustaining the kind of power output required to keep an airliner in the air would always require carbon-intensive jet fuel. But in just the past few years, major breakthroughs have been made in using hydrogen propulsion.

The beautiful thing about hydrogen is that burning it simply produces water—no harmful pollution at all. It’s basically the cleanest possible fuel.


The simplest approach, which is actually quite old, but until recently didn’t seem viable, is the use of liquid hydrogen as airplane fuel.

We’ve been using liquid hydrogen as a rocket fuel for decades; so we knew it had enough energy density. (Actually its energy density is higher than conventional jet fuel.)

The problem with liquid hydrogen is that it must be kept extremely cold—it boils at 20 Kelvin. And once liquid hydrogen boils into gas, it builds up pressure very fast and easily permeates through most materials, so it’s extremely hard to contain. This makes it very difficult and expensive to handle.

But this isn’t the only way to use hydrogen, and may turn out to not be the best one.

There are now prototype aircraft that have flown using hydrogen fuel cells. These fuel cells can be fed with hydrogen gas—so no need to cool below 20 Kelvin. But then they can’t directly run the turbines; instead, these planes use electric turbines which are powered by the fuel cell.

Basically these are really electric aircraft. But whereas a lithium battery would be far too heavy, a hydrogen fuel cell is light enough for aviation use. In fact, hydrogen gas up to a certain pressure is lighter than air (it was often used for zeppelins, though, uh, occasionally catastrophically), so potentially the planes could use their own fuel tanks for buoyancy, landing “heavier” than they took off. (On the other hand it might make more sense to pressurize the hydrogen beyond that point, so that it will still be heavier than air—but perhaps still lighter than jet fuel!)

Of course, the technology is currently too untested and too expensive to be used on a wide scale. But this is how all technologies begin. It’s of course possible that we won’t be able to solve the engineering problems that currently make hydrogen-powered aircraft unaffordable; but several aircraft manufacturers are now investing in hydrogen research—suggesting that they at least believe there is a good chance we will.

There’s also the issue of where we get all the hydrogen. Hydrogen is extremely abundant—literally the most abundant baryonic matter in the universe—but most of what’s on Earth is locked up in water or hydrocarbons. Most of the hydrogen we currently make is produced by processing hydrocarbons (particularly methane), but that produces carbon emissions, so it wouldn’t solve the problem.

A better option is electrolysis: Using electricity to separate water into hydrogen and oxyen. But this requires a lot of energy—and necessarily, more energy than you can get out of burning the hydrogen later, since burning it basically is just putting the hydrogen and oxygen back together to make water.

Yet all is not lost, for while energy density is absolutely vital for an aircraft fuel, it’s not so important for a ground-based power plant. As an ultimate fuel source, hydrogen is a non-starter. But as an energy storage medium, it could be ideal.

The idea is this: We take the excess energy from wind and solar power plants, and use that energy to electrolyze water into hydrogen and oxygen. We then store that hydrogen and use it for fuel cells to run aircraft (and potentially other things as well). This ensures that the extra energy that renewable sources can generate in peak times doesn’t go to waste, and also provides us with what we need to produce clean-burning hydrogen fuel.

The basic technology for doing all this already exists. The current problem is cost. Under current conditions, it’s far more expensive to make hydrogen fuel than to make conventional jet fuel. Since fuel is one of the largest costs for airlines, even small increases in fuel prices matter a lot for the price of air travel; and these are not even small differences. Currently hydrogen costs over 10 times as much per kilogram, and its higher energy density isn’t enough to make up for that. For hydrogen aviation to be viable, that ratio needs to drop to more like 2 or 3—maybe even all the way to 1, since hydrogen is also more expensive to store than jet fuel (the gas needs high-pressure tanks, the liquid needs cryogenic cooling systems).

This means that, for the time being, it’s still environmentally responsible to reduce your air travel. Fly less often, always fly economy (more people on the plane means less carbon per passenger), and buy carbon offsets (they’re cheaper than you may think).

But in the long run, we may be able to have our cake and eat it too: If hydrogen aviation does become viable, we may not need to give up the benefits of routine air travel in order to reduce our carbon emissions.

Is there hope for stopping climate change?

pnrj development economics, ethics, public policy , , , , , , , , , , ,

JDN 2457523

This topic was decided by vote of my Patreons (there are still few enough that the vote usually has only two or three people, but hey, what else can I do?).

When it comes to climate change, I have good news and bad news.

First, the bad news:

We are not going to be able to stop climate change, or even stop making it worse, any time soon. Because of this, millions of people are going to die and there’s nothing we can do about it.

Now, the good news:

We can do a great deal to slow down our contribution to climate change, reduce its impact on human society, and save most of the people who would otherwise have been killed by it. It is currently forecasted that climate change will cause somewhere between 10 million and 100 million deaths over the next century; if we can hold to the lower end of that error bar instead of the upper end, that’s half a dozen Holocausts prevented.

There are three basic approaches to take, and we will need all of them:

1. Emission reduction: Put less carbon in

2. Geoengineering: Take more carbon out

3. Adaptation: Protect more humans from the damage

Strategies 1 and 2 are classified as mitigation, while strategy 3 is classified as adaptation. Mitigation is reducing climate change; adaptation is reducing the effect of climate change on people.

Let’s start with strategy 1, emission reduction. It’s probably the most important; without it the others are clearly doomed to fail.

So, what are our major sources of emissions, and what can we do to reduce them?

While within the US and most other First World countries the primary sources of emissions are electricity and transportation, worldwide transportation is less important and agriculture is about as large a source of emissions as electricity. 25% of global emissions are due to electricity, 24% are due to agriculture, 21% are due to industry, 14% are due to transportation, only 6% are due to buildings, and everything else adds up to 10%.

global_emissions_sector_2015

1A. Both within the First World and worldwide, the leading source of emissions is electricity. Our first priority is therefore electrical grid reform.

Energy efficiency can help—and it already is helping, as global electricity consumption has stopped growing despite growth in population and GDP. Energy intensity of GDP is declining. But the main thing we need to do is reform the way that electricity is produced.

Let’s take a look at how the world currently produces electricity. Currently, the leading source of electricity is “liquids”, an odd euphemism for oil; currently about 175 quadrillion BTU per year, 30% of all production. This is closely followed by coal, at about 160 quadrillion BTU per year, 28%. Then we have natural gas, about 130 quadrillion BTU per year (23%), wind, solar, hydroelectric, and geothermal altogether about 60 quadrillion BTU per year (11%), and nuclear fission only about 40 quadrillion BTU per year (7%).

This list basically needs to be reversed. We will probably not be able to completely stop using oil for transportation, but we have no excuse for using for electricity production. We also need to stop using coal for, well, just about anything. There are a few industrial processes that basically have to use coal; fine, use it for that. But just as something to burn, coal is one of the most heavily-polluting technologies in existence—the only things we burn that are worse are wood and animal dung. Simply ending the burning of coal, wood, and dung would by itself save 4 million lives a year just from reduced pollution.

Natural gas burns cleaner than coal or oil, but it still produces a lot of carbon emissions. Even worse, natural gas is itself one of the worst greenhouse gases—and so natural gas leaks are a major source of greenhouse emissions. Last year a single massive leak accounted for 25% of California’s methane emissions. Like oil, natural gas is also something we’ll want to use quite sparingly.

The best power source is solar power, hands-down. In the long run, the goal should be to convert as much as possible of the grid to solar. Wind, hydroelectric, and geothermal are also very useful, though wind power peaks at the wrong time of day for high energy demand and hydro and geothermal require specific geography to work. Solar is also the most scalable; as long as you have the raw materials and the technology, you can keep expanding solar production all the way up to a Dyson Sphere.

But solar is intermittent, and we don’t have good enough energy storage methods right now to ensure a steady grid on solar alone. The bulk of our grid is therefore going to have to be made of the one energy source we have with negligible carbon emissions, mature technology, and virtually unlimited and fully controllable output: Nuclear fission. At least until fusion matures or we solve the solar energy storage problem, nuclear fission is our best option for minimizing carbon emissions immediately—not waiting for some new technology to come save us, but building efficient reactors now. Why does France only emit 6 tonnes of carbon per person per year while the UK emits 9, Germany emits 10, and the US emits a whopping 17? Because France’s electricity grid is almost entirely nuclear.

“But nuclear power is dangerous!” people will say. France has indeed had several nuclear accidents in the last 40 years; guess how many deaths those accidents have caused? Zero. Deepwater Horizon killed more people than the sum total of all nuclear accidents in all First World countries. Worldwide, there was one Black Swan horrible nuclear event—Chernobyl (which still only killed about as many people as die in the US each year of car accidents or lung cancer), and other than that, nuclear power is safer that every form of fossil fuel.

“Where will we store the nuclear waste?” Well, that’s a more legitimate question, but you know what? It can wait. Nuclear waste doesn’t accumulate very fast, precisely because fission is thousands of times more efficient than combustion; so we’ll have plenty of room in existing facilities or easily-built expansions for the next century. By that point, we should have fusion or a good way of converting the whole grid to solar. We should of course invest in R&D in the meantime. But right now, we need fission.

So, after we’ve converted the electricity grid to nuclear, what next?
1B. To reduce the effect of agriculture, we need to eat less meat; among agricultural sources, livestock is the leading contributor of greenhouse emissions, followed by land use “emissions” (i.e. deforestation), which could also be reduced by converting more crop production to vegetables instead of meat because vegetables are much more land-efficient (and just-about-everything-else-efficient).

1C. To reduce the effect of transportation, we need huge investments in public transit, as well as more fuel-efficient vehicles like hybrids and electric cars. Switching to public transit could cut private transportation-related emissions in half. 100% electric cars are too much to hope for, but by implementing a high carbon tax, we might at least raise the cost of gasoline enough to incentivize makers and buyers of cars to choose more fuel-efficient models.
The biggest gains in fuel efficiency happen on the most gas-guzzling vehicles—indeed, so much so that our usual measure “miles per gallon” is highly misleading.

Quick: Which of the following changes would reduce emissions more, assuming all the vehicles drive the same amount? Switching from a hybrid of 50 MPG to a zero-emission electric (infinity MPG!), switching from a normal sedan of 20 MPG to a hybrid of 50 MPG, or switching from an inefficient diesel truck of 3 MPG to a modern diesel truck of 7 MPG?

The diesel truck, by far.

If each vehicle drives 10,000 miles per year: The first switch will take us from consuming 200 gallons to consuming 0 gallons—saving 200 gallons. The second switch will take us from consuming 500 gallons to consuming 200 gallons—saving 300 gallons. But the third switch will take us from consuming 3,334 gallons to consuming only 1,429 gallons—saving a whopping 1,905 gallons. Even slight increases in the fuel efficiency of highly inefficient vehicles have a huge impact, while you can raise an already-efficient vehicle to perfect efficiency and barely notice a difference.

We really should measure in gallons per mile—or better yet, liters per megameter. (Most of the world uses liters per 100 km; almost!)

All right, let’s assume we’ve done that: The whole grid is nuclear, and everyone is a vegetarian driving an electric car. That’s a good start. But we can’t stop there. Because of the feedback loops involved, we only reduce our emissions—even to near zero—the amount of carbon dioxide will continue to increase for decades. We need to somehow take the carbon out that is already there, which brings me to strategy 2, geoengineering.

2A. There are some exotic proposals out there for geoengineering (putting sulfur into the air to block out the Sun; what could possibly go wrong?), and maybe we’ll end up using some of them. I think iron fertilization of the oceans is one of the more promising options. But we need to be careful to make sure we actually know what these projects will do; we got into this mess by doing things without appreciating their long-run environmental impact, so let’s not make the same mistake again.

2B. But really, the most effective form of geoengineering is simply reforestation. Trees are very good at capturing carbon from the atmosphere; it’s what they evolved to do. So let’s plant trees—lots of trees. Many countries already have net positive forestation (such as the US as a matter of fact), but the world still has net deforestation, and that needs to be reversed.

But even if we do all that, at this point we probably can’t do enough fast enough to actually stop climate change from causing damage. After we’ve done our best to slow it down, we’re still going to need to respond to its effects and find ways to minimize the harm. That’s strategy 3, adaptation.

3A. Coastal regions around the world are going to have to turn into the Netherlands, surrounded by dikes and polders. First World countries already have the resources to do this, and will most likely do it on our own (many cities already have plans to); but other countries need to be given the resources to do it. We’re responsible for most of the emissions, and we have the most wealth, so we should pick up the tab for most of the adaptation.

3B. Some places aren’t going to be worth saving—so that means saving the people, by moving them somewhere else. We’re going to have global refugee crises, and we need to prepare for them, not in the usual way of “How can I clear my conscience while xenophobically excluding these people?” but by welcoming them with open arms. We are going to need to resettle tens of millions—possibly hundreds of millions—of people, and we need a process for doing that efficiently and integrating these people into the societies they end up living in. We must stop presuming that closed borders are the default and realize that the burden of proof was always on anyone who says that people should have different rights based on whether they were born on the proper side of an imaginary line. If open borders are utopian, then it is utopian we must be.

The bad news is that even if we do all these things, millions of people are still going to die from climate change—but a lot fewer millions than would if we didn’t.

And the really good news is that people are finally starting to do these things. It took a lot longer than it should, and there are still a lot of holdouts; but significant progress is already being made. There are a lot of reasons to be hopeful.