When we talk about reducing carbon release in order to slow down and hopefully stop anthropogenic global warming much of the focus is on the energy and transportation sectors. There is a good reason for this – the energy sector is responsible for 25% of greenhouse gas (GHG) emissions, while the transportation sector is responsible for 28% (if you separate out energy production and not include it in the end-user category). But that is just over half of GHG emissions. We can’t ignore the other half. Agriculture is responsible for 10% of GHG emissions, while industry is responsible for 23%, and residential and commercial activity 13%. Further, the transportation sector has many components, not just cars and trucks. It includes mass transit, rail, and aviation.

Any plan to deeply decarbonize our civilization must consider all sectors. We won’t get anywhere near net zero with just green energy and electric cars. It is tempting to focus on energy and cars because at least there we know exactly what to do, and we are, in fact, doing it. Most of the disagreement is about the optimal path to take and what the optimal mix of green energy options would be in different locations. For electric vehicles the discussion is mostly about how to make the transition happen faster – do we focus on subsidies, infrastructure, incentives, or mandates?

Industry is a different situation, and has been a tough nut to crack, although we are making progress. There are many GHG intensive processes in industry (like steel and concrete), and each requires different solutions and difficult transitions. Also, the solution often involves electrifying some aspect of industry, which works only if the energy sector is green, and will increase the demand for clean energy. Conservative estimates are that the energy sector will increase by 50% by 2050, but if we are successful in electrifying transportation and industry (not to mention all those data centers for AI applications) this estimate may be way off. This is yet another reason why we need an all-of-the-above approach to green energy.

Let’s focus on agriculture and aviation, which are also considered difficult  sectors to decarbonize, starting with agriculture. Often the discussion on agriculture focuses on meat consumption, because the meat industry is a very GHG intensive portion of the agricultural sector. There is a good argument to be made for moderating meat consumption in industrialized nations, both from a health and environmental perspective. This doesn’t mean banning hamburgers, and it is often strawmanned, but some voluntary moderation would be a good thing. There is also some mitigation possible – yes, I am talking about capturing cow farts.

There are also efforts to shift farming from a net carbon emitter to a net carbon sequester. A recent analysis finds that this is plausible, by switching to certain farming practices that could be a net financial benefit to farmers and help maintain farming productivity in the face of warming. This includes the use of cover crops, combining farming with forestry, and using no-till methods of farming. With these methods farms can turn into a net carbon sink.

Obviously this is a temporary mechanism, but could help buy us time. Right now we are doing the opposite – cutting down forest to convert to farmland, and eliminating carbon sinks. Farming forests, or incorporating more trees into farmland, can help reverse this process.

What about aviation? This is also a difficult sector, like industry, because we don’t have off-the-shelf solutions ready to go. A recent report, however, outlines steps the industry can take over the next five years that can put it on track to reach net zero by 2050. One step, which I had not heard of before, is deploying a global contrail avoidance system. Contrails are vapor trails that form when the hot jet exhaust mixes with cool moist air. These act like artificial cirrus clouds, which have a mild cooling effect during the day but a much more significant warming effect at night (by trapping heat). Contrails are responsible for 35% of the aviation industry’s warming effect. Using AI and satellite data, pilots can be directed to routes that would minimize contrail formation.

They also recommend system-wide efficiency strategies, which they find can halve fuel burn from aviation by 2050. That seems incredible, but they argue that there are efficiencies that individual companies are unable to address, but that can be achieved with system wide policies.

The next point is a bit more obvious – switching to sustainable aviation fuel (SAF). This mostly means making jet fuel from biomass. They mostly recommend policy changes that will help the industry rapidly scale up biofuel production from biomass. That’s really the only way to decarbonize jet travel. Hydrogen will never be energy dense enough for aviation.

We are on the verge of seeing commercial electric planes, mainly because of advances in battery technology. These could fill the regional service and small city routes, with ranges in the 300-400 mile zone (and likely to increase as battery technology continues to advance). Not only would an electric plane industry replace current fossil-fuel burning regional flights, but they could expand the industry and displace other forms of travel. Many more people may choose to take a quick flight from a regional airport than drive for 8 hours.

Their last recommendation is essentially a roll of the dice: “Launching several moonshot technology demonstration programmes designed to rapidly assess the viability and scalability of transformative technologies, bringing forward the timeline for their deployment.”

This sounds partly like an admission that we don’t currently have all the technology we would need to fully decarbonize aviation. Maybe they consider this to be not absolutely necessary but a good option. In any case, I am always in favor of supporting research in needed technology areas. This has generally proven to be an investment worth making.

As is often the case, this all looks good on paper. We just have to actually do it.