Three months ago the Glasgow Climate Pact (COP26) declared that by 2030 the world must cut total carbon dioxide emissions by 50 percent relative to the 2010 level, which was 30.4 billion tonnes. This would bring annual emissions to less than 20 billion tonnes, a level last seen more than 30 years ago.
What are the chances of that? Let’s look at the arithmetic.
First, assume that all energy-consuming sectors share the cuts equally and that global energy demand stays constant (instead of increasing by 2 percent a year, as it did in the prepandemic decade). Today our best commercial batteries have energy densities of about 300 watt-hours per kilogram, less than 3 percent as much as kerosene; among some 25,000 planes in the global commercial fleet, there is not a single high-capacity electric or hydrogen-powered aircraft. A 50 percent cut in kerosene-fueled flying would mean that by 2030 we would have to build about 12,000 new airplanes with capacities of from 100 people (the Embraer 190) to 400 people (the Boeing 777-300ER), all powered by as-yet-nonexistent superbatteries or equally nonexistent hydrogen systems. That’s what we’d need to fly about 2.2 billion passengers a year, for a total of about 4.3 trillion carbon-free passenger-kilometers. What are the chances of that?
In 2019 the world produced 1.28 billion tonnes of pig (cast) iron in blast furnaces fueled with coke made from metallurgical coal. That pig iron was charged into basic oxygen furnaces to make about 72 percent of the world’s steel (the rest comes mostly from electric arc furnaces melting scrap metal). Today there is not a single commercial steel-making plant that reduces iron ores by hydrogen. Moreover, nearly all hydrogen is now produced by the reforming of natural gas, and zero-carbon iron would require mass-scale electrolysis of water powered by renewable energies, something we still haven't got. A 50 percent cut of today’s carbon dependence would mean that by 2030 we would have to smelt more than 640 million tonnes of iron–more than the annual output of all of the blast furnaces outside China–-by using green hydrogen instead of coke. What are the chances of that?
In 2021 there were some 1.4 billion motor vehicles on the road, of which no more than 1 percent were electric. Even if the global road fleet were to stop growing, decarbonizing 50 percent of it by 2030 would require that we manufacture about 600 million new electric passenger vehicles in nine years—that’s about 66 million a year, more than the total global production of all cars in 2019. In addition, the electricity to run those cars would have to come from zero-carbon sources. What are the chances of that?
To set goals that correspond to available technical capabilities while taking into account reasonable advances in the production and adoption of non-carbon energy sources, we must start with grade-school algebra. What are the chances of that?
This article appears in the February 2022 print issue as “Decarbonization Algebra.”
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Vaclav Smil writes Numbers Don’t Lie, IEEE Spectrum's column devoted to the quantitative analysis of the material world. Smil does interdisciplinary research focused primarily on energy, technical innovation, environmental and population change, food and nutrition, and on historical aspects of these developments. He has published 40 books and nearly 500 papers on these topics. He is a distinguished professor emeritus at the University of Manitoba and a Fellow of the Royal Society of Canada (Science Academy). In 2010 he was named by Foreign Policy as one of the top 100 global thinkers, in 2013 he was appointed as a Member of the Order of Canada, and in 2015 he received an OPEC Award for research on energy. He has also worked as a consultant for many U.S., EU and international institutions, has been an invited speaker in more than 400 conferences and workshops and has lectured at many universities in North America, Europe, and Asia (particularly in Japan).