Counting Carbon
1It is often said that what cannot be measured cannot be managed. In climate policy the maxim is truer than most, and more awkward. Every international climate agreement since the 1992 UN Framework Convention on Climate Change has rested on a quiet assumption: that countries know how much greenhouse gas they emit. Frequently, they do not.
2The problem is not uniform. Carbon dioxide from burning coal, oil and gas can be estimated with reasonable confidence from fuel statistics, since the carbon content of each fuel varies within known limits. Methane from leaking pipelines, landfill and livestock, and the carbon released or absorbed by forests and soils, are another matter. These are estimated not by counting but by multiplying assumed “emission factors” by activity data, and small errors in the assumptions compound into large ones in the totals. When independent researchers have compared national reports with what instruments detect in the atmosphere, the gaps have sometimes exceeded the entire reported emissions of mid-sized economies.
3History explains part of the gap. The 1997 Kyoto Protocol set binding targets only for industrialised countries (on average, cuts of about 5 per cent below 1990 levels over the period 2008–2012), and only they were required to submit detailed annual inventories. Developing countries, including China and India, reported far less often and in far less detail. The United States never ratified the protocol, and Canada withdrew in 2011. The 2015 Paris Agreement abandoned imposed targets in favour of pledges that each country sets for itself. In exchange, it asked all countries, for the first time, to report on a common basis. The first such reports were not due until the end of 2024.
4Even accurate inventories answer a narrower question than they appear to. National totals count emissions produced within a country's borders, not those embodied in the goods it imports, and they leave out international aviation and shipping altogether. By this measure China now emits nearly a third of the world's carbon dioxide, and the United States about an eighth. Yet the average American still emits nearly twice as much as the average Chinese citizen and roughly seven times as much as the average Indian, and the United States has produced around a quarter of all the carbon dioxide emitted since the industrial revolution. Which figure is “right” depends on whether one asks who is emitting now, who emits most per person, or who filled the atmosphere in the first place.
5Satellites that can spot individual methane plumes from space, and denser networks of ground-based sensors, promise to narrow the technical uncertainty. It would be a mistake, however, to treat better measurement as a substitute for action. Precise accounting will not in itself remove a single tonne of emissions. What it can do is make it harder for governments to claim credit for reductions that have not happened. Under an agreement whose targets are voluntary, that may be the only discipline available.