
Harmonious Taxes
Emitting carbon dioxide has a social cost, as we saw in the previous module, so any actions to reduce emissions give some benefit. But, making a measurably significant difference in the future of global climate will require major reductions in CO2 emissions across large parts of the whole world’s economy, and really solving the problem will involve almost all of us. International cooperation thus is almost surely required to address global warming seriously.
Treaties
One possible approach is to use treaties or other agreements to limit the quantity of CO2 that can be emitted. The Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC) takes this approach, setting limits on allowable emissions from many, primarily industrialized countries. The UNFCCC commits signatories (essentially the whole world) to “…stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system” (Article 2), and Kyoto attempted to start a strategy to achieve that objective (United Nations Framework Convention on Climate Change, Background on the UNFCCC.(link is external))
Kyoto can claim some successes among countries in reducing greenhouse-gas emissions. Overall, however, emissions have risen since the protocol was enacted. One could argue that the task is so difficult that we should not expect immediate success, but one could also argue that this approach is not working as well as it should.
Internationally Harmonized Carbon Taxes
Another possible approach is through internationally harmonized carbon taxes. (Again, we are leaning on the work of W. Nordhaus, among many others.) As this was being written, carbon taxes were functioning in many places including British Columbia and several European countries, and discussions were ongoing in additional countries including China. Suppose that the international community broadened this participation by negotiating use of a carbon tax in all countries. The tax rate might be targeted at the economically efficient level, possibly with variations in when it became fully active based on the status of economic development or other issues. Monitoring and enforcement would involve some discussions, as would issues of what in detail to include. For example, deforestation does contribute to global warming, so are trees included? Where Dr. Alley lives, in Pennsylvania in the USA, trees were cut down in previous centuries, and many trees have been growing back—is it right for Pennsylvania to get credit for regrowing trees when other countries are penalized for cutting down their trees?

But, start with the simplest possible model: a tax on the extraction of fossil fuels, set at an initially small level for everyone and then raised at a rate such as 2% per year. Suppose that more than half of the world’s economy initially agreed to this. They could then, perhaps through the UN, offer a deal to countries not yet participating—participate, tax your own carbon, and keep the money for any purpose except stimulating fossil-fuel use; or, refuse to participate, and the participating countries will keep the funds raised from tariffs they will levy on all trade into and out of the nonparticipating countries, and set at a level equal to that for harmonized carbon taxes. (This probably would require changes to international trade rules, but changing such rules is not impossible.) Such an arrangement might turn out to be much simpler than extending the Kyoto Protocol to greatly reduce fossil-fuel emissions of CO2. Many people will have many questions about such a plan, but it is an interesting alternative that is receiving serious if cautious support.
Problems with Treaties and International Carbon Taxes
Any international treaty runs into the issue of verification—how can a nation tell whether other nations are cheating? The US National Research Council looked into that question in 2010 (Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements), and found that verification of compliance is practicable. This would include a combination of national inventories (econometric data; who is buying what), and geophysical techniques (satellite, airborne and surface-based monitoring of atmospheric concentrations and isotopic ratios). The small variations in concentration of CO2 around the planet reveal sources and sinks of the gas, and the isotopic composition can separate biological (higher carbon-12 to carbon-13 ratio; either recently living plants or long-dead fossil fuels) from abiological (volcanic, for example) carbon, and modern-biosphere (lower carbon-12 to carbon-14 ratio) from fossil-fuel carbon. Combining the geophysical and economic data can provide a clearer picture than is available from either source by itself.
A carbon tax rising by 2% or 4% per year cannot be a solution for government funding forever because as decades become centuries, the cost per gallon would pass the cost of the car and continue onto huge values. Clearly, policies are reexamined before decades become centuries. The goal of ultimately reaching a sustainable energy system means that taxing fossil fuels cannot continue forever. But, for decades at least, harmonized carbon taxes could supply much government revenue while reducing global warming, having little direct effect on the economy, and improving the economy if the value of avoiding the global warming is considered.