Editor’s note: Yesterday the world’s most influential newspaper finally did what CTC and other carbon tax proponents have sought for years: publish a ringing endorsement of a U.S. carbon tax. With its editorial, The Case for a Carbon Tax, the New York Times joins the growing community of opinion leaders, policy experts and, yes, elected officials who not only recognize the power of carbon taxes to quickly and equitably reduce emissions but also sense the emergence of a political critical mass that can enact fees into law. This heartening development signals that it’s not too soon to focus on the design of a U.S. carbon tax, especially its magnitude and rate of increase, as CTC senior policy analyst James Handley does in this post.
Which is the more effective way to set a tax on carbon pollution?
A. Start aggressively, then raise the rate slowly (“sprint”).
B. Start modestly, then raise the rate briskly and predictably (“marathon”).
You probably guessed that if the goal is to instill incentives that will bring about big emission reductions fast enough to avoid runaway global warming, the answer is B, the marathon. Yet a leading U.S. Senate advocate of legislative action on climate seems to be starting off like a sprinter, perhaps because his legislation is pegged to estimates of the Social Cost of Carbon that don’t account for the possibility that climate change will turn out to be catastrophically costly.
More on that senator in a moment — after this tutorial:
The Social Cost of Carbon (SCC) is a construct to quantify in monetary terms the damage caused by each additional ton of CO2 added to the atmosphere. While the SCC may sound arcane or academic, estimating its magnitude has real world implications: governments are pegging climate-related regulatory decisions to SCC estimates. A low SCC can make all but the lowest-cost clean-energy policies pencil out as expensive; higher estimates justify more rapid and aggressive measures, since moving too slowly to reduce emissions shows up as a mistake whose costs accumulate at a frightening pace.
Calculating the damage from a ton of CO2 turns on a host of assumptions that span wide ranges. Not surprisingly, estimates of the SCC reported in the peer-reviewed economics literature range from as little as $10 per ton of CO2 to over $400. A profoundly important modeling choice is how heavily to weigh the risks of climate-induced catastrophes. High-risk climate scenarios with nearly infinite costs, such as rapid release of methane from arctic permafrost or sudden sliding of vast ice masses into the ocean, “misbehave” in the equations used for conventional cost-benefit analysis, leading some modelers to omit them altogether.
One widely-used model assumes that economic growth rates will not be affected by climate change, thereby predicting that half of the world’s economic activity would continue after a whopping 18 degrees C of global warming. Other models dilute the high-risk scenarios by assigning them arbitrarily low probabilities that suppress their impact when their costs are averaged in with low-risk scenarios. A further problem in estimating the SCC is the bias toward high “discount rates” that telescope future impacts down to seemingly manageable proportions.
Amidst fraught debate and widely-divergent estimates, the Interagency Working Group has settled on $42 per ton of CO2 as the “official” U.S. government social cost of carbon. While that’s an improvement over past practice that omitted climate costs entirely — tacitly, an SCC equal to zero — the $42 figure grossly understates the large-scale global risks that dominate concern over global warming and climate change. [Read more…]