"Americans and Climate Change: Closing the Gap Between Science and Action" (PDF) is a report synthesizing the insights of 110 leading thinkers on how to educate and motivate the American public on the subject of global warming. Background on the report here. I’ll be posting a series of excerpts (citations have been removed; see original report). If you’d like to be involved in implementing the report’s recommendations, or learn more, visit the Yale Project on Climate Change website.

It’s perhaps the most disheartening facet of the global warming discussion: Every target for reducing emissions that’s taken seriously in political circles is woefully inadequate. How can we begin discussing targets commensurate with the task at hand? That’s what gets chewed over in today’s excerpt. (It’s another long one — sorry.)


Emissions Reduction Targets

In formulating climate change goals, we are naturally inclined to start with "targets and timetables" for emissions reductions (and allow for market- based trading to reduce overall compliance costs) since this has become the dominant strategy in the global response to climate change to date.

This "cap-and-trade" model is embodied in the Kyoto Protocol, which imposes an aggregate reduction target of 5.2 percent below 1990 levels averaged over the 5-year period 2008-2012, with each country’s target varying based on case-by-case negotiations.

Within this basic framework, there are many other design options and variations to consider (for example, sector-by-sector targets or emissions-intensity reductions indexed on a per unit of GDP or per capita basis, rather than caps on absolute emissions), but these are beyond the purview of this report.

Given our focus in this Conference on the U.S., it is also worth noting that the U.S. government has continued to refrain from ratifying the Kyoto Protocol and instead announced on July 28, 2005, an alternative technology development and diffusion strategy that forgoes any overarching cap on emissions. Known as the Asia Pacific Partnership on Clean Development and Climate, it includes Australia, India, Japan, the People’s Republic of China, South Korea, and the United States.

Against that background, our Conference did not spend a great deal of time debating different emissions target levels as a whole. But the Business & Finance group’s eight-principle framework included a goal that we will unpack here to illuminate the context and issues associated with goal-setting on climate change (Recommendation #33). The group’s goal reads: "Support a long-term goal for global greenhouse gas emissions from all segments of the U.S. economy at or below today’s levels by 2050." This goal is:

  • pegged to 2005 emissions as a baseline, which is somewhat less stringent than the Kyoto Protocol’s 1990 baseline, when emissions were lower.
  • a longer-term target than Kyoto, thereby following most leading policy-designers working on climate change in recognizing that a vital attribute of an effective goal on this issue is that it be long-term. As S. Pacala and R. Socolow put it, in favoring a mid-century target: "The next 50 years is a sensible horizon from several perspectives. It is the length of a career, the life-time of a power plant, and an interval for which the technology is close enough to envision" (Science Vol. 305, No. 5686: 968).
  • a point-year emissions target that leaves open what the emissions path and interim targets between now and 2050 should be, though the implication is that one would want to avoid significant increases in the meantime since that would force deeper reductions later, as 2050 approaches.
  • ambiguous, and therefore open to a crucial negotiation, on whether 2050 emissions should be held to today’s levels or reduced, potentially by the 60 percent or greater amount that many experts now believe will be needed by that time (see more on this below).
  • silent on what should happen after 2050, whereas many experts contend that the second half of the century will need to be a period of significantly reduced emissions, converging on net zero emissions, if we are to stabilize concentrations in the atmosphere, rather than simply add to them at a level rate.

While our entire Conference, and this goal, intentionally focused on the U.S., we should note that a major challenge ahead is how to ensure inclusion of all major emitting countries — including developing countries — in a climate change goal, since failure to do so will not solve the problem. That, of course, is the most famous oversight in the Kyoto Protocol, which served as a fatal Achilles heel for its opponents to exploit in domestic advertisements that said, to great apparent effect: "It’s not global and it won’t work."

Various ingenious models for bridging developing countries into a post-Kyoto compliance regime have been advanced by experts in market-based mechanisms such as Robert Stavins of Harvard University and others. They include, for example, proposals through which developing countries would incur increasingly stringent emissions reductions targets at trigger points along the trajectory of their increases in average per capita income. This would allow them an allocation of atmospheric capacity sufficient to advance their developmental needs over time, while eventually bringing them into line with the global imperative to stabilize concentrations.

The present U.S. Administration has objected to the Kyoto Protocols as draconian. Indeed, given the emissions growth since 1990 (2004 emissions in the U.S. were 15.8 percent above 1990 levels), achieving the Kyoto targets in the short time remaining would be difficult, if not as economically damaging as the Administration has contended. As a reference point, Canada, which has ratified the Kyoto Protocol has also experienced rapid economic growth since 1990 and seen its emissions rise 24 percent. It is now struggling with how to comply with its Kyoto obligation, and some say that its failure is all but inevitable.

What is striking, then, is that the Kyoto targets are both challenging and, in scientific terms, inadequate. Those who have advocated for Kyoto ratification and compliance have therefore been in the uncomfortable position of calling for a costly solution that won’t solve the problem. Robert Stavins’ verdict on Kyoto: "Too little, too fast."

On the other hand, the proverbial journey of a thousand miles begins with the first step and the Kyoto Protocol is directionally correct, unlike our current business-as-usual trajectory toward ever-growing emissions. Had U.S. ratification occurred soon after its 1997 completion, Kyoto would have entered into force much sooner than February 2005. U.S. ratification, moreover, would have sent a signal to its domestic market, the most entrepreneurial in the world, and we would have been on a lower emissions path. Furthermore, earlier ratification of the Kyoto Protocol would have meaningfully underscored the seriousness of the industrialized world about addressing climate change, potentially drawing developing country participation into the next phase. Kyoto was not designed to "work" in terms of solving the problem by itself — its very timetable makes clear that it was but a first step.

As it is, the post-Kyoto regime is now a matter of great suspense, and the latest round of negotiations — at the Montreal "Conference of the Parties" in December 2005 — was ambiguous in terms of building confidence that the world is on track for an effective goal-setting effort on climate change.

What should the goal be? Experts usually start from a maximum acceptable temperature increase consistent with minimizing the risks of a wide range of damages, and work back from that to atmospheric concentration levels for greenhouse gases that would, based on current modeling, be likely to keep temperatures under that targeted ceiling.

If we stay on a business-as-usual trajectory, the scenarios from the Intergovernmental Panel on Climate Change show atmospheric concentrations rising anywhere from 90 percent to 250 percent (i.e., 530 to 970 parts per million) over the benchmark pre-industrial level of 280 parts per million by the year 2100. (The current concentration is approximately 381 parts per million.)

In 2005, the European Union formally reaffirmed its view that the global mean temperature increase should not exceed 2° Centigrade (3.6° Fahrenheit). Models indicate that preventing this level of temperature increases will require stabilization of carbon dioxide levels at somewhere between 450 and 550 parts per million by 2100, or less than a "doubling" of the pre-industrial level. But this remains a probabilistic game complete with bands of uncertainty and unknown triggers that could cause abrupt climate changes along the way.

So given this stabilization goal and its associated uncertainties, then the issue turns to what the pathway to that goal should be (i.e., how stringent should the near term targets be, and what is the extended time-path of targets thereafter?).

One of the most thoughtful discussions of the need to begin greenhouse gas emissions reductions without further delay (and by how much to reduce them) can be found in Malte Meinshausen et al., "Multi- Gas Emission Pathways to Meet Climate Targets" (PDF) (Climatic Change, Vol. 5, No. 1-2, March 2006). Consistent with our earlier discussion about the limited dissemination of scientific findings, it is probably safe to assume that most readers of the present report do not have this issue of Climatic Change on their bedside table, so we reprint the conclusion of this important article here, with emphases added:

Achieving climate targets that account for, say, the risk of disintegrating ice sheets (Oppenheimer, 1998; Hansen, 2003; Oppenheimer and Alley, 2004) or for large scale extinction risks (Thomas et al., 2004) almost certainly requires substantial and near term emission reductions. For example, to constrain global-mean temperatures to peaking at 2° C above the pre-industrial level with reasonable certainty (say > 75%) would require emission reductions of the order of 60% below 1990 levels by 2050 for the GWP-weighted sum of all greenhouse gases … If the start of significant emission reductions were further delayed, the necessary rates of emissions reduction rates were even higher, if the risk of overshooting certain temperature levels shouldn’t be increased (den Elzen and Meinshausen, 2005; Meinshausen, 2005).

Thus, since more rapid reductions may require the premature retirement of existing capital stocks, the cost of any further delay would be increased, probably non-linearly. There are a number of other reasons why one might want to avoid further delay. Firstly, future generations face more stringent emission reductions while already facing increased costs of climate impacts. Secondly, the potential benefits of `learning by doing’ (Arrow, 1962; Gritsevskyi and Nakicenovi, 2000; Grubb and Ulph, 2002) were limited due to the more sudden deployment of new technology and infrastructure. Thirdly, a further delay of mitigation efforts risks the potential foreclosure of reaching certain climate targets. Thus, a delay might be particularly costly if, for example, the climate sensitivity turns out to be towards the higher end of the currently assumed ranges (cf. Andronova and Schlesinger, 2001: Forest et al., 2002: Knutti et al., 2003).

Let us first acknowledge that this excerpt, while authoritative, is not emblematic of the accessible language we must increasingly see in communications to the general public about climate change goals. This is a journal article intended primarily for scientists and other inside specialists. Someone needs to translate and carry this kind of work to key constituencies and the general public — see Conference Recommendation #1 calling for a bridging institution capable of fulfilling this need.

Meanwhile, in interpreting the authors’ bracing conclusion, it is worth noting that even the +2° C global average warming (+3.6° F) ceiling cited here may prove too lenient to prevent ice sheet melting, widespread coral bleaching, ecosystem disruption, agricultural losses and other adverse consequences. That +2° C rise would be over three times the warming experienced in the 20th century.

Moreover, the 60 percent reduction by 2050 called for here is a globally averaged reduction target. The industrial countries, and especially the United States, would, in all likelihood, have to make deeper cuts to allow for inevitable acceleration of developing country emissions. Thus, the long- term target announced by California Governor Arnold Schwarzenegger in June 2005 to reduce emissions of greenhouse gases to 80 percent below 1990 levels by 2050 is close to what could be expected for the United States as a whole under the prescriptions advanced in the article.

As noted earlier, the February 2006 U.S. EPA draft of the National Emissions Inventory estimates that U.S. emissions grew 15.8 percent from 1990-2004, so any targeted cuts below 1990 levels, as called for above, would need to account for the fact that we are already well above 1990 levels today — further compounding the reductions that would be needed.

Of course, the relative urgency of undertaking near-term emissions reductions in line with this article’s conclusion is not without controversy. For example, some economists have argued that the optimal emissions reductions plan is to start modestly. Then, if damages rise more quickly in the future than expected, stringency can be tightened. In this view, short-term targets are often favored over long- term ones since it is posited that humanity can learn in the interim and shouldn’t foreclose future options. One might counter that this does not account adequately for the path-dependence of our emissions trajectory and the likelihood that future reduction costs will be higher once high- emitting infrastructure is locked in. Moreover, in the absence of long- term targets, and the price signal they send, businesses may lack the regulatory predictability needed to guide long-term capital budgeting, including investments in low-carbon infrastructure.

Another line of argument from those advocating modest rather than urgent action is based on studies showing potential benefits of climate change at certain latitudes, usually in polar and mid-latitude regions, at least up to 2.5° C (4.5° F) of warming in the latter case, with damages expected to set in if temperatures go higher than that. These methodologies frequently sum up these potential benefits with warming- induced damages in other regions, such as the sub-tropics. One might counter that it is simplistic to sum positives and negatives across geographies like this. Won’t sub-tropical damages cause global ramifications, environmentally and socially, including for those living at latitudes supposedly benefiting from the changes (mass immigration pressures and other potential consequences)? Moreover, such projections may reflect exaggerated confidence in humanity’s ability to engineer a soft landing precisely after the interim pleasantness leading up to 2.5° C concludes, but before the potentially dangerous changes kick in thereafter.

It is also important to discern whether such studies analyze the benefits or damages beyond a single sector, such as agriculture; extrapolating from one sector to economy-wide implications is rarely warranted. Scientists and economists have, in fact, distinguished different sectors based on the shape of their "damage curves" in relation to different temperature levels. Some find that while agriculture, terrestrial ecosystems and forests may yield interim productivity gains up to some, difficult-to-estimate temperature threshold before turning negative, other sectors like coastal and marine ecosystems are more likely to experience damages even during initial temperature increases.

Finally, calls for modest and short-term goals may fail to reflect the risk of non-linear, abrupt change or potentially irreversible thresholds. The standard, linear economic method of quantifying and discounting future damages cannot really capture these largely incommensurable risks along the way.

The point here is not to presume to resolve such long-running and complex debates in these pages, but to spotlight briefly how important it is for American society to engage much more fully on the myriad dimensions of this enormously important goal-setting exercise. Currently, this is largely a debate of inside specialists, in part because the technical nature of the content creates obstacles to public participation. But the relevant work — in its scientific, economic and other variants — can and should be translated into more accessible terms so that American values and interests can be engaged, honest tradeoffs debated and choices made about how we will address the challenge of climate change. We need to broaden the debate and bring it out into the light.