Spring in Connecticut brings renewal, rebirth and Earth Day celebrations.  This year, perhaps, we will celebrate because spring will also bring climate change back to the national stage.  Next week, for example, Senators Kerry, Graham and Lieberman will “drop” a climate bill into the Senate’s hopper where it will vie with finance reform, nuclear proliferation concerns, and a Supreme Court nomination for attention.  This is stiff competition, to be sure, but its bi-partisan sponsorship brings the hope that the spring and summer will some significant progress toward building a national policy supported by sound science and reasonable economics.

The Senator’s efforts to build support for climate policy will be supported by the release of four separate reports on climate by the National Academies of Science under the rubric of “America’s Climate Choices” and the release of another Academy report on the implications of stabilizing greenhouse gas concentrations.  They will also be augmented by a National Climate Adaptation Summit hosted by the Obama Administration.  They will be opposed by Senators who will try to use pilfered e-mails to undercut the credibility of climate science and misguided aggregate economics to argue that none of this matters anyway.  In anticipation of the fireworks, it struck me as useful to suggest how to communicate urgency even for a wealthy and developed country like the United States.

Five “Reasons for Concern” (about climate change) were first described in the Third Assessment Report of the Intergovernmental Panel on Climate Change.  They were reconfirmed as “a viable framework to consider key vulnerabilities” in the Fourth.  In both cases, their content was unanimously approved word for word by member countries, including the United States where the decision to do so was made in the Bush White House.  These aggregate metrics include:

1. Risk to Unique and Threatened Systems – the likelihood of imposing increased damage or irreparable loss to unique and threatened systems such as coral reefs, tropical glaciers, endangered species, unique ecosystems, biodiversity hotspots, indigenous communities, etc.
2. Risk of Extreme Weather Events – the likelihood of extreme events with substantial consequences for societies and natural systems such as increases in frequency or intensity of heat waves, floods, droughts, wildfires or tropical cyclones, etc.
3. Distribution of Impacts – the likelihood of disparities of impacts (positive or negative) across regions or sectors.  Some regions, sectors or communities could face harm from climate change while others could even benefit.
4. Aggregate Net Damages – the likelihood of recognizing damages in aggregate. There are impacts distributed across the globe that can be aggregated into a single economic measure.
5. Risks of Large Scale Discontinuities – the likelihood of committing the planet to certain large scale phenomena that may have abrupt and irreversible consequences; partial deglaciation of the West Antarctic or Greenland ice sheets, substantial reduction in the strength of ocean currents, or triggering a “run-away greenhouse effect” driven by methane emissions from melting permafrost have all been discussed in the literature.

Recent work has added a sixth “Reason for Concern” for the United States.  It highlights Risks to National Security to reflect growing attention within the defense community to climate change risks and vulnerabilities that will occur beyond national borders.  A report released by the Military Advisory Board, for example, concluded that “the national security consequences of climate change should be fully integrated into national security and national defense strategies” in large measure because “climate change acts as a threat multiplier for instability in some of the most volatile regions of the world” and because “projected climate change will add to tensions even in stable region.”

The most recent assessments of climate risk show some relatively modest reasons for concern from observed effects for “Unique and Threaten Systems,” “Extreme Weather Events,” and “National Security Risk”; these concerns escalate to levels that are judged to be serious after about 1 degree C of additional warming (calibrated in global mean surface temperature).  Risks of committing to “Large Scale Discontinuities” turn serious with 2 or 3 degrees C of further warming, but concern about “Aggregate Impacts” does not turn serious for the United States until about 4 or 5 degrees.  Even “Distributed (economic) Impacts” have been judged to be relatively benign for the United States until the planet experiences 2 more degrees C of warming.  The details can be found at http://www.springerlink.com/content/98403021086522r4.

It is important to recognize that unabated warming would see 2-5 degrees C of warming over the coming century.  Moreover, holding concentrations of greenhouse gases below twice preindustrial levels would still leave more than an 80% chance that warming this century would climb irreversibly to levels that are 3 degrees C higher than today and stay there for thousands of years.

Two qualitative conclusions that are particularly germane for the forthcoming policy deliberations in Washington can be drawn from these conclusions.  First of all, if the coming policy debate is informed about the significance and urgency of the climate issue only by aggregate economic measures, then a majority in Congress could easily decide that the country as a whole will not experience the ramifications of “dangerous anthropogenic interference with the climate system” any time soon.  Supporters of legislation would, quite simply, see their concerns undercut by even well-meaning members who would not be impressed given the many claims on their time and the treasure over which they hold sway.

These conclusions nonetheless clearly demonstrate that “dangerous anthropogenic interference” could easily be discovered by careful consideration of how a changing climate will influence the intensities, frequencies, consequences, and regional distributions of extreme weather events both at home and abroad.

It must be emphasized that none of this means that the United States will never experience the economic consequences of “dangerous anthropogenic interference.”  It means, instead, that aggregate economic indicators miss the point and lull decision-makers and their constituents into a false sense of security.  The coming discussions must, instead, recognize that danger lies in the often non-economic reflections of even short-term climate change impacts that are driven by human contributions to greenhouse gas concentrations and exacerbated by ill-informed decisions.