Blog Post

Question 1 for COP 21: Long-term Goal

Nov 19, 2015 | Brian P. Flannery, Raymond J. Kopp, Clayton Munnings

In this blog series, Questions for COP 21, we are posing several questions that should be considered before—and after—the negotiations. Here we address the long-term goal: Does the 2 °C goal encourage or discourage long-term cooperation?

Long-term goals for the Paris Agreement include several options, for example:

  • Net emissions to peak by 2030;
  • Global emissions to decrease (either 40 – 70 percent or 70 – 95 percent) below 2010 levels by 2050; or
  • Net zero emissions by (2050 or 2100). 

Nonetheless, for many years the United Nations Framework Convention on Climate Change (UNFCCC), reinforced by many other processes, has framed a dominant narrative for the Agreement to place the world “on track” to limit warming to 2 (or, more recently, even 1.5) °C to avoid a climate catastrophe. For many, especially notably for the media, 2 °C has become symbolic telltale for success or failure in Paris.

Analyses of anticipated actions reveal that getting “on track” will require require far more effort in increasingly less time in future years. Recognizing this, over the past year political leaders have begun to temper expectations, but it may be too late. Once again pressures are growing, as before Copenhagen six years ago, for an ambitious outcome. So, it becomes essential to ask whether the 2 °C goal promotes or inhibits cooperation, or if some other goal might better align and unify long-term, cooperative effort.

Editor's note: The following paragraph has been revised to reflect that the IPCC Budget is for CO2, not CO2-equivalent as incorrectly stated in the initial post. With appreciation to Steven Stoft for calling this to our attention.

Analyses have framed the 2 °C challenge as one of managing a cumulative global emissions budget going forward. While CO2 emissions predominate, the budget must account also for other gases and factors, such as particulates and albedo changes. For the CO2 component, the Intergovernmental Panel on Climate Change (IPCC) discusses a budget (beyond 2010) of approximately 1,000 billion tons (Gton). The sobering reality is that at today’s rate of emissions (over 35 Gton per year and growing), that budget would be consumed by about 2040. (On a CO2-equivalent basis, reflecting all changes as though they were produced solely by CO2, emissions today are about 53 Gton annually.)

Analyses have framed the 2 °C challenge as one of managing a cumulative global emissions budget. Although the actual budget and probability of achieving the goal depend on a number of uncertain factors, the Intergovernmental Panel on Climate Change (IPCC) discusses a budget for future CO2 equivalent emissions of approximately 1,000 billion tonnes (Gton). (Equivalent CO2 emissions include the total greenhouse contribution from emissions of all gasses and other factors, such as particulates and albedo changes, as though they were produced solely by CO2.) The sobering reality is that at today’s rate of emissions (over 50 Gton per year and growing), that budget would be consumed before 2035.

Climate negotiations do not occur in a silo: sovereign nations have other essential and politically compelling priorities. Many are unwilling today to allow decisions in the UNFCCC to foreclose options in critical areas such as poverty alleviation, energy security, access to energy for citizens without electricity or transport, and other development priorities. Consequently, in fact, negotiators have not posed emissions mitigation in the Paris Agreement as allocating a fixed budget. That would force them to resolve in stark, unforgiving numbers some of the most challenging aspects of the deal, e.g. equity, burden sharing, finance and compliance. Indeed, mitigation is not being negotiated at all; rather, proposed actions will be compiled based on self-determined Intended Nationally Determined Contributions (INDCs). Moreover, the United States and several other nations insist that emissions outcomes should not be binding.

Serious questions are now being raised about viability of the 2 °C goal, and the status and reliability of conclusions from presumably authoritative analyses; for example, claims that the goal could be met only if global emissions peaked before 2015 (IPCC AR4) or 2020 (UNEP). More recent reports assert that the goal remains in reach, but requires far greater future effort in far less time. Proponents characterize the challenge as merely one of “political will,” others argue that 2 °C is “already in the rear view mirror”—or soon will be. In a challenging environment for consensus, 2°C generates heated controversy, even among analysts. The debate and developments going forward have implications for the credibility of the UNFCCC.

Further considerations provide additional perspectives on challenges associated with operationalizing the 2 °C goal.

  • Policies offer no tools (besides geoengineering) that directly constrain temperature. Policy can affect emissions, but even the link between emissions, concentrations, and temperature change presents significant uncertainty. Indeed, the 5th IPCC Assessment provided less certain guidance for these relations than previous reports.
  • Measuring, reporting, and verification (MRV) of temperature change to assess progress towards meeting a temperature goal appears to be problematic, e.g. how well might future observations inform progress to being “on track” or falling behind in efforts? Fundamental challenges include accounting for the time lag between changes in greenhouse gas concentrations and temperature, and for natural variability—caused, e.g., by volcanic eruptions, El Niño and other variations in sea-surface temperature, and inherent chaotic variability of climate. Several decades of observations might be required to draw conclusions concerning ultimate temperature outcomes.
  • The CO2-equivalent concentration today of all well-mixed greenhouse gases—over 480 parts per million (ppm)—already exceeds the level (450 ppm) typically associated with 2 °C equilibrium warming. Large but quite uncertain offsetting cooling effects, especially from particulates, keep equivalent forcing below 450 ppm. However, strong concerns regarding the direct health effects of particulates are creating increased efforts to reduce their emissions, which would accelerate the increase of net greenhouse gas warming.   
  • Dramatically decreasing future CO2 emissions and drawing down atmospheric concentrations, as would apparently be required to reach a 2 °C goal, would require future deployment of technology systems combining carbon capture and storage and bioenergy on a truly massive scale. Besides cost, deployment faces significant challenges because of the vast infrastructure required for pipelines, reservoirs, biomass production, harvesting, processing, and transport.

Because of its importance and controversy, scientists, technologists, and policy analysts should carefully reassess the implications and feasibility of the 2 °C goal, as well as other possible long-term objectives. Unless climate sensitivity lies at the low end of estimates or innovators develop affordable, rapidly deployable, low-carbon technologies, with each passing year, 2 °C appears to be increasingly questionable, with consequences for the credibility of the UNFCCC process and its future. Perhaps better information could reduce needless controversy and help to identify and inform options that might better align and unify long-term cooperative effort.

Read more posts in the series, Questions for COP 21: