Wednesday, November 5, 2014

IPCC Response Essay #2: Achieving Dramatic Reductions in Greenhouse Gas Emissions through Sustainable Development

John C. Dernbach, Distinguished Professor of Law at Widener University and Director of Widener’s Environmental Law Center

What do we need to do to have a decent chance of preventing large and growing emissions and atmospheric concentrations of greenhouse gases from dangerously interfering with the climate system? The answer, according to the Intergovernmental Panel on Climate Change (IPCC), is that the world needs to reduce greenhouse gas emissions by at least 40 to 70 percent by 2050, and to zero or below by 2100.  Other scientific reports would say we must proceed faster. The IPCC also indicates that the many paths to this reduction should all be guided by sustainable development. That is, nations must find ways to reduce greenhouse gas emissions that also foster equitable economic and social development and promote security.

The task, then, can be succinctly stated as follows: starting now, we must rapidly reduce greenhouse gas emissions to zero or below, creating as much social, environmental, economic, and security benefit as we can, and on an equitable basis. The IPCC reports don’t say so as succinctly or directly, but that is among the most essential tasks of our time. 


Here is one of the most important paragraphs in the entire three volumes of the IPCC reports. It is from the Summary for Policymakers for IPCC Working Group I, which concerns the physical science basis for climate change. It is also likely to be among the densest, most tightly packed paragraphs you will ever read:

Limiting the warming caused by anthropogenic CO2 emissions alone with a probability of >33%, >50%, and >66% to less than 2°C since the period 1861–1880, will require cumulative CO2 emissions from all anthropogenic sources to stay between 0 and about 1570 GtC (5760 GtCO2), 0 and about 1210 GtC (4440 Gt CO2), and 0 and about 1000 GtC (3670 GtCO2) since that period, respectively. These upper amounts are reduced to about 900 GtC (3300 Gt CO2), 820 GtC (3010 GtCO2), and 790 GtC (2900 Gt CO2), respectively, when accounting for non-CO2 forcings as in RCP2.6. An amount of 515 [445 to 585] GtC (1890 [1630 to 2150] GtCO2), was already emitted by 2011.[1]  

Got it? 

To unpack this, it helps to know that the objective of the U.N. Framework Convention on Climate Change is “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.”[2] The Conference of the Parties to the Convention has translated that objective as “a likely chance of holding the increase in global average temperature below 2 °C or 1.5 °C above pre-industrial levels.”[3] The period of 1861 to 1880 provides a baseline for pre-industrial levels.

The paragraph specifies three different probabilities of holding the increase to 2 °C (the higher of the two temperatures)—greater than (>) one out of three, fifty-fifty, and two out of three. To put these probabilities in perspective, it helps to recall that the U.S. Environmental Protection Agency has traditionally regulated chemicals under its major statutes when they create a risk of cancer of between one in 10,000 and one in 10 million.[4] Cancer risks from chemicals are different from the risks of climate change, of course, but the contrasting probabilities are striking nonetheless. Even in Russian roulette, a player has only a one in six chance of dying. 

The entire paragraph is about just one greenhouse gas—carbon dioxide(more on that later). The acronyms GtC and GtCO2 refer to gigatons of carbon and gigatons of carbon dioxide, respectively. A gigaton is one billion tons. As the last sentence states, approximately 515 gigatons of carbon, or 1890 gigatons of carbon dioxide, were already emitted by 2011. 

The term “cumulative emissions” refers to all human (anthopogenic) emissions—past, present, and future. In effect—and this is critical—the paragraph says there is an overall carbon budget (or, for our purposes, carbon dioxide budget) that we cannot exceed if we want to have a specified chance of holding the increase to 2 °C.   To have better than a one-in-three chance, all human carbon dioxide emissions have to stay below 5,760 gigatons.  For a better than fifty-fifty chance, the figure is 4,440 gigatons.  For better than a two-thirds chance, the number is even lower—3,670 gigatons. 

But that is not the whole story because carbon dioxide is not the only greenhouse gas.  When the effect of other greenhouse gases (e.g., methane, nitrous oxide, certain industrial chemicals) is taken into account, the numbers become even lower: 3,300 gigatons of carbon dioxide (better than one in three), 3,010 gigatons (better than fifty-fifty), and 2,900 gigatons (better than two out of three). 

Subtracting what was already emitted in 2011 (a calculation not made in the paragraph), we are left with the following: The world cannot emit more than 1,410 additional gigatons of carbon dioxide (one-in-three chance of not exceeding 2 °C), 1,120 additional gigatons (fifty-fifty chance), or 1,010 additional gigatons (two-in-three chance).  

That is essentially what this paragraph says. The meaning of the paragraph is explained elsewhere.  

The Working Group III Summary for Policymakers explains both the scale of cuts, and how much time is available, if we are to have a “likely” (two-in-three) chance of not exceeding 2 °C.  By its assessment, global greenhouse gas emissions need to be 40 to 70 percent lower by 2050 and “near zero” gigatons of carbon dioxide equivalent or “below” by 2100.[5] 

Other calculations of a carbon budget provide less time to get emissions that low. The writers of a frequently cited 2009 paper in Nature focus on the time period between 2000 and 2050, not 2000 and 2100, and calculated carbon budgets to avoid exceeding 2 °C based on cumulative emissions in the first half of this century.[6] Given past and projected emissions, they conclude, “we would exhaust the CO2 emission budget by 2024, 2027 or 2039, depending on the probability accepted for exceeding 2 °C (respectively 20%, 25% or 50%).”[7]

One doesn’t need to be a scientist or a statistician to judge which of these carbon dioxide budgets gets the timing correct. A set of normative propositions—all discussed in various places throughout the IPCC reports, [8]—are equally applicable to either approach.  The precautionary approach, intergenerational equity, intragenerational equity, human rights, and basic morality all suggest that we need to reduce greenhouse gas emissions as rapidly as possible to an ultimate goal of zero or below.   In fact, the parties to the 2012 Conference of the Parties of the Framework Convention agreed on the importance of “accelerating the reduction of global greenhouse gases.”[9]

Accelerating Mitigation through Sustainable Development

Sustainable development is a decision-making framework to foster human wellbeing by ensuring that development and environment goals are achieved at the same time.[10] A specific objective of the Framework Convention is sustainable development,[11] and the Convention is suffused with sustainable development principles and language—including precaution,[12] equity,[13] and, perhaps most importantly, integrated decision-making.[14] In fact, the Convention requires all countries to integrate climate change mitigation and adaptation into their national development plans and processes.[15]

Sustainable development offers the only realistic approach to accelerating the reduction of greenhouse gas emissions, because it would have governments frame their legal and policy approach not only in terms of reducing emissions, but also in terms of the social, economic, security, and environmental benefits that they can obtain by doing so. In addition, according to the IPCC, articulating the equitable or moral basis for sustainable development approaches to climate change enhances the likelihood that these approaches will be agreed to and implemented.[16] By creating a space for new approaches to development based on equity that produce both climate change and non-climate change benefits, sustainable development provides a way for public and private decision makers in all countries to get past the seemingly intractable conflict between development and climate change mitigation. 

In fact, this policy space is now being filled by a variety of new or modified laws that foster renewable energy; energy efficiency and conservation in buildings, transportation, and industry; and distributed energy, among other things. As states discovered more than a decade ago, the co-benefits of addressing climate change—including new jobs; growing businesses; greater stability in energy production; reduced emissions of sulfur dioxide, mercury, and other air pollutants; and reduced energy costs for businesses and the poor—produced more immediate and tangible results than the greenhouse gas emission reductions that accompanied these benefits.[17]  

Those who draft, modify, advocate, and implement laws relating to climate change need to look—and are already looking—for ways of doing so that maximize equity and co-benefits.  Particularly but not exclusively in developed countries, the greater the co-benefits, the greater greenhouse gas emission reductions that are often politically available. The task, then, is to craft, adopt, and implement approaches to reducing greenhouse gas emissions that are not only sensible and ambitious but are also so attractive that they will overcome all the many obstacles to change, including not only fossil fuel interests but also simple inertia.

To be very sure, sustainable development may not work to address the global problem of climate change. Governments may refuse to enter or treat seriously this new space, taking unsustainable approaches to mitigation or simply adhering to conventional development paths and fossil fuels.  Alternatively, runaway greenhouse gas emissions could so destabilize governments and societies as to make any prospect for sustainability out of reach. But sustainable development provides an internationally accepted and widely applied framework for reducing greenhouse gases, and is an attractive approach for accelerating the reduction of greenhouse gas emissions.

[1] WGI: Summary for Policymakers, supra note 3, at 27 (footnotes omitted). 

[2] United Nations Framework Convention on Climate Change, art. 2, May 29, 1992, S. Treaty Doc. No. 102-38, 1771 U.N.T.S. 107. U.N. Doc. A/AC.237/18 (Part II)/Add.1; 31 I.L.M. 849 [hereinafter Framework Convention].

[3] See, e.g., Conference of the Parties, United Nations Framework Convention on Climate Change, Decision 1/CP.17 (Establishment of an Ad Hoc Working Group on the Durban Platform for Enhanced Action), in Report of the Conference of the Parties on its Seventeenth Session, held in Durban from 28 November to 11 December 2011, Addendum, Part Two: Action taken by the Conference of the Parties at its Seventeenth Session, FCCC/CP/2011/9/Add.1 (2012), available at

[4] John D. Graham, The Legacy of One in a Million, Risk in Perspective 1-2 (1993) (Harvard Center for Risk Analysis), available at

[5] Intergovernmental Panel on Climate Change, Climate Change 2014: Mitigation of Climate Change: Summary for Policymakers 13 (2014) available at [hereinafter WGIII: Summary for Policymakers] (footnote and emphasis in first sentence omitted). The term “likely” means a “66-100 %” chance of a particular outcome. Id. at 4, no. 2.

[6] Malte Meinshausen et al., Greenhouse-Gas Emission Targets For Limiting Global Warming To 2 °C, 458 Nature 1158 (2009). 

[7] Id. at 1159. 

[8] See, e.g., Climate Change 2014: Mitigation of Climate Change, Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Chapter 4 (Sustainable Development and Equity),  (2014) available at

[9] Conference of the Parties, U.N. Framework Convention on Climate Change, Advancing the Durban Platform, FCCC/CP/2012/L.13 (Dec. 8, 2012), available at  

[10] Id. at 11-12. 

[11] Framework Convention, supra note 14, art. 3.4. 

[12] Id. art. 3.3.

[13] Id. art. 3.1. 

[14] Id. art. 3.4. 

[15] Id. art. 4.1(f). 

[16] Chapter 4 (Sustainable Development and Equity), supra note 20, at 4.

[17] John Dernbach and the Widener University Law School Seminar on Global Warming, Moving the Climate Debate from Models to Proposed Legislation: Lessons from State Experience, 30 Envtl. L. Rep. (Envtl. L. Inst.) 10,933 (2000).

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