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The Metric

Jun 11, 2015

Getting to Two Degrees: Measuring What Cities, Companies, and Others Have Promised

Two separate reports from Yale’s Environmental Performance Index (EPI) and the United Nations Environment Programme (UNEP) have measured the potential of non-state and sub-national actors to mitigate climate change by eliminating about one-fifth of the emissions gap.
Drawing: Rooftops by Joshua Tabti
Art Credit: "Rooftops" by Joshua Tabti (Creative Commons:

As the climate community waits anxiously for countries to announce their intended climate commitments for the upcoming Paris climate deal, a new range of actors has emerged. Companies, cities and states, and civil society organizations are filling in gaps of leadership and much-needed emission reductions.

The reality is that global emissions aren't slowing, they’re growing – and so are the risks they pose. Perhaps that’s why so many people are looking for solutions outside the official international climate negotiations from cities, provinces, businesses, and regions. The burning question is how much can these “non-state and sub-national” initiatives contribute? As of the last few weeks, there are now two new independent analyses to estimate this potential: an analysis in Nature Climate Change by our team at Yale and a separate report just released last week by the UN Environment Programme (UNEP).

Side by Side Comparison

Did we reach the same conclusion, or do we agree to disagree? At first glance, our results appear to be similar with the overarching finding that sub-national action can reduce the 2020 emissions gap by around one-fifth. The Yale study in Nature Climate Change (summarized in Grist) quantified the commitments made by sub-national actors at the NY Climate Summit (NY Summit) last fall, and collectively, they could reduce approximately 2.54 Gt of carbon dioxide equivalent emissions (GtCO2e) in 2020 - an amount roughly equivalent to India’s annual emissions in 2012. In the non-state and sub-national actions they evaluated, UNEP’s report found that their mitigation potential was around 2.90 GtCO2e in 2020. However, digging a little deeper into the scopes, sources, and methodologies of these two studies reveals some substantial differences.

First, our research scopes differ. We assessed the potential effectiveness of 29 action statements and plans that non-state actors pledged at the NY Summit, whereas UNEP quantified the efforts of three times as many non-state actors (5 vs. 15). Essentially, they focused on the entire range of non-state actors derived from the Climate Initiatives Platform (CIP), which includes over 180 mitigation initiatives from more than 20,000 actors. But their analysis stops just shy of the NY Summit, where ours picks up. For instance, UNEP found that cities could reduce twice as many emissions our analysis (1.08 GtCO2e vs. 454 MtCO2e) primarily because their analysis simply captures more cities. We only quantified the Compact of Mayors’ commitments whereas UNEP also included cities that belong to the carbonn Climate Registry and the C40 Cities Climate Leadership Group, accounting for overlaps.

While the scope of what we included in our respective analyses were different, the methods employed are consistent between the two reports. Figure 3.1 (adapted below) in UNEP’s report describes how UNEP narrowed the 180 initiatives to 15 initiatives with quantifiable mitigation emissions. We used a similar method: categorizing the NY Summit initiatives, and then selecting from those which ones had explicit emission reductions tied to actions that were measurable and time-bound.

Click here to download a full-sized pdf version.

Main Conclusions

  1. ​​​As they are structured, only a few sub-national and non-state initiatives actually contribute to global climate mitigation. In both the UNEP and Yale analyses, it is clear that the bulk of efforts registered do not have concrete emission reductions. UNEP estimated only 15 out of 180 cooperative initiatives add up, while we found 8 of 29 (reduced to 5 after accounting for overlaps between the initiatives) had mitigation potential. There was so much attrition because most of these groups made promises without specifics. Most lacked emission reduction goals, targets, or baseline reference points, and nearly everyone chose not to put their money where their mouth was. UNEP even excluded actors whose goals would not reduce over 50 MtCO2e per year by 2020, a criterion that would have eliminated all but three of our studied actors.

  2. More information is needed to accurately account for overlaps. Both studies required assumptions to discount initiatives that may have 1) overlapped with each other (e.g., a company’s reduction of greenhouse gas emissions could also be counted within its city’s mitigation target); 2) overlapped with national targets. It’s a methodological headache to disentangle the individual initiatives recorded in the CIP or NY Summit and determine if they occur in addition to existing actions or state-level efforts. And researchers like us and at UNEP are making certain assumptions to aggregate all the disparate numbers together. In a perfectly open-data world, bolstered with common standards and reporting, emission reductions and commitments made by various actors might be filtered as if through a coin sorter. Unfortunately, we’re just not there yet.

  3. Efforts to quantify the range of climate actions are primarily limited to mitigation. Both the UNEP and Yale reports confine their analyses to mitigation.  The common metric between the two are gigatons of carbon. But we know that many of the other initiatives recorded in the CIP and NY Summit are much broader than climate mitigation. Some efforts relate to capacity building, adaptation, resilience, financing, and health, to name a few. While these aspects and “co-benefits” (e.g., programs that tackle air pollution but result in positive impacts on climate change) are important, they are much more difficult to register and measure. As a result, they often get lost in quantitative exercises like UNEP and Yale’s. We still don’t have a way to evaluate how a program will bolster a country’s ability to adapt to a warming climate, in discrete units like gigatons of carbon.

Click here to download a full-sized pdf version.

Looking Ahead

A few messages can be drawn from our analysis. First, if only a few subnational actions can eliminate one-fifth of the emissions gap, imagine what the whole body of actions - including those that are not strictly mitigation-related - could achieve. Nation-states cannot tackle climate change alone, nor can they achieve the necessary finance, institutions, or mobilization to help people adapt to inevitable climate change. Secondly, the elevation of sub-national actors and non-state initiatives into the formal UN climate negotiations and greater international significance should pressure these actors to think more critically about their commitments. ‘What level of emissions reductions can we realistically deliver, and by when?  How are we going to do it?’  If these institutions have more momentum than an international agreement - a belief many people hold - then they need to convince policymakers with specificity.  We’re far from reaching a consensus on how many emissions non-state actors can reduce, but our early estimates are optimistic and foreshadow what’s possible.