Approach and Assumptions
We identified 20 US states plus Puerto Rico, 135 cities, and 4 counties as being aligned with Paris goals. This group includes states who are members of the Under2 MOU and/or the United States Climate Alliance, as well as states with official greenhouse gas reduction targets that were at least 85% as strong as the US climate pledge. From the lists maintained by the Climate Mayors and by We Are Still In we created a list of cities and counties outside of those 20 states who had committed to adopt the goals of the Paris Agreement. For the line graph of emissions projections, we included cities and counties that had joined either agreement as of June 23, 2017. (The pie charts are updated as of September 25, 2017.)
Using data from the Energy Information Agency for 2014 CO2 emissions for states and 2016 data from the US Census we were able to calculate the share of emissions represented by those states and the share of population represented by the cities and counties.
To approximate the share of emissions represented by the cities and counties, we estimated the ratio of the per capita carbon emissions of a subset of the cities to the US average per capita carbon emissions, and used that ratio to create a correction factor to estimate the share of emissions from those cities and counties.
We found that approximately 40% of 2014 carbon emissions were attributed to the cities, counties, and states aligned with the Paris Agreement.
To estimate the contribution of these cities, counties and states we used the C-ROADS climate simulator to compare three scenarios. In the first scenario, we used the C-ROADS reference scenario (business as usual), which is based on projected rates of change in population, GDP per capita, and carbon intensity of GDP. In the second scenario, emissions followed the US Paris Agreement climate pledge. In the third scenario, 36.4% of emissions followed the US pledge, while the remaining 63.6% of emissions followed the C-ROADS reference scenario.
When carbon policy is stronger in some regions of a country than others, there is a concern for leakage, where reductions in emissions within the region with strong carbon policy are accompanied by emissions increases outside the region. For instance, businesses may move to regions with fewer regulations, or falling demand for fossil fuels within the region may result in lower prices and thus increased consumption outside the region. While there are few studies on carbon leakage from sub-national policy, the studies that have been done show that, depending on the design of the carbon policy, leakage can be significant. We used estimates from a modeling study of leakage in California to provide an approximation of the possible degree of leakage, to include a lower bound (9%) and a higher bound (45%) of the range of potential leakage. More studies are needed to better inform our understanding of this effect, but it will be important for those implementing carbon policy in the cities and states that have adopted Paris goals to make every effort to avoid carbon leakage.
Implications and observations
- The mobilization of commitments was rapid and strong. In less than two weeks, decision makers representing about half of the US population aligned themselves with climate protection and the transition to a low-carbon economy. From very small towns like Bayfield, WI (pop 530) to New York City and Los Angeles, the communities stepping forward are very diverse, but are now connected in a common pursuit. These ties will be important in the work and shared learning that will be required to meet Paris goals.
- More is needed. Climate Interactive analysis showed that, even when the US was a committed participant in the Paris Agreement, the collective ambition of countries wasn’t yet enough to meet the Paris goal of limiting temperature increase to well below 2°C. Without 100% commitment to Paris goals in the US, that gap widens.
- Momentum is possible. The reasons to align with Paris goals extend beyond protecting the global climate. The drivers include improving public health, seizing economic opportunity, and creating more equitable communities. To the extent that half the country is embarking together on a change process that is expected to produce these multiple benefits, the number of dots on the map below may well grow during the coming weeks and months.
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