Shortcomings in the state’s greenhouse gas inventory pose issues for energy planning
While Massachusetts has mandated major reductions in greenhouse gas emissions over the coming decades, its greenhouse gas inventory may be underestimating the true level of emissions in the state. As government officials plan for the transition to a clean energy economy, climate advocates worry that these issues with the state’s inventory—largely centered around how the state calculates the carbon impact of its gas system—could lead to false solutions on the path to decarbonization.
“All these accounting errors in the GHG inventory process, they really stack up to make a significant impact, especially when you’re looking at these future scenarios,” said Ben Butterworth, Director of Climate, Energy & Equity Analysis at the Acadia Center, a nonprofit that focuses on climate and clean energy policy. “Underestimating the methane leaks from the gas distribution system makes the continued existence of gas distribution at scale seem like a more viable climate solution.”
While the state legislature has set an aggressive climate goal for 2030, amounting to about a 35% reduction in emissions compared to 2019 levels (the most recent year with complete data), its energy and transportation systems remain heavily reliant on fossil fuels. The state has also lagged far behind its implementation targets for clean technologies like electric vehicles and heat pumps.
With decarbonization deadlines fast approaching, state officials have also been busy drafting future energy plans in the contentious ongoing “Future of Gas” proceedings at the Department of Public Utilities (DPU), while the Commission on Clean Heat, established by the Baker administration, just released its final report. With the state’s decarbonization planning efforts ultimately reliant on the inventory for accurate emissions data, these proceedings have highlighted the need for a renewed focus on how the inventory is calculated.
According to the Massachusetts Department of Environmental Protection (MassDEP), emissions in the Commonwealth declined by about 23% between 1990 and 2019. However, this estimate is based on a series of assumptions which, if slightly changed, could drastically change the total amount of emissions in the state.
The main points of controversy in the state inventory center around how the state calculates warming from natural gas, a fuel primarily made up of methane. Methane is a powerful greenhouse gas, but only lasts in the atmosphere for about 12 years before breaking down (in contrast to carbon dioxide, which can last in the atmosphere for thousands of years). Because of methane’s short lifespan, the timescale used for calculating its warming impact can make a huge difference—the longer the timescale used, the weaker its impact will appear.
Currently, Massachusetts calculates the warming impact of methane on a 100-year timescale, which results in a global warming potential (GWP) of 25—meaning its warming impact would be 25 times larger than the same mass of carbon dioxide. But changing the calculation to the 20-year timescale would increase the GWP all the way to 84.
Climate advocates argue that the state should be using this 20-year timescale in the inventory, since the state’s climate goals focus on the decades leading up to 2050, not the distant future of 2123.
But even using the 100-year timescale, the warming potential calculation is outdated. The GWP in the state’s inventory is based on the Intergovernmental Panel on Climate Change’s (IPCC) Fourth Assessment Report (AR4) from 2007, which was updated in 2014 in the IPCC AR5, which increased the GWP from 25 to 28.
As to why the number hasn’t been updated, “The Massachusetts GHG inventory has historically used the same convention as the United States Environmental Protection Agency (EPA), which uses the IPCC AR4 100-year GWPs,” according to a MassDEP spokesperson.
Another point of contention for the state’s inventory is that it doesn’t factor in out-of-state emissions for fuels burned in the state. While natural gas leaks from out-of-state extraction and transportation are a major source of emissions, they are overlooked in emissions modeling based on the inventory.
In contrast to Massachusetts, New York lawmakers changed their emissions inventory in 2019 to account for out-of-state emissions, while also adjusting its inventory to use methane’s 20-year GWP. According to an analysis by the Acadia Center using data from New York’s 2021 emissions report, this led to a 90% increase in the Empire State’s estimation of natural gas emissions.
So what does this mean for Massachusetts? How far off is the overall inventory?
Using New York’s inventory, we can reach a rough estimate. According to an analysis by the Acadia Center, factoring in New York’s out-of-state gas leaks with a 20-year GWP increased the state’s estimate for natural gas combustion emissions by 79.3 percent. Applying this same multiplier to Massachusetts’ inventory (which likely has very similar out-of-state natural gas emissions to New York), and then using a 20-year GWP to account for in-state methane leaks, this results in an approximate 27% increase in overall emissions.
However, this calculation still likely still falls short of the real number of emissions, because it doesn’t take into account the well-documented issue of how Massachusetts drastically underestimates the extent of methane leaks from within the state.
A 2021 study by researchers at Harvard found methane leaks from the gas system in eastern Mass to be six times higher than the state’s inventory estimates. According to a MassDEP spokesperson, the agency has not updated its estimates of methane leak rates in the state following the publication of this study.
However, in 2022 the agency did update its methodology to include post-meter gas leaks, such as those from appliances like gas stoves and furnaces. This move generated pushback from National Grid, one of the state’s largest gas providers, which wrote in the public comment period for the recent update, “MassDEP should wait to include post-meter emissions until more reliable data is available as noted in attached American Gas Association comments to EPA.”
The authors of the Harvard study on methane leaks also found no difference in the actual level of methane emissions in the state over the study period, despite major efforts by the state to patch up methane leaks.
“We’ve been sold natural gas as this transitional fuel that has less greenhouse emissions than coal or oil,” lead author Maryann Racine Sargent said in an interview following the release of the study. “But actually, if the emissions of methane directly to the atmosphere from the supply chain are around three to six percent, the climate impact actually becomes almost equivalent to that of coal.”
As the state investigates how to decarbonize its gas system, ultimately “the most effective way to reduce emissions is going to be to transition away from natural gas,” Racine Sargent added.
In the transition away from natural gas, climate and health advocacy groups such as the Acadia Center, Conservation Law Foundation, and Physicians for Social Responsibility have called on the state to pursue an aggressive decarbonization strategy focused on rapid electrification.
Meanwhile, certain business interests, including the powerful gas utility lobby, have pushed to keep the state’s gas system running largely on biomethane (also known by the industry-friendly term “renewable natural gas”)—despite various issues with the fuel including cost, availability, and health impacts.
Biogenic fuels like biomethane, which are created from organic matter but still release greenhouse gases when burned, pose another looming challenge for the state’s carbon footprint. While today biofuels make up only a small portion of the state’s energy, variations in how their climate impact is calculated could have major impacts on the state’s decarbonization planning.
While biofuels like “renewable natural gas” or “renewable diesel” are often marketed as clean fuels, their climate benefits can vary greatly depending on how they are produced. They typically generate significant carbon emissions even when taking into account their carbon sequestration benefits. While it may have a smaller carbon footprint than fracked methane, biomethane or “renewable natural gas” is chemically the same as natural gas, with the exact same effect on the climate when leaked or burned.
“The lifecycle accounting of biofuels becomes of critical importance when you’re trying to compare these scenarios against scenarios that lean more heavily into electrification of buildings,” Butterworth of the Acadia Center said.
Sidestepping these complexities, the gross emissions calculation used by the state to indicate overall emissions levels simply doesn’t include biofuel emissions. While the state must take lifecycle emissions into account for its net-zero-by-2050 requirement, they are not set to factor into the 85% reduction in gross emissions required by that time, nor are they included in the state’s emissions limits leading up to 2050.
Planning for the future
In June of 2020, the office of Attorney General Maura Healey petitioned the Department of Public Utilities (DPU) to investigate how to decarbonize the operations of the state’s gas utility companies, in what is frequently called the “future of gas” proceedings.
In the ensuing investigation, the DPU tasked the state’s gas providers with hiring consultants to assess potential scenarios of decarbonization, which varied in levels of electrification and continued use of the gas system. The consultant’s report that resulted ultimately favored a scenario where the existing gas system would be largely maintained, with most of its energy coming from biomethane.
This consultant’s report, criticized by a wide range of environmental groups, concerned citizens, and the Attorney General’s office itself, formed the bedrock for the decarbonization plans presented by the gas providers to the DPU. Meanwhile, the state inventory formed the bedrock for the consultants report, which contained just a few brief disclaimers about some of the inventory’s shortcomings.
“In this study, consistent with the Massachusetts GHG inventory, the Consultants have assumed that renewable fuels have a net-zero GHG impact,” the report noted. “The Consultants recognize that treating renewable fuels as having net-zero emissions is a simplification of the complex carbon flux associated with these fuels… As such, pathways that rely more heavily on renewable fuels bear risks related to lifecycle emissions and GHG accounting methods.”
Meanwhile, in November of 2022 the state’s Commission on Clean Heat, established by the Baker Administration, issued their final report. One of the major recommendations from this report called for the implementation of a “Clean Heat Standard” by 2024 to target emissions from buildings, the majority of which come from natural gas.
While acknowledging that alternative fuels like biomethane may be included in the standard, the report ultimately downplayed their role, while highlighting the need for accurate emissions accounting.
“Zero or, potentially, very low carbon fuels may represent an interim opportunity to reduce emissions in existing fossil fuel systems that have yet to reach the end of their useful life and may be included only after a rigorous scientific assessment of their full life cycle GHG emissions, including leakage assessments,” the commission’s report wrote. “However, these fuels are not a long-term solution for most of Massachusetts’ building stock.”
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Jon is a freelance journalist and a senior at Colorado College. He oversees the school's student publications and covers environmental issues for the Catalyst newspaper. Sign up for his newsletter at newenglandclimate.substack.com.