May 10, 2023

Emissions from New England power generation rose in 2021, but levels remained well below historical averages

A warmer summer and colder winter in 2021 led to more generation by the region’s power plants, driving a year-over-year increase in annual air emissions, according to the recently published 2021 ISO New England Electric Generator Air Emissions Report.

New England continues to see emissions levels well below those observed in the early 2000s, the report said, noting that annual carbon dioxide (CO₂)emissions fell 20% over the previous 10 years and 41% from 2001 through 2021. Meanwhile, despite the increase in annual emissions, the report found emission rates—that is, the amount of CO₂, sulfur dioxide (SO₂), and nitrogen oxides (NO_x) given off for every megawatt-hour (MWh) of electricity produced—were similar to those reported for 2020.

By the numbers

The table below summarizes annual emissions and emission rates for 2021, as well as the year-over-year changes from 2020. The table includes figures for emissions from native generation (electricity produced by power plants in New England), as well as data on emissions associated with native generation plus electricity imported from other regions.

Annual emissions and emission rates

Native generation	2021 emissions (kilotons)	Change from 2020	2021 emission rate (lbs./MWh)	Change from 2020
NO_x	12.44	+2.9%	0.24	-4.0%
SO₂	2.11	+12.2%	0.04	0.0%
CO₂	33,439	+7.8%	658	+0.6%
Native generation and imports
CO₂	34,555	+4.2%	574	+2.4%

Report takeaways

Generation up: The region’s native generation rose by 7.1% in 2021, with output increasing year over year for all resource types except hydroelectric generation. Plants fueled by natural gas—which account for the majority of the region’s native generation—produced 9% more electricity in 2021 than in 2020.
Weather and the resource mix: Coal- and oil-fired generation had year-over-year increases of 281% and 53%, respectively. Resources fueled by coal or oil produced more power than usual during colder weather in January and February 2021, and production by oil-fired resources also increased during hot weather in June and August. These resources, which have higher emission rates than plants fueled by natural gas, often contribute generation during peak energy demand periods in the summer, or when winter heating demand limits the availability of natural gas or drives up its price.
Impact of imports: Hydroelectric generation accounts for a significant share of the region’s imported electricity, so the CO₂ emission rate of 199 lbs./MWh for imports is lower than the rate of 658 lbs./MWh for native generation. This results in a lower combined emission rate for native generation plus imports, and it also affects annual emissions. Net imports in 2021 were 20% lower than the previous year. Estimated CO₂ emissions from imports were included for the first time in the 2020 report, to reflect the total emissions associated with New England’s electricity use.
Solar and wind rise: Solar and wind resources supplied 10% more power to the grid in 2021 than the previous year, with generation rising by 589 gigawatt-hours (GWh). Generation by these resources grew by 50%—more than 2,100 GWh—over the previous five years.

Long-term trends

Annual air emissions from native generation declined from 2012 through 2021. In addition to the 20% drop in CO₂ emissions, NO_X emissions fell by 39% and SO₂ emissions fell by 87%. From 2001 through 2021, CO₂ emissions fell by 41%, NO_X emissions fell by 80%, and SO₂ emissions fell by 99%.

The increased use of highly efficient natural-gas-fired generators, mandated use of lower-sulfur fuels, retirements of coal- and oil-fired generation, increasing amounts of wind and solar generation, and higher net energy imports have all contributed to the trend.

About the data

The report’s emissions estimates for native generation are based on data from the US Environmental Protection Agency’s Clean Air Markets Program database and the agency’s eGRID database, New England Power Pool Generator Information System monthly data, and the ISO’s calculation of emission rates based on unit type and age. CO₂ emission rates for imports are based on data from the eGRID database for the New York ISO and on Canada’s Greenhouse Gas Inventory Report.

Some data releases the report relies on occur roughly 12-13 months after the end of a calendar year.

In addition to the annual report, the ISO publishes data on estimated CO₂ emissions from New England power plants in a monthly recap of the wholesale electricity markets. Real-time estimates of CO₂ emissions are available on ISO Express.