By William Opalka

MILFORD, Mass. — Carbon dioxide emissions rose about 7% in New England last year as the loss of the Vermont Yankee nuclear plant increased fossil fuel generation, ISO-NE said last week.

CO₂ emissions rose to just more than 30 million tons in 2015, up from 28 million tons in 2014, Patricio Silva, ISO-NE senior analyst for system planning, told the Planning Advisory Committee during its annual environmental update Wednesday. That reversed a trend that has seen carbon emissions fall from 32 million tons in 2012 to 31 million tons in 2013. The figures are based on EPA data.

“Emissions rose slightly, probably because of the closing of Vermont Yankee” at the end of 2014, Silva said. (See Vermont Yankee Retirement Leaves ISO-NE More Dependent on Gas.)

A separate data set from ISO-NE, which runs through only 2014 and includes emissions from smaller power plants not counted by EPA, shows CO₂ emissions had declined 26% from 2001 through 2014.

Entergy, which owns Vermont Yankee, also plans to shut the Pilgrim nuclear plant in Massachusetts no later than mid-2019. Its closure would leave New England with only three nuclear generators: the Seabrook plant in New Hampshire and the two-unit Millstone plant in Connecticut. (See Entergy Closing Pilgrim Nuclear Power Station.)

Ozone Standard

In addition to a discussion of the region’s carbon emissions, the meeting also touched on EPA’s stricter ozone standards. In a rule adopted in October, the standard was reduced to 70 parts per billion from the 75 ppb adopted in 2008.

“Rhode Island and most of Connecticut would be non-attainment for the 2015 ozone standard,” Silva said.

Preliminary 2013-2015 data, based on eight-hour concentrations, show southwestern Connecticut exceeds even the less strenuous standard, at 81 ppb or more. Rhode Island and the much of the rest of Connecticut fall into the 71 to 80 ppb range. The rest of New England meets the new standard at less than 70 ppb.

The regulation has a seven-year phase-in period.