Critics say the Omaha Public Power District should follow other utilities’ lead and commit to absolute carbon reduction instead.

Clean energy advocates say an Omaha utility’s recent carbon pledge gives it significant leeway to continue burning fossil fuels and still hit its target.

Across the Midwest, utilities have adopted voluntary goals to boost renewable generation or reduce total carbon emissions, notably Xcel Energy, which recently announced intentions to be carbon-free by 2050.

The Omaha Public Power District has chosen a more flexible metric to measure itself by: carbon intensity.

Carbon intensity is the amount of carbon dioxide released per another unit of measurement, such as power generated or products sold. It is sometimes preferred in corporate sustainability as a way to compensate for growth.

The OPPD board in October adopted a goal of reducing the utility’s carbon intensity by 20 percent by 2030 compared to 2010 levels. The utility’s management will be required to give annual progress reports to the board.

But critics, including a member of OPPD’s board, say the goal will do little to address the utility’s actual carbon emissions.

“For clear and transparent reporting of environmental impact, we need to know the amount of carbon emitted,” said Rick Yoder, an elected member of the OPPD board of directors. “It’s the carbon that has the impact, not the carbon intensity.”

Yoder distrusts the carbon intensity metric because changes don’t necessarily coincide with actual increases or decreases in the amount of carbon going into the atmosphere. He tried repeatedly to convince the board and staff “to make it more clear by having total pounds, and failed each time.”

Related: Xcel Energy has an ambitious climate plan. Will carbon capture be part of the solution?

Measuring carbon intensity “is not a bad thing,” said Peter Miller, western region director of the Climate & Energy Program for the Natural Resources Defense Council. “It’s just not a complete picture. What we ultimately care about is the total amount of emissions.”

Mary Fisher, OPPD’s vice president for energy production and nuclear decommissioning, said being held to reducing absolute CO2 emissions likely would wreak havoc with the utility’s reliability and resilience. She sees no generation alternative that could replace her utility’s fossil fuel generation.

“I need the same generating units I have today … because we have nothing else in our fleet that serves that load in a baseload manner,” Fisher said.While other utilities transition from fossil fuels, Fisher said she is “hesitant to put something out there that we don’t have an answer for how we get there.”

She is confident, however, that the utility can meet the goal it has set for itself.

The carbon intensity goal passed on a 6-2 vote. The goal could change if the board revisits the issue after January, when newly elected board members — including three clean energy supporters — are seated.

A debate about carbon intensity also surfaced recently in Iowa, where MidAmerican Energy won regulatory approval last week for a 591-megawatt wind farm known as Wind XII. In its application, the utility’s president and CEO, Adam Wright, noted that the project would lower the utility’s carbon intensity to about 638 pounds per net megawatt-hour, compared to 1,839 pounds per megawatt 15 years ago, before it began investing in wind energy.

“The carbon intensity, even if it’s calculated correctly, doesn’t mean they’ve reduced their emissions that much,” said Paul Chernick, an attorney representing the Sierra Club in the case. “It means they, as a generating company, are shifting their mix. It means they’re a larger generation fleet.”

Related: Iowa utility’s wind farm approved over objections from clean energy groups

While he commends MidAmerican for its investment in wind energy, clean energy supporter Josh Mandelbaum contends that the reduction is less dramatic than the utility is taking credit for. The reason: the use of the carbon intensity metric to characterize emissions changes.

Adding wind to its mix of generation reduces the amount of carbon per megawatt-hour, but only because the utility is generating more electricity overall — not because it’s necessarily burning any less coal. The utility remains among the nation’s top 20 in terms of its use of coal to generate power, according to testimony filed with state regulators by Mandelbaum, a senior attorney with the Environmental Law & Policy Center.

“It is not possible to reduce CO2 emissions without reduction in fossil fuel generation or the use of carbon capture technology, which MidAmerican has not proposed,” Mandelbaum said in testimony. “The benefit that MidAmerican discusses necessarily impacts MidAmerican’s fossil fuel fleet, because if that fossil fuel fleet is not running less and/or retired, there will not be a reduction in emissions and the benefits that come from that.”

MidAmerican spokesperson Tina Hoffman said the directive to use the “carbon intensity” metric is in Iowa law, which states that it is “the intent of the general assembly to encourage rate-regulated public utilities to consider altering existing electric generating facilities, where reasonable, to manage carbon emission intensity in order to facilitate the transition to a carbon-constrained environment.”

The Iowa Utilities Board was unswayed by arguments that the new wind farm will not result in reduced emissions. Although it has made a point of its continually shrinking carbon intensity, MidAmerican said it will not close any of its coal-fired plants, but will continue to depend on coal as an essential part of its resource mix.