The think tank Third Way just published an interesting look at the effect of planned and potential nuclear plant closures on carbon emissions in the U.S. power sector.

Why it matters: Even if just some of the early retirements come to pass, it will knock the country farther away from cutting greenhouse emissions by 80% below 2005 levels by 2050, a target set under President Obama.

Check out the chart above: The top shows how much zero-carbon power — from renewables and nuclear plants — is needed to support the economy-wide 2050 goal (based on analysis underlying a 2016 White House report).

The colored lines show how much varying levels of nuclear retirements will cause the U.S. to fall short of generating 2,750 million megawatt-hours of zero-carbon power annually by 2030.

show how much varying levels of nuclear retirements will cause the U.S. to fall short of generating 2,750 million megawatt-hours of zero-carbon power annually by 2030. One level deeper: The report looks at three levels of projected early nuke plant retirements — 20%, 55% and 66%. It notes that much of this generation will likely be replaced by natural gas, which means more emissions — and even if it was all replaced by renewables, it's still a setback. From Ryan Fitzpatrick, deputy director of the centrist think tank's clean energy program:

"The only way we win is if we grow the amount of zero-carbon energy we’re producing. As nuclear plants get shut down, new renewables will have to pay-off that zero-carbon debt before they actually start increasing our totals again."

The big picture: "Even if we limit the loss of nuclear generation between now and 2030 to just 20%, that’s a setback of 4.5 years’ worth of clean energy growth," Fitzpatrick writes. The setback is more severe as retirement rates grow.

As nuclear plants face heavy market pressure from natural gas and renewables, the number of planned or possible closures keeps rising. Most recently, FirstEnergy Solutions Corp. announced plans in late March to shutter two plants in Ohio and one in Pennsylvania by 2021.

A state focus: Fitzpatrick chatted with Axios about the group's views on policies that could ward off retirements.He is hopeful about stronger state-level efforts in areas where retirements loom in the next few years.

“It is really going to be incumbent on the states to start working on policy efforts right away, if they have not already,” he said.

to be incumbent on the states to start working on policy efforts right away, if they have not already,” he said. The group supports expansion of so-called zero-emissions credits programs to more states beyond existing efforts in Illinois and New York.

of so-called zero-emissions credits programs to more states beyond existing efforts in Illinois and New York. Fitzpatrick also sees potential for states that already have renewable electricity standards to expand them into wider clean energy standards that greatly raise the target while crediting existing nuclear generation. This idea has been floated in Arizona.

The federal picture: Third Way does not support FirstEnergy's recent bid for sweeping use of the Energy Department's emergency powers to keep coal-fired and nuclear plants in the PJM Interconnection region operating with guaranteed cost recovery.