April 30 (Reuters) - A U.S. appeals court on Tuesday

upheld federal approvals for a natural gas pipeline system

expansion project in Louisiana and Mississippi, rejecting

environmentalists' claims that the government performed an

insufficient review of its climate harms.

A unanimous three-judge panel of the U.S. Circuit Court of

Appeals for the D.C. Circuit held that the Federal Energy

Regulatory Commission (FERC) was right to determine the

Evangeline Pass Expansion Project is functionally separate from

four related gas infrastructure developments being developed

independently. FERC therefore did not need to analyze their

emissions together, the D.C. Circuit said.

The Kinder Morgan ( KMI )-backed project would expand existing

pipelines to feed more fuel to Venture Global's Plaquemines

liquefied natural gas export terminal in the Gulf of Mexico.

The Sierra Club and Healthy Gulf said in their 2022 lawsuit

seeking to vacate FERC's approvals that the expansion and the

related projects - new pipeline infrastructure projects that

connect to the same export terminal and to the terminal itself -

would together cause a massive release of greenhouse gas

emissions.

But the D.C. Circuit said on Tuesday that since the other

projects have separate ownership and would likely be built

anyway, FERC was not obligated under federal environmental

review laws to consider their collective emissions when issuing

approvals.

The environmental groups, Kinder Morgan ( KMI ) and FERC didn't

immediately respond to requests for comment.

The projects are all part of a major build up of LNG export

capacity in the Gulf. The U.S. last year became the world's

largest LNG exporter, and that capacity is expected to double

before the decade ends.

The environmental groups had argued FERC violated the

National Environmental Policy Act when it segmented its analysis

of Evangeline Pass' environmental harms from the other projects.

The groups said the projects are connected because the

terminal won't be able to export gas without supply from the

pipelines, and the pipelines wouldn't have anywhere to put the

gas without the terminal.

FERC had argued in court that the cumulative analysis

demanded by the environmental groups wasn't necessary because

the individual projects would likely proceed regardless of

whether the Evangeline Pass project is approved.

The Evangeline Pass expansion is currently under

construction. Work on the Plaquemines terminal is also ongoing

and its first exports are expected later this year.

The case is Alabama Municipal Distributors Group v. Federal

Energy Regulatory Commission, U.S. Circuit Court of Appeals for

the D.C. Circuit, lead case No. 22-1101.

For the environmental challengers: Nathan Matthews and

Rebecca McCreary of the Sierra Club

For FERC: Matthew Christiansen of FERC