The landmark ruling came after a challenge from a community organisation founded in the ashes of a devastating bushfire that swept through Tathra in 2018.

Bushfire Survivors for Climate Action had argued the EPA had a duty to protect the environment from significant threats and climate change was a "grave" and "existential" threat.

The EPA had failed to do this, BSCA contended in the NSW Land and Environment Court, with whatever instruments the agency had developed to ensure environment protection were not enough or even intended to deal with the threat of climate change.

The government said its current measures were adequate, including measures that incidentally regulate greenhouse gas emissions such as methane in landfill. But first and foremost, it said its environmental protection duty was a general duty and wasn't a duty to ward off particular threats, such as climate change.

Chief Judge Brian Preston on Thursday found none of the documents the EPA presented to the court was an instrument that showed it was ensuring the protection of the environment from climate change.

He ordered it develop environmental quality objectives, guidelines and policies to meet their duty on climate change.

But the EPA will maintain discretion on how it fulfils its duty, as the judge knocked back the BSCA's wish for specific objectives including the regulation of sources of greenhouse gas emissions consistent with limiting a global temperature rise to 1.5C above pre-industrial levels.

"This is a significant win for everyone who has been affected by bushfires," BSCA president Jo Dodds said in a statement.

"Bushfire survivors have been working for years to rebuild their homes, their lives and their communities. This ruling means they can do so with confidence that the EPA must now also work to reduce greenhouse gas emissions in the state"

The Nature Conservation Council said most people would be astonished to learn the EPA had not regulated greenhouse gas but the ruling should "a chill through the state's most polluting industries, including the electricity and commercial transport sectors".

"Allowing politicians to set greenhouse gas emission targets and controls rather than scientific experts has led us to the precipice," NCC chief executive Chris Gambian said.

In a statement, the EPA said it was reviewing the judgment.

It described itself as an active government partner on climate change policy, regulation and innovation and was involved in work that "assists with and also directly contributes to measures to mitigate and adapt to climate change".

"The EPA supports industry to make better choices in response to the impacts of climate change," the agency said.

Last month, a federal judge ruled federal Environment Minister Sussan Ley had a duty of care to protect children from future personal injury caused by climate change.

Ms Ley is appealing the decision, which resulted from her involvement in the approval of the expansion of a northern NSW coal mine.

Australian Associated Press