The Supreme Court has overturned the Government's "excessively vague and aspirational" plan to combat climate change.
A seven- judge court ruled the National Mitigation Plan (2017-2022) lacks specificity.
It also found the plan does not comply with Ireland’s obligations under the Climate Action and Low Carbon Development Act 2015 to give sufficient detail about achieving the national transition objective of a low carbon economy by the end of 2050.
The Government is obliged to give "some realistic level of detail" about how it intended to meet the objective and the plan "falls a long way short" of the sort of specificity the 2015 Act requires, the Chief Justice, Mr Justice Frank Clarke, said.
He said he did not consider any reasonable and interested observer would know, in any sufficient detail, how it really is intended, under current Government policy, to achieve the objective by 2050 on the basis of the information in the plan.
The plan does not comply with the requirements of the 2015 Act, in particular section 4, and should be quashed, he held.
The Government must now devise a new plan taking into account the court’s findings, made in an appeal by Friends of the Irish Environment (FIE).
In other findings, the court ruled FIE, as a corporate entity, could not pursue claims of breach of personal rights to life and bodily integrity under the Constitution and European Convention on Human Rights Act 2003.
Had the case been brought by an individual or individuals, the court might have had to consider whether the climate change measures, or lack of same, interfered with those rights, it said.
In an important observation concerning whether there is a "derived" right to a healthy environment, the Chief Justice said he considered Mr Justice Max Barrett's finding in an unrelated High Court case of a right to a healthy environment consistent with human dignity as "impermissibly vague" and "ill-defined".
He said he would not suggest a right so described can be derived from the Constitution. There may well be environmental cases, such as this one, where constitutional rights and obligations may be engaged if pursued by individuals, he stressed.
In its proceedings against the Government, Ireland and the Attorney General, FIE argued the National Mitigation Plan fails to set out measures to substantially reduce emissions by 20 per cent by 2050 and achieve further reductions in the short to medium term.
In a judgment delivered via video link on Friday, the Chief Justice, with whom Justices Mary Irvine, Donal O'Donnell, John MacMenamin, Elizabeth Dunne, Iseult O'Malley and Marie Baker agreed, allowed FIE's appeal over the High Court's dismissal of its challenge.
The Chief Justice noted the broad underlying scientific evidence as to the causes of, and problems created by, climate change, was not in dispute and the case centred on the measures the environmental group argued the Government is legally required to take to alleviate climate change.
He rejected the State’s arguments that the plan simply involves adoption of policy and is therefore not “justiciable” by the courts. In this case, there is legislation - namely the 2015 Act - and not policy, he said.
Where the legislation requires a plan formulated under its provisions does certain things, the law requires a plan comply with those obligations.
The overriding requirement of a compliant National Mitigation Plan is that it must, in accordance with section 4.2, “specify the manner in which it is proposed to achieve the national transition objective”.
While section 4 requires a new plan at least every fifth year, that did not mean a series of five-year plans but rather of “rolling plans”, each designed to specify, in general terms and on a sectoral basis, how it is proposed the national transition objective be achieved.
The National Mitigation Plan, adopted in 2017, was required to be a 33 year plan, albeit one likely to be adjusted every five years to take developments into account.
While the Government argued a more recent plan - the 2019 Climate Action Plan - was an example of how policy was evolving, and had identified measures first envisaged in the 2015 plan aimed at partially closing the carbon gap, the 2019 plan is not a plan in the sense that term is used in the 2015 Act, he said.
The 2019 plan had not, for example, been through a public consultation process as mandated by the 2015 Act, he said.
Whatever level of clarity is required by the Act about Government policy to achieve the objective by 2050, it must be provided in a formal plan adopted in accordance with public participation measures in the 2015 Act.
While the Government was not bound by the views of the Climate Change Advisory Council, it seemed appropriate to place significant weight on the latter’s views, he said.
In its 2018 annual report, the council - a body established by statute - had said Ireland is “completely off course” in terms of its commitments to addressing climate change.
It also appeared reasonable to characterise significant parts of the policies the National Mitigation Plan suggested should be followed as “excessively vague or aspirational”, including those related to agriculture, he said.
On foot of those and other findings, the plan does not comply with the 2015 Act, particularly section 4, and should be quashed, the court held.
Commenting on the ruling, Clodagh Daly of Climate Case Ireland said it was “ground-breaking and a landmark verdict” for climate action in Ireland and across the world.
“It means the Irish Government can no longer make promises that it cannot fulfil,” she said.
Speaking on RTÉ’s News at One, Ms Daly said Ireland could now take the lead internationally in transitioning the country to a low carbon economy.
She said the Supreme Court had demonstrated that there was “no legal basis for a lack of political will.”
Ms Daly said the impact of the ruling is that the Government cannot make long-term commitments about climate change without showing how they would be achieved.
She said environmental campaigners were looking forward to seeing the Government’s reaction to the ruling but warned it would be “a grave situation” if it did not comply with the court’s verdict.