The State's plan for reducing carbon emissions is a "ladder without bottom rungs", the Supreme Court has heard.
Seven judges of the country's top court are hearing a challenge by environmentalists to the State's failure to adequately address the climate crisis.
The challenge by Friends of the Irish Environment (FIE) centres on the 2017 National Mitigation Plan which was drawn up to tackle carbon emissions.
FIE argues that the plan lacks clear targets or strong enough practical actions to do the job.
Barrister Eoin McCullough, who represents FIE, told the court there was no dispute between the group and the Government on the science of climate change or that it represented the single biggest threat to humanity.
With agreement on those key issues, several judges sought to clarify the points of difference.
"We are all grasping for a metaphor," said Judge John MacMenamin. He asked if the case could be summarised as follows: "The State is saying it has built a ladder but you are saying the ladder has no bottom rungs."
In other words, it aimed high but didn't provide a strong starting point to begin the climb. Mr McCullough agreed that was a useful summary.
The National Mitigation Plan remains the only statutory, or legally binding, plan for carbon reduction although it has been largely overtaken by the 2019 Climate Action Plan, which also has been criticised.
The mitigation plan allowed carbon emissions to continue increasing, even though scientists say they have to reduce by at least 7pc-8pc a year with immediate effect if we are to slow global temperature rise and avoid the worse effects of climate breakdown.
FIE argues that the lack of an adequate plan also breaches human rights by failing to protect people's lives and the environment from climate breakdown.
The case was heard in the High Court last year but FIE lost and appealed to the Supreme Court.
The State rejects the claims.