Fianna Fáil and Fine Gael have committed to reducing carbon emissions on average by 7pc a year over the next decade, to break the deadlock in government formation talks with the Green Party.
The breakthrough came over the weekend, when the two parties wrote to the Greens committing to developing measures to reduce emissions over the next 10 years.
The move cleared the way for the leaders of the three parties to meet today to formally begin talks on the formation of the next government.
However, the landmark commitment will prove divisive among the memberships of both Fianna Fáil and Fine Gael.
Micheál Martin, Leo Varadkar and Eamon Ryan will meet this morning to decide on the format of the programme for government talks.
All three parties will then appoint negotiating teams and the talks will officially begin.
The decision to commit to reducing carbon emissions by on average 7pc a year over the next 10 years is in line with the Green Party's General Election manifesto, which noted that it is a 10-year challenge to reduce emissions and will take more than one government.
The firm political commitment to a decade of reductions - which will go beyond the lifetime of a new government - will make it very hard for any successor to reverse the cuts pattern, especially given Ireland's EU and other international obligations to deliver big carbon emission reductions.
"In essence the three parties are committed to a 7pc annual reduction, measured as an average over the 10-year period," a source familiar with the process told the Irish Independent.
Another source confirmed the 7pc agreement. It was also pointed out that all the Dáil parties, including Fianna Fáil and Fine Gael, signed off on the principle of a yearly 7pc cut in a report by the all-party Oireachtas Climate Action Committee before the Dáil was dissolved for last February's General Election. "With proper scientific expert advice, achieving the 7pc cut will not be as daunting a task as it first appeared," the source said.
But it may prove very difficult to sell to Fianna Fáil's and Fine Gael's rural heartland.
"It will be a hard balancing act to meet Green Party demands and not lose traditional voters for the two big parties," a source said.