Taoiseach Enda Kenny said financial challenges will prevent Ireland from making deep cuts in emissions from our agriculture sector to help prevent dangerous climate change.
He warned that not until after 2020, and when the economy recovers, would the State be in a position to meet "aggressive targets".
And he added that "hard bargaining" would take place over the coming weeks to achieve goals which were "fair and reasonable".
Speaking to the Irish Independent at the UN climate summit in Paris, Mr Kenny said that existing European Commission targets to reduce emissions from agriculture by 2020 were "unrealistic".
He said the commission "overestimated" the contribution that the agri-food sector could make, and that as Ireland produced food more sustainably than other countries, it should be treated as a special case.
"We have lost a decade of investment in our country because of what happened. That cannot be recovered, and until we have an economic engine to allow us change structures, and continue to invest in research and innovation for more sustainable ways of doing agriculture, that presents us with a challenge," the Taoiseach said.
"We don't want to see a situation where we are limited in what we can produce to find that food is being produced in other countries with inferior standards and higher emissions levels."
Agriculture is the biggest contributor to Ireland's greenhouse gas emissions, currently accounting for more than 30pc of the total. Ireland also has the highest proportion of emissions of any EU member state from this sector.
Emissions are expected to increase by 2pc by 2020 as Government plans to ramp up food production are realised.
However, the EU requires a 20pc cut by 2020 over 2005 levels - on the current pathway, they will have reduced by just 5pc, well below the target.
"The European Commission in setting out targets for 2020 overestimated what agriculture could actually deliver," Mr Kenny added. "What we want is an understanding that we are serious about achieving fair and sustainable targets, but we need space to deliver on them.
"What we have to have here is plenty of ambition, but one tempered with reality."
The Taoiseach was among 147 heads of state who addressed the 21st Conference of the Parties (COP21) climate summit.
He said that tackling climate change required action by "everybody, big and small", and that Ireland was "determined to play its part".
Almost 200 countries have gathered in Paris for two weeks of intense negotiations aimed at striking a deal.
Most have committed to reducing emissions, but scientists warn the pledges are not enough to keep warming below 2C - the tipping point beyond which catastrophic change is expected.
Average global temperatures have already increased by 1C this century.
French president Francois Hollande told the summit that an agreement was needed to secure global peace, and that it was possible to prevent disaster if countries acted together.
"Climate change will bring conflict just like clouds bring storms," he said.
US president Barack Obama described the talks as an "act of defiance" against terrorism, and said a grim future could be avoided if leaders took action.
"I came here personally to say the United States not only recognises the problem but is committed to doing something about it," he said.
Ireland has pledged at least €6m towards helping developing countries adapt to climate change.
The State joins 10 other countries, including Canada, the US, France, Germany and the UK in committing to provide $248m (€235m) of 'new' money to support the most vulnerable countries on the planet.
The money will be provided to the Least Developed Countries Fund (LDCF), a climate fund hosted by the Global Environment Facility (GEF).
It will be provided between now and 2020 to help countries adapt to droughts, violent storms, sea-level rise and other impacts caused by climate change.
Former President of Ireland and United Nations Secretary-General's Special Envoy on Climate Change Mary Robinson said the money would be used to support millions of people.
'Ireland is determined to play its part." Taoiseach Enda Kenny set out the Government's position at the Convention on Climate Change in Paris last night.Ireland is committed to the EU's collective target of reducing greenhouse gas emissions by at least 40pc by 2030.