They warn that there is “limited to no” room left for further sales of petrol and diesel vehicles, saying ideally sales of new private cars run on these fuels would end next year and goods vehicles by 2027.
Use of oil, coal and peat for home heating needs to end by 2030, they say, and most gas shortly afterwards.
They say the shift required will be “the most significant change since the foundation of the State”.
It will be “highly disruptive”, “initially expensive” and will require “strong political leadership”, they warn.
However, failure to act will bring “profound costs to the Irish economy and to the people of Ireland”.
The warnings from the Climate Change Advisory Council come as the council sets out the annual reductions in greenhouse gas emissions the country must achieve between now and 2040.
Emissions must fall by at least 6.3pc on average every year from now.
The council says energy-related emissions will have to fall by 90pc by 2040
If cuts of that scale are not achieved in the early years – and the council says it is unlikely they will be – then the cuts in subsequent years will have to be deeper.
The implications for Irish society and the economy are far-reaching.
Almost 83pc of Ireland’s energy needs – for electricity, heating, transport and industry – is provided by fossil fuels.
The council says energy-related emissions will have to fall by 90pc by 2040, which means fossil fuels will have to disappear.
Methane emissions, mainly from agriculture, will have to fall by 22-30pc by 2040 and nitrous oxide emissions, also chiefly from farming, will have to fall by 66-69pc.
The national Climate Action Plan contains measures aimed at reducing emissions in all these areas but the council says: “There will have to be significant ramping up of ambition and delivery across all sectors, well beyond what has already been demonstrated.”
The council is legally required to produce “carbon budgets” to show the amount of greenhouse gas emissions (carbon for short) that Ireland can still produce over the next 25 years while moving towards zero emissions so that the country no longer contributes to global temperature rise.
The overall budget is very tight and is broken down into five-year periods, each smaller than the one preceding.
The budgets must be approved by the next Oireachtas before they become legally binding
The budget for 2021-2025 is 295 million tonnes (mt), falling to 200mt for 2026-2030, to 160mt for 2031-2035 and to 120mt for 2036-2040.
On average in recent years, Ireland has produced around 60mt per year.
The budgets must be approved by the next Oireachtas before they become legally binding and the incoming government will then have to decide how to share out the allowable emissions between transport, agriculture, electricity generation and other key sectors.
Council chair Marie Donnelly said the budgets were “challenging but necessary” for climate action and for avoiding the billions of euros in European Union fines Ireland faces for failing to do its fair share.