The Sustainable Energy Authority of Ireland said today that energy-related CO2 emissions fell by 12.4%, or 4.6 million tonnes, last year on the back of Covid-19 travel restrictions.
The SEAI said this resulted in CO2 emissions from fossil fuels used for energy falling to their lowest level since 1993.
It also marked the biggest annual reduction in CO2 emissions since the depth of the recession in 2009.
It said that oil products used for transport accounted for the largest reduction in energy use, attributable to the public health travel restrictions.
Overall energy use fell by 9.2%, relative to an economic contraction of 5.4% during the year.
Today's figures show that oil use decreased by 16.5% last year - the largest annual reduction ever recorded by the authority.
The SEAI said that almost all the reduction in oil use was in transport as a result of restrictions and disruptions during the public health emergency.
Total transport energy use last year was down 25.9%.
The largest reduction in oil products was in jet kerosene, which was down 64.4%, followed by diesel, down 13.6%, and petrol, which decreased by 24.1%.
Meanwhile, peat use fell by 33.6% mostly through a halving of peat used for electricity generation.
The SEAI said that energy from renewable sources grew by 8.5% in 2020.
42% of electricity generated was from renewable sources in 2020, with 36.1% generated from wind.
The CO2 intensity of electricity also fell by 8.8% last year - less than a third what it was in 1990, due to less use of coal, oil and peat, and more renewables and high efficiency gas turbines.