The annual ACT greenhouse gas inventory showed the territory was still on track to achieve net-zero emissions by 2045, but could struggle to achieve a 50 to 60 per cent cut to 1989-90 emissions levels within four years.

The report said changes to point-of-consumption technologies, such as zero-emissions vehicles and a transition away from natural gas, may be needed to achieve the target.

"Achieving this can take time. Further, it is uncertain how the economic recovery following the COVID pandemic will impact emissions," the report said.

Emissions in the ACT were down 45 per cent compared to the 1989-90 baseline in 2020-21, but had risen slightly from 2019-20, when emissions were done 47 per cent on the baseline.

In 1989-90, the ACT produced 3077 kilotonnes of carbon dioxide equivalent emissions. In 2020-21, the ACT produced 1685 kilotonnes, despite a 65 per cent increase in the population.

The 2019-20 was the first year the ACT had reduced its emissions below the baseline, after the territory offset 100 per cent of residual electricity emissions with renewable power.

Transport now makes up the largest portion of the ACT's emissions, accounting for 63.5 per cent of total emissions. Transport emissions rose 5 per cent between 2019-20 and 2020-21.

"Per capita transport energy use rebounded in 2020-21, in-line with increases in [compressed natural gas], petrol and diesel use to almost reach levels from before the pandemic," the report said.

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Natural gas, the second largest portion, makes up 22 per cent of the territory's emissions, but output remained flat from this sector between the 2019-20 and 2020-21 reporting periods.

Emissions Reduction Minister Shane Rattenbury said the report showed the overall trend in the ACT was on the right track, but there would be further challenges to reduce transport and natural gas emissions.

"Our climate actions this year reflect our commitment to reduce emissions from these sectors, some of which include continuing to support the uptake of active travel and electric vehicles to reduce transport emissions and launching zero-interest loans for households to complete energy efficiency and gas-to-electric upgrades or purchase an electric vehicle," Mr Rattenbury said.

A previous greenhouse gas inventory report warned emissions in the ACT could again rise if rapid action was not taken to curb transport emissions.

The 2018-19 inventory report said there was a "serious risk" the territory's emissions could rise after the switch to renewable power, driven by growing transport emissions.

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