David Cameron's attempt to neutralise the toxic political issue of airport expansion until after the next election has been thwarted by the climate change watchdog, which has announced it will report this summer on the impact of the plans on the UK's climate commitments.

The news is a blow to politicians who hoped they could avoid taking a view on a politically fraught decision until after the 2015 election, when the Davies commission will report on Britain's airport needs.

The government's climate change committee said it expected to report to parliament in the summer on the environmental implications of airport expansion.

Citing figures from Howard Davies' interim report, the committee's chief executive, David Kennedy, also said that the cost of long-haul flights would need to rise by up to £200 to curtail demand and stay within the UK's carbon emissions targets.

The Liberal Democrat leader Nick Clegg said last week that he would not allow expansion if it breached the government's climate change commitments.

The Davies commission interim report, published last week, referred to the previous recommendations of the climate change committee, but was opaque on how those targets could be met, expansion permitted.

Ministers are committed by law to cut carbon emissions by 80% by 2050 compared with 2005 levels, with emissions from aviation and shipping to be included in this target. The climate change committee has said this would require aviation emissions to return to 2005 levels by 2050.

The Davies commission has said this is achievable if passenger demand growth is kept to 67% by 2050.

Kennedy told the Guardian: "We said back in 2009 that it would be possible for the government to plan for 60% demand growth, and stay inside the climate change commitments. That is the scope for demand to increase.

"We are due to report to parliament next July on the progress on meeting carbon budgets, and that would be the occasion for us to consider the report of the Davies commission.

"The expansion of Heathrow by one runway would stay within the 60% limit, depending on the extent of demand growth at other locations."

He said it was an open question whether government targets could be met if a second runway at Heathrow was proposed or expansion was allowed at Gatwick.

The Davies commission favoured three options: a third runway north-west of Heathrow, the airport's preferred choice; a second proposal to double the length of an existing runway at Heathrow, put forward by the unconnected Heathrow Hub group; and a second runway to the south of Gatwick.

The Davies commission itself suggested that to meet government targets, the carbon price would have to rise to £600 per tonne of CO2 by 2050, as opposed to the current price of £3 per tonne, if runway capacity was totally unconstrained, and no other fuel-efficiency measures were found. That would require the current average short-haul fare rising from £103 to £146, and the average long-haul fare rising from £397 to £602.

Kennedy explained: "The Davies commission has said if capacity is unconstrained and demand rose for example by 200%, it would be necessary for the carbon price, and cost of flights, to rise by the figures in the report to keep the increase in demand to 60%."

Kennedy stressed other environmental factors would be in play, but were not his committee's responsibility. He said: "If the climate change targets are being met, then the remaining issues become cost, and local impacts relating to the economy, air quality, noise and traffic congestion, but these are issues for which the climate change committee does not have responsibility."

He expressed confidence that the commission will not ignore the climate change implications of expansion. He said: "We wrote to the Davies commission and they seem to be taking commitments under the Climate Change Act seriously.

"The higher the level of aviation emissions, the deeper the emissions cuts required in other sectors to meet the economy-wide targets".