The capacity of the new runway would be restricted initially
The government's decision to expand Heathrow has provoked fury from green groups, climate scientists, local MPs, local people and opposition parties.
The long list of concessions to protect the environment involves genuinely new initiatives, but opponents of the expansion don't trust they'll be upheld and say they don't go far enough anyway.
In the Commons, the scheme was dismissed as an environmental disaster.
The Liberal Democrats said it had driven a jumbo jet through climate policy.
The Conservatives said it was a bleak day for the environment. John McDonnell, a Heathrow MP, was expelled after refusing to be silenced.
The government believes it has made major steps to mitigate the environmental impact of the expansion in three areas of policy - climate change emissions, local air quality and noise.
It gained widespread credit for abandoning an option of all-day operation on existing runways, which would have brought round-the-clock noise for local people.
It also said the capacity of the new runway would be restricted initially to 125,000 (rather than 222,000) flights a year until standards on local air quality and noise can be met.
The standards would be upheld by statutory bodies, the Civil Aviation Authority (for noise) and the Environment Agency (for pollution).
But critics point out that the area is already in breach of EU rules on air quality because of pollution from cars as well as planes.
Slots on the new runway would only be allocated to the cleanest planes, Transport Secretary Geoff Hoon said.
But Simon Retallack from the influential think-tank IPPR said: "Does anyone really think that if BAA spends the money to build another runway they'll be told they can't use it because planes aren't clean enough?
Pressing ahead with the expansion of Heathrow now is highly irresponsible
Hugh Raven, Sustainable Development Commission
"The government will come under enormous pressure to change the rules - and it will give in."
The green group Environmental Protection UK (EPUK) said the clean aircraft condition for the new runway was meaningless because older, dirtier aircraft would simply be displaced on to the existing runways.
EPUK's chief executive Philip Mulligan said: "With the current economic situation leading to collapsing sales of new aircraft and cars, the chances of meeting air quality and noise conditions around Heathrow are becoming more and more remote.
"The government's optimistic position assumed a quick introduction of cleaner, quieter aircraft and road vehicles around Heathrow, which now looks highly unlikely to happen."
The aviation industry has a voluntary promise to reduce noise and CO2 emissions by 50% and NOx (nitrogen oxides) emissions by 80% by 2020.
The BBC asked Keith Mans, chief executive of the Royal Aeronautical Society, if these targets would be achieved.
"I honestly don't know," he said. "There is a good prospect that they are achievable by 2020 but the science and the engineering solutions to the science are not totally reliable.
"We are narrowing the scope for doubt on estimates."
Mr Mans said design measures to reduce CO2 measures sometimes counteracted measures to reduce noise, and vice versa. Some engineers fear planes will not achieve these standards before 2030.
The government accept that on current projections Heathrow alone will be responsible for around a fifth of UK emissions by 2050.
The government's own green advisers, the Sustainable Development Commission, recently called for an independent commission to examine uncertainties on aviation and climate before any major expansion.
SDC commissioner Hugh Raven said on Thursday: "Pressing ahead with the expansion of Heathrow now is highly irresponsible.
"Air transport's true contribution to the UK economy has yet to be adequately reckoned, and we haven't yet understood the full impact of the current economic downturn on future transport patterns.
"Air transport will continue to play an important role in our lives in the 21st century, but massive questions remain over exactly what that role should be, and what proportion of carbon emissions we want to devote to it as opposed to our homes, food production and other forms of travel."
How local authorities monitor Heathrow air quality
The government made other announcements to win over green critics, including the idea of a high-speed rail line.
This is strongly backed by the Conservatives as an alternative to expansion of Heathrow - but the government sees it as additional.
Hundreds of homes in Sipson will be bulldozed if the runway is built
No money was allocated for the rail line and critics doubt it will be built, or that people will choose to use it with rail fares often so much higher than plane tickets.
The government is relying on the EU Emissions Trading Scheme to make aviation pay its way for its damage to the climate. But many independent studies suggest it will have negligible effect on fares.
The government has also promised to spend £250 million bringing low emissions cars on to the market.
Even a relatively small take-up of electric cars would negate any increases in CO2 from planes, Mr Hoon said.
In another innovation the government has set a long-term target for getting aviation emissions back to 2005 levels by 2050.
This is claimed to be the first time any government has set a target to restrict aviation emissions - and it sends a signal to motorists and householders than frequent fliers will not be given an indefinite free ride in the journey towards a low-carbon economy.
Some congratulated Mr Hoon for taking steps to protect the environment.
The chief executive of the airline umbrella body BAR UK, Mike Carrivick, said: "Aircraft waiting to land are often held in stacking queues leading to wasted time for travellers and unnecessary emissions for those areas over which aircraft are held.
"Departing aircraft are also held in lengthy queues on the ground causing similar damaging effects."
John Ling, head of transport at the Institution of Mechanical Engineers, said: "With Heathrow operating at 99% capacity and with aircraft stacking up waiting for landing slots we believe that a third runway is necessary to get them out of the sky and allow flight optimisation and hence reduce emissions."
But many of the positive moves in the report were drowned out by the rush of fury over the expansion, which is seen as a key test of the government's green credentials.
Local people and green groups have been tracking a history of broken government promises on Heathrow since the 1960s.
They see no reason to trust the promises in Thursday's announcement.
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