Update 24 February: The “Heathrow 13” were today spared jail, with Judge Deborah Wright issuing six-week sentences, suspended for a year. The protestors have been banned from Heathrow airport and will each do 120 hours unpaid community service, rising to 180 hours for those with previous convictions. They will not be ordered to pay compensation but will receive fines.

Thirteen people found guilty of aggravated trespass whilst protesting against the proposed expansion of Heathrow airport are due to be sentenced next week. It could see the first custodial sentences handed down to environmental protesters in the UK in two decades.

The high-profile trial of the “Heathrow 13” has gone down the rare – but not unprecedented – route of enlisting a climate scientist as an expert witness for the defence.

Prof Alice Bows-Larkin, professor of climate science and policy at the University of Manchester, gave evidence to the court on the impact of aviation on climate change. Exclusively, Carbon Brief has her full statement, exactly as it was submitted to the judge in the trial.

Awaiting sentence

The “Heathrow 13”, part of the Plane Stupid campaign group, were arrested on 13 July last year after chaining themselves to a railing on Heathrow’s northern runway for six hours to protest against the impact of aviation emissions on climate change.

The protesters were arrested and later found guilty of aggravated trespass. District Judge Deborah Wright said that while it was clear the defendants were “principled people” and committed to their cause, she didn’t accept their actions were necessary to protect people from climate change. They should be prepared for jail time, she said, because of the “astronomical” cost of disrupting more than 20 flights.

With their final sentences due to be passed at Willesden magistrates court on 24 February, the case of the “Heathrow 13” has garnered a fair amount of media coverage and high-profile political support in recent weeks. One law expert told the Independent that custodial sentences for a peaceful, non-violent protest would be “unprecedented in modern times”.

The criminal charge of aggravated trespass came into force in 1994, following a series of road-building protests. While it can technically carry a custodial sentence “not exceeding three months”, no one has since faced jail time as a result of a non-violent environmental protest in the UK.

A statement on the Plane Stupid website says:

“The defendants argue that their action was necessary due to the airport’s contribution to life-threatening climatic changes. Furthermore, Heathrow expansion is inhumane to the local residents and those at the sharp end of climate change, and hugely environmentally destructive.”

“Necessity defence”

The “Heathrow 13” case isn’t the first time climate change has been used as a defence in a court of law. In 2008, the “Kingsnorth Six”, arrested for trying to shut down a coal-fired power plant in Kent, were acquitted after arguing what’s known in law as a “necessity defence”.

The defendants successfully argued that their actions were legally justified since they were intending to prevent the far greater harms to society posed by climate change. The nine-person jury cleared the defendants of any wrongdoing by a majority verdict.

Unlike the “Heathrow 13”, whose lesser charges of aggravated trespass warranted a trial by magistrate, the reported £30,000 damages caused by “Kingsnorth Six” meant they appeared before a jury instead.

In January 2016, a judge allowed lawyers to present climate change as a necessity defence for the first time in the US, in the case of the “Delta Five”, a group of activists accused of obstructed a train carrying coal and crude oil.

The defence was less successful that time, however, with the same judge later ruling that the evidence was insufficiently strong for the jury to take into account in its verdict. The protesters were found guilty of trespass, though not guilty of obstructing the train, and spared jail time.

On the rare occasions when climate change has been used as a criminal defence, it’s not unknown for a climate scientist to be called on to give supporting evidence.

Dr James Hansen, veteran climate scientist and former director of the NASA Goddard Institute for Space Studies, appeared as an expert witness in both the “Kingsnorth Six” and “Delta Five” cases, and again in 2010 in the trial of 20 activists accused of planning to trespass on a coal plant near Nottingham.

In the trial of the “Heathrow 13”, Prof Alice Bows Larkin, a professor of climate science and energy policy at the University of Manchester, specialising in shipping and aviation emissions, gave evidence on behalf of the defence. She did not appear in court, instead submitting a written statement to the judge, parts of which were read out as a summary in court.

Bearing witness

Bows-Larkin’s statement begins with a general outline of the impact on climate change of carbon dioxide (CO 2 ) and other substances present in aircraft emissions, such as nitrous oxides, soot, water vapour and sulphur dioxides. She explains:

“Estimates of the historical warming…suggest that the total warming impact of aviation has been around twice that than would be caused by the CO 2 alone.”

Bows-Larkin then explains how, to be consistent with the legally-binding obligation in the Paris Agreement of limiting warming to “well-below 2C above pre-industrial levels”, emissions from the aviation sector, like all other sectors, will need to be reduced to near-zero. She says:

“The vast majority of academics working on climate change mitigation would agree that a rapid and significant reduction in the combustion of fossil fuels is needed in the coming decades…I am unaware of any analysis that can demonstrate how aviation could be an exception to this.”

The combination of growing demand and few technical options on the horizon that could dramatically reduce aircraft emissions means that the inability of the aviation industry to curb its environmental impact constitutes a public health risk, says Bows-Larkin. She says:

“All CO 2 emitting sectors are damaging to human health through contributing to further warming, but particularly concerning are sectors that do not foresee a significant cut in CO 2 going into the future.”

Bows-Larkin acknowledges the potential for technology, such as bioenergy with carbon capture and storage, to offset greenhouse gas emissions. But there is a big question mark over whether we can assume such technologies will materialise in time to meet climate targets, she explains.

Full text

Below is Bows-Larkin’s expert witness statement to the trial of the “Heathrow 13” in full, exactly as it was submitted to the judge.

It’s a detailed account of where the aviation industry sits alongside UK domestic and international law, and is worth reading in full. Or, for a flavour of exactly what the court heard, Raj Chada, partner at Hodge Jones & Allen and defence lawyer for four of the accused, has confirmed to Carbon Brief that sections 2.2, 2.6, 3, 8 and parts of 9 were read out in court as a summary of her testimony.

Main image: Plane Stupid activists and supporters wave placards in opposition to a third runway at Heathrow airport outside Uxbridge Magistrates court in West London.