A group of 150 prominent UK and international lawyers has called on law firms and in house lawyers to be ethically obliged to advise clients of the risks associated with deals at odds with the UN's climate change targets.

In an open letter to the legal profession, published this week, the signatories argue that lawyers whose work is incompatible with limiting global warming expose themselves and their clients to substantial legal risk as well as the real-world risk of catastrophe.

It urges lawyers to understand the extreme risks of the world exceeding the 1.5˚C increase in temperature limit set by the Paris Agreement and ‘advise their clients, where relevant and appropriate, of the serious risks (legal and otherwise) of pursuing any investment, project or transaction that is inconsistent' with the agreement.

A number of King's Counsel (KCs) specialising in environmental law are among the signatories, including Estelle Dehon, of Cornerstone Barristers, and Paul Brown, of Landmark Chambers, which acted for the UK Government in legal challenges to the expansion of Heathrow airport in London.

Another signatory is Jolyon Maugham KC, founder of campaign group Good Law Project, which published the letter along with registered UK charity Plan B, which support's strategic legal action against climate change.

Others signatories include UN legal adviser and former Freshfields Bruckhaus Deringer partner Paul Watchman, Farhana Yamin, a lawyer and climate activist known for being an architect of the Paris Agreement, and Dr Gearóid Ó Cuinn, director of Global Legal Action Network. 

The letter noted UN Secretary General António Guterres’s warning in April that: “We are on a pathway to global warming of more than double the 1.5°C limit agreed in Paris. Some Government and business leaders are saying one thing, but doing another. Simply put, they are lying. And the results will be catastrophic.”

The letter highlights a scorecard produced by US Law Students for Climate Accountability last year that ranked leading global law firms from A to F, based on the impact of their legal advice on climate change. Only a trio of firms – Cooley, Schulte Roth & Zabel and Wilson Sonsini Goodrich & Rosati – achieved an ‘A’ grade, while an array of top firms received the lowest ‘F’ grade. 

‘Our lawyers advise on these deals and defend them in court, actively undermining the international community’s commitment to reduce carbon dioxide emissions as a matter of urgency,’ the letter says, adding: ‘It is unconscionable to pursue a course of conduct for short-term profit knowing that it exposes the public to intolerable risks of disaster.’ 

The letter brings to the fore the difficulty law firms face reconciling pledges to conduct their businesses in a sustainable manner - which extend to cross-profession initiatives such as the Greener Litigation Pledge - with the impact of their advisory work for longstanding clients in a highly competitive market. 

But it also emphasises the legal risk that activities that accelerate global warming could pose to lawyers’ clients, pointing to a ruling by the Massachusetts high court earlier this year that ExxonMobil must face trial over accusations it lied about the climate crisis and covered up the fossil fuel industry’s role in worsening environmental damage.

Last year, an open letter signed by more than 100 Canadian lawyers urged Prime Minister Justin Trudeau and the incoming minister of justice and attorney general to protect Canadian citizens from the destabilising effects of climate change.