The UN has today urged business leaders to step up efforts to slash carbon emissions as part of a co-ordinated effort to rally support for tougher national climate targets at a crunch summit in New York in September.

In an open letter to business leaders, executives from across the UN urge firms to adopt science-based targets (SBT) to bring their emissions pathways in line with 1.5C degrees of warming.

A 1.5C SBT, which requires companies to reduce emissions to net zero by 2050 at the latest, is seen as one of the most ambitious corporate emissions targets available to large organisations. Only a handful of firms, including Tesco and BT, have adopted a 1.5C SBT, although they are growing in popularity.

The letter is signed by Lise Kingo, CEO and executive director of the UN Global Compact, one of the member organisations of the SBT initiative, alongside more than 20 leaders including UN General Assembly president María Fernanda Espinosa Garcés, UN climate chief Patricia Espinosa, and former Unilever CEO Paul Polman.

"We know that our ambition and actions need to be bolder if we are to stand any chance of winning this race," the letter reads. "That is why we are calling on you to step up and commit your business to set science-based targets aligned with limiting global temperature rise to 1.5C above pre-industrial levels."

The "visionary leaders" who commit their companies to a 1.5C target will be recognised at the upcoming summit in New York on September 23, the letter adds.

The September event is the centrepiece of UN Secretary-General Antonio Guterres' plan to encourage leaders to ratchet up their emissions reduction strategies ahead of the Paris Agreement entering fully into force in 2020.

Guterres' is calling on world leaders to come to New York with "concrete, realistic plans" to reduce emissions to net zero by 2050.

Ambassador Luis Alfonso de Alba, UN Special Envoy for the 2019 Climate Action Summit and one of the co-signatories to the letter, said a strong signal from business ahead of the event will help convince world leaders to bring forward more ambitious measures in September.

"Climate change requires an unprecedented effort from all sectors of society and business leadership demonstrated by setting science-based targets at 1.5C will send strong market signals as we look to identify the scalable and replicable solutions needed to secure a world where no one is left behind," he said.

Global support for net zero emission targets is growing fast. In recent months, Sweden, Finland, New Zealand, and the UK have all announced targets, while France and the EU  are considering net zero goals and Japan this week announced plans to become carbon neutral soon after 2050. Meanwhile, all of the leading Democrat candidates for next year's US presidential race have unveiled net zero emission plans.