My colleague John Lanchbery, who has died suddenly of sepsis aged 71, was a physicist and climate change expert.

A veteran of international climate change negotiations, John attended the Rio Earth summit in 1992, and every UN summit on climate change since, representing the RSPB and BirdLife International since 1998.

John’s deep knowledge of climate science and understanding of the world of international negotiations made him a quietly significant figure. He argued consistently for the protection of tropical forests as a key step towards meeting environmental goals, helping build alliances between conservation, development and human rights advocates.

He was so well known that negotiators sought him out in his usual haunts, whether at a coffee table in the conference halls, or with his fellow smokers, where he would share a mixture of physics, political analysis and gossip.

Born in Surbiton, south-west London, John was brought up on Christmas Island, in the Indian Ocean, and then in Tanzania, where his father, Bill Lanchbery, a mechanical engineer, ran a power station. His mother, Betty (nee Ball), was a furnishings designer. John returned to Britain to take his A-levels at Dulwich college, in south London.

John’s early career was at ERA Technology in the development of innovative thin film and microelectronics technologies for a variety of applications. Meanwhile he studied part-time for a degree in mathematics at the Open University and then a master’s in solid state physics at the City of London Polytechnic (now London Metropolitan University).

A year teaching at the Open University followed and in 1991 he started at Vertic, the NGO that supports the implementation of international agreements, working on climate change monitoring, which led to his engagement in the climate negotiations and ultimately working for the RSPB.

John operated through calm consideration, in both his scientific and personal lives. He was a rock for colleagues and a friend and mentor to many. He would always find time to explain the intricacies of the climate negotiations, enlivening the driest of topics with amusing anecdotes – especially over a glass of wine.

John is survived by his partner of 28 years, Nicola Jenkins, his son, Christopher, and daughter, Alexandra, from a marriage that ended in divorce; and by a granddaughter, Pippa.