Close to 1,000 health professionals from around the world have thrown their weight behind an open letter asking the multi-billion pound health charity, the Wellcome Trust, to move its money out of fossil fuels on ethical grounds.

The letter invokes one of the foremost principles of medical ethics, asking the Trust to “do no harm” because of the current and future impacts of climate change on global public health.

The 946 signatories to the letter span the health profession and include nurses, academics, therapists, doctors, students, retired practitioners and dentists. While hundreds come from the UK, the US and Australia, many other countries such as Mexico, Colombia and Malaysia are also represented.

It is also signed by Dr Richard Horton and Dr Fiona Godlee, the respective editors of the Lancet and the British Medical Journal (BMJ); Dr Fiona Sim, chair of the Royal Society for Public Health as well as Prof Hugh Montgomery and Prof Anthony Costello, co-chairs of the UCL/Lancet commission, that launched a major report in June warning that climate change could put back medical advances by 50 years.

Many signatories told the Guardian that they are alarmed by the lack of understanding of climate change as a health issue, citing impacts such as increased diseases, extreme weather events and food, water and energy security leading to conflict, mass displacement and migration.

Dr Thomas Wassmer, lecturer in cell biology at Aston University told the Guardian: “For the UK academic community the Wellcome Trust is highly influential in terms of its funding for medical research. People living in areas of the Earth that will be turned into semi-permanent disaster zones by global warming will have a rather limited ability to benefit from Wellcome Trust-funded medical research. Science historians will look back at this episode and be left speechless by how pillars of the scientific community such as the Wellcome Trust got their priorities so catastrophically wrong.”

Many others described climate change specifically as a mental health issue, with some stating that they are already seeing the effects in their patients.

Lara Newton, a professional counsellor based in Colorado said: “I am concerned about climate change as a mental health issue. So many of the people with whom I work are lost and suffering from a feeling that the society in which they live doesn’t truly care about the quality of life for us humans, for the animals and the environment that we are wantonly destroying.”

Chris Bird, a retired biomedical scientist from the UK who specialised in haematology said: “I worked in the NHS for 30 years to improve people’s lives. climate change will negate my life’s work.”

The letter, which was co-ordinated by the global health NGO MedAct and the Climate and Health Council reads: “Divestment rests on the premise that it is wrong to profit from an industry whose core business threatens human and planetary health, bringing to mind one of the foundations of medical ethics – first, do no harm. We believe that, in aligning organisations’ investments with their aims and values, it goes beyond a ‘grand gesture’. The question is not only one of direct, short-term impacts, but of leadership. Health organisations such as the Wellcome Trust have considerable moral and scientific authority, and a decision to divest has the potential to influence policy-makers, other investors and the public, in the UK and internationally.”

Godlee told the Guardian: “This letter reflects the powerful new consensus among health professionals in the UK and beyond. We are deeply concerned about the threat of climate change to human health and survival. A decision by Wellcome to divest from fossil fuels and reinvest in alternative energy would be hugely important both symbolically and practically ... I am hugely encouraged by the strong voice now coming through from senior figures within healthcare globally calling for action to tackle climate change. Personally, of all the work I am involved in to improve health and healthcare through the BMJ, I consider this the most important.”

Sim said: “It has never been more important to act on climate change, and health professionals and policy makers should be doing everything in their power to join the dots in the public’s mind between the environment and health. As an internationally respected scientific organisation, the Wellcome Trust is especially well placed to demonstrate leadership in the quest to protect the long term health of the world’s population.”

In March the Guardian launched a campaign calling on the world’s two largest medical charities – the Wellcome Trust and the Gates Foundation – to divest from fossil fuels. More than 226,000 readers from around the world have since joined the campaign.

Jeremy Farrar, director of the Wellcome Trust, responded by writing in the Guardian: “We consider individual companies on their merits, including the extent to which they meet their environmental responsibilities, when we decide whether or not to invest or stay invested. All companies engaged in fossil-fuel extraction are not equal. We combine this approach with active engagement with the companies in which we invest.”

The letter from health professionals asks the Trust to make public “what, specifically, the Trust aims to achieve through shareholder engagement, and by when. We would particularly like to know at what point the Trust will divest should these aims not be met, whether on a company-by-company or sector-wide basis.”

The Trust has so far given one example of when shareholder engagement has led to progress: a shareholder resolution backed by Shell and BP which asks the companies to review the extent to which their business is in line with the trajectory of climate change. However, although the resolutions mandate extra reporting by the companies, they do not require any substantial change to the business.

Dr David McCoy, director of MedAct, said: “The Wellcome Trust is a socially responsible and leading scientific institution and the arguments it uses to support continued investment in fossil fuel companies must be taken seriously. However, we have looked at these arguments in detail and have found them wanting. We can only hope that the Wellcome Trust will take our counter-arguments as seriously as we have taken theirs.”

The letter follows similar calls by health professionals published in the BMJ, which were lead by McCoy and Dr Taavi Tilmann, a doctor and Wellcome Trust fellow who also signed the letter.

A spokesperson for the Wellcome Trust said: “The range of individuals and organisations working to improve human health is wide and it would be surprising if this community did not contain a diversity of opinion about how best to reduce carbon emissions. The Wellcome Trust believes that engagement with the small number of energy companies in which we invest gives us the best opportunity to contribute to change, but we understand and respect the views of those who disagree.”

Read the letter calling on the Wellcome Trust to divest from fossil fuels on grounds of medical ethics.