The denial of climate change is not just ignorant, but “malign and evil”, according to Mary Robinson, because it denies the human rights of the most vulnerable people on the planet.

The former UN high commissioner for human rights and special envoy for climate change also says fossil fuel companies have lost their social licence to explore for more coal, oil and gas and must switch to become part of the transition to clean energy.

Robinson will make the outspoken attack on Tuesday, in a speech to the Royal Botanical Gardens at Kew in London, which has awarded her the Kew International Medal for her “integral work on climate justice”.

She also told the Guardian she supports climate protests, including the school strikes for climate founded by “superstar” Greta Thunberg, and that “there is room for civil disobedience as a way of communicating, though we also need hope”.

Robinson is chair of the Elders, an independent group of global leaders founded by Nelson Mandela that works for human rights. She will say in her speech: “I believe that climate change denial is not just ignorant, it is malign, it is evil, and it amounts to an attempt to deny human rights to some of the most vulnerable people on the planet.”

“The evidence about the effects of climate change is incontrovertible, and the moral case for urgent action indisputable,” she will say.

“Climate change undermines the enjoyment of the full range of human rights – from the right to life, to food, to shelter and to health. It is an injustice that the people who have contributed least to the causes of the problem suffer the worst impacts of climate change.”

Robinson, a former president of the Republic of Ireland, told the Guardian her angry words were the result of seeing the impact on people’s lives. “In Africa, I saw the devastating impacts on poor farmers, villagers and communities when they could not predict when the rainy season was going to come.”

She also attacks big oil, gas and coal companies in her speech. She is expected to say: “We have entered a new reality where fossil fuel companies have lost their legitimacy and social licence to operate.” She says exploration for new reserves must end, given that most of existing reserves must be kept in the ground if global warming is to be tackled.

Robinson condemns the UK government for the £4.8bn support given by its export finance body for fossil fuels from 2010-16. “It stirs painful memories of past exploitative behaviour to see the UK and other rich, industrialised countries proclaim their good intentions and act in a progressive way at home, whilst effectively exporting their emissions to poorer foreign countries and leaving them to pay the price socially and environmentally.”

The US president, Donald Trump, is also criticised by Robinson for his “egregious act of climate irresponsibility” in withdrawing from the Paris climate agreement. “Bad leadership has consequences now that are really bad for the people in the poorest communities, including in the US,” she told the Guardian.

Robinson says as well as taking personal action – she has given up meat – people need to get angry with those who have more power and are not meeting their responsibilities, saying: “Just as the suffragettes needed to embrace militant tactics to win the fight for female emancipation, so today we need to be fiercely determined to challenge vested interests, especially in the fossil fuel sector.”

There have been several strong attacks on climate change denial in recent months, with critics saying that proposals in the US for a new national security council panel of climate change deniers are “Stalinist”.

In November, the New York Times columnist Paul Krugman said: “Smoking kills people, and tobacco companies that tried to confuse the public about that reality were being evil. But climate change isn’t just killing people; it may well kill civilisation. Trying to confuse the public about that is evil on a whole different level. Don’t some of these people have children?”

The BBC accepted in September it gets coverage of climate change “wrong too often” and told staff: “You do not need a ‘denier’ to balance the debate.”