The Head of Conservation at a Christian charity is appealing to the new Prime Minister to attend the COP27 climate summit in Egypt next month.
Rishi Sunak has been accused of "a failure of leadership" after No 10 yesterday said he would not attend the conference.
Opposition parties and environmental groups said the decision suggested the government was not taking the climate crisis seriously enough.
Andy Lester told Premier the Prime Minister needs to think again: "The bottom line with Rishi Sunak is he's our new leader. Yesterday they announced that he wouldn't be attending alongside President Putin, which I think sends out entirely the wrong message.
"So our message to Rishi Sunak is very simple. We need you. It's the most important climate conference in the history of the COP summits. We need you there; you are our new leader, and we're expecting you to represent us. And we would very much hope that you don't join the ranks of those like Vladimir Putin in not attending."
Sunak's predecessor, Liz Truss, had planned to attend the conference, but the Environment Secretary Therese Coffey suggested the summit in Sharm El-Sheikh isn't as high profile as last year's event in Glasgow.
Downing Street said Rishi Sunak had "other pressing domestic commitments" which will prevent him from going to COP27, but that he remains "absolutely committed" to supporting the event.
It comes as the UN environment agency said countries' pledges to cut carbon emissions had been "woefully inadequate" and there was "no credible 1.5C in place".
Andy Lester says prayer is critical to the Christian response to climate change:
"We all believe in the power of prayer. We recognise that prayer is critical. We recognise that without prayer, we can often not move the major mountains. And so we can kneel down as a community and say, Lord, our nation, our world is in trouble because of climate change. Let us kneel down and pray before you and seek your face. Ask for your forgiveness for the way we have lived our lives and ask an appeal to you to help intervene in the situation."