A new global pact on climate change, due to be signed this year in Paris, should be a “Magna Carta for the Earth”, Prince Charles has urged.

He said this year marked potentially the “last chance” to save the world from the perils of global warming, with the Paris conference and the United Nations’ plan to replace the millennium development goals with a new set of sustainable development targets. “We simply cannot let this opportunity go to waste. There is just too much at stake, and has been for far too long.”

He told a meeting of forestry and climate experts in London: “In the 800th anniversary year of the Magna Carta, perhaps this year’s agreement of the new sustainable development goals and a new climate agreement in Paris should be seen as a new Magna Carta for the Earth, and humanity’s relationship with it.”

But he warned of difficulties ahead as the negotiations build up: “[This is] an absolutely crucial opportunity, if not the last chance before we end up in an irreversible situation, for the international community to establish a new set of interlocking, coherent and ambitious frameworks governing human development, poverty, disaster risk reduction, the natural environment and climate change. We could, and should, see an agenda set for the coming decades that is capable of transforming the prospects for humanity by improving and nurturing the state of the planet upon which we all depend.”

His insistence that 2015 will be a make-or-break year for the climate, and environmental sustainability, were echoed by Mary Robinson, former president of Ireland and now the UN’s special envoy for climate change, charged with bringing nations together for a successful outcome at the Paris conference in December.

She told the Guardian: “This is the most important year since 1945. In 1945, at the end of the second world war, we got the charter for the United Nations, the international institutions [that embodied it], the Marshall Plan, and a few years later we got the Universal Declaration of Human Rights. This year we have to get a similar order of decisions, which will determine the future for decades, and longer.”

She pointed to the possible Paris agreement and the sustainable development goals as twin aims that would complement each other in building a more environmentally and socially secure future for the world.

At Paris, governments are expected to sign a new global pact by which nearly all of the world’s nations, both developed and developing, would set out clear targets and measures to curb greenhouse gas emissions, to come into effect from 2020. These goals would replace the current targets, set out in 2009 at the Copenhagen summit, to curb emissions – and, in the case of industrialised nations, to make absolute cuts in carbon output – by the end of this decade

Already, the world’s two biggest emitters and economies – the US and China – have set out carbon targets, in the case of the US to cut by 26% to 28% by 2025, compared with 2005 levels, and in China’s case to cause emissions to peak by 2030. The EU has also set out its plans for a 40% cut in emissions by 2030, compared with 1990 levels. Other major economies are expected to come forward with their proposals by April, followed by a period in which the plans will be evaluated before the crunch negotiations take place over two weeks in December.

However, emissions targets – and the crucial question of whether they will be adequate to stave off the worst effects of global warming – are not the only sticking point. Developed countries are also being urged to reassure poorer nations that they will provide financial assistance to help them cut carbon and cope with the effects of climate change, amounting to more than the $100bn a year that should be flowing to the developing world by 2020. As yet, there is no agreement on this.

Separately, but also under the auspices of the UN, governments are expected to pass a set of goals on issues as diverse as poverty, environmental protection, water, nutrition and health, to take over from the millennium development goals that expire this year.

Robinson said both were needed. “On Paris, I am increasingly hopeful that we will get an agreement. But that will not come into effect until 2020. The sustainable development goals will come into effect next year, and they will be vital to the pre-2020 period,” she explained.

She added: “This is the most important year of my lifetime, for the sake of future generations and to see intergenerational justice. We cannot miss this opportunity.”