The pope has issued a stark warning over the urgent need to tackle "extraordinary climate change and an unprecedented destruction of ecosystems" in an eagerly-awaited message on the environment.

In the encyclical Pope Francis has written, he said climate change was mostly down to human activity and policies were urgently needed to cut carbon emissions, such as by reducing fossil fuels and developing renewables.

People in wealthy countries need to change their unsustainable lifestyles, as exploitation of the planet has already exceeded acceptable limits and millions of tonnes of waste are being generated, making the Earth look more and more "like an immense pile of filth".

In a hard-hitting message on environmental degradation and poverty, the pontiff warned that "doomsday predictions can no longer be met with irony or disdain", and that resource shortages could lead to new wars.

Setting out the moral case for action on the environment, the pope said climate change represented "one of the principal challenges facing humanity in our day", and warned its worst impact would be felt in poorer countries.

"We are faced not with two separate crises, one environmental and the other social, but rather with one complex crisis which is both social and environmental," he warned.

The papal encyclical, a letter sent to 5,000 Catholic bishops worldwide, is published in five languages and the pontiff has said the document is "addressed to everyone", not just the world's 1.2 billion Catholics.

The pontiff has spoken before on the effects of climate change on people and nature but the encyclical comes ahead of a UN meeting to decide new "sustainable development goals" in September and crucial international talks aimed at securing a new global climate deal in Paris at the end of the year.

In the face of opposition from conservative climate sceptics in the US, including many Catholics, the pope spells out human responsibility for climate change.

"A very solid scientific consensus indicates that we are presently witnessing a disturbing warming of the climatic system," he writes.

"Humanity is called to recognise the need for changes of lifestyle, production and consumption, in order to combat this warming or at least the human causes which produce or aggravate it."

Though he acknowledged other factors influencing the climate, he said: "A number of scientific studies indicate that most global warming in recent decades is due to the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxides and others) released mainly as a result of human activity."

And he warned: "If present trends continue, this century may well witness extraordinary climate change and an unprecedented destruction of ecosystems, with serious consequences for all of us."

He said: "There is an urgent need to develop policies so that, in the next few years, the emission of carbon dioxide and other highly polluting gases can be drastically reduced, for example, substituting for fossil fuels and developing sources of renewable energy."

And he attacked the extreme consumerist lifestyle, warning: "We all know that it is not possible to sustain the present level of consumption in developed countries and wealthier sectors of society, where the habit of wasting and discarding has reached unprecedented levels.

"The exploitation of the planet has already exceeded acceptable limits and we still have not solved the problem of poverty."

He also spoke out against the destruction of the natural world by human beings, saying: "Because of us, thousands of species will no longer give glory to God by their very existence, nor convey their message to us. We have no such right."

In what will be seen as an attack on opponents of climate change action, the pope said previous failures of global meetings on the environment showed there were too many special interests, and economic interests ended up "trumping the common good and manipulating information so that their own plans will not be affected".

He criticised efforts to develop carbon trading schemes, with buying and selling of "carbon credits", warning they could lead to a new form of speculation which would not help reduce greenhouse gas emissions worldwide.

And he said: "Reducing greenhouse gases requires honesty, courage and responsibility, above all on the part of those countries which are more powerful and pollute the most."

ARCHBISHOP'S PRESENTATION

Archbishop Charles J. Scicluna will give a presentation on the encyclical on Wednesday at 7pm at the seminary in Tal-Virtu, Rabat.

The presentation is open for the public.