Pope Francis on Wednesday praised youth climate campaigners for their efforts to tackle global warming and encouraged them to carry on with their work "for the good of humanity".

Thousands of young activists have converged on Milan this week for a Youth4Climate event, with some 400, from about 190 countries, due to engage with policymakers to hammer out proposals for tackling climate change.

"It is said that you are the future, but in these matters, you are the present, you are those who are making the future today, in the present," the Pope told participants in a video message.

Francis has strongly supported the goals of the 2015 U.N. Paris accord to reduce global warming, and Scotland's bishops have said he will take part in the COP26 global climate summit in Glasgow in November, health permitting.

Since becoming pope in 2013, he has repeatedly urged governments to take drastic measures to combat global warming and reduce the use of fossil fuels.

In 2015, Francis wrote an encyclical on the need to protect the environment, reduce wasteful lifestyles, stem global warming and protect the poor from the effects of climate change.

"It is time to take wise decisions so that we can make use of the many experiences gained in recent years, in order to make possible a culture of care, a culture of responsible sharing," the pope told the activists.

"There must be harmony between people, men and women, and the environment. We are not enemies: we are not indifferent. We are part of this cosmic harmony."