Pope Francis challenged governments on Sunday to take "drastic measures" to combat global warming and reduce the use of fossil fuels, saying the world was experiencing a climate emergency.

Francis issued his appeal, a written message for Sunday's World Day of Prayer for the Care of Creation, ahead of the United Nations Climate Action Summit this month in New York, a follow up to the 2016 Paris Agreement to curb global warming.

Calling the UN summit "of particular importance," he added:

"There, governments will have the responsibility of showing the political will to take drastic measures to achieve as quickly as possible zero net greenhouse gas emissions and to limit the average increase in global temperature to 1.5 degrees Celsius with respect to pre-industrial levels, in accordance with the Paris Agreement goals."

Francis has made many calls for environmental protection and has clashed over climate change with sceptics leaders such as US President Donald Trump, who has taken the US out of the Paris accord.

"We have caused a climate emergency that gravely threatens nature and life itself, including our own," the leader of the world's 1.3 billon Roman Catholics said in the message for the prayer day, which is marked by various Christian Churches.