* Pope returns to Rome after African trip
* Holds trademark airborne news conference
* Speaks of climate change, Africa, development
* Says Paris summit last chance to thwart disaster
By Philip Pullella
ABOARD THE PAPAL PLANE, Nov 30 (Reuters) - The U.N. climate conference in Paris is most likely humanity's last chance to thwart global environmental disaster, Pope Francis said on Monday, warning the world was "at the limits of suicide".
The pope, who wrote a major document on the environment last June, made the comment in an hour-long news conference aboard the plane returning him to Rome at the end of a six-day trip to Africa.
The freewheeling conversations have become a trademark of his papacy and the few times he takes direct questions from journalists.
Francis, who visited Kenya, Uganda and the Central African Republic, also said the continent was "a martyr of exploitation" by wealthy countries who lust after its natural resources and try to impose Western values instead of concentrating on development.
The pope was asked if the U.N. climate summit in Paris would mark a turnaround in the fight against global warming.
"I am not sure, but I can say to you 'now or never'," he said. "Every year the problems are getting worse. We are at the limits. If I may use a strong word I would say that we are at the limits of suicide."
He spoke of retreating glaciers in Greenland and low-lying countries at risk from rising sea levels.
"I am sure that the (Paris delegates) have goodwill to do something. I hope it turns out this way and I am praying that it will," he said.
World leaders launched an ambitious attempt on Monday to hold back the earth's rising temperatures, with the United States and China -- the world's biggest carbon emitters -- urging the U.N. climate summit in Paris to mark a decisive turn in the fight against global warming.
The pope's last stop in Africa was the Central African Republic, one of the continent's poorest nations.
He made an unscheduled stop at the country's only paediatric hospital, where doctors told him that they did not have oxygen and that most of the children there were destined to die of malnutrition or malaria.
He delivered medicines donated by a Rome hospital.
"Africa is a victim," he said. "Africa has always been exploited by other powers ... there are some countries that want only the great resources of Africa.
"But they don't think about developing the countries, about creating jobs. Africa is martyr, a martyr of the exploitation of history," he said.
He sidestepped a question about the Church's ban on the use of condoms to stop the spread of HIV-AIDS, saying it was reductive to talk about condoms while African countries were mired in poverty, social injustice, wars and human trafficking.
The pope confirmed that next year he planned to visit Mexico and hoped to be able to visit Armenia.
"But I am old and these trips are heavy," he said. (Reporting By Philip Pullella; Editing by Janet Lawrence)