Pope Francis will describe climate change as one of the "principal challenges" facing humanity and say it is mainly caused by human activity in his encyclical on the environment, according to a leaked draft of the upcoming papal document. The 192-page draft of Pope Francis's encyclical on the environment, Laudato Si, which will officially be released at a press conference in the Vatican’s synod hall on Thursday, has been leaked by an Italian magazine. The leaking of the draft by L'Espresso has been described as a "heinous act" by a Vatican spokesman, who also added that the leaked document was "not the final text". According to a translation by the Wall Street Journal, the Pope says there is a “very consistent scientific consensus that we are in the presence of an alarming warming of the climatic system.” He writes that there is an “urgent and compelling” need for policies that reduce carbon emissions, such as “replacing fossil fuels and developing sources of renewable energy.” He adds that “numerous scientific studies indicate that the greater part of global warming in recent decades is due to the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxide and others) emitted above all due to human activity” and calls on people to change their lifestyles.