Increased logging and burning in the Amazon rainforest will worsen already disastrous droughts, a leading Brazilian scientist warned in a new report on climate change.

Trees in the Amazon rainforest emit into the atmosphere the equivalent of 20 billion tons of water daily, Antonio Donato Nobre, a researcher at Brazil's National Institute for Space Research, told AFP in an interview Monday.

They do this, in part, through "aerial rivers and vaporclouds" that form over the forest and bring rain to thousands of kilometers of terrain to the southeast, he said.

"It's like a pump sending water to other regions," said Nobre.

"The problem is we are destroying the source of these rivers," he stressed.

Over the last two decades, the Amazon has lost 763,000 square kilometers (295,000 square miles) of forest -- an area twice the size of Germany.

"That is 2,000 trees per minute," said Nobre.

Already the mega-city of Sao Paulo is suffering its worst drought in a century, the scientist noted.

He credited Brazil with reducing deforestation over the last decade, from 27,000 square kilometers a year in 2004 to 4,000 square kilometers in 2012.

But he warned that "a new forestry code gave an amnesty to deforesters and sent out a signal of impunity so it all started afresh."

Moreover, he said, "zero deforestation is not enough."

"We must replant the forest and recreate ecosystems in degraded zones. We are destroying the ecosystem," said Nobre, adding similar urgency must be shown to save forests elsewhere, including Congo and Siberia.

"Governments around the world, businessmen and elites must act as they did in the face of the (economic) crisis of 2008. In a fortnight they found trillions of dollars to save the banking system.

"We must do the same to avoid falling into the climactic abyss and save humanity -- and it will not even cost as much."