In a joint declaration made in London, climate scientists, physicists, biologists, engineers and others from at least 20 countries, including Australia, broke with the caution traditionally associated with academia to side with peaceful protesters from The Netherlands to Australia.

Wearing white laboratory coats to symbolise their research credentials, a group of about 20 of the signatories gathered on Saturday to read out the text outside London's Science Museum.

"We believe that the continued governmental inaction over the climate and ecological crisis now justifies peaceful and non-violent protest and direct action, even if this goes beyond the bounds of the current law," said Emily Grossman, a science broadcaster with a PhD in molecular biology, who read the declaration on behalf of the group.

"We therefore support those who are rising up peacefully against governments around the world that are failing to act proportionately to the scale of the crisis," she said.

The declaration was co-ordinated by a group of scientists who support Extinction Rebellion, a civil disobedience campaign that formed in Britain a year ago and has since sparked offshoots in dozens of countries.

The group launched a fresh wave of international actions on Monday, aiming to get governments to address an ecological crisis caused by climate change and accelerating extinctions of plant and animal species.

A total of 1,307 volunteers had since been arrested at various protests in London by Saturday, Extinction Rebellion said. A further 1,463 volunteers have been arrested in the past week in another 20 cities, including Brussels, Amsterdam, New York, Sydney and Toronto, according to the group's tally. More protests in this latest wave are due in the coming days.

While many scientists have tended to shun overt political debate, preferring to confine their public pronouncements within the parameters of their research, the academics backing Extinction Rebellion say they feel compelled to speak out.

"The urgency of the crisis is now so great that many scientists feel, as humans, that we now have a moral duty to take radical action," Grossman told Reuters.

Other signatories included several scientists who contributed to the UN-backed Intergovernmental Panel on Climate Change, which has produced a series of reports underscoring the urgency of dramatic cuts in carbon emissions.

Extinction Rebellion has electrified supporters who said they had despaired at the failure of conventional campaigning to spur action. But its success in paralysing parts of London has also angered critics who complained the movement has inconvenienced thousands of people and diverted police resources.

The group said more than half the signatories of the declaration are experts in the fields of climate science and the loss of wildlife. Although British universities and institutes were well represented, signatories also worked in countries including Australia, the United States, Spain and France.

Australian Associated Press