Protesters who allegedly blockaded the entrance to Australia's peak body for oil and gas claim "civil disobedience" is the only way to combat the "galloping nature of the climate crisis".
"We need to go further. I believe we are actually at the end game," Anna Molan told the ACT Magistrates Court on Tuesday.
"If our governments won't save us, we have to save ourselves," she said while giving evidence.
Molan, alongside John Max Wurcker, Nicholas Orde Jamison Abel, Katherine Kelly, and Catherine Anne Adams, is charged with one count each of unreasonable obstruction.
They have all pleaded not guilty.
The five defendants were arrested on February 27 at an Extinction Rebellion protest.
They are accused of blocking two entrances to the Australian Petroleum Production and Exploration Association building.
Lawyer Bernard Collaery flagged his intention to argue the protesters believed their actions were the only reasonable way to deal with a sudden or extraordinary emergency, meaning they could not be held criminally responsible.
In the hearing, commonwealth prosecutor Luke Fomiatti said the activists had blocked entry to the Marcus Clarke Street building and refused to leave.
Three of the protesters had super glued their hands to the building with police officers eventually using acetone to free them.
Mr Fomiatti said police arrested the five defendants after waiting about 40 minutes for them to move.
"The prosecution concedes ... not that there is a climate emergency, per se, but that the defendants reasonably believe that circumstances of extraordinary emergency exist," he stated.
On the stand on Tuesday, Kelly said climate change was "an existential threat to humanity and other creatures on the planet".
"Our children are going to have to face this," Kelly told the court while crying.
"I've been standing on roadsides with banners for years, been to see my local MP and other MPs, I've done all of those things that I can think people do ... and it seems to be falling on deaf ears."
Giving evidence, Molan told the court she was "increasingly alarmed at the galloping nature of the climate crisis".
"We are facing a dire emergency the likes of which human kind has never had on this planet," she said.
"There ought to be a mass movement to stop the gas industry in particular from cashing in on our destruction."
In body-worn camera footage played to the court, the activists can be seen standing or sitting in front of the building with an inflatable dinghy while wearing life jackets.
As police officers arrested and escorted the defendants, other protesters could be heard clapping and cheering.
While the footage was being played, Wurcker could be seen reading a book while sitting in the public gallery.
When he took the stand, Wurcker said "non-violent direct action" was one of the only ways to combat climate change.
Abel told the court he broke the law knowing the consequences.
"If it wasn't for the emergency I wouldn't have done it," he said.
The hearing before magistrate Ian Temby is set to run for three days.
