A massive alliance of more than 11,000 scientists have signed, sealed and delivered an important message to the world: if we don't make rapid, deep and lasting changes to our lives, they write, there will soon come "untold human suffering".
For more than 40 years, the word's scientists have warned of a looming climate crisis, and yet so far, their cries have been met with little attention and even fewer changes.
Now, in the throes of a global emergency, with the echoes of their foresight gradually fading, experts have no choice but to try, try again.
"Scientists have a moral obligation to warn humanity of any great threat," says environmental scientist Thomas Newsome from the University of Sydney.
"From the data we have, it is clear we are facing a climate emergency."
Two years after authoring one of the most talked about climate papers - signed by the largest international group of scientists ever - Newsome and his colleagues have penned another urgent warning to the world.