The message updates an original warning sent from the Union of Concerned Scientists that was backed by 1,700 signatures 25 years ago.
And "scientists, media influencers and lay citizens" aren't doing enough to fight against it, according to the letter.
If the world doesn't act soon, there be catastrophic biodiversity loss and untold amounts of human misery, they warn.
But humanity isn't doing nearly enough to make the most of them and soon won't be able to reverse its fate.
"Soon it will be too late to shift course away from our failing trajectory, and time is running out," the letter warns.
"We must recognize, in our day-to-day lives and in our governing institutions, that Earth with all its life is our only home.".
Prof Ripple and his colleagues have formed a new independent organisation called the Alliance of World Scientists to voice concerns about environmental sustainability and the fate of humanity. »
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