On the 25th anniversary of its landmark 1992 "Warning to Humanity", the Union of Concerned Scientists has updated its concerns about the human race's response to the red alert over runaway consumption and dwindling resources:  We're blowing it.

"Humanity has failed to make sufficient progress in generally solving these foreseen environmental challenges, and alarmingly, most of them are getting far worse," they write in a letter signed by 15,000 scientists from various disciplines and from 184 different countries.  "Soon it will be too late to shift course away from our failing trajectory."

At the top of the list of things-we-did-to-ourselves is Global Warming.  The earth's average temperature has risen by more than half a degree Celsius since 1992, and annual carbon dioxide emissions have increased by 62 percent.

"Those who signed this second warning aren't just raising a false alarm.  They are acknowledging the obvious signs that we are heading down an unsustainable path," wrote Oregon State University ecologist William Ripple, the letter's lead author.  "We are hoping that our paper will ignite a widespread public debate about the global environment and climate."

But it gets worse:  The human population grew by 2 billion in 25 years.  The populations of all other mammals, reptiles, amphibians and fish have declined by nearly 30 percent, with over-fishing standing out as a problem.  The oceans have 75 percent more dead zones, area where life can't exist because of pollution or oxygen starvation.  Deforestation has gotten worse, soil is less productive.  Access to fresh water has declined by 26 percent per person.

The one bright spot is that the hole in the ozone layer has gotten smaller, thanks to phasing out chlorofluorocarbons - the chemicals once used in refrigerators, air conditioners, and aerosol cans.

Professor Ripple and his colleagues have formed a new independent organization called the Alliance of World Scientists to express concerns about environmental sustainability and the fate of humanity.