Earth Nears Warmest in 12,000 Years

Sept. 25, 2006 — Earth's climate is now moving into unknown territory — warming up more than any time in the last 12,000 years, report top U.S. climate researchers. Accelerated warming over the last 30 years has pushed up world surface temperatures to the highest they've been since the last ice age ended.

And the mercury is still rising.

That means there is no time to waste in slowing the burning of fossil fuels that releases the majority of greenhouse gases which, in turn, are causing the warming, say the researchers.

The alarming conclusion is based on climate data gathered from instruments around the world over the last century, combined with ancient paleoclimate data from ocean sediments. The conclusions are reported in a paper in the current issue of the Proceedings of the National Academy of Sciences.

The paleoclimate data indicate more than just a 12,000-year record on the brink of being smashed. We are now closing in on the warmest climate for any of the warm periods between ice ages — called interglacials — in the last million years, said James Hansen of NASA's Goddard Institute for Space Studies.

"We're within one degree Celsius (1.8 degrees Fahrenheit) of the warmest interglacial," Hansen told Discovery News.

That's a crucial degree, he said. If warming can be held below that level, the effects of global warming should stay within those of other interglacials, which were fairly similar to today.

"But if further global warming reaches 2 or 3 degrees Celsius," said Hansen, "we will likely see changes that make Earth a different planet than the one we know."

The last time Earth's climate exceeded that critical 1 degree Celsius was in the Pliocene, three million years ago, when sea level was 25 meters (80 feet) higher than today. Among the possible effects are more La Niña events in the Pacific, followed by an almost permanent El Niño condition, which causes droughts, floods and other dramatic weather changes worldwide.

The 20th century data show that Earth has been warming at the steep rate of approximately 0.36 degrees Fahrenheit (0.2 degrees Celsius) per decade for the past 30 years. This pretty much matches the warming rate predicted in the 1980s in the first global climate simulations of the effects of rising greenhouse gases.

"The big picture is very clear," said paleoclimatologist Christina Ravelo of the University of California at Santa Cruz. Ravelo has been looking for signs of what El Nino did during the Pliocene, when things were so much warmer, in hopes of finding clues to our the future, if global warming continues unabated.

Her work suggests a permanent El Niño can develop.

"People can get hung up on the details," said Ravelo, regarding what different climate models predict for specific cities or regions. "Even if we don't know exactly what's going to happen, we know it's going to happen."

Over the last few years those details have been getting clearer, said Hansen, but he agreed that they needn't be for people to start acting now to prevent a climate crash.

"It's clear from the science that there are fairly strong limits on what we can put into the atmosphere if we want to avoid impacts," said Hansen. "There is a big gap between what's understood (by scientists) and what is known" by decision makers.

And time is running out fast, he said.