Plot showing the variations, and relative stab...

Plot showing the variations, and relative stability, of climate during the last 12000 years. (Photo credit: Wikipedia)

Scientists Find an Abrupt Warm Jog After a Very Long Cooling

By ANDREW C. REVKIN (Dot Earth) March 9

There’s long been a general picture of the climate of the Holocene, the period of Earth history since the last ice age ended around 12,000 years ago. It goes like this: After a sharp stuttery warm-up following that big chill — to temperatures warmer than today — the climate cools, with the decline reaching bottom around 200 years ago in the period widely called the “little ice age.” (A graph produced by Robert Rohde for his Global Warming Art Web site years ago nicely captures the general picture.)

A new Science paper includes this graph of data providing clues to past global temperature. It shows the warming as the last ice age ended (left), a period when temperatures were warmer than today, a cooling starting 5,000 years ago and an abrupt warming in the last 100 years.
Science A new Science paper includes this graph of data providing clues to past global temperature. It shows the warming as the last ice age ended (left), a period when temperatures were warmer than today, a cooling starting 5,000 years ago and an abrupt warming in the last 100 years.

In a new study, researchers from Oregon State University and Harvard have analyzed 11,300 years of data from 73 sites around the world and added more detail to this picture. The work, posted online today, is being published Friday in the journal Science.

While the researchers, conclude that the globe’s current average temperature has not exceeded the warmth that persisted for thousands of years after the last ice age ended, they say it will do so in this century under almost every postulated scenario for greenhouse gas emissions.

In a news release, Candace Major, program director for ocean sciences at the National Science Foundation, which paid for the research, said:

The last century stands out as the anomaly in this record of global temperature since the end of the last ice age…. This research shows that we’ve experienced almost the same range of temperature change since the beginning of the industrial revolution as over the previous 11,000 years of Earth history – but this change happened a lot more quickly.

In sum, the work reveals a fresh, and very long, climate “hockey stick.”

The hockey stick climate analogy arose from a variety of studies of the last millennium or two of temperatures in the Northern Hemisphere, Arctic and planet. There’s a general pattern of a sharp warming from the 20th century onward. The shaft of the “stick” has a lot of wiggles and warps and still comes with substantial uncertainty, but the general pattern is well established. The Wikipedia entry is a reasonable starting point for reviewing varied views of this body of science.

 

While folks have long talked of “abrupt climate change” (as in NRC reports) as a plausible prospect, this paper builds on the idea that we’ve been in the midst of abrupt climate change since the early 20th century.

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