Global warming is epic, long-term study says

Image Credit: Carbon Dioxide Information Analysis Center

From CNN with comments below by WUWT regular Just The Facts:

Global warming has propelled Earth’s climate from one of its coldest decades since the last ice age to one of its hottest — in just one century.

A heat spike like this has never happened before, at least not in the last 11,300 years, said climatologist Shaun Marcott, who worked on a new study on global temperatures going back that far.

“If any period in time had a sustained temperature change similar to what we have today, we would have certainly seen that in our record,” he said. It is a good indicator of just how fast man-made climate change has progressed.

A century is a very short period of time for such a spike.

It’s supposed to be cold

The Earth was very cold at the turn of the 20th century. The decade from 1900 to 1909 was colder than 95% of the last 11,300 years, the study found.

Fast forward to the turn of the 21st century, and the opposite occurs. Between 2000 and 2009, it was hotter than about 75% of the last 11,300 years.

If not for man-made influences, the Earth would be in a very cold phase right now and getting even colder, according the joint study by Oregon State University and Harvard University. Marcott was the lead author of the report on its results. Read More

Here is the National Science Foundation article that the CNN article appears to be based upon and here is the paper, A Reconstruction of Regional and Global Temperature for the Past 11,300 Years, published in Science today. This is the abstract:

Surface temperature reconstructions of the past 1500 years suggest that recent warming is unprecedented in that time. Here we provide a broader perspective by reconstructing regional and global temperature anomalies for the past 11,300 years from 73 globally distributed records. Early Holocene (10,000 to 5000 years ago) warmth is followed by ~0.7°C cooling through the middle to late Holocene (<5000 years ago), culminating in the coolest temperatures of the Holocene during the Little Ice Age, about 200 years ago. This cooling is largely associated with ~2°C change in the North Atlantic. Current global temperatures of the past decade have not yet exceeded peak interglacial values but are warmer than during ~75% of the Holocene temperature history. Intergovernmental Panel on Climate Change model projections for 2100 exceed the full distribution of Holocene temperature under all plausible greenhouse gas emission scenarios.

While the warming of the second half of the 21st century, and its causes, are the subject of vigorous debate, the fundamentally erroneous element of the CNN article above is the attribution of warming from the first half of the 21st century to human influence. Per Overpeck et. al 1997:

“Together, they indicate that the Arctic has warmed up to 1.5°C since 1850 – the coolest interval of the Arctic “Little Ice Age.” Much of the recent Arctic warming took place between 1850 and 1920, most likely due to natural processes”

If you look at anthropogenic CO2 emissions;

it is apparent that the anthropogenic contribution to CO2 concentrations was minimal prior to 1945, thus attribution of the warming that occurred prior to 1945;

to “man-made influences”, is fundamentally erroneous. CNN should correct this error in their article.

For further information on Earth’s paleoclimate please visit WUWT’s under construction Paleoclimate Reference Page.