The world's oldest tree has been found in Sweden, a tenacious spruce that first took root just after the end of the last ice age, more than 9,500 years ago.

	The tree has rewritten the history of the climate in the region

The tree has rewritten the history of the climate in the region, revealing that it was much warmer at that time and the ice had disappeared earlier than thought.

Previously, pine trees in North America were thought to be the oldest, at around 5,000 years old.

But Swedish scientists report that in the mountains, from Lapland in the north to Dalarna in central Sweden, there are much more ancient spruce trees (Picea abies).

Prof Leif Kullman at Umeå University and colleagues found a cluster of around 20 spruces that are over 8,000 years old.

The oldest tree, in Fulu Mountain, Dalarna (“the dales”), was dated by carbon dating at a laboratory in Miami, Florida to 9,550 years old and around it were generations of clones 375, 5,660 and 9,000 years old that have the same genetic makeup.

According to a report in National Geographic News, average tropical temperatures during that era of the Cretaceous exceeded 100 degrees Fahrenheit (38 degrees Celsius), and the Polar regions were in the 50-degree-Fahrenheit (10-degree-Celsius) range.

In fact, atmospheric levels of the greenhouse gas carbon dioxide were four times higher then than they are today, scientists estimated.

While high, though, that doesnt seem to be sufficient to get the type of warmth that the temperature data suggest, said Lee Kump, a geologist at Pennsylvania State University.

There are several global climate models (GCMs) produced by many different groups. There are a half dozen from the USA, some from the UK Met Office, a well known one from Australia, and so on. GCMs are a truly global effort. These GCMs are of course referenced by the IPCC, and each version is known to the creators of the other versions.

Much is made of the fact that these various GCMs show rough agreement with each other. People have the sense that, since so many “different” GCMs agree, we should have more confidence that what they say is true. Today I will discuss why this view is false. This is not an easy subject, so we will take it slowly.

Suppose first that you and I want to predict tomorrow’s high temperature in Central Park in New York City (this example naturally works for any thing we want to predict, from stock prices to number of people who will vote for a certain USA presidential candidate). I have a weather model called MMatt. I run this model on my computer and it predicts 66 degrees F. I then give you this model so that you can run it on your computer, but you are vain and rename the model to MMe. You make the change, run the model, and announce that MMe predicts 66 degrees F.

As Climate Science offers, we are open to the presentation of announcement of papers and of viewpoints by individuals actively involved in the climate science and climate policy community who want to widely distribute their views and analyses on climate science. Today, Climate Science presents a guest weblog by Christopher Monckton on the issue of radiative feedback.  Christopher Monckton has been an outspoken commentator on climate policy issues, however, his guest weblog on Climate Science concerns a science issue; namely what is the magnitude of the radiative feedback as reported by the IPCC? Climate Science has weblogged on this subject in

Climate Metric Reality Check #1 - The Sum Of Climate Forcings and Feedbacks Is Less Than The 2007 IPCC Best Estimate Of Human Climate Forcing Of Global Warming

Other climate scientists are encouraged to submit guest weblogs which support or seek to refute the analysis presented below. Ultimately, each contribution of this type needs to be submitted to peer reviewed scientific journals which is the most appropriate aribitrator of science.

What if there’s no way to cut greenhouse emissions enough to make a real difference?

That’s the question raised by a commentary in Nature arguing that the Intergovernmental Panel on Climate Change has been too optimistic in its projections for the technological possibilities of reducing greenhouse emissions. Their calculations are called “a bombshell” in a separate news article in Nature about the paper. My colleague Andy Revkin analyzes it at DotEarth. The commentary was written by the political scientist Roger Pielke Jr., the climatologist Tom Wigley, and the economist Christopher Green.

I asked the lead author, Dr. Pielke, what implications he draws from his work:

As an alternative, Benford has cooked up a plan that amounts to a manmade Mount Pinatubo eruption. He has proposed shooting trillions of tiny particles of earth into the stratosphere, where they will remain suspended to help blot out incoming solar rays. Dirt is cheap, chemically unreactive and easily crushable, he argues, making it a simple matter to test this strategy on a small scale over the Arctic before total global deployment. This plan might seem a little too sci-fi to take seriously -- fittingly, Benford moonlights as a Nebula-winning novelist -- but he's far from the only scientist to lobby for a so-called geoengineering fix.