Tree rings suggest Roman world was warmer than thought

[xchrom]

http://www.newscientist.com/article/dn22040-tree-rings-suggest-roman-world-was-warmer-than-thought.html


Have human CO2 emissions interrupted a long cooling period that would ultimately have delivered the next ice age? (Image: Gyro Photography/amanaimages/Getty Images)

How did the Romans manage to grow grapes in northern England when most climate studies suggest the weather was much cooler then? We may now have an answer: it wasn't that cold at all.

Long-term temperature reconstructions often rely on the width of tree rings: they assume that warmer summers make for wider rings. Using this measure, it seems that global temperatures changed very little over the past two millennia. Such studies are behind the famous "hockey stick" graph, created by Michael Mann of Pennsylvania State University in University Park, which shows stable temperatures for a millennium before the 20th century.

Jan Esper of Johannes Gutenberg University in Mainz, Germany, thinks that at least some of those tree rings actually show something else: a long-term cooling trend that lasted right up until the Industrial Revolution. The trend came about because of reduced solar heating caused by changes to the Earth's orbit known as Milankovitch wobbles, says Esper. His results suggest the Roman world was 0.6 °C warmer than previously thought – enough to make grape vines in northern England a possibility.

Esper and his colleagues say that warmer summers do not necessarily make tree rings wider – but they often make them denser. He studied the density of tree rings in hundreds of northern Scandinavian trees and found that they showed evidence of a gradual cooling trend that began around 2000 years ago.

[gregoire]

1. That is illogical

Since it has been proving that the Earth is warming, it would have had to been colder then.

[xchrom]

2. partial answer here

The finding does not change our understanding of the warming power of carbon dioxide. In fact, it shows that human CO2 emissions have interrupted a long cooling period that would ultimately have delivered the next ice age.

Esper says temperature reconstructions will have to be redone because past studies probably underestimated temperatures during the medieval warm period and other warm periods going back to Roman times. The further back in time, the greater the underestimate would be.

But others have doubts. Mann argues that Esper's tree-ring measurements come from high latitudes and reflect only summer temperatures. "The implications of this study are vastly overstated by the authors," he says.


*** from the same article.

[mitchtv]

3. perhaps there were hardier varieties of grape

that tolerated the cold , like the N American varieties? Perhaps they have been lost.

[xchrom]

4. that was something i wondered when i first read it.

and i don't know.

but i also think that things will come along that challenge our notions of what was going on 2,000 years ago.

we have a lot of info -- but it's not like it was yesterday -- and some things may offer different views.
it's not challenging climate change now -- which is interesting.

does it say something about the mini-ice age that came up in the dark ages? i don't know.

[Motown_Johnny]

5. The Earth began warming when we started burning fossil fuels

~100 years ago.


The Earth should be cooling right now. If not for our polluting the planet, it would be.

[Odin2005]

6. The "making wine in England" thing is BS.

Wine grapes were perfectly viable in southern England even at the height of the Little Ice Age, people just decided not to grow wine grapes, mainly because England is a beer culture, not a wine culture.

[Southerner]

7. Very clever deception by New Scientist proliferated by the OP

If you go to the original article published by the scientists themselves:

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1589.html

it talks a lot about fluctuating solar radiation and distance betweent Earth and Sun as well as volcanic activity, but nowhere does it talk about rising temperatures starting at the Industrial Revolution. This tree ring study does not support that and the paper does not say it. New Scientist decided to edit that part in it seems by talking about some other unrelated study done at Northern Arizona University.

I decided to spend the time to look into this when I ran into this article also:

http://www.dailymail.co.uk/sciencetech/article-2171973/Tree-ring-study-proves-climate-WARMER-Roman-Medieval-times-modern-industrial-age.html

The Daily Mail seems to have accurately summarized the Esper conclusions with no spin.