'Global warming is nothing new'

How to Talk to a Climate Skeptic

Posted by Coby Beck (Guest Contributor) at 1:00 PM on 16 Dec 2006

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Global warming has been going on for the last 20,000 years.

Answer: It is true that 20,000 years ago the temperature was some 8 to 10° C colder than it is today. But to draw a line from that point to today and say, "look, 20K years of global warming!" is dubious and arbitrary at best.

If you have look at this graph of temperature, starting at a point when we were finishing the climb out of deep glaciation, you can clearly see that rapid warming ceased around 10,000 years ago (rapid relative to natural fluctuations, but not compared to the warming today, which is an order of magnitude faster). After a final little lift 8,000 years ago, temperature trended downward for the entire period of the Holocene. So the post-industrial revolution warming is the reversal of a many-thousand-year trend.

A closer look at today's trend, within the context of the last 1,000 and 2,000 years, makes it even clearer that today's trend is striking -- opposite to what one would expect without anthropogenic interference.

(Courtesy of Global Warming Art. See source for details on the various reconstructions tangled above.)

If you really want to play the "global warming started X years ago" game, you should talk about how we're reversing a 5-million-year cooling trend -- or go crazy and track global temperatures right back to the origins of the planet! Not that there'd be much point ...

For story: 'Global warming is nothing new'
5 Comments | Post a Comment

The mind of the skeptic

An in depth article looking at why some "prominent figures" believe that man made global warming is a myth. It's important to know the enemy!

by darudethedj at 8:40 AM on 20 Feb 2007

ChartJunk

This is a good example of chart junk -- where the visuals overwhelm the data. The link supporting that chart says:

This image is a comparison of 10 different published reconstructions of mean temperature changes during the last 2000 years. More recent reconstructions are plotted towards the front and in redder colors, older reconstructions appear towards the back and in bluer colors. An instrumental history of temperature is also shown in black. The medieval warm period and little ice age are labeled at roughly the times when they are historically believed to occur, though it is still disputed whether these were truly global or only regional events. The single, unsmoothed annual value for 2004 is also shown for comparison. (Image:Instrumental Temperature Record.png shows how 2004 relates to other recent years).
It is unknown which, if any, of these reconstructions is an accurate representation of climate history; however, these curves are a fair representation of the range of results appearing in the published scientific literature.

So, first of all, it says that this chart may be inaccurate and yet, we're still going to run off and make policy decisions using it!

Second, look at the scale. Even the black line goes no higher than a 0.4C ( .5 to .7 degrees Fahrenheit ) anomaly. All of the others fall within statistical range of the Medieval Warm Period.

This chart shows clearly that global warming is naturogenic, not anthrogenic.

by jabailo at 9:08 AM on 20 Feb 2007

umm, jabailo

It's hard to extrapolate data from more than 100 years ago, when the records began to be kept. That's why there's uncertainty in the past. However, the range of uncertainty in the past is far below the certainty of the present both in terms of range and directionality: notice how the lines converge and all go up???

Jeez, way to be a troll.

by atreyger at 9:36 AM on 20 Feb 2007

I'm confused by your 8-10 degrees cooler comment

On page 2 of the Jones/Mann report: "Climate Over Past Millennia (ftp://holocene.evsc.virginia.edu/pub/mann/JonesMannROG04.pdf), it states that at the last glacial maximum 21,000 years ago, global annual mean temperatures were about 4 degrees C colder than today. Why the discrepancy between your 8-10 degrees cooler figure and Jones/Mann's 4 degrees?

Dave

by DaveR at 5:10 PM on 28 Feb 2007

Past Warming

In the Pacific Northwest one finds Douglas-fir trees 600-800 years old at higher elevations than their natural range today. They date from the medievel warm period. In Alaska and in some of those Douglas-fir stands are found yellow cedars that are declining or dying because of early soil warming and late frosts. Many of these trees date from the little ice age.

Douglas-fir expanded its range when things were warmer and yellow cedar when it was colder.

Evidence of past fluctuations and current change is very visible if you know what you are looking at.

by Paul Wagner at 4:47 PM on 18 Jun 2007

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