View Full Version : Tree Ring Climate Study over 2000 years shows "cooling"

2012-Jul-11, 11:42 PM
A global warming denialist emailed me this article. My intuition says that it is off-point with respect to the realities of global warming but I'd like some concrete reasons anyone may have to counter why the results of this study (that show Earth warmer 2000 years ago and has cooled 0.6 degrees C over the past 2 millennia) do not diminish the realities/concerns of AGW.


2012-Jul-11, 11:58 PM
I don't think they do. I don't know anyone who denies that the earth was a different temperature then, or that we are in a completely natural warming cycle now. The whole reason for concern about AGW is that we are causing it to occur much faster than it would have naturally. Human civilization has just happened to arise between two periods of glaciation. The only difference in this cycle is that a species on the planet actually has real control over how quickly the next arrives.

But the article is making a big deal about thirty years. We're talking about tens and hundreds of thousands of years when we talk about global warming.

Ara Pacis
2012-Jul-12, 05:31 AM
The Medieval Warm Period (http://en.wikipedia.org/wiki/Medieval_Warm_Period) is known and here's some help debunking misconceptions stemming from it (http://www.skepticalscience.com/medieval-warm-period.htm). A tree ring can only record the data for the location of the tree, and not all locations experience the same climate or change in climate. Even then, it may be possible to extrapolate some human causes even back then. Human deforestation may have had a notable effect in some regions. The lack of trees may have allowed warming due to a different albedo. The burning of trees without new tree plantings would have created a net increase in CO2. Furthermore, burning wood would have resulted in soot and recent studies have shown that soot contributes to warming (http://www.skepticalscience.com/soot-and-global-warming.html) over time due to albedo (http://www.livescience.com/2420-soot-plays-big-role-global-warming.html) changes in the atmosphere, which also reduce precipitation in the area.

Ari Jokimaki
2012-Jul-12, 07:04 AM
The study in question is apparently this one:


Here's RealClimate take on it:


There are many reasons why this study doesn't take away anything from AGW. Some of the reasons are: 1) study is regional and it is well known that even in the case of AGW different regions of the Earth warm at different pace - there still are some places that haven't even experienced warming yet, 2) past climate changes don't affect the cause of the current one, 3) results of one study don't wipe out results of hundreds of other studies.