Climate in Northern Europe Reconstructed for the Past 2,000 Years: Cooling Trend Calculated Precisely for the First Time
ScienceDaily (July 9, 2012) — An international team that includes scientists from Johannes Gutenberg University Mainz (JGU) has published a reconstruction of the climate in northern Europe over the last 2,000 years based on the information provided by tree-rings. Professor Dr. Jan Esper's group at the Institute of Geography at JGU used tree-ring density measurements from sub-fossil pine trees originating from Finnish Lapland to produce a reconstruction reaching back to 138 BC. In so doing, the researchers have been able for the first time to precisely demonstrate that the long-term trend over the past two millennia has been towards climatic cooling.
http://www.sciencedaily.com/releases/20 ... 092606.htm
A bit of a sensationalist report about it in the Daily Mail I think:-
"Tree-rings prove climate was WARMER in Roman and Medieval times than it is now - and world has been cooling for 2,000 years"
http://www.dailymail.co.uk/sciencetech/ ... z20KvhOaAp
The tree-ring study is analysed and critiqued at RealClimate.org:-
The authors make much of the importance of long-term radiative forcing due to the changes in the earth’s orbit for millennial timescale temperature trends. They argue that TRW data which fail to record this forced long-term cooling might therefore underestimate variability on millennial timescales more generally, and potentially underestimate the warmth of past warm periods (e.g. medieval and Roman periods).
Orbital forcing is indeed substantial on the millennial timescale for high-latitudes during the summer season, and the theoretically expected cooling trend is seen in proxy reconstructions of Arctic summer temperature trends (Kaufman et al, 2009). But insolation forcing is near zero at tropical latitudes, and long-term cooling trends are not seen in non-tree ring, tropical terrestrial proxy records such as the Lake Tanganyika (tropical East Africa) (Tierney et al, 2010) (see below).
Long-term orbital forcing over the past 1-2 millennia is also minimal for annual, global or hemispheric insolation changes, and other natural forcings such as volcanic and solar radiative forcing have been shown to be adequate in explaining past long-term pre-industrial temperature trends in this case (e.g. Hegerl et al, 2007). Esper et al’s speculation that the potential bias they identify with high-latitude, summer-temperature TRW tree-ring data carry over to a bias in hemispheric temperature reconstructions based on multiple types of proxy records spanning tropics and extratropics, ocean and land, and which reflect a range of seasons, not just summer (e.g. Hegerl et al, 2006; Mann et al, 1999;2008) is therefore a stretch.
Indeed, there are a number of lines of evidence that contradict that more speculative claim. For example, if one eliminates tree-ring data entirely from the Mann et al (2008) “EIV” temperature reconstruction (see below; blue curve corresponds to the case where all tree-ring data have been withheld from the multiproxy network), one finds not only that the resulting reconstruction is broadly similar to that obtained with tree-ring data, but in fact the pre-industrial long-term cooling trend in hemispheric mean temperature is actually lessened when the tree-ring data are eliminated—precisely the opposite of what is predicted by the Esper et al hypothesis.
The wider hypothesis doesn’t get much support from looking at the pre-industrial millennial-scale temperature trends in published proxy reconstructions of Northern Hemisphere mean temperature, all of which indicate cooling of varying magnitudes. Ordered from smallest to largest cooling trend, we have:
Moberg et al (2006): -0.06 ºC/1000yr (0-1900)
Esper et al (2002): -0.11 ºC/1000yr (831-1900)
Hegerl et al (2007): -0.14 ºC/1000yr (558-1900, 30º-90ºN land, Chblend-dark)
Ljungqvist (2010): -0.18 ºC/1000yr (0-1900, 30º-90ºN)
Mann et al (1999): -0.19 ºC/1000yr (1000-1900)
Mann et al (2008): -0.23 ºC/1000yr (300-1900, nhcru_eiv_composite):
This can be loosely compared to the -0.31 ºC/1000yr estimate derived for N-Scan and trends of -0.10 and -0.19 ºC/1000yr at that latitude in summer seen in two model estimates discussed – though note that the model simulations will have smaller trends for the whole hemisphere and for the annual mean.
http://www.realclimate.org/index.php/ar ... elopments/
I have some reservations about paleoclimate methods - such as ice-cores and tree-ring reliability, to be honest. A lot of these may well serve as rather unrealiable "hooks" for AGW skeptics to latch onto. I advise sticking to basic facts that we know :- 1. The mainstream does not understand the sun, 2. The mainstream history of greenhouse-effect with respect to Venus is highly suspect, 3. Paleoclimatic data is open to question, and 4. Feedback mechanisms have yet to be empirically proven in reality.
http://www.dailymail.co.uk/news/article ... claim.html
But like every churchs we have schism.
