Trend calculated precisely for the first time (2012)
An international team including scientists from Johannes Gutenberg University Mainz (JGU) in 2012 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 were able for the first time to precisely demonstrate that the long-term trend over the past two millennia has been towards climatic cooling. The researchers were from Germany, Finland, Scotland, and Switzerland.
Here is a link to their article, and the high-resolution representation of the Temperature trends attached to it.
The Contact listed is Professor Dr. Jan Esper, Institute of Geography, Johannes Gutenberg University D 55099 Mainz, Germany.