Update: The article and paper are from 2012.
A study suggests the Britain of 2,000 years ago experienced a lengthy period of hotter summers than today.
German researchers used data from tree rings – a key indicator of past climate – to claim the world has been on a ‘long-term cooling trend’ for two millennia until the global warming of the twentieth century.
This cooling was punctuated by a couple of warm spells.
These are the Medieval Warm Period, which is well known, but also a period during the toga-wearing Roman times when temperatures were apparently 1 deg C warmer than now.
They say the very warm period during the years 21 to 50AD has been underestimated by climate scientists.
Lead author Professor Dr Jan Esper of Johannes Gutenberg University in Mainz said: ‘We found that previous estimates of historical temperatures during the Roman era and the Middle Ages were too low.
So much for tree rings as a temperature proxy.
Huge Canadian Tree Growth Study.
Our analyses of a new methodologically standardized tree-ring dataset covering Canada’s boreal forest provide insights into the growth responses of this ecosystem to climate change. Although revealing no overarching “growth enhancement” or “growth decline” in recent years, results do point to significant regional- and species-related trends in growth. The observed link between climate variation and growth variability revealed unique evidence of an intensification of the impacts of hydroclimatic variability on growth late in the 20th century, in parallel with the rapid rise of summer temperature.
Such response can be attributed to annual growth variability in these forests being mainly driven by negative sensitivity to summer temperature (warmer summers leading to less growth) and positive sensitivity to summer soil moisture (more moisture leading to more growth)