I just Googled "long term cooling trend" and saw that many media and blog commentary about the Esper tree proxy study have headings like this: "New Tree Ring Study Shows 2000 years of COOLING on Earth". Obviously, they think that the existence of some long term cooling is a new finding.
This just shows how easily people are misled.
As this Skeptical Science post (last updated in 2010) shows via a few graphs - knowledge of a long term cooling trend in the Northern Hemisphere (up to last century) is nothing new.
The point is also made in the Real Climate commentary on the Esper paper. The Esper cooling trend, based on its Lapland trees, is just a bit higher than other proxy studies conclude.
This really is frustrating.