Bjorklund et al., 2020:
A new 1876-present
temperature
reconstruction
for Northern Finland
shows the 1930s
were the warmest period
of the last 140 years.
And there has been
no net warming since.
Tree density analysis,
MXD, has a “more prominent
association with temperature”
than measuring tree ring
widths because it can
more clearly separate
precipitation factors
affecting tree growth
from temperature-limiting
factors (Bjorklund et al., 2020).
Northern Finland
is characterized as
“the most suitable place
in the world for temperature
reconstruction”
because it sits
on the edge
of where trees
can or cannot grow
(or survive) due to
clearly defined
temperature limits
on growth.
Forests used to extend
to the coast of the
Arctic Ocean during
the Early Holocene,
indicating the Arctic region
needed to have been
+2.5 to +7°C warmer
to accommodate such
tree growth in that area.
Pinus sylvestris (29 trees)
from northeastern Finland
indicate the warmest interval
since 1876 occurred
in the 1930s.
Since then
there has been
no net warming.
This is visible in both
tree ring width (RW) and
density (MXD) analysis:
Other new “dendroclimatic”
studies also show a similar
temperature pattern of a
warm early/mid-twentieth
century and then
a cooling in the
1960s and 1970s,
prior to another warming
in the 1990s-2000s.
For example, in China,
tree ring evidence
suggest such a pattern
for soil temperatures
(Yuan et al., 2020),
and Keyimu et al. (2020)
find “A.D. 1940–1965
witnessed the longest
extended warm period
at Big Snow Mountain
Scenic Area over the
past 180 years”.
Proxy evidence from
across the Northern
Hemisphere may also
show this same warming
-cooling-warming
temperature pattern.
They also show
the modern period
is not climatically
unusual relative
to past ~1,500 years
(Stoffel et al., 2015,
Schneider et al., 2015).