A paper by
Prof. Quansheng Ge published in
Advances in Atmospheric
Sciences shows that the warm period in the twentieth century is not unprecedented.
From Eurekalert:
A great
deal of evidence relating to ancient climate variation is preserved in proxy
data such as tree rings, lake sediments, ice cores, stalagmites, corals and
historical documents, and these sources carry great significance in evaluating
the 20th-century warming in the context of the last two millennia.
Prof.
Quansheng Ge and his group from the Institute of Geographic Sciences and
Natural Resources Research, Chinese Academy of Sciences, collected a large
number of proxies and reconstructed a 2000-year temperature series in China
with a 10-year resolution, enabling them to quantitatively reveal the
characteristics of temperature change in China over a common era.
“We found
four warm epochs,” says Prof. Ge, “which were AD 1 to AD 200, AD 550 to AD 760,
AD 950 to AD 1300, and the 20th century.
“Cold
periods occurred between AD 210 and AD 350, AD 420 and AD 530, AD 780 and AD
940, and AD 1320 and AD 1900. The temperature amplitude between the warmest and
coldest decades was 1.3°C.”
Prof. Ge’s
team found that the most rapid warming in China occurred over AD 1870-2000, at
a rate of 0.56 ± 0.42°C (100 yr)?1; however, temperatures recorded in the 20th
century may not be unprecedented in the last 2000 years, as reconstruction
showed records for the period from 981 to 1100, and again from 1201 to 1270,
were comparable to those of the present warm period, but with an uncertainty of
±0.28°C to ±0.42°C at the 95% confidence interval.
Since 1000
CE—the period covering the Medieval Climate Anomaly, Little Ice Age, and the
present warm period—temperature variations over China have typically been in
phase with those of the Northern Hemisphere as a whole.
Prof. Ge’s
team also detected some interactions between temperature variation and
precipitation change. The ensemble means of dryness/wetness spatial patterns in
eastern China across all Centennial warm periods illustrate a tripole pattern:
dry south of 25°N; wet from 25°-30°N; and dry to the north of 30°N.
For all
cold periods, the ensemble mean drought/flood spatial patterns showed an east
to west distribution, with flooding east of 115°E and drought dominant west of
115°E, with the exception of flooding between approximately110°E and 105°E.
The general characteristics of the impacts
of climatic change historically were negative in the cold periods and positive
in the warm periods. For example, 25 of the 31 most prosperous periods in Imperial
China during the past 2,000 years occurred during periods of warmth or warming.
[my emphasis]
A cooling
trend at the centennial scale and social economic decline run hand-in-hand. The
rapid development supported by better resources and a better environment in
warm periods could lead to an increase in social vulnerability when the climate
turns once more to being relatively colder.