Post-glacial climatic change and variability - The Global Climate System: Patterns, Processes, and Teleconnections - page 205

6.4.3 Did the Southern Hemisphere experience
the MWP and the LIA?
Jones and Mann ( 2004 ) argue that the MWP and LIA were defined based mainly
on European and North Atlantic climate periods, but could not be called global
phenomena. However, several other authors disagree. For example, Soon and
Baliunas ( 2003 ) suggest that there is global evidence for glacial retreat during
the MWP and significant glacial advance during the LIA. However, the start and
end dates are often not well established, and the timing varies in different parts of
the world. What evidence exists that either period occurred in the SH, given the
inconclusive indicators in Figure 6.7 ? There seems to be greater evidence for a
global LIA than for a MWP.
Figure 6.9a shows temperature records from tree-rings in New Zealand from
Cook et al.( 2002 ). Figure 6.9b compares oxygen-18 records from ice cores in
Greenland, Peru, China, and Antarctica (Thompson et al. 1993 ), and Figure 6.9c
presents speleothem records from Southern Africa (Lindesay 1998 ). Table 6.2
lists the coldest and warmest pre-1850 summers, decades, and centuries in each
hemisphere, based on the analysis of Jones et al.( 1988 ). These records indicate
the complexities of defining MWP and LIA periods outside of Europe.
Figure 6.9a indicates a period of strong cooling (13.5 8C) around AD 1000,
which does not appear in the NH records. Mayewski et al.( 2004 ) state that small
advances in New Zealand glaciers occurred, eastern Southern Africa was dry and
cool, and mid-latitude Chile was dry. The tropical regions were also consider-
ably drier than today. After 1000 temperature increased to 15.5 8C by about
1160, in Tasmania. The warmer period lasted until about 1300, with some
decadal fluctuations, which is a similar time period to the MWP in Europe.
The MWP-type period in Tasmania began about 300 years later, and seems to be
shorter in duration. Evidence for a colder period occurs between about 1520 and
1680, again a similar but shorter time scale to the LIA in Europe. Cook et al.
( 1995 ) state that a similar result emerges from tree-rings from Tasmania, and is
supported by carbon-14 measurements.
The ice core O 18 results in Figure 6.9b show a broadly similar variation in
timing, and that both a MWP-type warming and LIA-type cooling occurred in
Peru and Antarctica. Both the South Pole and Peru data sets clearly show a much
greater number of warm than cold years between 1100 and 1550. The timing of
warm year periods differs, and Antarctica had more and stronger cold years in
between the warm years. In comparison to the two NH records, warm years in the
SH were more abundant during this period. Between 1550 and 1850, all records
except Siple Station in Antarctica show more cold than warm years, but the SH
records are more consistent. At this time, the Quelccaya records also showed the
greatest precipitation accumulation (Markgraf 1998 ). Mayewski et al.( 2004 )
indicate that both polar regions were wet and windy, East Antarctica was cold,
the tropics remained wet, glaciers advanced in New Zealand, Chile was moist,