p. 63–64: Reference 240 [Broecker, 2001] is an overview rather than a detailed analysis of particular temperatures. Plimer cites it in respect of California enjoying warm times24 . The actual words in Broecker’s paper are late in the Medieval arm Period, California experienced several decade-long periods of profound drought. (Broecker is citing [Stine,
1994], Plimer’s reference 283.)
Boreholes give accurate temperature histories for about 1000 years into the past
because rock conducts past surface temperatures downward only slowly. In the Northern H e m i s p h e r e , b o r e h o l e d a t a s h o w s t h e M e d i e v a l a r m i n g a n d a c o o l i n g o f a b o u t 2 ◦ C f r o the Medieval arming to the Little Ice ge.255 — comparison with reference 255, a paper by Steig et al., reveals multiple misrepresentations by Plimer: i: the paper refers to data from a core extracted from ice, not a hole drilled into rock; ii: the ice core is from the southern hemisphere, not the northern hemisphere; iii: the paper does not analyse the Medieval Warm Period. ll data plots refer to the period from 20,000 BP to 10,000 BP — there appears to be absolutely no discussion of m
the Medieval period.
24. p. 66–67:
study of 6000 bore holes on all continents has shown that temperature in
arm Period was warmer than today and that the temperature fell 0.2 to
0 . 7 ◦ C d u r i n g t h e L i t t l e I c e
The cited reference (footnote 256) actually says that
temperature declined until about 200 years ago, reaching a minimum of about 0.2–0.7 K below present-day. (i.e. the 0.2 to 0.7 K is the amount of offset from ‘present-day’, not the amount of fall from the MWP). The words that Plimer completely ignores are in the preceding passage, saying (relative to the period 1300–1600 BP): warming followed, yielding temperatures that averaged 0.1–0.5 K above present-day in the interval 500– 1000 years ago. The reference does not specify the time interval that represents ‘present- day’, but this global-scale estimate clearly differs from Plimer’s repeated unsubstantiated
assertion that the MWP was 2 to 3 degrees warmer than present.
later paper (by the
authors of reference 256)
late Quaternary climate reconstruction based on borehole
heat flux data, borehole temperatures data and the instrumental record. in Geophysical Research Letters, 35, L13703 (2008) states s the authors of HPS97 we can be criticized for not stating explicitly in HPS97 that the ‘present’ (the zero on the time axis) really represents something like the end of the 19th centur , rather than the end of the 20th century. The range of reconstructions in the 2008 paper, show a peak warming between 500 and 800 years ago, whose peaks, relative to to 1961–1990 mean, range from about
0.4◦C to 0.3◦C.11
25. p. 70: The Ontario forests have ... not returned to the diversity and productivity of the Medieval warming281. Indeed — reference 281, [Campbell and Mc ndrews, 1993], notes that the wild forest of Southern Ontario, now largely cleared, is no longer a major carbon reserve ...
26. p. 87: Plimer correctly quotes reference 368 [Royer et al., 2007] as saying climate sensitivity g r e a t e r t h a n 1 . 5 ◦ C h a s b e e n a r o b u s t f e a t u r e o f t h e E a r t h ’ s c l i m a t e o v e r t h e l a s t 4 2 0
11The main issue here is that Plimer misrepresents reference 256, not that he failed to appreciate the significance of the upper 100 metres of data not being used.