The tenth IMSC, Beijing, China, 2007 - International Meetings on ...

Francis W. Zwiers, Gabriele C. Hegerl, F. Hugo Lambert, Nathan P. Gillett, Susan Solomon, Peter
Stott, Toru Nozawa
Human influence on climate has been detected in surface air temperature on global,
continental and some sub-continental scales, in sea level pressure, in free atmospheric
temperature, in tropopause height, and in ocean heat content. While precipitation change is
highly relevant to the impacts of climate change, large scale precipitation changes have not
previously been detected and attributed to human influence. A key reason for this is that
perhaps because compensating increases and decreases in different regions of the globe
reduce the global average signal. Models suggest that while anthropogenic forcing should
have caused a small increase in global mean precipitation, it also is expected to induce a
latitudinal redistribution of precipitation with moistening at high latitudes, drying in sub-tropical
latitudes, and perhaps a shift of the ITCZ. Here we compare the changes in the pattern of 20th
century land precipitation observations averaged in latitude bands to precipitation changes
simulated by fourteen climate models. We show that the influence of anthropogenic forcing on
observed zonal mean precipitation changes can be detected and that these changes cannot
be explained by internal climate variability or the effect of natural forcing. We estimate that
anthropogenic forcing contributed substantially to observed increases in precipitation in the
northern mid-latitudes, to drying in the northern subtropics and tropics, and to moistening in
the southern deep tropics and subtropics. <strong>The</strong> observed changes, which are larger than
estimated from presently available model simulations, have significant implications for
ecosystems, agriculture, and human health.
An assessment of regional record-breaking statistics in annual mean temperature
Speaker: Eduardo Zorita
Eduardo Zorita
GKSS
eduardo.zorita@gmx.de
Hans von Storch
GKSS
Different datasets of global mean surface air temperature show consistently increasing
values for the past 50 years. Since 1990, a large number of record warm years was detected:
the 12 warmest years since 1880 have all occurred after 1990. <strong>The</strong> probability p of the event E
of finding at least 12 of the largest values of a sequence of 126 random numbers (years 1880
to 2005) on the last 16 places (year 1990 to 2005) is 9.3·10–14. However, annual mean
surface air temperatures show serial correlations even in the absence of variations of external
forcing. Two null-hypothesis have been used to calculate the probability that such series of
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