Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 259

Current warming and likely future impacts

6

6.1 Currentbiologicalsymptomsofwarming

As noted in Chapter 2, climate change impacts on living species and so in turn these
impacts can be used as climatic proxies. As discussed in Chapter 3, climate change
throughout the Earth's history has been complex and features a number of distinct
and characteristic episodes as well as periods with defining trends. However, as was
observed in Chapters 3 and 4, the biological response of species and natural systems
to climate change is also complex, as is the biological response of (and impact on)
humans. A good proportion of this last is reflected in recorded history. Further,
these impact elements - of species response and climatic-event and natural-systems
response - are all discernable when applied to climate at the end of the 20th and
early 21st century and all exhibit varying degrees of complexity. Some responses
are sufficiently complex that they appear as the opposite to what might initially be
expected. Even in such cases, when examined carefully, they all clearly reflect the
fact that the planet is warming up.

6.1.1 Currentborealdendrochronologicalresponse

One illustrative example was briefly mentioned in Chapter 2 when looking at dendro-
chronology. Figure 2.1 portrays the pooling together of several dendrochronological
series from the northern hemisphere's high latitudes. This clearly shows that in the
20th century the north of the northern hemisphere warmed above the 1601-1974
average. However, some dendrochronological series (Figure 2.1, the dashed line on
the far right) seem to exhibit a late-20th-century return to average temperatures even
though others reflect continued warming (in line with instrumental measurements). 1
As indicated, this deviation from what would be expected may be due to increased
snowfall with the volume of the extra snow delaying the melting of snow cover and so
delaying the onset of spring greening. This is not unexpected, because, as previously
noted, a warmer planet would have increased ocean evaporation and hence increased
precipitation (be it rain or snow). Another explanation mentioned is that some other

1

It was this problem that required researchers to use what one called a 'trick' in a private e-mail
when presenting some dendrochronological records as climate proxies over the past few centuries. The
researchers' e-mails were hacked and then released in November 2009 just prior to the Copenhagen
climate change conference. Subsequently a number of enquiries into the affair confirmed, in the words
of the House of Commons Science and Technology Select Committee report (2011), that the use of
'phrases such as “trick” or “hiding the decline” were colloquial terms used in private e-mails and the
balance of evidence is that they were not part of a systematic attempt to mislead'.

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