Geoscience Reference
In-Depth Information
Why the delay in recognizing climate change?
The key reasons for the delay in recognizing the climate change were, first, the power of
the global mean temperature (GMT) data set and, second, the need for the emergence of
global environmental awareness. The GMT data set is calculated using the land-air and sea-
surface temperatures. From 1940 until the mid-1970s, the global temperature curve seems
to have had a general downward trend. This provoked many scientists to discuss whether
the Earth was entering the next great ice age. This fear developed in part because of in-
creased awareness in the 1970s of how variable global climate had been in the past. The
emerging subject of palaeoceanography (study of past oceans) demonstrated from deep-sea
sediments that there were at least 32 glacial-interglacial (cold-warm) cycles in the last 2.5
million years, not 4 as had been previously assumed. The time resolution of these studies
was low, so that there was no possibility of estimating how quickly the ice ages came and
went, only how regularly. It led many scientists and the media to ignore the scientific revel-
ations of the 1950s and 1960s in favour of global cooling. It was not until the early 1980s,
when the global annual mean temperature curve started to increase, that the global cooling
scenario was questioned. By the late 1980s, the global annual mean temperature curve rose
so steeply that all the dormant evidence from the late 1950s and 1960s was given promin-
ence and the global warming theory was in full swing.
It seems that the eventual recognition of the climate change issue was driven by the upturn
in the global annual mean temperature data set. The latest IPCC 2013 Science Report has
reviewed and synthesized a wide range of data sets and shows that, essentially, the trend in
global temperature first recognized in the late 1980s is essentially correct, and that this
warming trend has continued unstopped until the present day (see
Figure 5
). In fact, we
know that 1998 and 2010 were globally the warmest years on record. The temperatures for
these two years are so close that scientists are divided on which is the warmest. However,
1998 was an El Niño year, which we know adds up to 1°C on the average global temperat-
ures. So the warmest 'normal' year on record is 2010. If the global temperature records are
analysed in decadal blocks it is even clearer that the last three decades are all significantly
warmer than the previous ones (
Figure 5
).
The upturn in the global annual mean temperature data was not the sole reason for the ap-
pearance of the global warming issue. In the late 1970s and 1980s, there were significant
advances in global climate modelling and a marked improvement in our understanding of
past climates. Developments in general circulation models (GCMs) during this period in-
cluded taking into account the role of particles and clouds in affecting the global climate.
