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what the global temperature change would be if pre-industrial carbon dioxide levels were
doubled. These results have been very consistent over the last 40 years (see
Figure 18
)
and the 2013 IPCC report suggests the range is between 1.5°C and 4.5°C, which is con-
sistent with other measures. What is even more amazing is that in 2014 the UK climate
sceptical think tank the Global Warming Policy Foundation (GWPF) published its own re-
port, which looked into ECS. They concluded that ECS was between 1.25°C and 3.0°C
with a best estimate of 1.75°C. Though this is lower than the IPCC estimate it is still a
major breakthrough that an organization such as GWPF is now recognizing the impacts of
carbon emissions on the atmosphere.
(3) Climate models fail to predict weather.
Many people get weather and climate confused. Climate is generally defined as the aver-
age weather. The original definition of climate was the average weather over 30 years, this
has been changed because we now know that our climate is changing and significant
changes have been seen every decade for the last 50 years. It is the chaotic nature of
weather that can make it unpredictable beyond a few days, as the Earth's climate system is
sensitive to extremely small perturbations in initial conditions. For example, extremely
slight changes in air pressure over the USA have an influence on the direction and dura-
tion of a hurricane. Though there have been amazing advances in weather prediction over
the last decade, leading to storm warnings seven days in advance instead of two in the
1980s. Climate modelling is, however, much easier as you are dealing with long-term av-
erages. A good comparison is that though it is impossible to predict at what age any par-
ticular person will die, we can say with a high degree of confidence that the average life
expectancy of a person in a developed country is about 80 years. The modelling of climate
is not limited in the same way as the prediction of the weather because the longer term
systematic influences on the atmosphere are not reliant on the initial conditions. So the
longer term trends in regional and global climate are not controlled by small-scale influen-
ces. Also, as described above we now have the computer power to go back and test
whether extreme weather events were more intense or frequent due to anthropogenic cli-
mate change.
