Environmental Engineering Reference
In-Depth Information
The evidence and the certainty of the language hence have become confident over time.
But perhaps the focus has now moved to the national and city arenas - here it seems possible
to implement more radical strategies for emissions reduction. In parallel, the data trends are
revealing: concentration of atmospheric CO2 has increased from a pre-industrial value of
about 280 parts per million (ppm) to 379 ppm in 2005 (Intergovernmental Panel on Climate
Change, 2007), and the most recent, preliminary estimates suggest the 400 ppm level has been
reached in 2013. Projections of global concentrations rise to 550 ppm by 2050, under current
trends, or to 550-700 ppm by 2050, and 650-1200 ppm by 2100, without substantial
intervention. Atmospheric CO2 concentration increased by only 20 ppm over the 8,000 years
prior to industrialisation; multi-decadal to centennial-scale variations were less than 10 ppm
and most likely due to natural processes. However, since 1750, CO2 concentration has risen
by nearly 100 ppm. The annual CO2 growth rate was larger during the last 10 years (the
1995-2005 average is 1.9 ppm) than it has been since continuous direct atmospheric
measurements began (the 1960-2005 average is 1.4 ppm).
The rate of atmospheric CO2 concentration growth (now at 2-3 ppm p.a. ) means that we
are likely to reach the 450 ppm threshold within 30 years (at the latest by 2040). The IPCC
suggests that, for the next two decades, warming of about 0.2°C per decade is projected under
the most likely range of emission scenarios. Even if concentrations of all greenhouse gases
and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C
per decade would be expected based on the current build up of CO2 in the atmosphere.
There is a need to consider at least three factors when formulating policies for decarbon-
isation, namely the policy framework, the underlying philosophy and the likely impacts. The
current public policy framework for decarbonisation is highly reliant on rational decision theory
(Friedman and Savage, 1948) and on expected utility theory (von Neumann and Morgenstern,
1944), and these inform the dominant discourse on environmental economics (Nordhaus,
2008). In the Friedman framework, consumers maximise expected utility from the policies
that have emerged from government. Under Nordhaus, it is assumed policy-makers will weigh
costs and damages to arrive at a rational decision on decarbonisation. In the Stern Review
(2007), it was argued that early action in CO2 mitigation is the most cost-effective option,
but this view relies less on the conventional wisdom, as a lower discount rate is used, meaning
that future generations' welfare (in terms of CO2 mitigation) should be valued almost equally
to those that are currently alive.
Stern (2009; 2007) reports that a doubling of pre-industrial levels of greenhouse gases is
very likely to commit the Earth to a rise of 2-5°C in global mean temperatures, a level that
will be reached between 2030 and 2060, and argues for early action for financial reasons.
concentrations of CO2 to around 500 ppm CO2e gives a 96 per cent probability of a temperature
rise over 2°C, a 44 per cent probability of over 3°C, and 11 per cent of over 4°C (
Table 1.1
).
There are advocates for different stabilisation levels, but Stern argues that these are problematic:
lower targets being implausible in the short to long term; higher targets associated with
unacceptable negative impacts. In relation, the business-as-usual concentration level is estimated
at around 750 ppm CO2e.
The difficulty in presentation to the public is that a 5-6°C temperature change does not
sound cataclysmic, certainly not for the Western countries. However, this is a global average
figure with much differentiation spatially, and an average rise of 5°C would result in dramatic
climatic change in terms of flooding, drought, storms and rising sea levels. Such a rise in
of the world was swampy forest. The last ice age (100,000 years ago) was only 5°C cooler
