Sustainability and policy - Climate Change: Biological and Human Aspects - page 505

concerns, in the economic sense, given the finite nature of comparatively easy-to-
access economic fossil carbon? (Once again, note that resource sustainability and
climate change concerns coincide.) Indeed, what are our prospects for successful
carbon management?
8.4 Possiblefutureenergyoptions
8.4.1 Managingfossilcarbonemissions:thescaleoftheproblem
As noted, to have stabilised the global climate at 1990 levels around the turn of
the millennium a reduction in human greenhouse gas emissions of 60-80% would
have been needed (Chapter 5). Indeed, in order not to exceed an atmospheric carbon
dioxide concentration of 50% above pre-industrial levels - 420 ppm - then we would
have needed to start reducing emissions in the 1990s, or make greater cuts later, so
that they would be reduced by 50% of their 1990 value by the year 2050 (IPCC, 1990).
One question that repeatedly arose from audiences of the lectures I gave subsequent
to this topic's first edition (2007) was what were our chances of keeping warming to
below 2 ◦ C above the pre-industrial temperature? (Note that 2 ◦ C above pre-industrial
levels - or 1.2 ◦ C above the Earth's 2006-7 temperature - takes the Earth's global
temperature above that seen any time in the current, Quaternary, ice age of glacial
and interglacial cycles of the past two million years and this is considered the safe
limit for warming.) I therefore wrote an online essay to address this question in
2009 (Cowie, 2009). My conclusion then was that 'it seems very likely (without a
really major change in global human behaviour) that we will exceed our 'safe' 2 ◦ C
above pre-industrial level'. Subsequently a number of others (who are arguably more
informed than I) have come to the same conclusion (United Nations Environment
Programme, 2010; Levin and Bradley, 2010; Rogelj et al., 2010; Friedlingstein et al.,
2011).
The rate at which we are adding carbon to the atmosphere is so fast, and the amounts
sufficiently great, that there has not been enough time for the Earth system to adjust
and ultimately return to the pre-industrial state. It is therefore not so much a problem
of reducing the rate and amount of emissions released in any one year, but keeping the
cumulative total of carbon added since industrialisation to a specific limit. By 2009
humans added roughly half a trillion tonnes of carbon, 1000 GtC (or 1.83 t of CO 2 )to
the atmosphere. In 2009 a key analysis was conducted by primarily British scientists,
and one German, who concluded that the total addition of a trillion tonnes of carbon
(3.67 trillion t of CO 2 ) to the atmosphere since industrialisation would ultimately (a
century later) see the Earth warm by 2 ◦ C (Allen et al., 2009). This conclusion was
simultaneously echoed by a separate international team of Europeans (Meinhausen
et al., 2009). Clearly, as we are currently adding over 7 GtC a year (see Table 1.3)
and rising then, should current trends continue, it is likely that we will exceed this
trillion-tonne limit in a few decades' time. Such is the magnitude of the reductions
needed to keep within this limit, it is exceedingly unlikely that these limits will not
be breached, especially given the current drivers and trends outlined in this chapter.