Conclusion - Four Degrees of Global Warming - page 230

● be consistent with internationally agreed efforts to limit global average
warming to less than 2°C, or the safer lower goal of 1.5°C, above preindustrial
levels;
●● reflect the best available climate science with regard to the pace of
mitigation;
● be equitable in committing Australia to its fair share of the international
mitigation effort by taking into account Australia's historical emissions
profile ('polluter pays' principle), its national economic wealth ('beneficiary
pays' principle') and capacity, and the equal right of individuals to the global
atmospheric commons ('per capita emissions rights' principle).
Australia's carbon budget and 'ambition gap'
Australia's national carbon budget
Climate scientists have proposed a global carbon budget which defines the
maximum additional volume of emissions that still may accumulate in the
earth's atmosphere if global warming is to have a chance of staying below the
2°C 'guardrail'. Research suggests that this 'budgetary limit' will be reached when
approximately one trillion tonnes of CO 2 have been added to the amount already
in the atmosphere at the start of this century.
Further, in 2009 the German Advisory Council on Global Change (WGBU)
suggested that 'By the middle of the 21st century a maximum of approximately
750 billion tonnes CO 2 may be released into the Earth's atmosphere if the
guardrail is to be adhered to with a probability of 67 per cent. If we raise the
probability to 75 per cent, the cumulative emissions within this period would
even have to remain below 600 Gt CO 2 ' (WGBU, 2009: 2).
Human activities have already added some 420  50 billion tonnes of CO 2 to
the atmosphere since 2000 and we continue to add some 50 billion tonnes per
annum (Olivier et al., 2012: 18). We have used half or more of our global carbon
budget in 13 years. Only another 500 billion tonnes of CO 2 can be added if we
are to have only a 50 per cent chance of staying below the 2°C limit and avoiding
'dangerous climate change', around 330 billion tonnes if we are to have a 67 per
cent chance, only some 180 billion tonnes for a 75 per cent chance, and less
again for a target of 1.5°C (Schellnhuber et al., 2006; Meinshausen et al . , 2009;
WGBU, 2009).
A national carbon budget can be determined by building on the concept of
per capita emissions rights first proposed by Meyer (2000). As the WGBU puts it,
'The global CO 2 budget is distributed among the world's population on an equal
per-capita basis so that national CO 2 budgets can be calculated for all countries,
and adopted on a legally binding basis. These budgets provide an orientation
for countries on how swiftly and substantially their CO 2 emissions need to be
reduced' (WGBU, 2009: 3). This approach in part depends on the baseline
for population - which can be set contemporaneously (say, at 2013) or based
on projections (for instance, for 2050, when global population is commonly
estimated to peak).