Reductions of greenhouse gas emissions in Annex I and non-Annex I countries for meeting concentration stabilisation targets

Reductions needed to meet concentration targets

The IPCC Fourth Assessment Report, Working Group III, summarises in Box 13.7 the required emission reduction ranges in Annex I and non-Annex I countries as a group, to achieve greenhouse gas concentration stabilisation levels between 450 and 650 ppm CO₂-eq. Box 13.7 summarises the results of the IPCC authors’ analysis of the literature on the regional allocation of the emission reductions. The box states that Annex I countries as a group would need to reduce their emissions to below 1990 levels in 2020 by

• 25% to 40% for 450 ppm,
• 10% to 30% for 550 ppm,
• 0% to 25% for 650 ppm CO₂-eq,

even if emissions in developing countries deviate substantially from baseline for the low concentration target. In this paper, the IPCC authors of Box 13.7 provide background information and analyse whether new information, obtained after completion of the IPCC report, influences these ranges.

No reason to update IPCC reduction numbers

The authors concluded that there is no argument for updating the ranges in Box 13.7. The allocation studies, which were published after the writing of the IPCC report, show reductions in line with the reduction ranges in the box. From the studies analysed, this paper specifies the “substantial deviation” or “deviation from baseline” in the box: emissions of non-Annex I countries as a group have to be below the baseline in 2020 roughly between:

• 15% to 30% for 450 ppm CO₂-eq,
• 0% to 20% for 550 ppm CO₂-eq,
• from 10% above to 10% below the baseline for 650 ppm CO₂-eq.

These ranges apply to the whole group of non-Annex I countries and may differ substantially per country.

Main factors influencing the reduction ranges

The most important factor influencing these ranges above, for non-Annex I countries, and in the box, for Annex I countries, is new information on higher baseline emissions (e.g. that of Sheehan, Climatic Change, 2008, this issue). Other factors are the assumed global emission level in 2020 and assumptions on land-use change and forestry emissions. The current, slow pace in climate policy and the steady increase in global emissions, make it an enormous challenge to reach relatively low global emission levels in 2020 needed to meet 450 ppm CO₂-eq, as was first assumed feasible by some studies, 5 years ago.