V

Building insulation

Figure 11.26 Technical options for reducing greenhouse gases up to 2030 and their cost in euros per tonne of carbon saved as estimated by workers in the Stockholm office of McKinsey & Company. Only some of the main options are labelled. Options below the line produce net savings, above the line net costs. The x-axis shows abatement for each of the options below 'business as usual' in GtCO2e per year. By 2030 they total 26 GtCO2e per year, enough to meet the 450 ppm stabilization curve shown in Figure 11.27.

Figure 11.27 Waymarks for annual global energy carbon di oxide emissions road map to 2050 showing International Energy Agency (IEA) Reference scenario (red) and a profile (green) aimed at targets of < 2° C temperature rise from pre-industrial and 450 ppm CO2 stabilisation (cf Figure 10.3). The division between developed and developing countries from today until 2050 is a construction based on the developed countries' share, compared with that of developing countries, peaking earlier and reducing further e.g. by at least 80% by 2050..

2010

• CO2 emissions targets set for 2020, 2030, 2050

From 2010 onward

Rapid deployment:

energy efficiency

• renewable energies

2016

• Emissions peak

• Deforestation halved

• >10 CCS demo plants operating

'Business as usual' (IEA reference scenario)

2010

• CO2 emissions targets set for 2020, 2030, 2050

From 2010 onward

Rapid deployment:

• energy efficiency

• renewable energies

2016

• Emissions peak

• Deforestation halved

• >10 CCS demo plants operating

'Business as usual' (IEA reference scenario)

2050

• Energy emissions <50% 1990 levels

• Surface transport >90% carbon-free

199G

2GGG

2G2G

2G3G

2G4G

2G5G

Year

2050

• Energy emissions <50% 1990 levels

• Surface transport >90% carbon-free

199G

2GGG

2G2G

2G3G

2G4G

2G5G

Year deforestation begins now with its complete halting over the next twenty or thirty years (Figure 10.3).

3. The uncertainty in climate-carbon-cycle feedback presented in Figure 10.3 shows that, even if tropical deforestation is halted completely, emissions reductions in the energy sector as in the IEA BLUE Map scenario do not adequately allow for that feedback. To allow for likely values of that feedback, the emissions reduction curve constructed in Figure 11.27 assumes a larger reduction (from 1990, of 60% in global emissions or 50% in energy sector emissions) than that provided in the IEA BLUE Map scenario.

4. Cooling from aerosols (Chapter 10 page 313-14) provides an offset to some of the present warming. As pressure to reduce atmospheric pollution grows and as the use of coal and oil is phased out, the concentration of aerosols could reduce in future years faster than most scenarios suggest. These aerosol reductions will have to be matched by matching reductions in CO2 targets. But since reductions in aerosols take effect immediately (the lifetime of aerosols in the lower atmosphere is only a few days), these matching CO2 reductions need to be anticipated. There is a need to prepare now for that anticipation, for instance, by researching the most cost effective means of removing substantial amounts of CO2 from the atmosphere as mentioned on page 315.

5. It was assumed in Chapter 10 that some reduction of the concentration of other greenhouse gases, namely methane, nitrous oxide and halocarbons, from their 2005 levels would be possible and would compensate at least partially for the likely reductions in aerosols. Measures leading to these reductions need to be put in place but there is substantial uncertainty regarding their effectiveness.

6. Given only a 50% chance of meeting the 2 °C target, what are the chances of avoiding higher global average temperature rises that would bring much more severe consequences? For instance (see Tables 7.1, 7.5 and 7.6), with a 4 °C target, irreversible melting of some of the polar ice sheets becomes much more likely as does the possibility of changes in the large scale ocean circulation - in addition to much more severe impacts from extreme events. This is a point raised by the UK Climate Change Committee, the independent body appointed to give advice to the UK government about climate change targets and action, in their first report of December 2008.70 In addition to recommending the aim of a 50% chance of no more than 2 °C by 2100, they also consider it important to fulfil a further aim of less than 1% chance of 4 degrees by 2100. They present estimates showing that an emissions profile similar to that of Figure 11.27 would be likely to meet these criteria although the carbon dioxide equivalent concentration could reach at least 500 ppm by 2100 before

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