MITIGATION: Challenges and opportunities - Key findings of WGIII in the Fifth Assessment Report With some recent developments

Editor's Notes

1. GHG emission growth has accelerated during the last decade. Despite a growing number of climate change mitigation policies, annual GHG emissions grew on average by 1.0 giga tonne carbon dioxide equivalent (GtCO2eq) (2.2%) per year from 2000 to 2010 compared to 0.4 GtCO2eq (1.3%) per year from 1970 to 2000. Total anthropogenic GHG emissions were the highest in human history from 2000 to 2010 and reached 49 (±4.5) GtCO2eq/yr in 2010. The global economic crisis 2007/2008 only temporarily reduced emissions. CO2 emissions from fossil fuel combustion and industrial processes contribute most to GHG emission levels and growth. After 2010 these emissions continued to grow by about 3% between 2010 and 2011 and by about 1-2% between 2011 and 2012.
2. Long-term scenarios can be assessed in a policy-relevant, but non-prescriptive way, by outlining their technological, economic and institutional requirements. Let us first look at the different characteristics of emission pathways. In most baseline scenarios GHG emissions continue to grow over the 21st century leading to atmospheric concentrations of 1000ppm CO2eq and more.
3. Most mitigation scenarios span atmospheric concentration levels in 2100 from 430 ppm CO2eq to roughly 720 ppm CO2eq. These concentration ranges translate into different mean temperature increases by the end of the 21st century. Mitigation scenarios in which it is likely that the temperature change caused by anthropogenic GHG emissions can be kept to less than 2°C relative to pre-industrial levels are characterized by atmospheric concentrations in 2100 of about 450 ppm CO2eq. Scenarios reaching these concentrations by 2100 are characterized by lower global GHG emissions in 2050 than in 2010, 40% to 70% lower globally, and emissions levels near zero GtCO2eq or below in 2100. But also less ambitious mitigation scenarios, in which the likely temperature change can be kept below 3°C, require a substantial deviation from baseline.
4. In this section, the evidence on long-term scenarios is assessed. The long-term scenarios assessed in WGIII were generated primarily by large-scale, integrated models that project many key characteristics of mitigation pathways to mid-century and beyond. These models link many important human systems (e.g., energy, agriculture and land use, economy) with physical processes associated with climate change (e.g., the carbon cycle). For the purpose of this assessment, roughly 300 baseline scenarios and 900 mitigation scenarios were collected through an open call from integrated modelling teams around the world. The assessment of this literature reveals that limiting warming to 2°C involves substantial technological, economic and institutional challenges. But even much less ambitious mitigation scenarios require a fundamental deviation from baseline.
5. Pink: medium 2 °C scenarios—limiting warming during the twenty-first century to below 2 °C with 50–66% chance; orange: likely 2 °C scenarios—limiting warming during the twenty-first century to below 2 °C with >66% chance; blue: 1.5 °C scenarios—limiting warming in 2100 to below 1.5 °C with >50% chance. Thin black lines are scenarios included in the IPCC AR5 scenario database.
6. In this section, the evidence on long-term scenarios is assessed. The long-term scenarios assessed in WGIII were generated primarily by large-scale, integrated models that project many key characteristics of mitigation pathways to mid-century and beyond. These models link many important human systems (e.g., energy, agriculture and land use, economy) with physical processes associated with climate change (e.g., the carbon cycle). For the purpose of this assessment, roughly 300 baseline scenarios and 900 mitigation scenarios were collected through an open call from integrated modelling teams around the world. The assessment of this literature reveals that limiting warming to 2°C involves substantial technological, economic and institutional challenges. But even much less ambitious mitigation scenarios require a fundamental deviation from baseline.
7. In this section, the evidence on long-term scenarios is assessed. The long-term scenarios assessed in WGIII were generated primarily by large-scale, integrated models that project many key characteristics of mitigation pathways to mid-century and beyond. These models link many important human systems (e.g., energy, agriculture and land use, economy) with physical processes associated with climate change (e.g., the carbon cycle). For the purpose of this assessment, roughly 300 baseline scenarios and 900 mitigation scenarios were collected through an open call from integrated modelling teams around the world. The assessment of this literature reveals that limiting warming to 2°C involves substantial technological, economic and institutional challenges. But even much less ambitious mitigation scenarios require a fundamental deviation from baseline.
8. NOT FROM IPCC
9. NOT FROM IPCC!!
10. About CRV: Quoting Müller (2013): In accounting, the value of an asset can be expressed, among others, as the historical cost (original monetary value) or as the replacement cost (cost of replacing an asset with current prices). Similarly, the carbon footprint of a stock can be defined as the historical emissions produced to build up the stock, or as the carbon emissions that would be generated if the existing stock was replaced using current technologies. As emissions per ton of material produced tend to decline, the replacement value expressed in carbon (here called “carbon replacement value, CRV”) is generally smaller than the historical value expressed in carbon (here called “CHV”). In this study, we determine the CRV of stocks, because this value is better suited when using the stocks in industrialized countries as a benchmark for stocks in developing countries. The CRVP was determined for the year 2008 using the three key materials steel, cement, and aluminum as a proxy. In 2008, these materials accounted for nearly half of industrial emissions (25% steel, 19% cement, and 3% aluminum) and 17% of total energy- and process-related CO2 emissions.16 Emissions of other materials are either less significant for infrastructure stocks (e.g., plastic and paper, which together constitute about 3% energy- and process-related emissions) or contribute significantly smaller amounts of emissions (e.g., other metals, gravel). Talking points: Concerning emissions from building urban structures (building up stocks) it is important to understand the magnitude of future emissions awaiting us if the developing world would mimic the pathway western countries have taken. The y-axis shows the amount of emissions (per person) needed to build the infrastructures (houses, transport (streets, railways, bridges), industry plants) existing in respective countries. You can see that developed countries (Annex I) have a far greater stock than Non-Annex I countries.
11. Talking points: The shaded area shows how much emissions would be needed to build in the rest of the world infrastructure of the level as existing today in developed countries. This rough estimate takes the expected increase of world population until 2050 into account (see x-axis). Compare the size of this area to the yellow-red coloured bars to see that these emissions would far outstrip the emissions needed to build up today’s infrastructure.
12. Mitigation scenarios in which policies stabilize atmospheric concentrations (without overshoot) in the range from 430 to 530 ppm CO2eq by 2100 lead to substantial shifts in annual investment flows during the period 2010–2029 compared to baseline scenarios. Annual incremental energy efficiency investments in transport, buildings and industry is projected to increase by about USD 336 (1–641) billion, frequently involving modernization of existing equipment. Annual investment in conventional fossil fuel technologies associated with the electricity supply sector is projected to decline by about USD 30 (2–166) billion (median: -20% compared to 2010) while annual investment in low-carbon electricity supply (i.e., renewables, nuclear and electricity generation with CCS) is projected to rise by about USD 147 (31–360) billion (median: +100% compared to 2010). For comparison, global total annual investment in the energy system is presently about USD 1200 billion.
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14. NOT FROM IPCC just illustration
15. NOT FROM IPCC just illustration
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17. This figure shows four concepts by which urban form can be characterized – these also function as drivers of urban emissions. (1) The 2nd column shows the effect of the 4 drivers on Vehicles Kilometer Travelled (VKT). It turns out the increasing the drivers leads (in all but 2 cases) to a reduction of distances travelled, which in turn means less emissions. (2) the 3rd column describes how the drivers are measured. (3) The 4th column shows how the drivers co-vary with the (main) driver density. (4) the last columns illustrate what leads to higher resp. lower emissions.
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19. In this section, the evidence on long-term scenarios is assessed. The long-term scenarios assessed in WGIII were generated primarily by large-scale, integrated models that project many key characteristics of mitigation pathways to mid-century and beyond. These models link many important human systems (e.g., energy, agriculture and land use, economy) with physical processes associated with climate change (e.g., the carbon cycle). For the purpose of this assessment, roughly 300 baseline scenarios and 900 mitigation scenarios were collected through an open call from integrated modelling teams around the world. The assessment of this literature reveals that limiting warming to 2°C involves substantial technological, economic and institutional challenges. But even much less ambitious mitigation scenarios require a fundamental deviation from baseline.