IPCC: GHG emissions accelerating despite mitigation efforts; major institutional and technological change required to keep the heat down
The UN Intergovernmental Panel on Climate Change (IPCC) released a policymaker’s summary of Working Group III’s (WG III) latest report showing that despite a growing number of climate change mitigation policies, annual anthropogenic 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.
The increase in anthropogenic emissions comes directly from energy supply (47%); industry (30%); transport (11%); and buildings (3%) sectors, the WG reported with medium confidence. Globally, economic and population growth continue to be the most important drivers of increases in CO2 emissions from fossil fuel combustion.
The contribution of population growth between 2000 and 2010 remained roughly identical to the previous three decades, while the contribution of economic growth has risen sharply (high confidence). Between 2000 and 2010, both drivers outpaced emission reductions from improvements in energy intensity. Increased use of coal relative to other energy sources has reversed the long‐standing trend of gradual decarbonization of the world’s energy supply.
|Total anthropogenic GHG emissions (GtCO2eq/yr) by economic sectors. IPCC WG III. Click to enlarge.
The report on mitigation from Working Group III, which is part of the IPCC’s larger Fifth Assessment Report (AR5), finds that it would be possible, using a wide array of technological measures and changes in behavior, to limit the increase in global mean temperature to two degrees Celsius above pre-industrial levels based on climate model projections. However, only major institutional and technological change will give a better than even chance that global warming will not exceed this threshold, the report cautioned.
Scenarios show that to have a likely chance of limiting the increase in global mean temperature to two degrees Celsius, means lowering global greenhouse gas emissions by 40 to 70% compared with 2010 by mid-century, and to near-zero by the end of this century. Ambitious mitigation may even require removing carbon dioxide from the atmosphere.
Scenarios reaching atmospheric concentration levels of about 450 ppm CO2eq by 2100 (consistent with a likely chance to keep temperature change below 2°C relative to pre‐industrial levels) include substantial cuts in anthropogenic GHG emissions by mid‐century through large‐scale changes in energy systems and potentially land use (high confidence).
At the global level, scenarios reaching 450 ppm CO2eq are also characterized by more rapid improvements of energy efficiency; a tripling to nearly a quadrupling of the share of zero‐ and low‐carbon energy supply from renewables; nuclear energy and fossil energy with carbon dioxide capture and storage (CCS); or bioenergy with CCS (BECCS) by the year 2050.
These scenarios also describe a wide range of changes in land use, reflecting different assumptions about the scale of bioenergy production, afforestation, and reduced deforestation.
Scenarios reaching higher concentrations include similar changes, but on a slower timescale.
Cutting emissions from electricity production to near zero is a common feature of ambitious mitigation scenarios. But using energy efficiently is also important.
For the report, about 1,200 scenarios from scientific literature were analyzed. These scenarios were generated by 31 modeling teams around the world to explore the economic, technological and institutional prerequisites and implications of mitigation pathways with different degrees of ambition.
Estimates of the economic costs of mitigation vary widely. In business-as-usual scenarios, consumption grows by 1.6 to 3% per year. Ambitious mitigation would reduce this growth by around 0.06 percentage points a year, according to the models. However, the underlying estimates do not take into account economic benefits of reduced climate change.
Transport sector. The transport sector accounted for 27% of final energy use and 6.7 GtCO2 direct emissions in 2010, with baseline CO2 emissions projected to approximately double by 2050 (medium evidence, medium agreement).
Emissions growth from increasing global passenger and freight activity could partly offset future mitigation measures that include fuel carbon and energy intensity improvements, infrastructure development, behavioral change and comprehensive policy implementation.
Overall, the report suggests, reductions in total transport CO2 emissions of 15–40% compared to baseline growth could be achieved in 2050.
Technical and behavioral measures for all transport modes, plus new infrastructure and urban redevelopment investments, could reduce final energy demand in 2050 by around 40% below the baseline.
Projected energy efficiency and vehicle performance improvements range from 30–50% in 2030 relative to 2010 depending on transport mode and vehicle type. Integrated urban planning, transit‐oriented development, a more compact urban form that supports cycling and walking—all can lead to modal shifts as can, in the longer term, urban redevelopment and investments in new infrastructure such as high‐speed rail systems that reduce short‐haul air travel demand (medium evidence, medium agreement).
Such mitigation measures are challenging, have uncertain outcomes, and could reduce transport GHG emissions by 20–50% in 2050 compared to baseline (limited evidence, low agreement), the report suggests.
Strategies to reduce the carbon intensities of fuel and the rate of reducing carbon intensity are constrained by challenges associated with energy storage and the relatively low energy density of low‐carbon transport fuels, although opportunities for switching to low‐carbon fuels exist in the near term and will grow over time.
Methane‐based fuels are already increasing their share for road vehicles and waterborne craft. Electricity produced from low‐carbon sources has near‐term potential for electric rail and short‐ to medium‐term potential as electric buses, light duty and 2‐wheel road vehicles are deployed.
Hydrogen fuels from low‐carbon sources constitute longer term options. Commercially available liquid and gaseous biofuels already provide co‐benefits together with mitigation options that can be increased by technology advances.
Additionally, reducing transport emissions of particulate matter (including black carbon), tropospheric ozone and aerosol precursors (including NOx) can have human health and mitigation co‐benefits in the short term.
Mitigation strategies, when associated with non‐climate policies at all government levels, can help decouple transport GHG emissions from economic growth in all regions, they report suggests. These strategies can help reduce travel demand, incentivize freight businesses to reduce the carbon intensity of their logistical systems and induce modal shifts, as well as provide co‐benefits including improved access and mobility, better health and safety, greater energy security, and cost and time savings (medium evidence, high agreement).
WG III. The Working Group III report consists of the Summary for Policymakers, a more detailed Technical Summary, the underlying 16 chapters, and three annexes. Working Group III chapter teams were formed by 235 authors and 38 review editors from 57 countries, and 180 experts provided additional input as contributing authors. More than 800 experts reviewed drafts of the report and submitted comments.
The Working Group III contribution to AR5 assesses literature on the scientific, technological, environmental, economic and social aspects of mitigation of climate change. It builds upon the Working Group III contribution to the IPCC’s Fourth Assessment Report (AR4); the Special Report on Renewable Energy Sources and Climate Change Mitigation (SRREN); and previous reports and incorporates subsequent new findings and research.
The report also assesses mitigation options at different levels of governance and in different economic sectors, and the societal implications of different mitigation policies, but does not recommend any particular option for mitigation.
The degree of certainty in findings in the assessment, as in the reports of all three Working Groups, is based on the author teams’ evaluations of underlying scientific understanding and is expressed as a qualitative level of confidence (from very low to very high) and, when possible, probabilistically with a quantified likelihood (from exceptionally unlikely to virtually certain).
Confidence in the validity of a finding is based on the type, amount, quality, and consistency of evidence (e.g., data, mechanistic understanding, theory, models, expert judgment) and the degree of agreement. Probabilistic estimates of quantified measures of uncertainty in a finding are based on statistical analysis of observations or model results, or both, and expert judgment. Where appropriate, findings are also formulated as statements of fact without using uncertainty qualifiers. Within paragraphs of this summary, the confidence, evidence, and agreement terms given for a bolded finding apply to subsequent statements in the paragraph, unless additional terms are provided.
The full report will be published 15 April.