Friday, October 25, 2013

Getting to Zero Carbon Emissions – What Can Cities Do?

Rethinking wedges(9 page pdf, Steven J Davis, Long Cao, Ken Caldeira and Martin I Hoffert, Environmental Research Letters, Jan. 9, 2013)

Also discussed here: The link between a global 2 °C warming threshold and emissions in years 2020, 2050 and beyond(9 page pdf, Chris Huntingford, Jason A Lowe, Laila K Gohar,Niel H A Bowerman, Myles R Allen,, Sarah C B Raper and Stephen M Smith, , Environmental Research Letters, Mar. 5, 2012)

Today we review a recent approach to achieving climate equilibrium using advanced global climate models and as many as 31 scenarios of emission reductions, each identified with certain strategies as a “wedge”. The wedge concept was introduced in 2004 and that time only 7 wedges were necessary. With the continued increase in carbon emissions since then, the goal has become more challenging and may (or will) require negative emissions by scavenging CO2 from the atmosphere, in addition to achieving zero emissions into it. As ¾’s of the global emissions come from cities and most of that comes from vehicle emissions and the heating and cooling of buildings, the primacy of the role of Mayors and their citizens is clear, as demonstrated by Mayor Bloomberg in New York City in PlaNYC 2030 and, globally, in leading the C40 initiative over the last 8 years of his administration. One hopes that other Mayors will step up to the plate. wedges zero emissions  

Key Quotes:

“Since 2004, annual emissions have increased and their growth rate has accelerated, so that more than seven wedges would now be necessary to stabilize emissions”

“Phasing out emissions over 50 years could be achieved by deploying on the order of 19 'wedges', each of which ramps up linearly over a period of 50 years ….depends upon coordinated efforts to innovate, plan, and deploy new transportation and energy systems that can provide affordable energy at this scale without emitting CO2 to the atmosphere.”

“holding emissions constant at current levels for the next half-century would cause substantial warming, approaching or surpassing current benchmarks ”

“Most model scenarios that allow CO2 concentrations to stabilize at 450 ppm entail negative carbon emissions, for example by capturing and storing emissions from bioenergy “

Gross world product (GWP) projections embedded in the A2 scenario imply as many as 31 wedges would be required to completely phase-out emissions”

“eliminating emissions over 50 years would require 19 wedges: 9 to stabilize emissions and an additional 10 to completely phase-out emissions. And if historical, background rates of decarbonization falter, 12 'hidden' wedges will also be necessary, bringing the total to a staggering 31 wedges.”

“CCS [carbon capture and storage } has not yet been commercially deployed at any centralized power plant; the existing nuclear industry.. is in a period of retrenchment, not expansion; and existing solar, wind, biomass, and energy storage systems are not yet mature enough to provide affordable baseload power at terawatt scale. Each of these technologies must be further developed if they are to be deployed at scale and at costs competitive with fossil energy.”
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