Saving the planet: Emissions scenarios, stabilization issues, and uncertainties “NCAR Summer Colloquium on Climate and Health” NCAR, Boulder, CO. 19 July, 2006. Tom Wigley, National Center for Atmospheric Research, Boulder, CO. Introduction.
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Saving the planet: Emissions scenarios, stabilization issues, and uncertainties“NCAR Summer Colloquium on Climate and Health”NCAR, Boulder, CO.19 July, 2006
National Center for Atmospheric Research, Boulder, CO.
The climate change problem is essentially an energy problem that requires moving away from the use of fossil fuels as our primary energy source.
This will almost certainly require the development of new “carbon-free” (or “carbon neutral”) energy technologies.
To determine the magnitude of this technological challenge we need to know what will happen in the absence of policies to limit climate change, and what a safe level may be for future climate change.
Climate changes observed over the 20th century
Future climate change: the no-policy case
Future climate change: stabilization policies
Future changes in energy production
Carbon-free energy requirements for stabilization
The ‘wedge’ concept
PAST CLIMATE CHANGE issues, and uncertainties
5 of the 6 warmest years have occurred this decade.
1998 was unusually warm due to a large El Niño that occurred in 1997/8.
FUTURE CLIMATE CHANGE issues, and uncertainties
(in the absence of policies to reduce climate change)
“Special Report on Emissions Scenarios”, Eds. N. Nakicenovic & R. Swart, C.U.P. (2000)
Remember, the ‘B’ scenarios focus on sustainable development.
NOTE: Increasing CO2 is not only a climate problem.
Increasing CO2 makes the ocean more acidic, eventually making it impossible for carbonate shell-producing animals to produce shells.
Extinction of these animals will upset the ocean food chain and could lead to much larger scale extinctions
RELATIVE IMPORTANCE OF CO2 issues, and uncertainties
NOTE: Dominant role of CO2
THE POLICY CASE: CONCENTRATION STABILIZATION issues, and uncertainties
Article 2 provides the basis for climate policy. Its objective is …
“stabilization of greenhouse gas concentrations ….. at a level that would prevent dangerous anthropogenic interference with the climate system ….. within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner”.
POINTS TO NOTE
NOTE: Even in the absence of climate policies, large increases are projected for carbon-free energy
HOW MUCH ADDITIONAL CARBON-FREE ENERGY IS REQUIRED FOR CO2 CONCENTRATION STABILIZATION?
The answer depends on the assumed no-policy baseline scenario (35 possibilities in the SRES scenario set) – and on the chosen concentration stabilization level (also a wide range of possibilities).
This implies a wide uncertainty range.
The blue lines show how much carbon-free energy is already built into the baseline scenarios
In the B1 case, the vertical arrow shows the additional carbon-free energy required to move from the no-policy B1 scenario to the WRE450 stabilization pathway.
Note that B1 is a very optimistic scenario – other baseline scenarios require much greater amounts of additional carbon-free energy.
* Current carbon-free energy 2TW
POINTS TO NOTE
(1) The baseline scenarios show large increases in carbon-free energy even in the absence of climate policies. This limits the options for additional carbon-free energy.
(2) The large amounts of carbon-free energy required for stabilization levels of 450ppm or less will almost certainly require the development of new technologies.
* Current carbon-free energy 2TW
TECHNOLOGY OPTIONS CONCENTRATION STABILIZATION?
* Includes direct capture from the atmosphere
TECHNOLOGY “WEDGES” CONCENTRATION STABILIZATION?
A ‘wedge’ is a single existing technology that can be scaled up to reduce CO2 emissions by 1GyC/yr in 2055; or reduce cumulative emissions over 2005–2055 by 25GtC.
Pacala and Socolow claim that a 500 ppm stabilization pathway can be followed, at least to 2055, using existing technology. This is incorrect.
S. Pacala & R.Socolow: Science 305, 968–972 (2004)
The flaw in Pacala and Socolow is that they fail to account for wedges already built into the baseline scenario. SRES baselines all contain a large amount of carbon-free energy growth (red arrow) that arises spontaneously, in the absence of climate policy.
Wedges already built into no-policy baseline: neglected by Pacala and Socolow.
POINTS TO NOTE
Wedges already built into no-policy baseline
OTHER TECHNOLOGY OPTIONS: GEOENGINEERING CONCENTRATION STABILIZATION?
As an analogy, we consider a case where we know the effects of a known injection of SO2 into the stratosphere, the eruption of Mt Pinatubo (June, 1991)
Pinatubo released 10TgS of SO2 into the stratosphere. This is 15-20% of the current amount of SO2 that we release each year into the troposphere. The eruption cooled the planet by 0.5 – 0.7oC.
Scenarios like these produce immediate cooling, offsetting the short-term effects of increasing CO2.
This means that, with geoengineering, we would not have to reduce CO2 concentrations or emissions so rapidly.
This gives us more time to develop alternative, cost-effective carbon-free energy sources.
-3W/m2 is equivalent to Pinatubo every two years (5TgS/yr)
Overshoot is the case that includes geoengineering.
Note how this gives us much more time (around 20 years) to begin the required rapid reduction in CO2 emissions – i.e., more time to phase out existing energy systems and develop alternative technologies.
The important comparison here is between WRE450 (mitigation alone) and LOW, MID or HIGH GEO (geoengineering combined with slower mitigation, but with the same CO2 stabilization level).
Thankyou CONCENTRATION STABILIZATION?