Attribution of Extreme Weather & Natural Gas, Fracking and Methane Leaks Steve Pacala Princeton University February 2016
Attribution of Extreme Weather Humans are moved to action by personal, immediate and tangible threats. We seem to be adapted to reassess risk after damage. Climate change is seen as remote, impersonal and intangible. What does 2 degrees of global warming mean to me? This appears to be changing because of surprisingly rapid changes in extreme weather. You may have heard that it is impossible to attribute any one extreme weather event to climate change. This is no longer true.
Attribution of Extreme Weather Attribution of heat waves (the greatest killer), extreme precipitation (the greatest damager of property), drought (including the Californian drought) and some aspects of hurricanes (a portion of the coastal flooding) is already a fixture in the mainstream, peer reviewed scientific literature. Real-time attribution within the news cycle is just around the corner. This may be climate’s smoking and cancer moment.
Examples 1. >10-fold increase in frequency for a heat waves like the 2010 Moscow or 2003 European events. 2. 20X increase for a 2011Texas drought. 3. 10X decrease for a UK winter as cold as the 2009/2010. 4. 4X increase for a failure of the annual rains like that in 2011 in East Africa. 5. 2000X increase for the Australian heat of 2013 (from multiple independent studies) 6. > 2X for the heat in China in 2013. 7. 3X for the Welsh floods of 2000. 8. 25% increase for the extreme European 2013 precip. 9. >200X increase in a 9 foot storm surge in NYC 10. Significant enhancement of current Californian drought.
How does attribution work? IPCC AR5 It is virtually certain that internal variability alone cannot account for the observed global warming since 1951. It is virtually certain that human influence has warmed the global climate system.
Attribution of climate change IPCC AR5 Global Mean Temperature Model-Data Comparison With and Without Anthropogenic Forcing
Extremes have changed rapidly. IPCC SREX on Extremes and AR5 Coldest Hottest daytime daytime high high Model- estimates of Return time in changes due the 1990’s for solely to an extreme anthropogenic with a 20-year GHG’s and return time in aerosols. the 1960’s 1960’s coldest 1960’s hottest nighttime low nighttime low in 20-years in 20-years occurs every occurs every 8 38 years in the years in the 1990’s 1990’s
How does attribution work? Frequency : Return time for a temperature exceeding T degrees, daily precipitation exceeding P cm, season with less than R cm of rain, or windspeed in excess of W kph. Severity : Hottest/coldest temperature, highest 1-day precipitation, driest summer, or highest windspeed in Y years.
How does attribution work? Frequency Frequency 150 Severity 140 130 Severity 120 Severity Extreme 110 100 Value 90 80 Distributions 0 200 400 600 800 1000 Return Time = 1/ Frequency
How does attribution work? Fraction of Attributable Risk : FAR= (1- R N /R A,N ) Where: R A,N is the frequency of the event today and R N is the frequency of an event of the same severity without increased greenhouse gasses. REQUIRES MODEL . 140 130 Severity 120 110 Without With anthropogenic anthropogenic 100 = 1/380 forcing R A,N = 1/950. forcing R N 90 80 0 100 200 300 400 500 600 700 800 900 1000 Return Time
Attribution Literature IPCC AR5 Bull. Amer. Met. Soc. (BAMS) (2013) special reports on the previous year’s extreme events. 2012 2013 2014 IPCC Special Report on Extremes (2012)
Extremes have changed faster than the mean. ~1/2 of the events investigated in the BAMS reports had FAR’s > 0.9. This implies a more than 10X change in the frequency of these events. And real-time attribution is just around the corner.
Environmental Implications of Shale Gas BACKGROUND: Natural gas is used primarily for electricity production and heating and could be used as a dominant transport fuel. Gas, coal, nuclear and hydro are our only significant sources of base-load electricity. Gas is the primary source of peaking electricity. Wind and solar are limited by our inability to store energy at grid scales. EVIRONMENTAL BENEFIT: For the same useful energy gas has half the CO2 emissions of coal and three quarters that of oil. ENVIRONMENTAL COSTS: 1. Natural gas leaks could eliminate its greenhouse advantage because methane (CH4), the primary component of gas, is 120 more potent as a greenhouse agent than CO2. 2. Groundwater contamination. 3. Seismic events. 4. Slows adoption of renewables.
Environmental Implications of Shale Gas Dispute about methane leaks: 1. EPA estimates are not believable (and are low). 2. Anti-fracking groups assert large methane leaks (i.e. 6%), making gas worse than coal. 3. Industry groups say EPA estimates too high and that no regulation is required. A consortium including the Environmental Defense Fund, 10 big gas producers, and many academics measured the leaks from the US infrastructure.
Fugitive Methane Emissions • Is gas better for the climate than coal? Gas combustion emits half the CO 2 emissions of coal (per unit energy), but usually entails more fugitive methane emissions. • How does one compare emissions of CO2 and CH4?
Fate of Emissions Pulses (equal mass) 1.2 CH 4 is converted in the atmosphere to Fraction of Mass 1 CO 2 with a half life of ~12 years. CO 2 Remaining 0.8 CO2 has a complex residence time in the 0.6 atmosphere but a large fraction 0.4 CH4 remains for 100’s of years. 0.2 0 0 20 40 60 80 100 Time (years) 100 But remember that CH 4 in the atmosphere creates 120 times more radiative forcing than an 10 equal mass of CO 2 : Radiative forcing CH4 CO2 Note that the radiative forcing from a pulse of either CH 4 or CO 2 decreases over time, but the 1 0 50 100 CH 4 forcing decreases faster. *Radiative forcing values are normalized so that a unit mass 0.1 of CO 2 in the atmosphere has radiative forcing of one. Time (years)
Methane GWP 120 120 The Global Warming Potential The commonly used measure of the climate impact of a greenhouse gas is the cumulative 100 100 radiative forcing for the gas relative to that of CO 2 . 80 80 For methane, this is the cumulative radiative Methane GWP forcing caused by a pulse of CH4 emission up to TH years, divided by the corresponding forcing 60 60 from an equal-mass emissions of CO 2 . 40 40 20 20 There is no scientifically correct value for the time horizon! 0 0 0 10 20 30 40 50 60 70 80 90 100 Time Horizon (years)
Technology Warming Potential To compare the climate change from a gas and coal power plant, one uses a “technology warming potential” (TWP(TH)) (Alvarez et al. 2012, PNAS): Fugitive Emissions from production, processing and CH4 CO2 emissions distribution, scaled to the gas from the gas plant. GWP. used by the plant. CH4 CO2 emissions Methane emissions from coal GWP. from the coal mining scaled to the coal plant. consumed by the plant. Note that this depends on TH! TWP(TH)’s can be used to compare any two technologies that emit CH 4 and/or CO 2 .
GHG Comparisons Using an EPA estimate that 2.4% of methane is emitted during gas production, processing and distribution, and other assumptions in Alvarez et al. (2012, PNAS): CNG vs. CNG vs. Heavy Combined Cycle Gas Gasoline Car Diesel Truck vs. Coal Power Plant Because this is less than 1 for all TH, gas is always better than coal if EPA methane emissions estimates circa 2011 were correct. TH: Time since the switch to gas. Dotted line: TWP(TH) showing the effect of a single pulse of operation (i.e. a day). Dashed line: TWP (TH) for a pulse lasting the lifetime of the infrastructure (50 years for a power plant). Solid line: TWP(TH) for a permanent switch from coal to gas (i.e. the pulse persists from zero to TH).
Methane Leakage To achieve net greenhouse benefit over ALL time horizons, methane leaks must be less than: ~2% for a CNG vs. gasoline car ~1% for a CNG vs. heavy diesel truck ~3% for combined cycle vs. pulverized coal electricity From Alvarez et al. 2012. PNAS
EDF Study of Fugitive Methane emissions in the US
Note that this is 0.9% smaller than EPA estimate in Alvarez et al. (2012).
Barnett Shale 2013
Barnett Campaign Top-down and bottom-up emissions almost never agree. Top-down estimates are usually larger than bottom-up, which casts doubt on our ability to know the correct answer, allows pro-fracking forces to claim that EPA estimates are too high, and anti-fracking forces to claim that EPA methods miss the dominant sources of emissions .
Barnett Campaign In the end: Top-down measurements: 7 separate estimates from aircraft methane measurements. 6 separate estimates from aircraft ethane measurements. Bottom-up measurements: 1 extensive random sample 3 extensive non-random samples targeting the rare high emitters that dominate the total emission rate. The non-randomness is correctly accounted for when integrating the random and nonrandom samples. Helicopter Infrared: Imagery of large sample production wells, compressors and processing plants.
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