Comment Log Display

California Cap on Greenhouse Gas Emissions and Market-Based
Compliance Mechanisms for Methane will establish a regulation that
has fixed the methane GWP at 21, which conflicts with the best
available science. 

The Compliance Offsets Protocol - Rice Cultivation Projects uses a
Methane GWP of 21, referenced through Table A-1, p 52 of the
Regulation for the Mandatory Reporting of Greenhouse Gas Emissions.


The use of such a Methane GWP Coefficient is not in accord with the
latest IPCC Methane GWP coefficients, which are 28 and 34 for a 100
year interval and 84 and 86 for a 20 year interval. Use of the
Methane GWP 21 grossly underestimates the global warming impact of
methane, and any cap and trade program needs to update the methane
GWP expeditiously to be legally and ethically tenable. An intent to
update expeditiously this methane GWP is not expressed in the
document.

Pasted below as Exhibit A is a long segment of text from Robert
Howarth's seminal 2014 publication (attached) as support for my
claims above. It includes some language about natural gas as a fuel
but then moves into reasons for why shorter time frames and higher
methane GWPs should be considered in assessing methane's impact
upon climate change.

To conclude, I urge the CARB to address seriously the current
artificial deflation of methane GWP coefficients and methane global
warming impact that is currently reflected in this rule making
process for rice cultivation.

Please keep on the list to receive all communications on this
issue.

Respectfully submitted,

Mr. Ara Marderosian
Sequoia ForestKeeper®
P.O. Box 2134
Kernville, CA 93238
(760) 376-4434
www.sequoiaforestkeeper.org 

Exhibit A

A bridge to nowhere: methane emissions and the greenhouse gas
footprint of natural gas
Robert W. Howarth Department of Ecology & Evolutionary Biology,
Cornell University, Ithaca, New York 14853
 
2014 The Author. Energy Science & Engineering published by the
Society of Chemical Industry and John Wiley & Sons Ltd.
 
Received: 4 March 2014; Revised: 18 April 2014; Accepted: 22 April
2014
 
Pages 6-9

The GWP of Methane
 
While methane is far more effective as a greenhouse gas than carbon
dioxide, methane has an atmospheric lifetime of only 12 years or
so, while carbon dioxide has an effective influence on atmospheric
chemistry for a century or longer [34]. The time frame over which
we compare the two gases is therefore critical, with methane
becoming relatively less important than carbon dioxide as the
timescale
increases. 

Of the major papers on methane and the GHG for conventional natural
gas published before our analysis for shale gas, one modeled the
relative radiative forcing by methane compared to carbon dioxide
continuously over a 100-year time period following emission [2],
and two used the global warming approach (GWP) which compares how
much larger the integrated global warming from a given mass of
methane is over a specified period of time compared to the same
mass of carbon dioxide. Of
the two that used the GWP approach, one showed both 20-year and
100-year GWP analyses [3] while another used only a 100-year GWP
time frame [4]. Both used GWP values from the Intergovernmental
Panel on Climate Change (IPCC) synthesis report from 1996 [35], the
most reliable estimates at the time their papers were published. In
subsequent reports from the IPCC in 2007 [36] and 2013 [34] and in
a paper in Science by workers at the NASA Goddard Space Institute
[37], these GWP values have been substantially increased, in part,
to account for the indirect effects of methane on other radiatively
active substances in the atmosphere such as ozone (Table 2). 

In Howarth et al. [8], we used the GWP approach and closely
followed the work of Lelieveld and colleagues [3] in presenting
both integrated 20 and 100 year periods, and in giving equal
credence and interpretation to both timescales. We upgraded the
approach by using the most recently published values for GWP at
that time [37]. These more recent GWP values increased the relative
warming of methane compared to carbon dioxide by
1.9-fold for the 20-year time period (GWP of 105 vs. 56) and by
1.6-fold for the 100-year time period (GWP of 33 vs. 21; Table 2).


Our conclusion was that for the 20-year time period, shale gas had
a larger GHG than coal or oil even at our low-end estimates for
methane emission (Fig. 1); conventional gas also had a larger GHG
than coal or oil at our mean or high-end methane emission
estimates, but not at the very low-end range for methane emission
(the best-case, low-emission scenario). At the 100-year timescale,
the influence of methane was much diminished, yet at our high-end
methane emissions, the
GHG of both shale gas and conventional gas still exceeded that of
coal and oil (Fig. 1). Of nine new reports on methane and natural
gas published in 9 months after our April 2011 paper [8], six only
considered the 100-year time frame for GWP, two used both a 20- and
100-year time frame, and one used a continuous modeling of
radiative forcing over the 0–100 time period (Table 2). Of the six
papers that only examined the 100-year time frame, all used the
lower GWP value of 25 from the 2007 IPCC report rather than the
higher value of 33 published by Shindell and colleagues in 2009
that we had used; this higher value better accounts for the
indirect effects of methane on global warming. 

Many of these six papers implied that the IPCC dictated a focus on
the 100-year time period, which is simply not
the case: the IPCC report from 2007 [36] presented both 20- and
100-year GWP values for methane. And two of these six papers
criticized our inclusion of the 20-year time period as
inappropriate [14, 17]. I strongly disagree with this criticism. In
the time since April 2011 I have come increasingly to believe that
it is essential to consider the role of methane on timescales that
are much shorter than 100 years, in part, due to new science on
methane and global warming presented since then [34, 41, 42],
briefly summarized below. The most recent synthesis report from the
IPCC in 2013 on the physical science basis of global warming
highlights the role of methane in global warming at multiple
timescales, using GWP values for 10 years in addition to 20 and 100
years (GWP of 108, 86, and 34,
respectively) in their analysis [34]. The report states that “there
is no scientific argument for selecting 100 years compared with
other choices,” and that “the choice of time horizon . . .. depends
on the relative weight assigned to the effects at different times”
[34]. The IPCC further concludes that at the 10-year timescale, the
current global release of methane from all anthropogenic sources
exceeds (slightly) all anthropogenic carbon dioxide emissions as
agents of global warming; that is, methane emissions are
more important (slightly) than carbon dioxide emissions for driving
the current rate of global warming. At the 20- year timescale,
total global emissions of methane are equivalent to over 80% of
global carbon dioxide emissions. And at the 100-year timescale,
current global methane emissions are equivalent to slightly less
than 30% of carbon dioxide emissions [34] (Fig. 3). This difference
in the time sensitivity of the climate system to methane and carbon
dioxide is critical, and not widely appreciated by the policy
community and even some climate scientists. While some note how the
longterm momentum of the climate system is driven by carbon dioxide
[15], the climate system is far more immediately responsive to
changes in methane (and other short-lived radiatively active
materials in the atmosphere,
such as black carbon) [41]. 

The model published in 2012 by Shindell and colleagues [41] and
adopted by the United Nations [42] predicts that unless emissions
of methane and black carbon are reduced immediately, the Earth’s
average surface temperature will warm by 1.5°C by about 2030 and by
2.0°C by 2045 to 2050 whether or not carbon dioxide emissions are
reduced. Reducing methane and black carbon emissions, even if
carbon dioxide is not controlled, would significantly slow the rate
of global warming and postpone reaching the 1.5°C and 2.0°C marks
by 15–20 years. Controlling carbon dioxide
as well as methane and black carbon emissions further slows the
rate of global warming after 2045, through at least 2070 [41, 42]
(Fig. 4). 

Why should we care about this warming over the next
few decades? At temperatures of 1.5–2.0°C above the 1890–1910
baseline, the risk of a fundamental change in the Earth’s climate
system becomes much greater [41–43], possibly leading to runaway
feedbacks and even more global warming. Such a result would dwarf
any possible benefit from reductions in carbon dioxide emissions
over the next few decades (e.g., switching from coal to natural
gas,
which does reduce carbon dioxide but also increases methane
emissions). One of many mechanisms for such catastrophic change is
the melting of methane clathrates in the oceans or melting of
permafrost in the Arctic. Hansen and his colleagues [43, 44] have
suggested that warming of the Earth by 1.8°C may trigger a large
and rapid increase in the release of such methane. While there is a
wide range in both the magnitude and timing of projected carbon
release from thawing permafrost and melting clathrates in the
literature [45], warming consistently leads to greater release.
This release can in turn cause a
feedback of accelerated global warming [46]. 

To state the converse of the argument: the influence of
today’s emissions on global warming 200 or 300 years into the
future will largely reflect carbon dioxide, and not methane, unless
the emissions of methane lead to tipping points and a fundamental
change in the climate system. And that could happen as early as
within the next two to three decades. An increasing body of science
is developing rapidly that emphasizes the need to consider
methane’s influence over the decadal timescale, and the need to
reduce methane emissions. 

Unfortunately, some recent guidance for life cycle assessments
specify only the 100-year time frame [47, 48], and the EPA in 2014
still uses the GWP values from the IPCC 1996 assessment and only
considers the 100-year time period when assessing methane emissions
[49]. In doing so, they underestimate the global warming
significance of methane by 1.6-fold compared to more recent values
for the 100-year time frame and by four to fivefold compared to the
10- to 20-year time frames.