Hi Peter,
As regards "immediate global warming potential (GWP)", Mike MacCracken
has just explained that, as you reduce the duration
from 20 years (when GWP is 72) down to near zero, the global warming
potential converges on a
value - which he estimates at around 100. That was the figure I was
looking for. Thanks, Mike.
However Peter, you are right that it is integration over time which
matters. This is
partly why Copenhagen is doomed to failure. Global warming is
proportional to climate forcing from excess greenhouse gases in
the atmosphere
(excess above pre-industrial levels), where this excess is an integration
of anthropogenic contributions over many decades. There is already an
enormous excess of CO2 in the atmosphere, sufficient for
global warming to continue for millennia. Emissions cuts just cannot
be
drastic enough to halt global warming in the required timescale.
I don't know how any scientist can deny this. Yet, in a desperate
attempt to
get government commitments at Copenhagen to cut CO2 emissions, it
appears that
scientists have conspired to lie to governments and the media,
by stating that emissions reductions by themselves can make the planet
safe for future generations. Having lied about this, they cannot then
turn round and say sorry but actually there need to be additional
actions:
(1) to actively remove CO2 from the atmosphere by
geoengineering techniques such as biochar;
(2) to cool the Arctic
by solar radiation management (SRM) geoengineering.
A consequence of the big lie is that scientists are now afraid to
admit that geoengineering is needed. And the SRM geoengineering is
needed particularly urgently, because they underestimated the speed of
sea ice
retreat in particular.
This is essentially cowardice, but there is also money at stake,
because
there is no financial motivation for scientists to come clean, and
accept both my simple argument for SRM geoengineering and your equally
simple argument for biochar, Peter. Climate scientists are only too
happy to continue
their research indefinitely, which somebody here described as
"fiddling while Rome burns" - quite an apt analogy.
How do we break out of this impasse? Can we hope that the media picks
up on the arguments, and the scientific consensus moves rapidly towards
a rational and comprehensive approach to saving the planet, taking the
politicians with them? Time is in short supply. A myopic focus on
emissions reduction, to exclusion of geoengineering, would be an
unmitigated disaster for humanity. Perhaps failure at Copenhagen will
provide an opportunity for a new, comprehensive approach, so
desperately needed.
Cheers from Chiswick,
John
---
Mike MacCracken wrote:
Re: [geo] Re: Rejected - a simple argument for SRM
geoengineering
Agreed, one has to consider a time period, so
assume one takes a day that when injected there is no decay over this
period—so it might as well be a second of time one takes—so virtually
instantaneous. And I’ll assume linearity on methane absorption and
logarithmic for CO2.
So, for methane, humans have caused an increase of roughly 1000 ppb
which converts to about 3 GtCH4, and this causes a forcing of about 0.5
W/m**2 (at the tropopause) per IPCC.
For CO2, we know that a doubling (so we’ll say from 300 to 600 ppm so
we are in the range of interest) causes a forcing of about 3.6 W/m**2
(at the tropopause). So, 300 ppm of CO2 in the atmosphere is roughly
600 GtC or 2200 GtCO2 (and global warming potential is done for CO2, I
believe.
So, if we take the ratio of forcing to mass for CH4 divided by the
ratio of forcing to mass for CO2, we get a rough estimate of the
instantaneous GWP, so
[0.5/3]/[3.6/2200] equals roughly 100
for the ratio at t=0 (so allowing for no decay) of the radiative
forcing caused by a unit mass of CH4 added to the atmosphere to a unit
mass of CO2 added to the atmosphere.
Not exact, but plausible.
Mike
On 11/16/09 3:42 AM, "Peter Read" <[email protected]> wrote:
John,
Andrew
Re "BTW, does anybody know the _immediate_
warming potential of methane?"
Someone will correct me no doubt but my
understanding is that warming is a rate process measured in W/m^2
So "instantaneous" [[== "immediate"?]] warming is an incorrect concept
Unless it continues for a second, a week, a year, 25 years, for
whatever, no warming takes place.
So it is necessary to multiply by a duration to get joules/m^2
It's how many joules get into the low albedo meltwater on top of
Greenland's ice that decides how much gets melted each year to fall
down crevasses and lubricate the eventual collapse of large areas of
ice into the oceans.
Meaning that the integral [[roughly]] under the CO2 level curve is what
matters [multiplied by the warming potential over that period] when it
comes to measuring threats of Greenland's collapse
So the key issue is duration - how long elevated greenhouse gas levels
last and how to get them down.
Think that's right
Peter
----- Original Message -----
From: John Nissen <mailto:[email protected]>
To: [email protected]
Cc: geoengineering <mailto:[email protected]>
Sent: Monday, November 16, 2009 6:18 PM
Subject: Re: [geo] Re: Rejected - a simple argument for
SRM geoengineering
Hi Andrew,
You say: "I don't oppose John's argument, but the evidence on the
severity of the problem is far from conclusive." I disagree.
The methane presents a very real risk - because of the uncertainty on
timing combined with the potential size of methane discharge - perhaps
even enough to cause thermal runaway due to positive feedback, as is
thought to have happened in the past [1]. Risk management involves
identifying events and assessing them in terms of their likelihood and
magnitude of impact [2]. Thus something with a small likelihood (such
as rapid massive methane excursion) can have a high risk, if the
magnitude of impact is sufficiently large (and you can't get much
larger than thermal runaway).
It is possible that much or most of the methane trapped in frozen
structures has built up over hundreds of thousands of years. There is
little sign of massive methane discharge in the ice record. In fact
methane seems to track the temperature even better than CO2 [3].
But of course methane discharge is not the only high risk event -
there is also the Greenland ice sheet disintegration.
BTW, does anybody know the _immediate_ warming potential of methane,
as opposed to the 20 year value (72), 100 years (25) or 500 years
(7.6)? The lifetime is only 12 +/- 3 years. See [4].
Cheers,
John
[1] http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis
[2] http://en.wikipedia.org/wiki/Enterprise_risk_management
[3] http://answers.yahoo.com/question/index?qid=20090329215018AAxqYFk
[4] http://en.wikipedia.org/wiki/Greenhouse_gas
---
Andrew Lockley wrote:
At present the likely
methane excursion is far from clear. Further, it is also unclear how
quickly the total excursion will occur. The excursion rate is highly
significant due to the short life of methane in the atmosphere. The
methane ends up as CO2, in itself a major issue. However, the CO2's
likely effect is nothing compared to the devastating temperature spike
which may result from a sudden methane excursion.
I don't oppose John's argument, but the evidence on the severity of the
problem is far from conclusive. We need much more research into:
1) The methane reservoir in clathrates and permafrost
2) The size of potential methane sources currently frozen as organic
detritus
3) The likely changes to the GWP of methane in future atmospheres, as
the levels of hydroxyl radicals etc. shift over time and as a direct
result of methane excursion. Recent research on this asks more
questions than it answers.
My personal feeling is that the range of likely outcomes is from a
significant amplification of AGW, right up to a 'Great Dying' sized
mass-extinction event when we come within a sneeze of sterilising the
entire planet. I'd be tempted to bet on the latter, but I wouldn't be
around to collect the winnings, so I'll keep my wallet in my pocket.
My suggestions is that geoengineers look at ways to clean up the
methane from the atmosphere, and then lock down the resulting carbon.
My guess is we've got about 50 years to do this, but virtually no
time at all if the methane can't be dealt with once it's in the
atmosphere. Therefore, I'd support John out of precautionary
principle-based reasoning.
A
2009/11/15 jim woolridge <[email protected]>
Nice one, John; the train of
argument is clear (of limpid clarity, in
fact!) The problem is that the people and institutions addressed are
in the business of politics, the art of the possible, rather than in
the business of logical evaluation. They hear what you are saying and
must see the validity of it. But politically what is true and what is
doable do not always coincide, as we all know from as many examples as
one cares to ennumerate.
We have to keep hammering away at the arguments, to the point at which
they are generally understood and accepted, and also keep on
politicking in the sure and certain hope that eventually the
acceptance of the arguments and the cowardice/caution/horse sense/
opportunistic careerism of the politicos will achieve the right kind
of intersection. In the next year or so (& wouldn't it be a great
help to have the environmental NGOs on board.)
On Nov 12, 10:51 pm, John Nissen <[email protected]> wrote:
> It is incredible. It is so obvious.
>
> 1. Global warming is driven largely by atmospheric CO2 according
to the
> concentration above its pre-industrial level; and
>
> 2. After emissions are stopped it could take millenia for the
> concentration to fall back to that level, because the effective
lifetime
> of some of that excess CO2 is many thousands of years.
>
> Therefore:
> 3. Drastic emissions reduction, even to zero overnight, cannot
and will
> not stop the Arctic continuing to warm for decades.
>
> Therefore:
> 4. The Arctic sea ice will continue to retreat, accelerating the
warming
> due to the albedo effect.
>
> Therefore:
> 5. The permafrost will continue to thaw releasing increasing
quantities
> of methane, a potent greenhouse gas, potentially adding many
degrees to
> global warming; and
>
> 6. The Greenland ice sheet will become increasingly unstable,
> potentially contributing to an eventual sea level rise of 7
metres.
>
> Therefore:
> 7. To avoid these two catastrophes, we need to cool the Arctic
quickly
> enough to save the Arctic sea ice; and
>
> 8. Probably the only feasible way to do this is through solar
radiation
> management (SRM) geoengineering.
>
> 9. SRM is not a last resort, it is needed now to cool the Arctic.
>
> It is incredible that people do not seem to follow this train of
logic -
> it is so obvious.
>
> Yet when I challenged a panel of geoengineering experts to refute
this
> argument, the response was that geoengineering (even just to cool
the
> Arctic) was too dangerous - not that the argument was false! [1]
>
> So we continue to hear politicians and their advisers claiming
that
> emissions reduction alone can be sufficient to keep the planet
safe. [2]
>
> And we continue to hear geoengineering experts saying that
> geoengineering should only be used as a last resort. [3]
>
> How can this mindset be changed quickly, to avoid leaving
geoengineering
> too late?
>
> John
>
> P.S. Apologies to those who have heard this all before and accept
the
> logic as self-evident.
>
> [1] This challenge was put to the panel at the launch of the
Royal
> Society geoengineering report, on September 1st, with response
from the
> team leader and panel chairman, Professor John Shepherd.
>
> [2] For example at the geoengineering hearing at the House of
Commons,
> November 2008.
>
> [3] For example at the congressional hearing on geoengineering,
November
> 2009.
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