I’ve been following this though it is far away from my focus on mitigation
and I may well be missing something obvious here.
Reto’s answer makes sense to me. If CO2 emissions cease, the warming caused
by the elevated CO2 concentration remains, but only in holding the new
equilibrium temperature (with some short term lead-lag dynamics). Just
holding a new equilibrium temperature requires warming - that’s what the
greenhouse effect does. Ceteris paribus, as CO2 gradually comes out of the
atmosphere so the temperature gradually declines. Changes in aerosols,
non-CO2 GHGs, carbon-cycle feedbacks etc all make for a more complicated
picture, but the fundamentals of Reto’s argument certainly hold to this
simple engineer.
As a thought experiment - and if the counter were true - the temperature
would have continued to rise with the pre-industrial CO2 concentration -
indeed any set concentration of CO2 would see an ongoing temperature rise
forever … which would not fit into the physics I recall from school - or my
engineering thermodynamics. But as I say I may well be missing something.
Kevin (Anderson)
On 18 Nov 2016, at 10:48, John Nissen <[email protected]>
wrote:
Hi Mike,
I am astonished by Reto’s answer to my simple question about what
would happen if CO2 emissions were to cease overnight. All I have
ever been told about greenhouse gases is that they have a warming
effect on the planet. How could this warming effect be suddenly
cancelled by the cessation in emissions of the main greenhouse gas,
CO2?
Reto is completely out on a limb as far as I am concerned.
You have pointed out that, not only would the greenhouse effect of the
existing CO2 in the atmosphere continue, but that aerosol cooling
would also be removed (e.g. in the turning off of coal-fired power
stations which emit SO2), leading to an even faster rate of
temperature increase, albeit temporarily.
You quoted from Phillip Williamson:
“With regard to Mike McCracken's email below, if all emissions were to
be very rapidly (instantly?) ended, the outcome is likely to be
accelerated warming over the short-term, since the cooling effect of
aerosols would be reduced more rapidly than the warming effects of
greenhouse gases. See FAQ 12.3 of IPCC AR5 WG1.”
Cheers, John
On Fri, Nov 18, 2016 at 4:09 AM, Michael MacCracken
<[email protected]> wrote:
I'd just note that one also has to consider tropospheric
ozone response, and the methane effect would also likely
have an influence over the first decade, so a lot to
consider, though I agree that the loss of the sulfate
cooling influence is indeed an important aspect to
consider.
Mike
On 11/17/16 2:08 PM, Phillip Williamson (ENV) wrote:
Dear all
Two short comments on the latest postings in this
very informative exchange:
1. With regard to Mike McCracken's email below, if
all emissions were to be very rapidly (instantly?)
ended, the outcome is likely to be accelerated
warming over the short-term, since the cooling
effect of aerosols would be reduced more rapidly
than the warming effects of greenhouse gases. See
FAQ 12.3 of IPCC AR5 WG1.
2. With regard to Bernard Mercer's separate email
sent just a few minutes earlier, I am particularly
interested in "I think you would find non-profit
foundations falling over themselves to fund
syntheses, but they need well-thought through
proposals!". That's because the UK Greenhouse Gas
Removal programme
(http://www.nerc.ac.uk/research/funded/programmes/ggr/),
led by the Natural Environment Research Council, is
likely to be in the situation in a few months time
that it is only able to fund a minority of high
quality proposals - including syntheses - considered
worthy of support. If anyone has suggestions for
additional co-support partnerships, e.g. via
foundations, I would be pleased to explore such
possibilities and bring them to the attention of the
current GGR programme funders
Regards
Phil Williamson
____________________________________________________________________________
From: [email protected]
<[email protected]> on behalf of Michael
MacCracken <[email protected]>
Sent: 17 November 2016 18:26
To: [email protected]; John Nissen
Cc: David Lewis; geoengineering; Kevin Anderson;
[email protected]; Greg Rau; Peter Wadhams; Sev
Clarke; Alan Gadian; Kevin Lister; Kevin Lister; Adam
Rutherford - Science; Hugh Hunt
Subject: Re: [geo] Negative Emissions: Arrows in the
Quiver, Life Preserver, and/or Moral Hazard?
I would just add that if one considers the effects of
short-lived species like methane, black carbon, sulfate
and tropospheric ozone that also introduce substantial
forcings, going to zero CO2 emissions would also likely
imply going to (near) zero emissions of these species as
well, so there is lots of potential for reducing forcing
and stopping the increase in temperature and even pushing
it down (with all emissions going to zero)--the challenge
is doing something so large in a short time.
Mike
On 11/17/16 12:25 PM, Knutti Reto wrote:
Dear John,
Thanks for your comments.
> I would love you to publish this result if you
can.
Why would I want to publish it if it is wrong? To
publish a result you need to provide quantitative
evidence. Claiming that someone else is wrong is not
enough. The figure you show is based on a climate
carbon cycle model, so please tell me what
specifically is wrong in that model (and in all
other climate models that show similar results), and
provide another model that is more credible, then we
can discuss again.
In your letter to COP22 you state:
>The climate community and consensus of scientists,
represented by IPCC, had assumed that, by reducing
net emissions of CO2 to zero, global warming could
be halted. They had also assumed that such a
reduction would halt Arctic warming, by the process
which has kept Arctic warming proportional to global
warming but amplified by a factor of around two.
Unfortunately evidence indicates that these
assumptions are no longer valid.
So “evidence indicates”, but where it that evidence?
In your whole letter not one quantitative argument
or number is given that contradicts the scientific
consensus as represented in IPCC, not a single one.
What is the evidence?
You also assert that the scientists “assume” things.
These are *results* based on our best understanding
of the system, the best data we have, and the most
objective and quantitative models we can build. They
may not be perfect, but they are *results*,
conclusions drawn from data, not assumptions.
>The temperature curve in red is complete nonsense,
because the forcing from the ~500 ppm of CO2 will
continue the radiative forcing on the planet and
hence the temperature will continue rising.
In my previous email I demonstrated that the forcing
will decrease, and that temperature will not
increase for long if the forcing decreases, based on
basic conservation of energy and timescales of the
carbon cycle. You can go back to work by Wigley,
Hansen and others thirty years ago and it’s there,
and nobody has disproven it. You provide no
counterargument but simply restate your claim. See
my other email to Kevin. This is about science, not
beliefs. I don’t see this discussion going anywhere.
Best regards,
Reto
From: John Nissen [mailto:[email protected]]
Sent: Donnerstag, 17. November 2016 02:48
To: Knutti Reto <[email protected]>
Cc: Michael MacCracken <[email protected]>; David
Lewis <[email protected]>; geoengineering
<[email protected]>; Kevin Anderson
<[email protected]>;
[email protected]; Greg Rau
<[email protected]>; Peter Wadhams
<[email protected]>; Sev Clarke
<[email protected]>; Alan Gadian
<[email protected]>; Kevin Lister
<[email protected]>; Kevin Lister
<[email protected]>; Adam Rutherford -
Science <[email protected]>; Hugh Hunt
<[email protected]>
Subject: Re: [geo] Negative Emissions: Arrows in the
Quiver, Life Preserver, and/or Moral Hazard?
Hi Knutti,
I would love you to publish this result if you can.
A number of us have been trying to defy the
modelling community which seems to manage to get
results which conflict with observations and, I
belatedly find, with basic physics. We have been
bombarded with weasel words, as Stephen Salter puts
it. But it is this diagram attached that astonished
me, because it shows up the basic premise, promoted
by IPCC, that cessation of emissions will cause the
temperature to peak and start falling. The
temperature curve in red is complete nonsense,
because the forcing from the ~500 ppm of CO2 will
continue the radiative forcing on the planet and
hence the temperature will continue rising.
It is when we try to reduce CO2 from its peak that
we get into trouble, because the 50% CO2, absorbed
by land and ocean when we put a certain amount of
CO2 into the atmosphere, will then be emitted by
land and ocean. We have to work twice as hard to
reduce CO2 level as one might have thought: taking
two tons out to reduce the amount in the atmosphere
by one ton.
It sounds like common sense to say that "our CO2
emissions caused global warming, so ceasing our CO2
emissions will stop the temperature rising". I can
see why IPCC was tempted to promote this nonsense:
they wanted a simple story for the public. But it's
simply not true.
I am copying in Adam Rutherford as an impartial
scientist, not bound up in the politics of climate
change or the machinations of IPCC and COP. I have
been putting my point to several distinguished
climate scientists, and they can't fault my
physics. They will argue endlessly about other
points, but not my point on the basic physics: that
zero emissions won't halt temperature rise.
I am also copying to Hugh Hunt, who I hear is at
COP22, so could pass on this message.
Of course the implications are huge: we have a
colossal challenge to remove CO2 fast enough from
the atmosphere to avoid dangerous climate change.
We have to start immediately on a CDR initiative -
which I had hoped COP22 would do (hence the letter
to COP which I wrote and attach again for Hugh's
benefit). On the other hand the rewards of
restoring the Earth System to Holocene conditions
would be fantastic. The possibility of doing so is
really good news for everyone on the planet.
BTW, I have been spending most of my energy over the
past few years on battling against the modelling
community about the Arctic sea ice, observed to be
in exponential decline as should be expected from
the physics of positive albedo feedback. I only
realised in January this year how badly we've also
been led astray on the CO2 front when I did a few
simple calculations for myself.
Kind regards, John
On Wed, Nov 16, 2016 at 9:34 PM, Knutti Reto
<[email protected]> wrote:
Dear John,
> The arithmetic gives a frightening answer,
which I expect is why you never hear it and
nobody publishes it.
Nature and Science love frightening results
and would be happy to publish those if they
are correct. But not if they contradict the
evidence we have. You seem to imply that
scientists only publish what they like or what
people want to hear. I don’t see any evidence
for that. If I had strong evidence for things
being much worse, I would publish that
tomorrow. Same if I could prove that climate
change is a hoax. We are not “selling a dream
to the media, politicians, environmentalists
and the UN”, we publish and assess what the
science and the data tell us.
There are two main errors in your analysis:
> The CO2 would only fall very slowly for the
rest of the century, because of CO2's long
life in the atmosphere. Thus the forcing from
nearly 500 ppm CO2 would persist for the rest
of the century.
First, the initial decrease of CO2 isn’t that
slow for zero emissions because the exchange
with the surface ocean and land is fast. CO2
doesn’t have a single lifetime, and it’s the
long tail that is slow. For a single pulse
emission into the atmosphere, after 50 years
only half remains in the air (Joos,
doi:10.5194/acp-13-2793-2013, Fig. 1a).
Second, other gases would also be reduced and
some have shorter lifetimes. Even without
going abruptly to zero, e.g. as in RCP2.6, the
radiative forcing decreases after 2050. For
zero emissions in 2050 the forcing would drop
more.
> Even if the warming rate remained at only
0.25C for the rest of century, temperature
would rise a further 1.25C to reach 3.2C above
pre-industrial.
That is simply wrong. There is no reason for
the warming rate to remain the same if the
forcing decreases. For *constant* forcing
(today) the additional warming is about 0.5°C
after 200 years (IPCC AR5 WG1 p.1103 bottom
left). For 50 years it’s about half (Knutti,
2008 doi:10.1029/2007JD009473, Fig. 1b). That
is for constant forcing, so obviously for
*decreasing* forcing it’s even less. RCP2.6
temperature is constant after 2050, it doesn’t
increase. As I said before, the climate system
is complex, but conservation of energy is not.
Look at the simple Q=F-lambda T discussed
below: if forcing F is constant or even
decreasing, then temperature T only increases
a bit because heat uptake Q reduces, but in
equilibrium T is proportional to F. So the
assumptions that T would continue to increase
at the same rate if F is decreasing violates
conservation of energy.
We are in the fortunate position to have
dozens of simple and comprehensive climate
models which have run such scenarios, and the
models do incorporate all those timescales in
the climate and carbon cycle, they include
other gases, and the feedbacks. RCP2.6 has
zero CO2 emissions around 2075 (IPCC AR5 WG1
Fig. TS.19, p. 94) and stays “likely” below
2°C relative to preindustrial (IPCC AR5 WG1
SPM p.20). Zero CO2 emissions in 2050 would
result in less warming than that.
Even if the models underestimate the Artic sea
ice loss, that would not change those numbers
a lot. The albedo feedback is only about a
quarter of the total global feedback (IPCC AR4
WG1 Fig. 8.14, p.631). Even the models with
the steepest sea ice decline do not support
your analysis. No model is perfect, but I’d
rather base my conclusions on the best
possible representation of all processes, the
best data, and a quantitative analysis, than
on a naïve and wrong extrapolation of past
trends. Climate change is a serious issue, but
it doesn’t help if people go out with scary
extrapolations that have no scientific basis.
Best regards,
Reto
From: John Nissen
[mailto:[email protected]]
Sent: Mittwoch, 16. November 2016 11:45
To: Knutti Reto <[email protected]>
Cc: Michael MacCracken <[email protected]>;
David Lewis <[email protected]>;
geoengineering
<[email protected]>; Kevin
Anderson <[email protected]>;
[email protected]; Greg Rau
<[email protected]>; Peter Wadhams
<[email protected]>; Kevin Lister
<[email protected]>; Sev Clarke
<[email protected]>; Alan Gadian
<[email protected]>
Subject: Re: [geo] Negative Emissions: Arrows
in the Quiver, Life Preserver, and/or Moral
Hazard?
Hello Knutti,
The arithmetic gives a frightening answer,
which I expect is why you never hear it and
nobody publishes it.
Suppose the CO2 level had got to 500 ppm by
2050, when net emissions reached zero. The
CO2 would only fall very slowly for the rest
of the century, because of CO2's long life in
the atmosphere. Thus the forcing from nearly
500 ppm CO2 would persist for the rest of the
century.
The current underlying trend rate of global
warming is somewhere between 0.2C and 0.3C per
decade, given that the average rate over the
past 45 years was 0.18C per decade [1].
Taking 0.25C as a conservative average till
2050, and assuming we have had 1.1C global
temperature rise since pre-industrial times,
the global temperature would rise 0.85C by
2050 to reach 1.95C above pre-industrial.
Even if the warming rate remained at only
0.25C for the rest of century, temperature
would rise a further 1.25C to reach 3.2C above
pre-industrial.
Unfortunately leading climate scientists, in
their efforts to get CO2 emission reduced,
sold a dream to the media, politicians,
environmentalists and the UN: that we can
adapt to climate change providing net
emissions are reduced to zero over the next
few decades.
According to this dream, the sea ice will last
indefinitely, see the figure SPM.7(b)
reproduced in Peter W’s book, page 89. Sea
level will rise about half a metre this
century: 44cm is the ‘best estimate’ in range
28cm to 61cm maximum according to AR5 [2].
There is no need for interventions, except
possibly some "negative emissions" to achieve
net zero emissions. We can make the planet
safe for future generations. But it is a
dream.
The reality is that we need to reduce the net
effect of climate forcing agents to zero,
which includes restoring Arctic albedo.
Saving the sea ice is crucial. We risk losing
a critical element of the control of the
planet’s climate system if we allow the Arctic
Ocean to become seasonally free of sea ice,
since it will probably be locked into this
state indefinitely which could have
catastrophic consequences for sea level rise,
methane emissions and NH weather extremes.
The Arctic has already warmed 7C according to
Peter Carter.
The most natural climate restoration CDR
involves putting carbon into trees, soil and
marine biomass. This simply involves
improving forestry, agriculture and
aquaculture practices on a massive scale. It
is also returning the planet’s biosphere to a
state before human population explosion when
forests were cut down, soils denuded of carbon
and marine biomass reduced. Surely this can
only be good for the planet – and something
positive that every environmentalist can work
for.
We can also use weathering of crushed olivine
rocks on a large scale to neutralise CO2 and
halt ocean acidification. This, together with
local cooling, could save corals – even
possibly the Great Barrier Reef. (Diatoms
might help purify the water.)
Who is standing in the way of this progress
towards a safer planet? It is the scientists
who continue to promote a dream: a totally
unrealistic scenario of the future and a plan
to get there. COP is just doing what seems to
be required from this plan, though they know
they cannot get to net zero emissions quickly
enough with current pledges.
And Trump now could throw a spanner in the COP
works.
However the plan is doomed, not because of
Trump, but because it is based on a dream. We
now need to focus on reality and how we can
use CDR and albedo enhancement to restore the
Earth System back to the Holocene norm, with
potentially huge benefits for humanity and
biodiversity.
Kind Regards, John
[1]https://www.theguardian.com/environment/2016/oct/03/global-temperature-clim
ate-change-highest-115000-years
[2]http://www.realclimate.org/index.php/archives/2013/10/sea-level-in-the-5th-
ipcc-report/
On Tue, Nov 15, 2016 at 11:38 PM, Knutti Reto
<[email protected]> wrote:
Dear John,
> an embarrassment to IPCC, as it
conflicts with their story that global
warming can be restricted to 2C or even
1.5C by getting net CO2 emissions to
zero. This is obviously not true from
the physics, as I pointed out to you and
some other distinguished scientists a
few days ago without challenge! When
net emissions fall to zero the rise in
atmospheric CO2 flattens off but the
climate forcing remains, so temperature
will continue rising. I wish I was
wrong about this, and we could halt
temperature rise so easily. But, if we
are halt global warming we have to
reduce the net forcing from all
radiative forcing agents, including
Arctic albedo loss, to zero.
I don’t deny the need for strong
mitigation, but let’s try to inform
decisions by the best possible science.
Where is the evidence that zero CO2
emissions soon (say before 2050) would
be insufficient to limit warming to 2°C.
Please send me the papers or your
analysis. I’d like to know what is
“obviously not true from the physics”.
If by “halt global warming” you mean
limit/stabilize warming at some level
above preindustrial (e.g. 1.5 or 2°C),
then your statement is simply wrong: net
forcing does not need to be zero as I
showed below. By definition net zero
forcing implies zero warming in after
sufficient time, because the forcing is
defined as an anomaly from a reference
temperature, typically preindustrial.
Best regards,
Reto Knutti
From: John Nissen
[mailto:[email protected]]
Sent: Dienstag, 15. November 2016 14:53
To: Michael MacCracken
<[email protected]>
Cc: Knutti Reto
<[email protected]>; David Lewis
<[email protected]>;
geoengineering
<[email protected]>; Kevin
Anderson
<[email protected]>;
[email protected]; Greg Rau
<[email protected]>; Peter Wadhams
<[email protected]>; Kevin Lister
<[email protected]>; Sev
Clarke <[email protected]>; Alan Gadian
<[email protected]>
Subject: Re: [geo] Negative Emissions:
Arrows in the Quiver, Life Preserver,
and/or Moral Hazard?
[Please excuse if this arrives twice]
Hi Mike,
I suppose I might have expected you to
loyally defend IPCC. But their position
is untenable.
On the sea ice, Peter Wadhams presented
the death spiral to an audience of sea
ice modelling experts at the Royal
Society, and not a single person rose to
say it is not happening. The
exponential trend of sea ice volume
decline has been followed until 2012,
and even the subsequent volume estimates
(which are tricky due to so much broken
ice and surface slush) are within
natural variability. Therefore on the
precautionary principle we must act on
the expectation of losing sea ice at the
end of summer within a few years,
despite what modellers might hope.
Peter Wadhams points out in his book
that the trend towards nearly ice-free
conditions in September is "blindingly
obvious" and he cannot understand why
IPCC clings to models. "The trend in
the PIOMAS data effectively gives us a
drop-dead date of about 2020 for summer
sea ice" [1].
As Kevin Lister points out, a rapid
demise of sea ice would be an
embarrassment to IPCC, as it conflicts
with their story that global warming can
be restricted to 2C or even 1.5C by
getting net CO2 emissions to zero. This
is obviously not true from the physics,
as I pointed out to you and some other
distinguished scientists a few days ago
without challenge! When net emissions
fall to zero the rise in atmospheric CO2
flattens off but the climate forcing
remains, so temperature will continue
rising. I wish I was wrong about this,
and we could halt temperature rise so
easily. But, if we are halt global
warming we have to reduce the net
forcing from all radiative forcing
agents, including Arctic albedo loss, to
zero. This means we have the huge
challenge of reducing levels of CO2,
methane and other greenhouse gases to
their pre-industrial levels. And we
have to restore Arctic albedo.
When we have done all this, we will have
saved the sea ice, halted sea level rise
from Greenland ice melt and hopefully
restored climate in the Northern
Hemisphere, reducing the weather
extremes to their old level.
Thus we should be close to restoring the
Earth System to the 'old norm' of the
Holocene in which our civilisation
developed and flourished.
In the process we can actually improve
food production, as I point out in the
attached letter which I was hoping could
be presented to COP22.
Restoration is the only path to a safe
future for our children and
grand-children. It can be done. It
must be done.
Best wishes, John
[1] Wadhams (2016) "A farewell to ice"
page 88.
On Tue, Nov 15, 2016 at 7:38 PM, Michael
MacCracken <[email protected]> wrote:
Dear Knutti--Thank you for
your note and full
explanation. I have been
trying to point out these
misconceptions of John's for
a number of years now. I
hope your note will finally
convince him.
I have also been trying to
convince him that the really
significant drop in albedo
leading to large amounts of
additional solar absorbed
comes when the fresh snow on
ice melts (presumably in
late spring), reducing the
surface albedo from
something like 70-80% to or
order 20-30% and that the
albedo effect of going from
melting ice surface albedo
to the albedo of open water
(with Sun at low slant
angle) will not lead to a
catastrophic increase in the
absorbed heat in the fall
(though it may well set the
situation up for an earlier
melting of the snow surface
in the spring, etc.). What
would be really interesting
to have is a graph of the
amount of solar heat uptake
at the surface over the warm
season (I guess, as well,
actually having a comparison
of what the uptake is now
with what it would be were
there no sea ice).
Best regards, Mike
MacCracken
On 11/15/16 2:18 PM, Knutti Reto
wrote:
Dear John, all
As a coordinating lead
author of IPCC AR5 WG1 (and
someone how has done work on
these topics) I’m surprised
to read such comments.
> Blunder 1. IPCC has
ignored the increasing loss
of Arctic albedo, which is
already contributing the
equivalent of 30 ppm CO2 to
the radiative budget, i.e. a
quarter of the forcing from
CO2. […] The first blunder
is symptomatic of IPCC's
treatment of the Arctic sea
ice, where they refuse to
accept the observations that
it is in a death spiral,
preferring to rely on models
of proven inadequacy which
predict that the sea ice
will last for decades. You
can read all about it in
Peter Wadhams' new book "A
Fairwell to Ice".
The change in albedo is part
of every climate model as
snow cover and sea ice
change. Indeed some many
models show smaller Arctic
sea ice decline than
observed. But the natural
variability is very large
(e.g. Kay 2011, Swart 2015,
Screen 2013, 2016). There is
no reason why short term
trends could simply be
extrapolated, and the
predictions by Peter Wadhams
of sea ice disappearing by
today have not happened so
far
(https://www.theguardian.com/environment/2012/sep/17/arctic-collapse-sea-ic
e,http://www.independent.co.uk/environment/climate-change/arctic-could-become
-ice-free-for-first-time-in-more-than-100000-years-claims-leading-scientist
-a7065781.html). Maybe the
models are missing
something, but it’s just as
plausible (and in most
scientist’s view more
likely) that the models are
largely consistent with
observations within natural
variability.
Many studies have used
observations to recalibrate
and weight models, and even
IPCC has explicitly made
projections for Arctic sea
ice based on those models
that best reproduce various
aspects of sea ice (section
12.4.6.1). All of these
studies indicate that using
observations point to a
somewhat steeper decline of
Arctic sea ice (Boe 2009,
Massonnet 2012, Mahlstein
2012, Wang 2013, Notz 2016),
but not a “death spiral”.
I’m not downplaying the
strong changes in the
Arctic, but the science
suggests a fairly linear
(and reversible)
relationship between Arctic
sea ice and temperature with
large variability
superimposed. In my view
they do not support a “death
spiral”.
>Blunder 2. IPCC has ignored
the warming effect of
accumulated CO2. They say
that global temperature rise
will be halted when net CO2
emissions have fallen to
zero, ignoring the effect of
accumulated CO2 and other
forcing agents in the
atmosphere.[…] The second
blunder can be illustrated
by AR5 WG1 figure 6-40
attached and available here
[1]. The red curves are
supposed to show the effect
if net emissions were to
suddenly fall to zero at
2050, when CO2 has reached
about 500 ppm. The
temperature (red curve in
bottom diagram) should
continue to rise as a result
of the forcing from 500 ppm
CO2; but instead the
temperature flattens off as
if the accumulated CO2
ceased to have a warming
effect!
Of course CO2 continues to
have an effect, but as
emissions are set to zero
the atmospheric
concentration and therefore
forcing decrease.
>It is absolutely
astonishing and frightening
that such a fundamental
mistake can be made.
Where is the evidence for a
fundamental mistake?
>If we want to halt global
warming at any particular
temperature, then we need to
bring net forcing down to
zero by the time that
temperature has been
reached.
No, that is simply wrong.
The forcing has to decrease
to compensate the slowly
decreasing ocean heat
uptake, but it does not have
to be zero at any time to
limit warming, not even in
equilibrium. The global
energy balance is
Q=F-lambda*T where Q is heat
uptake, F is forcing, lambda
is the inverse of climate
sensitivity and T is warming
(see Knutti and Hegerl 2008
for example). If today
F~=2.3 Wm-2 and Q~=0.9 Wm-2
and we want to keep T
constant and Q=0 towards
equilibrium then F needs to
decrease to about
2.3-0.9=1.4 Wm-2 on the
timescale on which the ocean
warms (decades to
centuries), but not zero.
Climate is complex, but
conservation of energy
isn’t.
IPCC WG1 chapter 12 has an
long discussion of the
difference concepts of
commitment warming (section
12.5.2) with plenty of
references from different
models going back many
decades. There is even an
FAQ 12.3 discussing that,
and it also does discuss
non-CO2 forcings. There are
models which show some
warming after zero CO2
emissions, and others that
show some cooling, but in
general these concepts of
commitment warming are well
understood. IPCC isn’t
perfect, but it’s probably
the best reviewed document
on climate, with hundreds of
scientist contributing. It
seems rather unlikely that
it would contain
“fundamental mistakes”, and
in my view the claims you
made here have no scientific
basis.
Best regards,
Reto Knutti, ETH Zurich
http://www.iac.ethz.ch/people/knuttir
Swart, Neil C., John C.
Fyfe, Ed Hawkins, Jennifer
E. Kay, and Alexandra Jahn.
2015. “Influence of Internal
Variability on Arctic
Sea-Ice Trends.” Nature
Climate Change 5 (2). Nature
Publishing Group: 86–89.
doi:10.1038/nclimate2483.
Kay, Jennifer E., Marika M.
Holland, and Alexandra Jahn.
2011. “Inter-Annual to
Multi-Decadal Arctic Sea Ice
Extent Trends in a Warming
World.” Geophysical Research
Letters 38 (15): 2–7.
doi:10.1029/2011GL048008.
Screen, James a., Clara
Deser, Ian Simmonds, and
Robert Tomas. 2013.
“Atmospheric Impacts of
Arctic Sea-Ice Loss,
1979–2009: Separating Forced
Change from Atmospheric
Internal Variability.”
Climate Dynamics 43 (1–2):
333–44.
doi:10.1007/s00382-013-1830-9.
Screen, James A., and
Jennifer A. Francis. 2016.
“Contribution of Sea-Ice
Loss to Arctic Amplification
Is Regulated by Pacific
Ocean Decadal Variability.”
Nature Climate Change 6 (9):
856–60.
doi:10.1038/nclimate3011.
Boé, Julien, Alex Hall, and
Xin Qu. 2009. “September
Sea-Ice Cover in the Arctic
Ocean Projected to Vanish by
2100.” Nature Geoscience 2
(5). Nature Publishing
Group: 341–43.
doi:10.1038/ngeo467.
Mahlstein, Irina, and Reto
Knutti. 2012. “September
Arctic Sea Ice Predicted to
Disappear near 2°C Global
Warming above Present.”
Journal of Geophysical
Research 117 (D6): 1–11.
doi:10.1029/2011JD016709.
Notz, Dirk, and Julienne
Stroeve. 2016. “Observed
Arctic Sea-Ice Loss Directly
Follows Anthropogenic CO2
Emission.” Science,
November, 1–9.
doi:10.1126/science.aag2345.
Overland, James E., and
Muyin Wang. 2013. “When Will
the Summer Arctic Be Nearly
Sea Ice Free?” Geophysical
Research Letters 40 (10):
2097–2101.
doi:10.1002/grl.50316.
Massonnet, F., T. Fichefet,
H. Goosse, C. M. Bitz, G.
Philippon-Berthier, M. M.
Holland, and P.-Y. Barriat.
2012. “Constraining
Projections of Summer Arctic
Sea Ice.” The Cryosphere 6
(6): 1383–94.
doi:10.5194/tc-6-1383-2012.
Knutti, Reto, and Gabriele
C. Hegerl. 2008. “The
Equilibrium Sensitivity of
the Earth’s Temperature to
Radiation Changes.” Nature
Geoscience 1 (11): 735–43.
doi:10.1038/ngeo337.
From:
[email protected]
[mailto:[email protected]]
On Behalf Of John Nissen
Sent: Montag, 14. November
2016 16:06
To: David Lewis
<[email protected]>
Cc: geoengineering
<[email protected]>;
Kevin Anderson
<[email protected]>;
[email protected];
Greg Rau
<[email protected]>; Peter
Wadhams
<[email protected]>;
Kevin Lister
<[email protected]>;
Sev Clarke
<[email protected]>; Alan
Gadian
<[email protected]>
Subject: Re: [geo] Negative
Emissions: Arrows in the
Quiver, Life Preserver,
and/or Moral Hazard?
Dear David,
I think Klaus et al have the
voice of realism. Global
warming is far more serious
than we have been led to
believe, and without several
rapid interventions, we are
heading for many degrees of
global warming this
century.
IPCC are guilty of two
colossal blunders in their
projections of global
warming. The effect has
been to lull the
international community into
a false sense of security.
Rapid interventions are now
required to avoid a lethal
combination of climate
change, ocean acidification
and rising sea levels. Here
are the facts:
Blunder 1. IPCC has ignored
the increasing loss of
Arctic albedo, which is
already contributing the
equivalent of 30 ppm CO2 to
the radiative budget, i.e. a
quarter of the forcing from
CO2.
Blunder 2. IPCC has ignored
the warming effect of
accumulated CO2. They say
that global temperature rise
will be halted when net CO2
emissions have fallen to
zero, ignoring the effect of
accumulated CO2 and other
forcing agents in the
atmosphere.
The first blunder is
symptomatic of IPCC's
treatment of the Arctic sea
ice, where they refuse to
accept the observations that
it is in a death spiral,
preferring to rely on models
of proven inadequacy which
predict that the sea ice
will last for decades. You
can read all about it in
Peter Wadhams' new book "A
Fairwell to Ice".
The second blunder can be
illustrated by AR5 WG1
figure 6-40 attached and
available here [1]. The red
curves are supposed to show
the effect if net emissions
were to suddenly fall to
zero at 2050, when CO2 has
reached about 500 ppm. The
temperature (red curve in
bottom diagram) should
continue to rise as a result
of the forcing from 500 ppm
CO2; but instead the
temperature flattens off as
if the accumulated CO2
ceased to have a warming
effect! It is absolutely
astonishing and frightening
that such a fundamental
mistake can be made.
If we want to halt global
warming at any particular
temperature, then we need to
bring net forcing down to
zero by the time that
temperature has been
reached. This involves
bringing all GHGs down to
their pre-industrial level
and restoring Arctic albedo,
unless their residual
heating (positive forcing)
is counteracted by an equal
amount of cooling (negative
forcing), e.g. from
aerosols.
CDR has to suck CO2 out of
the atmosphere faster than
it is being emitted into the
atmosphere, in order to
bring the level down from
over 400 ppm to
pre-industrial 280 ppm.
Methane emissions have to be
suppressed (including
fugitive emissions from
coal, oil and gas
extraction) in order to
bring the level down from
1850 ppb to pre-industrial
750 ppb.
The retreat of sea ice has
to be halted and then Arctic
albedo has to be restored to
its level of at least thirty
years ago.
Thus our best chance to halt
global warming is through
CO2 emissions reduction
(better than already
committed) combined with
several immediate and
aggressive interventions:
CDR, methane emissions
reduction, and rapid cooling
of the Arctic.
As Klaus Lackner et al say
in their comment, CDR is
indeed like throwing a
lifebelt to a drowning
person. We need to start
CDR as quickly as we can, to
be as certain as we can be
to save the planet.
In parallel we must suppress
methane and cool the Arctic
before we lose any more
albedo from snow and sea ice
retreat.
The ultimate objective must
be to restore the Earth
System to Holocene
conditions of climate
stability, ocean alkalinity
and sea level constancy.
Cheers, John
[1]http://www.ipcc.ch/report/graphics/images/Assessment%20Reports/AR5%20-%20WG
1/Chapter%2006/thumbnail/Fig6-40.jpg
On Mon, Nov 14, 2016 at 4:55
PM, David Lewis
<[email protected]>
wrote:
Anderson could
maintain his
stance as a
voice for
realism while
adding his voice
to those calling
for research
into all forms
of
geoengineering.
He could compare
the cost of
reducing
emissions to the
current cost of
removing them
from the
atmosphere, call
for a vigorous
program of
further
research, then
state that it is
still his
opinion that
civilization
needs to
urgently and
fundamentally
transform its
social,
economic, and
political
relations if it
wants to
continue to
exist.
Moral: Do
not ignore
or
downplay
potentially
useful
actions,
especially
if you
have the
time and
resources
to
carefully
evaluate
them.
____________________________________________________________________________
From: Greg
Rau
<[email protected]>
To:
Geoengineering
<[email protected]>
Sent:
Friday,
November
11, 2016
4:50 PM
Subject:
[geo]
Negative
Emissions:
Arrows in
the
Quiver,
Life
Preserver,
and/or
Moral
Hazard?
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http://science.sciencemag.org/content/354/6313/714.1
GR: Disclaimer -
I was a
co-signer.
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