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-ice,
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-%20WG1/Chapter%2006/thumbnail/Fig6-40.jpg
On Mon, Nov 14, 2016 at 4:55 PM, David Lewis <[email protected]
<mailto:[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]
<mailto:[email protected]>>
*To:* Geoengineering <[email protected]
<mailto:[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
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