cc: 'TAR LA list' <tar_la@meto.gov.uk>, 'TAR CLA list' <tar_cla@meto.gov.uk>, "'tar_ts@meto.gov.uk'" <tar_ts@meto.gov.uk>
date: Wed, 26 Jan 2000 10:15:27 +0100
from: joos <joos@climate.unibe.ch>
subject: Re: Technical Summary informal review
to: "Griggs, Dave" <djgriggs@meto.gov.uk>

Dear Dan LAs and TS writing team,

Thank you very much for putting toghether such a nice technical
summary.  

Please find below a few comments and proposals for
revisions. I hope the comments are helpful. 

With best wishes, Fortunat

General Comment:
----------------
(1) Overall, I find the text balanced, interesting, and easy to
read. The structure is excellent. I very much like
the leading main messages set in italic.

F. Joos, Bern

(2) p39: The text needs to address the
consequences of stabilization scenarios, as you suggest on page
39. This is directly relevant to the UNFCCC.  How do projected
emissions in CO2 change when using the new generation of models? What
are the potential implications of the feedbacks on this
projections. What are the climatic consequences?

F. Joos, Bern

(3) p. 23 l 43 ff: I am somewhat unsatisfied how the present text deals
with the processes responsible for the oceanic uptake of excess carbon
and the natural carbon cycle. 

The solubility and biological pumps have been defined
for an atmosphere - ocean system that is in EQUILIBRIUM and in the
context of variations of the NATURAL carbon cycle, namely
glacial-interglacial CO2 variations. While the pump concept is very
usefull to characterize carbon cycle models and the natural carbon
cycle, it may not be readily applied to a transient situation. The
text under the bullet solubility pump is in my opinion not consistent
with the
definition of the solubility pump given in the scientific literature
(Volk and Hoffert, 1985). 

I suggest to replace the first two bullets by the following
text. Unfortunately, the new bullets are much longer and you may wish
to shorten the text here and there and to improve the English.  

If you and the Chapter 3 authors agree on this revision, then of
course several points raised below needs also to be considered in the
main text of Chapter 3 (e.g. improved gas exchange rate; carbonate
chemistry field
studies; model comparison to WOCE, GEOSECS, TTO/SAVE results).


FIRST BULLET: 
------------

{\italics The solubility based mechanism for uptake of excess CO2.}
Ocean uptake of CO2 emitted into the atmosphere is primerely a
physicochemical process governed by three processes: (1) air-sea
exchange, (2) the carbonate chemistry, and (3) the transport of excess
carbon into the deep sea.

(1) The net air-to-sea flux of carbon is driven by the partial
pressure difference in CO2 between the atmosphere and the surface
ocean. The ocean's surface layer equilibrates typically within a year
to an atmospheric CO2 perturbation. Since SAR significant progress has
been made in reducing the uncertainty in the gas transfer
rate. 

(2) Gaseous CO2 dissolves in the surface ocean and reacts with water
to form bicarbonate and carbonate ions. This process occurs virtually
instantaneously. The chemical equilibrium between gaseous CO2 and
dissolved inorganic carbon (DIC) determines together with the ocean
volume primarily the ultimate {\italic uptake capacity} of the ocean
for excess CO2. The system reacts such that the higher the
carbon emissions into the atmosphere the higher the fraction that
remains airborne. The equilibrium constants of the carbonate system
are very well known both from laboratory studies and extensive field
studies in the open ocean.

(3) Excess DIC is transported from the surface ocean to the deep. This
process occurs on timescales of decades to many centuries and is
{\italic the rate limiting process} for the uptake of excess
carbon. The ocean circulaton is the process most uncertain in model
projections of future ocean carbon uptake. Our knowledge on the
circulation are based on observations of tracers that contain a time
information. Since SAR, extensive modeling studies have been carried
out where modeled distribution of CFCs, and bomb- and natural-produced
radiocarbon are compared to oceanic observations. The large scale
features in the observed oceanic tracer fields are resolved by the
models. Models have also shown to simulate well the
reconstructed oceanic distribution of anthropogenic CO2.
 
SECOND BULLET 
-------------
{\italics The natural carbon cycle.} The natural carbon cycle
determined the pre-industrial equilibrium partitioning of carbon
between the atmosphere and the ocean. The uptake of excess CO2 does
not primarily depend on the natural carbon cycle. This is demonstrated
by the similar results obtained with models that include the natural
carbon cycle or models that include only the solubility based
mechanism. The equilibrium partitioning is dependent on the non-linear
interplay between ocean circulation, air-sea exchange, carbonate
chemistry, the oceanic distributions of temperature, salinity, and
alkalinity, and marine productivity. DIC is on average depleted in the
surface ocean relative to the deep through biological and
physicochemical processes. Thus, atmospheric CO2 is several hundred
ppm lower for the present ocean than for an ocean that would be well
mixed in DIC. The deep ocean is on average
substantially cooler than the surface ocean and hence the surface ocean
is depleted in DIC relative to the deep, because CO2 is more soluble
in cold water. Marine ecosystem export organic carbon and calcite from
surface waters to the deep where it is remineralized. This causes the
surface ocean to be depleted in DIC, and enriched in
alkalinity as compared to the deep. 

F. Joos, Bern


Further comments
--------------

page 9: line 13-15: Are differences in spatial coverage really a
physical reason? Should the impact of limitated data resolution not be
already reflected in the uncertainty range of the estimate?
F. Joos, Bern

p12, B6: it might be noted that trends in extrem events are
notoriously difficult to detect because of their rare occurence.
F. Joos, Bern

p14: l. 43: 'For thousand of years before the Industrial Era GHG
remained relatively constant.'  CH4 concentration has changed by about
a factor of two during the Holocene.
F. Joos, Bern

p15, l. 6-8: Does the 'very likely' (99 percent confidence) really
hold also for the Alkenone and paleosol based data? Probably the 'very
likely' holds only for the period covered by ice core data (400 kyr
B.P.). If this is correct then the sentence might be change to
consider only the last 400'000 years or modified by using a different
qualifier for the pre-400 kyr period.
F. Joos, Bern

p15 l. 37-39: This needs some clarification. 

Atmospheric measurements have shown that during the last five decade
the terrestrial biosphere has acted as a small sink or that the
terrestrial
carbon stock is close to balance. This suggests the existence of a
substantial terrestrial sink process that offset carbon emission by
land use, land use changes, and deforestation (estimated to be 1.8
GtC/yr+-.. during the 1980 decade).
F. Joos, Bern

p16: line 7: '..models can now simulate natural interannual
variability of CO2'.  It is suggested to delete the part related to
the natural interannual variability or to modify it as suggested below. 

The variability in atmospheric CO2 is well established. However, how
much the ocean and the terrestrial biosphere contributes to the
atmospheric variability is still controversly discussed. Different
reconstructions (e.g. Keeling et al, Nature 95, Francey et al., Nature
1995, Rayner et al, Tellus, 1999, Joos et al., GRL, 1999, Lee et al,
Nature 1999, Feely et al, Nature 1999, LeQuere et al) yield very
different results. Furthermore, the success of models to simulate the
interannual variability in atm. CO2 is not always convincing.

The word 'natural' is also questionable, because the variability in
atm. CO2 is also modified through anthropogenic activities,
e.g. biomass burning.

The following sentence might be added: 'The observed interannual
variability in atmospheric CO2 offers an opportunity to evaluate
models of the global carbon cycle. First simulations have been
successfully carried out.'

p16, l. 40: typo: '.. support has some support..' 
F. Joos, Bern

p17, l. 27: the word 'effective' might be qualified: 'radiatively
effective, long-lived GHGs'.
F. Joos, Bern

p17, l. 35: remove word 'long-lived' here. CH4 life time of 9 years is
much shorter than that of most halocarbons.
F. Joos, Bern

p19, l. 52: 'Figure 6.12 estimates..' English correct?
F. Joos, Bern

p20, l. 4ff: Land-use change: clarify that here only the impact of LUC
on the albedo is discussed, but not the direct effect of GHGs
emissions.
F. Joos, Bern

p 24, l. 16-18: Do not really understand this sentence. What do you
want to say here?  Uptake can be fast or slow irrespectively whether a
reservoir is well mixed or not.
F. Joos, Bern

p25, l. 9-10: should probably read: '.. perturbations in the surface
BUOYANCY balance... , sea ice formation, and the exchange of HEAT,
processes that ..'

Then, the text is also consistent with the last sentence of F4.

p25, l. 27: 'simple models demonstrate ..' This has also been
demonstrated by A/OGCMs (Frank Bryan, Manabe and Stouffer). replace
'simple models' with 'a hierarchy of models'

p26, l. 12/13: 'However, not all aspects of the record have been
successfully simulated' Is this not to be expected as there are
random/stochastical processes in the climate system.

p26, l. 31: suggest to remove: 'Nevertheless, useful information is
being provided'


p27, l. 40/41: 'It is necessary to .. simulate ALL aspects of the
climate system.' This sentence should be modified. Probably it should
read: 'It is necessary to use climate models that simulate the main
processes governing the future evolution of climate.'

p29, l. 5: add: '..during El Nino; this tends to decrease atmospheric
CO2. On the other hand, CO2 is released from the terrestrial biota
forced
by changes in temperature, precipitation, droughts, and fires.

p30, l. 44-46: suggest to split sentence into more sentences for
clarity.

p35 l.50 - p36 l. 14: clarify whether the given temperature changes
are changes in the global mean or at high-latitudes.

p48, l.48 Figures may be included that show the projected evolution
of the atmospheric concentration of the major GHGs for the four SRES
scenarios.

p38 l.5 and l.6: Should the words 'sensitivity to' not be deleted?

p39 F.8: Yes, stabilization scenarios are indeed important and should
be included.

Tab. 1: - wrong unit for CO2 in 3. line. replace pptv by ppm.
- modify: 'Atmospheric lifetime of a perturbation' 


-- 

NEW FAX NUMBER; NEW FAX NUMBER; NEW FAX NUMBER; NEW FAX NUMBER;

Fortunat Joos, Climate and Environmental Physics
Sidlerstr. 5, CH-3012 Bern
Phone:    ++41(0)31 631 44 61      Fax:      ++41(0)31 631 87 42
e-mail:   joos@climate.unibe.ch;   Internet:
http://www.climate.unibe.ch/~joos/
