[Coral-List] HadISST 1.1 data: Bleaching is not due to Warming

Mark Eakin Mark.Eakin at noaa.gov
Wed Jun 2 13:02:56 EDT 2004


I concur with Ove.  It will take more details of the analysis to make  
this case convincingly.  I also recommend you be more careful about  
your conclusions:

"I must conclude that, although temperature is an obvious parameter (as  
irradiance), Global Warming is not the primary cause of bleaching. This  
lets a direct bleaching action of CO2 rise and seawater acidification  
as the only possible other global cause of coral reef mass bleaching."

Even if global temperature patterns are ruled out, that leaves more  
than just CO2 increases as a possible cause.  To conclude that the  
cause is CO2, you need to provide data that CO2 in coral reef waters is  
increasing in a way that you feel temperature is not.


On Jun 1, 2004, at 9:10 PM, Ove Hoegh-Guldberg wrote:

> Dear Martin,
> The only problem is that one can use, very successfully, satellite
> measurements of SST anomalies and predict mass coral bleaching by as  
> much as
> days and even weeks in advance.  Also - how many major bleaching  
> events have
> occurred without an associated SST anomaly?  Not many, it seems.  These
> things need explanation.
> "Facts are facts" except yours are unreviewed and unsubstantiated. Why  
> not
> use the age-old method and submit your manuscript to proper  
> peer-review?
> Cheers,
> Ove
> -----Original Message-----
> From: coral-list-bounces at coral.aoml.noaa.gov
> [mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Martin  
> Pêcheux
> Sent: Wednesday, 2 June 2004 8:56 AM
> To: coral-list at coral.aoml.noaa.gov
> Subject: [Coral-List] HadISST 1.1 data: Bleaching is not due to Warming
> Dear Coral-listers,
> I know that I will shock the common belief on this very important  
> topic. But
> the facts are the facts. I was myself surprised. So I decided to send  
> this
> draft to the list before submission to a publication, hoping for  
> comments or
> critics. Thanks a lot. A long version is available at request.
> HadISST 1.1 data : Coral Reef Mass Bleaching is not due to Global  
> Warming.
> Martin Pêcheux, June 2004
> Nice University, 94260 Fresnes, France
> Email : martin-pecheux at wanadoo.fr
> Coral reef mass bleaching is the main threat on an Earth ecosystem.  
> There is
> a consensus among reef researchers that Global Warming is the cause.  
> Here I
> analyse HadISST 1.1 data, a new release of Sea Surface Temperature  
> set, from
> 1950 to 2000, with 1° degree resolution, monthly averaged, at 50 reef  
> sites
> with known bleaching record. First, the Global Warming is all but  
> global.
> Whereas in Indian ocean the warming of yearly maximum SST is  
> significative,
> as well as in the Pacific, the Caribbean has seen a general cooling  
> from
> 1950 to about 1986, then a warming. Secondly, I determine for the  
> studied
> sites the relevant parameter for bleaching ÆT, i.e. the minimum  
> temperature
> at which bleaching has occurred, minus the maximum temperature at which
> bleaching was absent during the 1950-1978¹s. In fact, only 16% of the  
> sites
> have positive ÆT : there was generally higher temperature in 1950-1978
> without bleaching than now with bleaching eliciting. Bleaching  
> threshold is
> also analysed. I must conclude that, although temperature is an obvious
> parameter (as irradiance), Global Warming is not the primary cause of
> bleaching. This lets a direct bleaching action of CO2 rise and seawater
> acidification as the only possible other global cause of coral reef  
> mass
> bleaching.
> Coral reef mass bleaching begin in 1979 (reviews in Williams and
> Bunkley-Williams, 1990, Smith and Buddemeier, 1992, Glynn, 1996, Brown,
> 1997, Pêcheux, 1997 - unpublished/online, Hoegh-Guldberg, 1999, Coles  
> and
> Brown, 2003). Reef researchers were at first destabilised about its  
> cause.
> But with repetitive reports of bleaching with "above average"  
> temperatures
> in summer, and the following of "hot spot" formation from satellite  
> (Goreau
> and Hayes, 1994) in particular in real time (NOAA indices, Strong et  
> al.,
> 1997, Lui and Strong, 2003,
> orbit-net.nesdis.noaa.gov/orad/coral_bleaching_index), an overwhelming
> consensus emerges as to pinpoint Global Warming as the cause. But, by
> definition, "above average" temperatures and "hot spots" are a normal
> phenomenon, which have occurred also before mass bleaching began. My  
> goal
> was to examine such phenomenon, i. e. what is the difference ÆT between
> present temperatures with bleaching and past maximum without bleaching.
> Mainly due to lack of historical data, there have been only one serious
> attempt to check this feature. Coffroth et al. (1989) examine the 1982  
> event
> of the (well studied) Great Barrier Reef. They conclude unambiguously  
> that
> the temperature was elevated but not exceptional. They also discard any
> conjunction with other physical factors, such as luminosity, water
> transparency, winds, rainfall or tide. Elms (1992, discussed in Atwood  
> et
> al., 1992) analyses the GOSTA data from 1950 to 1989 over fifteen 5°x5°
> zones in Caribbean and found cooling of the yearly mean in fourteen of  
> them,
> with a mean of ­1.00°C/century. Some other less relevant works are  
> analysed
> in Pêcheux (1997). Lough (2000) studies the GISST data (1903-1994) and  
> data (1982-1999) at 47 world-wide coral reef sites, in an approach  
> rather
> similar to mine. She focuses on global trends and on the unprecedented
> 1997-1998 event. Nonetheless, she pinpoints that 1958 was more extreme  
> for
> pooled Caribbean sites. Last but not least, it is known that bleaching  
> of
> large foraminifers peaks at summer solstice and not during the maximum
> temperature a few months later (Williams et al., 1997).
> Here I used the HadISST 1.1 data, newly released by the British  
> Atmospheric
> Data Centre, Met Office Hadley Centre, UK, an improved reconstructed  
> Sea
> Surface Temperature record (Rayner et al., 2003;
> badc.nerc.ac.uk/home/index.html) and descendant of GOSTA-GISST data. I
> restricted my analysis to the years 1950-2000. SST are averaged on a 1°
> longitude x 1° latitude grid for each month. Bleaching records at 50  
> world
> wide sites are taken from the literature or from the Reef Base
> (www.reefbase.org) and the GCRMN reports (www.aims.gov.au). The  
> bleaching
> temperature was taken as the temperature of the month at which the  
> bleaching
> began if it was known, or (rarely) of the month before if the  
> temperature
> was superior, otherwise it was used the maximum temperature of the year
> (Table 1).
> RESULTS (Table 2)
> Variance of yearly maximum SST.
> At each site, yearly maxima appear as normal distributed (stochastic)  
> (Fig.
> 2). There is a slight excess of "abnormal" standard score greater than  
> 3
> standard deviations (return time >741 years - Gauss integral). They
> correspond to the El Niño 1983 (Panama, Galapagos) and the 1998 cycle
> (Bahamas, Galapagos, Phuket, Seychelles, Maldives and Kenya), and also
> Lizard Island, GBR, January 1970. For the 50 sites, the standard  
> deviation
> of the yearly maximum is Poisson-distributed, being 0.384°C±0.137  
> (range
> 0.240 to 0.966). A geographical differentiation exists: Caribbean is  
> less
> variable, 0.298°C±0.030, than Pacific, 0.461°C±0.173, and Indian ocean,
> 0.350°C±0.040. Warming of the yearly maximum SST. A simple analysis of
> warming, not of the year data, but only of the maximum each year, is
> informative. In Indian ocean (9 sites, without Persian Gulf), the  
> warming is
> regular, being +1.055°C/century, p<0.0001. In Pacific (20 sites), the
> warming is not so great, being +0.707°C/century, p=0.008. At contrast,  
> in
> Caribbean (18 sites), there is a cooling during a first period,  
> 1950-1986
> (determined by maximising slope) of -1.075°C/century, p<0.0001, then a
> strong recent warming, 1987-2000, +1.803°C/century, p=0.008. ÆT,  
> minimum SST
> with bleaching minus maximum SST 1950-1978 without. ÆT is generally
> negative. Only 9 sites have a positive value. The mean value is
> -0.668°C±0.685 (-2.25 to 1.01), normally distributed. Values are all
> negative for Caribbean (-0.821°C±0.466, -1.68 to ­0.02), negative for  
> Indian
> ocean (-0.331°C±0.493, -1.15 to 0.41). It is flat distributed for  
> Pacific
> (-0.672°C±0.883, -2.25 to 1.01), where positive value are encountered  
> mainly
> in the East Pacific with the El Niño 1983 (Coco Islands and  
> Galapagos), and
> in the West Pacific. The 1950-1978 maxima are rather evenly  
> distributed,
> apart 13 world wide occurrences of the year 1969, as already noted by  
> Elms
> (1992) in Caribbean.
> Bleaching threshold from maximum mean.
> I search for a bleaching threshold by subtracting the mean of yearly  
> maximum
> SST 1950-2000 from the minimum bleaching SST. The value is, without  
> high
> values of the El Niño 1983 at Galapagos and Coco Island,  
> -0.0057°C±0.540
> (-1.184 to 1.157). The threshold is well correlated with ÆT (r2=O.785,
> p<0.0001). The discrepancy with NOAA indices (bleaching at 1°C above  
> maximum
> mean) does not come from different maximum means.
> Bleaching record
> .It is certainly incomplete. But a more precise record could only  
> lower the
> minimum temperatures at which bleaching begin. There is some inverse
> correlation between ÆT and the number of event per site (r2=0.274,
> p=0.0001), but whatever the sites are well monitored or not. The ÆT is  
> based
> on the assumption that no "unexplained" mass bleaching took place  
> before
> 1979 (in Bonaire, Hot in Williams and Bunkley-Williams, 1990). This
> certainly holds since 1950. There was enough coverage of reefs by
> scientists, at least in enough places. There are several reports of  
> mass
> bleaching before 1979, always with obvious local causes (heated reef  
> flat,
> thermal pollution, fresh or turbid water, cold event, sedimentation  
> (see
> ref. in Pêcheux, 1997). And, at contrast to corals which stop  
> calcification,
> foraminifers show frequent spectacular shell abnormalities in  
> association
> with bleaching, which were unknown in previous time (Talge et al.,  
> 1997,
> Pêcheux, 1997) apart at the Cretaceous/Tertiary boundary (Pêcheux,  
> 1999).
> Relevance of HadISST data for coral reef mass bleaching. Its accuracy  
> might
> not be perfect, but I used only the most recent data. In any case, the
> magnitude of the mean ÆT, 0.68°C, is far above any inaccuracy. The  
> average
> over one month may not capture the exact value of SST, but the time  
> dynamics
> are slow and regular. The 1°x1° grid (~110 km square) may obscure  
> slightly
> the formation of relevant "hot spots", and be less significative for  
> shore
> reefs. But this surely does not hold for fore reefs well bathed by  
> oceanic
> waters. And I am confident that the physical relationship between  
> mesoscale
> open ocean temperatures and local shore ones could not have changed so
> dramatically since 1979. HadISST data can be well compared with the  
> satellite bleaching-warning indices in real time, which are quite
> successful. They have a slight higher spatial resolution (50 km) but
> bleaching events show extended zone of warm waters. Time resolution is  
> twice
> a week, but the most precise index, the Degree Heating Weeks, must  
> reach 4
> on its scale before bleaching, corresponding to 1 degree above maximum  
> mean
> during 4 weeks. Bleaching threshold. It is null because I used the  
> minimum
> bleaching SST, at contrast to Goreau and Hayes (1994) and NOAA indices,
> which established empirically a +1°C threshold from all records. The  
> value
> of the mean standard deviation, 0.384°C, means that a SST with "1°C  
> above
> mean maximum", i.e. 2.6 time the standard deviation, occurs each 217  
> years
> (range 63500 to 6.65 years), which is obviously false. The standard
> deviation has not increase recently (mean SD=0.362°C for 1990-2000). I  
> guess
> that NOAA indices capture important events but not all, in particular  
> in
> Caribbean with low variance. A null minimum bleaching threshold means  
> that
> bleaching is in the yearly maximum mean, said, it has a 50%  
> probability, or
> can occurs every two years, which is also obviously false. This does  
> not
> mean that the data are false, of course. Temperature is a factor but  
> not the
> only one. There are also other triggering factors, the firsts in mind  
> being
> clear sky (full light and
> UV) and dolldrum time (reduced cooling evaporation, more water  
> transparency,
> less circulation, and, more important in my opinion, impaired  
> exchanges at
> organism interface, i.e. the "unstirred layer effect"). Whatever the  
> case,
> the small variances mean a high sensitivity to a few tenth of °C. A  
> very
> crude calculation of the true bleaching threshold can be done using the
> frequency of the bleaching events and the variance of the maximum
> temperature. The mean frequency of bleaching is 14.2% (mean of event  
> number
> 2.98/21 years) (return time 7.05 years), corresponding to 1.076  
> standard
> deviation of the maximum mean (0.384°C), thus giving a bleaching  
> threshold
> of 0.413°C.
> The cooling of the maximum SST over the Caribbean till 1986 and, more
> definitive, the negative values of most ÆT, almost twice the standard
> deviation, conduce to the disturbing but inescapable conclusion that  
> the
> increasing temperature is not the primary cause of coral reef mass
> bleaching. It appears when maximum summer stress, of course, but my  
> result
> call for other synergetic factor(s). And this is not contradictory  
> with the
> fact that mass bleaching may occur also more and more frequently with  
> future
> Global Warming. Ultra-violets, at first often considered, are not in  
> cause,
> as they have not increase in tropics, and there is no relationship  
> between
> ozone drawdowns and bleaching events (Pêcheux, 1996a). Moisture deficit
> increases over warm pools in tropics (Flohn and Kapala, 1989, Graham,  
> 1995),
> but it is of low probability that it induces in the 80¹s an  
> hydrological
> pattern change great enough to be responsible of local new maxima 0.7°C
> above previous one. It would also rather increase nebulosity over warm
> waters ("cirrus anvil thermostat"). And of course there were summer  
> dolldrum
> times with clear sky before 1979. This lets a direct effect of CO2  
> rise as
> the last possible global cause. There are many arguments in favor of  
> this
> hypothesis (Pêcheux, 1997). CO2 is, like many other parameters, a  
> bleaching
> factor (Pêcheux, 1994, 1996b). CO2 rise from 280ppm to 360ppm CO2 is  
> already
> equivalent to a warming of 0.4°C, more probably 1.2°C (Pêcheux, 2002),  
> which
> fits well with ÆT. Often forgotten, the fact that bleaching affects  
> not only
> corals but also all other cnidarians, molluscs, sponges, ascidians, and
> large foraminifers in symbioses with either dinoflagelates, diatoms or
> cyanobacteria implies a fundamental limitation of their  
> photosynthesis, the
> two main of which being photoinhibition and photorespiration, both  
> under
> strong influence of symbiose-limited CO2. Given future expected CO2  
> level,
> and with the addition of Global Warming, coral reefs must be  
> considered in
> great danger. The belief in adaptation to CO2 and temperature rises 100
> faster than at the interglacial termination is rather a matter of  
> opinion,
> with very few facts (discussion in Coles and Brown, 2003, Hughes et  
> al.,
> 2003). I think that coral reefs will disappear in the next decades if  
> CO2
> rise is unabated. If so, fight for strong mitigation of anthropogenic  
> CO2
> rise must be our top priority.
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C. Mark Eakin, Ph.D.
Director of the World Data Center for Paleoclimatology

NOAA/National Climatic Data Center
325 Broadway E/CC23
Boulder, CO 80305-3328
Voice: 303-497-6172                  Fax: 303-497-6513
Internet: mark.eakin at noaa.gov

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