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Summary of CO2 and climate change related studies
(From CO2science.org)

(1) Atmospheric CO2 Enrichment Impacts Three Trophic Levels in a Study of Transgenic Cotton
(2) Effects of UV-B Radiation on Terrestrial Ecosystems
(3) Glaciers of North America
(4) Problems with Global Climate Models: Cloud Representations
(5) Negative Climate Feedback and Short Response Time Seen in Mt. Pinatubo Eruption
(6) Climate and Marine Fishing in Medieval Europe
(7) Can Rising Atmospheric CO2 Concentrations Prevent the Thermal Bleaching of Corals?

Atmospheric CO2 Enrichment Impacts Three
Trophic Levels in a Study of Transgenic Cotton

Reference

Chen, F., Ge, F., and Parajulee, M.N.  2005.  Impact of elevated CO2 on tri-trophic interaction of Gossypium hirsutum, Aphis gossypii, and Leis axyridis.  Environmental Entomology 34: 37-46.

What was done

Transgenic Bacillus thuringiensis Berliner cotton (Gossypium hirsutum L. cv GK-12) plants were grown from seed for 30 days in well watered and fertilized sand/vermiculite mixtures in pots located in controlled-environment chambers maintained at atmospheric CO2 concentrations of 370, 700 and 1050 ppm. Three generations of cotton aphids (Aphis gossypii Glober) were subsequently allowed to feed on some of the plants, while a subset of the aphid-infected plants was additionally supplied with predatory ladybugs (Leis axyridis Pallas). Throughout this complex set of operations, several types of measurements were made on both the aphids and the ladybugs.

What was learned

The authors found that (1) "plant height, biomass, leaf area, and carbon:nitrogen ratios were significantly higher in plants exposed to elevated CO2 levels," (2) "more dry matter and fat content and less soluble protein were found in A. gossypii in elevated CO2," (3) "cotton aphid fecundity significantly increased ... through successive generations reared on plants grown under elevated CO2," (4) "significantly higher mean relative growth rates were observed in lady beetle larvae under elevated CO2," and (5) "the larval and pupal durations of the lady beetle were significantly shorter and [their] consumption rates increased when fed A. gossypii from elevated CO2 treatments."

What it means

Chen et al. say their study "provides the first empirical evidence that changes in prey quality mediated by elevated CO2 can alter the prey preference of their natural enemies," and in this particular case, they found that this phenomenon could "enhance the biological control of aphids by lady beetle."
Reviewed 18 May 2005
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Effects of UV-B Radiation
on Terrestrial Ecosystems - Summary


Zhao et al. (2004) report that "as a result of stratospheric ozone depletion, UV-B radiation (280-320 nm) levels are still high at the Earth's surface and are projected to increase in the near future (Madronich et al., 1998; McKenzie et al., 2003)."  In reference to this potential development, they note that "increased levels of UV-B radiation are known to affect plant growth, development and physiological processes (Dai et al., 1992; Nouges et al., 1999)," stating that high UV-B levels often result in "inhibition of photosynthesis, degradation of protein and DNA, and increased oxidative stress (Jordan et al., 1992; Stapleton, 1992)."  In light of these observations, it is only natural to wonder how the ongoing rise in the air's CO2 content might impact the deleterious effects of UV-B radiation on earth's vegetation.

To investigate this question, Zhao et al. grew well watered and fertilized cotton plants in sunlit controlled environment chambers maintained at atmospheric CO2 concentrations of 360 or 720 ppm from emergence until three weeks past first-flower stage under three levels of UV-B radiation (0, 8 and 16 kJ m-2 d-1); and on five dates between 21 and 62 days after emergence, they measured a number of plant physiological processes and parameters.  Over the course of the experiment, the mean net photosynthetic rate of the upper-canopy leaves in the CO2-enriched chambers was increased -- relative to that in the ambient-air chambers -- by 38.3% in the low UV-B treatment (from 30.3 to 41.9 m m-2 s-1), 41.1% in the medium UV-B treatment (from 28.7 to 40.5 m m-2 s-1), and 51.5% in the high UV-B treatment (from 17.1 to 25.9 m m-2 s-1).  In the medium UV-B treatment, the growth stimulation from the elevated CO2 was sufficient to raise net photosynthesis rates 33.7% above the rates experienced in the ambient air and no UV-B treatment (from 30.3 to 40.5 m m-2 s-1); but in the high UV-B treatment the radiation damage was so great that even with the help of the 51.5% increase in net photosynthesis provided by the doubled-CO2 air, the mean net photosynthesis rate of the cotton leaves was 14.5% less than that experienced in the ambient air and no UV-B treatment (dropping from 30.3 to 25.9 m m-2 s-1).

It should be noted, however, that the medium UV-B treatment of this study was chosen to represent the intensity of UV-B radiation presently received on a clear summer day in the major cotton production region of Mississippi, USA, under current stratospheric ozone conditions, while the high UV-B treatment was chosen to represent what might be expected there following a 30% depletion of the ozone layer, which has been predicted to double the region's reception of UV-B radiation from 8 to 16 kJ m-2 d-1.  Consequently, a doubling of the current CO2 concentration and the current UV-B radiation level would reduce the net photosynthetic rate of cotton leaves by just under 10% (from 28.7 to 25.9 m m-2 s-1), whereas in the absence of a doubling of the air's CO2 content, a doubling of the UV-B radiation level would reduce cotton net photosynthesis by just over 40% (from 28.7 to 17.1 m m-2 s-1).

Viewed in this light, it can be seen that a doubling the current atmospheric CO2 concentration would compensate for over three-fourths of the loss of cotton photosynthetic capacity caused by a doubling of the current UV-B radiation intensity; and it may possibly do even better than that, for in the study of Zhao et al. (2003), it was reported that both Adamse and Britz (1992) and Rozema et al. (1997) found that doubled CO2 totally compensated for the negative effects of equally high UV-B radiation.

In another noteworthy study, Deckmyn et al. (2001) grew white clover plants for four months in four small greenhouses, two of which allowed 88% of the incoming UV-B radiation to pass through their roofs and walls and two of which allowed 82% to pass through, while one of the two greenhouses in each of the UV-B treatments was maintained at ambient CO2 (371 ppm) and the other at elevated CO2 (521 ppm).  At the mid-season point of their study, they found that the 40% increase in atmospheric CO2 concentration stimulated the production of flowers in the low UV-B treatment by 22% and in the slightly higher UV-B treatment by 43%; while at the end of the season, the extra CO2 was determined to have provided no stimulation of biomass production in the low UV-B treatment, but it significantly stimulated biomass production by 16% in the high UV-B treatment.

The results of this study indicate that the positive effects of atmospheric CO2 enrichment on flower and biomass production in white clover are greater at more realistic or natural values of UV-B radiation than those found in many greenhouses.  As a result, Deckmyn et al. say their results "clearly indicate the importance of using UV-B transmittant greenhouses or open-top chambers when conducting CO2 studies," for if this is not done, their work suggests that the results obtained could significantly underestimate the magnitude of the benefits that are being continuously accrued by earth's vegetation as a result of the ongoing rise in the air's CO2 content.

In a study that did not include UV-B radiation as an experimental parameter, Estiarte et al. (1999) grew spring wheat in FACE plots in Arizona, USA, at atmospheric CO2 concentrations of 370 and 550 ppm and two levels of soil moisture (50 and 100% of potential evapotranspiration).  They found that leaves of plants grown in elevated CO2 had 14% higher total flavonoid concentrations than those of plants grown in ambient air, and that soil water content did not affect the relationship.  An important aspect of this finding is that one of the functions of flavonoids in plant leaves is to protect them against UV-B radiation.  More studies of this nature should thus be conducted to see how general this beneficial response may be throughout the plant world.

In a study of UV-B and CO2 effects on a natural ecosystem, which was conducted at the Abisko Scientific Research Station in Swedish Lapland, Johnson et al. (2002) studied plots of subarctic heath composed of open canopies of downy birch and dense dwarf-shrub layers containing scattered herbs and grasses.  For a period of five years, they exposed the plots to factorial combinations of UV-B radiation -- ambient and that expected to result from a 15% stratospheric ozone depletion -- and atmospheric CO2 concentration -- ambient (around 365 ppm) and enriched (around 600 ppm) -- after which they determined the amounts of microbial carbon (Cmic) and nitrogen (Nmic) in the soils of the plots.

When the plots were exposed to the enhanced UV-B radiation, the amount of Cmic in the soil was reduced to only 37% of what it was at the ambient UV-B level when the air's CO2 content was maintained at the ambient concentration.  When the UV-B increase was accompanied by the CO2 increase, however, not only was there not a decrease in Cmic, there was an actual increase of 37%.  The story with respect to Nmic was both similar and different at one and the same time.  In this case, when the plots were exposed to the enhanced level of UV-B radiation, the amount of Nmic in the soil experienced a 69% increase when the air's CO2 content was maintained at the ambient concentration; and when the UV-B increase was accompanied by the CO2 increase, Nmic rose even more, by a whopping 138%.

These findings, in the words of Johnson et al., "may have far-reaching implications ... because the productivity of many semi-natural ecosystems is limited by N (Ellenberg, 1988)."  Hence, the 138% increase in soil microbial N observed in this study to accompany a 15% reduction in stratospheric ozone and a 64% increase in atmospheric CO2 concentration (experienced in going from 365 ppm to 600 ppm) should significantly enhance the input of plant litter to the soils of these ecosystems, which phenomenon represents the first half of the carbon sequestration process, i.e., the carbon input stage.  With respect to the second stage of keeping as much of that carbon as possible in the soil, Johnson et al. note that "the capacity for subarctic semi-natural heaths to act as major sinks for fossil fuel-derived carbon dioxide is [also] likely to be critically dependent on the supply of N," as is indeed indicated to be the case in the literature review of Berg and Matzner (1997), who report that with more nitrogen in the soil, the long-term storage of carbon is significantly enhanced, as more litter is chemically transformed into humic substances when nitrogen is more readily available, and these more recalcitrant carbon compounds can be successfully stored in the soil for many millennia.

In light of these several findings, we conclude that the ongoing rise in the air's CO2 content is a powerful antidote for the deleterious biological impacts that might possibly be caused by an increase in the flux of UV-B radiation at the surface of the earth due to any further depletion of the planet's stratospheric ozone layer.

References

 Last updated 18 May 2005
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http://www.co2science.org/scripts/Template/MainPage.jsp?Page=subject/n/summaries/northamgla

Glaciers (North America) -- Summary

Does the history of North American glacial activity support the climate-alarmist claim that anthropogenic CO2 emissions drove temperatures to new and unprecedented heights near the end of the 20th century?  We here review some studies of North American glaciers that speak to this issue.
Dowdeswell et al. (1997) analyzed the mass balance histories of the 18 Arctic glaciers that have the longest observational records, finding that just over 80% of them displayed negative mass balances over the last half of the 20th century.  However, they note that "ice-core records from the Canadian High Arctic islands indicate that the generally negative glacier mass balances observed over the past 50 years have probably been typical of Arctic glaciers since the end of the Little Ice Age."  Also, they emphatically state "there is no compelling indication of increasingly negative balance conditions which might, a priori, be expected from anthropogenically induced global warming."  Quite to the contrary, they report that "almost 80% of the mass balance time series also have a positive trend, toward a less negative mass balance."  Hence, although most of these High Arctic Canadian glaciers continue to lose mass, as they have probably done since the end of the Little Ice Age, they are losing smaller amounts each year, in the mean, which is not what one would expect in the face of rapidly rising atmospheric CO2 concentrations if they truly drive global warming as dramatically as climate-alarmists say they do.

Also reporting from Canada, Clague et al. (2004) documented glacier and vegetation changes at high elevations in the upper Bowser River basin in the northern Coast Mountains of British Columbia, based on studies of the distributions of glacial moraines and trimlines, tree-ring data, cores from two small lakes that were sampled for a variety of analyses (magnetic susceptibility, pollen, diatoms, chironomids, carbon and nitrogen content, 210Pb, 137Cs, 14C), similar analyses of materials obtained from pits and cores from a nearby fen, and by accelerator mass spectrometry radiocarbon dating of plant fossils, including wood fragments, tree bark, twigs and conifer needles and cones.  All this evidence suggested a glacial advance that began about 3000 years ago and may have lasted for hundreds of years, which would have placed it within the unnamed cold period that preceded the Roman Warm Period.  There was also evidence for a second minor phase of activity that began about 1300 years ago but was of short duration, which would have placed it within the Dark Ages Cold Period.  Finally, the third and most extensive Neoglacial interval began shortly after AD 1200, following the Medieval Warm Period, and ended in the late 1800s, which was, of course, the Little Ice Age, during which time Clague et al. say that "glaciers achieved their greatest extent of the past 3000 years and probably the last 10,000 years."
These data clearly depict the regular alternation between non-CO2-forcecd multi-century cold and warm periods that is the trademark of the millennial-scale oscillation of climate that reverberates throughout glacial and interglacial periods alike.  That a significant, but by no means unprecedented, warming followed the most recent cold phase of this cycle is in no way unusual, particularly since the Little Ice Age was likely the coldest period of the last 10,000 years.  The significant warming of the 20th century would have occurred within the same timeframe and been just as strong even if the atmosphere's CO2 content had remained constant at pre-industrial levels; it was simply the next scheduled phase of this ever-recurring natural climatic oscillation.

In a study based in Alaska, Calkin et al. (2001) reviewed the most current and comprehensive research of Holocene glaciation along the northernmost portion of the Gulf of Alaska between the Kenai Peninsula and Yakutat Bay, where several periods of glacial advance and retreat were noted during the past 7000 years.  Over the latter part of this record, there was a general glacial retreat during the Medieval Warm Period that lasted for a few centuries prior to A.D. 1200, after which there were three major intervals of Little Ice Age glacial advance: the early 15th century, the middle 17th century, and the last half of the 19th century.  During these latter time periods, glacier equilibrium line altitudes were depressed from 150 to 200 m below present values as Alaskan glaciers also "reached their Holocene maximum extensions."  Hence, it is only to be expected that Alaska's temperatures would rise significantly and its glaciers would lose mass at significant rates during the planet's natural recovery from the coldest period of the current interglacial.

In another study from Alaska, Wiles et al. (2004) derived a composite Glacier Expansion Index (GEI) for the state based on "dendrochronologically-derived calendar dates from forests overrun by advancing ice and age estimates of moraines using tree-rings and lichens" for three climatically-distinct regions -- the Arctic Brooks Range, the southern transitional interior straddled by the Wrangell and St. Elias mountain ranges, and the Kenai, Chugach and St. Elias coastal ranges -- after which they compared this history of glacial activity with "the 14C record preserved in tree rings corrected for marine and terrestrial reservoir effects as a proxy for solar variability" and with the history of the Pacific Decadal Oscillation (PDO) derived by Cook (2002).

As a result of their efforts, Wiles et al. discovered that "Alaska shows ice expansions approximately every 200 years, compatible with a solar mode of variability," specifically, the de Vries 208-year solar cycle; and by merging this cycle with the cyclical behavior of the PDO, they obtained a dual-parameter forcing function that was even better correlated with the Alaskan composite GEI, with major glacial advances clearly associated with the Sporer, Maunder and Dalton solar minima.
In describing the rational for their study, Wiles et al. said that "increased understanding of solar variability and its climatic impacts is critical for separating anthropogenic from natural forcing and for predicting anticipated temperature change for future centuries."  In this regard, it is most interesting that they made no mention of possible CO2-induced global warming in discussing their results, presumably because there was no need to do so.  Alaskan glacial activity, which in their words "has been shown to be primarily a record of summer temperature change (Barclay et al., 1999)," appears to be sufficiently well described within the context of centennial (solar) and decadal (PDO) variability superimposed upon the millennial-scale (non-CO2-forced) variability that produces longer-lasting Medieval Warm Period and Little Ice Age conditions.
Dropping down into the conterminous United States, Pederson et al. (2004) used tree-ring reconstructions of North Pacific surface temperature anomalies and summer drought as proxies for winter glacial accumulation and summer ablation, respectively, to create a 300-year history of regional glacial Mass Balance Potential (MBP), which they compared with historic retreats and advances of Glacier Park's extensively-studied Jackson and Agassiz glaciers.  What they found was most interesting.  As they describe it, "the maximum glacial advance of the Little Ice Age coincides with a sustained period of positive MBP that began in the mid-1770s and was interrupted by only one brief ablation phase (~1790s) prior to the 1830s," after which they report that "the mid-19th century retreat of the Jackson and Agassiz glaciers then coincides with a period marked by strong negative MBP."  From about 1850 onward, for example, they note that "Carrara and McGimsey (1981) indicate a modest retreat (~3-14 m/yr) for both glaciers until approximately 1917."  At that point, they report that "the MBP shifts to an extreme negative phase that persists for ~25 yr," during which period the glaciers retreated "at rates of greater than 100 m/yr."

Continuing with their history, Pederson et al. report that "from the mid-1940s through the 1970s retreat rates slowed substantially, and several modest advances were documented as the North Pacific transitioned to a cool phase [and] relatively mild summer conditions also prevailed."  Thereafter, however, from the late 1970s through the 1990s, they say that "instrumental records indicate a shift in the PDO back to warmer conditions resulting in continuous, moderate retreat of the Jackson and Agassiz glaciers."

The first illuminating aspect of this glacial history is that the post-Little Ice Age retreat of the Jackson and Agassiz glaciers began just after 1830, in harmony with the findings of a number of other studies from various parts of the world (Vincent and Vallon, 1997; Vincent, 2001, 2002; Moore et al., 2002; Yoo and D'Odorico, 2002; Gonzalez-Rouco et al. 2003; Jomelli and Pech, 2004), including the entire Northern Hemisphere (Briffa and Osborn, 2002; Esper et al., 2002), which finding stands in stark contrast to what is suggested by the IPCC-endorsed "hockeystick" temperature history of Mann et al. (1998, 1999), which does not portray any Northern Hemispheric warming until around 1910.  The second illuminating aspect of the glacial record is that the vast bulk of the glacial retreat in Glacier National Park occurred between 1830 and 1942, over which time the air's CO2 concentration rose by only 27 ppm, which is less than a third of the total CO2 increase experienced since the start of glacial recession.  Then, from the mid-1940s through the 1970s, when the air's CO2 concentration rose by another 27 ppm, Pederson et al. report that "retreat rates slowed substantially, and several modest advances were documented."

It is illuminating to note, in this regard, that the first 27 ppm increase in atmospheric CO2 concentration coincided with the great preponderance of glacial retreat experienced since the start of the warming that marked the "beginning of the end" of the Little Ice Age, but that the next 27 ppm increase in the air's CO2 concentration was accompanied by little if any additional glacial retreat, when, of course, there was little if any additional warming.
Clearly, and contrary to the strident claims of climate alarmists, something other than the historic rise in the air's CO2 content has been responsible for the disappearing ice fields of Glacier National Park.  It should also be clear to all that the historical behavior of North America's glaciers provides no evidence whatsoever for unprecedented or unnatural CO2-induced global warming over any part of the 20th century.

References
 Last updated 18 May 2005
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Problems with Global Climate Models:
Cloud Representations


Reference
Siebesma, A.P., Jakob, C., Lenderink, G., Neggers, R.A.J., Teixeira, J., van Meijgaard, E., Calvo, J., Chlond, A., Grenier, H., Jones, C., Kohler, M., Kitagawa, H., Marquet, P., Lock, A.P., Muller, F., Olmeda, D. and Severijns, C.  2004.  Cloud representation in general-circulation models over the northern Pacific Ocean: A EUROCS intercomparison study.  Quarterly Journal of the Royal Meteorological Society 130: 3245-3267.

What was done
 Quoting the authors, "simulations with nine large-scale models [were] carried out for June/July/August (JJA) 1998 and the quality of their results [were] assessed along a cross-section in the subtropical and tropical North Pacific ranging from (235°E, 35°N) to (187.5°E, 1°S)," in order to "document the performance quality of state-of-the-art GCMs (general-circulation models) in modeling the first-order characteristics of subtropical and tropical cloud systems."

What was learned
The main conclusions, according to Siebesma et al., were that "(1) almost all models strongly underpredicted both cloud cover and cloud amount in the stratocumulus regions while (2) the situation is opposite in the trade-wind region and the tropics where cloud cover and cloud amount are overpredicted by most models."  In fact, they report that "these deficiencies result in an overprediction of the downwelling surface short-wave radiation of typically 60 W m-2 in the stratocumulus regimes and a similar underprediction of 60 W m-2 in the trade-wind regions and in the intertropical convergence zone (ITCZ)," which discrepancies are to be compared, we note, with a radiative forcing of only 4 W m-2 for a 300-ppm increase in the atmosphere's CO2 concentration.  They also state that "similar biases for the short-wave radiation were found at the top of the atmosphere, while discrepancies in the outgoing long-wave radiation are most pronounced in the ITCZ."

What it means
 The seventeen scientists from nine different countries state that "the representation of clouds in general-circulation models remains one of the most important as yet unresolved [our italics] issues in atmospheric modeling."  This is partially due, they continue, "to the overwhelming variety of clouds observed in the atmosphere, but even more so due to the large number of physical processes governing cloud formation and evolution as well as the great complexity of their interactions."  Nevertheless, they conclude that through repeated critical evaluations of the type they conducted, "the scientific community will be forced to develop further physically sound parameterizations that ultimately [our italics] result in models that are capable of simulating our climate system with increasing realism."  Until that time (indeed, until climate simulations can be done, not with increasing realism, but with true realism), we suggest it is not too wise to put much credence in what these admittedly inadequate state-of-the-art GCMs suggest about the future; and to actually mandate drastic reductions in fossil-fuel energy production on the basis of what they suggest currently is downright foolish.
Reviewed 18 May 2005
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Negative Climate Feedback and Short Response
Time Seen in Mt. Pinatubo Eruption


Reference
Douglass, D.H. and Knox, R.S.  2005.  Climate forcing by the volcanic eruption of Mount Pinatubo.  Geophysical Research Letters 32: 10.1029/2004GL022119.

What was done
 The authors "determined the volcano climate sensitivity and response time for the Mount Pinatubo eruption, using observational measurements of the temperature anomalies of the lower troposphere, measurements of the long wave outgoing radiation, and the aerosol optical density," perhaps inspired by what Hansen et al. (1992) had said of this eruption, i.e., that it had the potential to exceed "the accumulated forcing due to all anthropogenic greenhouse gases added to the atmosphere since the industrial revolution began," and should "provide an acid test for global climate models."

What was learned
 Douglass and Knox's analysis revealed "a short atmospheric response time, of the order of several months, leaving no volcano effect in the pipeline, and a negative feedback to its forcing."

What it means
 One of the issues raised by the results of this study, in the words of the University of Rochester physicists who conducted it, "is the origin of the required negative feedback."  In response, they report that "negative feedback processes have been proposed involving cirrus clouds (Lindzen et al., 2001)," and that "Sassen (1992) reports that cirrus clouds were produced during the Mt. Pinatubo event."  In addition, they note that the adaptive infrared iris concept of Lindzen et al. "yields a negative feedback factor of -1.1, which is well within the error estimate of the feedback found by us."  They also note that the short intrinsic response time they derived (6.8 ± 1.5 months) "confirms suggestions of Lindzen and Giannitsis (1998, 2002) that a low sensitivity and small lifetime are more appropriate" than the "long response times and positive feedback" that are characteristic of the reigning climatic paradigm.

In this regard, it is also worth mentioning that the adaptive infrared iris phenomenon has the capacity, in Lindzen et al.'s words, to "more than cancel all the positive feedbacks in the more sensitive current climate models" that are used to predict the consequences of projected increases in atmospheric CO2 concentration.  As a result, Douglass and Knox conclude that "Hansen et al.'s hope that the dramatic Pinatubo climate event would provide an 'acid test' of climate models has been fulfilled, although with an unexpected result."

References

 Reviewed 18 May 2005
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 Climate and Marine Fishing in Medieval Europe

Reference
Barrett, J.H., Locker, A.M. and Roberts, C.M.  2004.  The origins of intensive marine fishing in medieval Europe: the English evidence.  Proceedings of the Royal Society of London B 271: 2417-2421.

What was done
To obtain an idea of the true magnitude of historical over-fishing of the seas and what it has done to marine fish stocks requires, in the words of the authors, "comparison of current observations with baseline records of marine ecosystems in their 'pristine' state."  Hence, they set about to "determine the origin of intensive, probably commercial, cod and herring fishing by assessing the relative abundance (by number of identified specimens) of these taxa in 127 English archaeological fish bone assemblages that date from the seventh to the sixteenth centuries AD."

What was learned
Barrett et al. report that "zooarchaeological evidence shows that the clearest changes in marine fishing in England between AD 600 and 1600 occurred rapidly around AD 1000."  Surprisingly, however, they say this revolution in marine fishing "coincided with the Medieval Warm Period - when natural herring and cod productivity was probably low in the North Sea," according to what is known about "climatically determined patterns in fish abundance."

In explaining this conundrum, they say "the counterintuitive discovery can be explained by the concurrent rise of urbanism and human impacts on freshwater ecosystems," and that "rapid population growth may also have increased the demand for marine fish (Dyer, 2002; Hoffmann, 2002)."  In addition, they note that "the most important variable ... may have been declining freshwater fish stocks - owing to siltation from more intensive agriculture."

What it means
It is interesting to note that this "revolutionary expansion of marine fishing in England within a few decades of AD 1000" was likely driven by the growth of human society and improved and expanded agricultural production associated with the higher temperatures of the Medieval Warm Period.  Not only do these observations demonstrate the positive value of the warmth of this period, as compared to the lower temperatures of the prior Dark Ages Cold Period and subsequent Little Ice Age, they also speak volumes about the reality of the non-CO2-induced millennial-scale oscillation of climate that alternately produces these multi-century warm and cold periods, and which has most recently led to the development of the Modern Warm Period, all without any help from the concurrent historical increase in the air's CO2 content.
Hey, it's nice out. Let's go fishin'!

References
 Reviewed 18 May 2005
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Can Rising Atmospheric CO2 Concentrations
Prevent the Thermal Bleaching of Corals?
Volume 8, Number 20: 18 May 2005

In the introduction to their intriguing review of the thermal aspects of coral bleaching, Smith et al. (2005) note that "photoinhibition of photosynthesis and photodamage to photosystem II of the zooxanthellae, with the consequent increase in the production of damaging reactive oxygen species (ROS), have been implicated as the cause of thermal bleaching (Brown, 1997; Fitt et al., 2001; Lesser, 2004; Tchernov et al., 2004)."  At the end of their review, they additionally report that the "thermal bleaching of many corals is ultimately the result of the destruction of photosynthetic pigments by ROS," and that the production by the zooxanthellae of one particular ROS, hydrogen peroxide, "may be a signal that triggers a response in the host cell to eject the zooxanthellae or shed the host cell from the coral."

These facts resonate with other findings we have reviewed on our website and suggest that the ongoing rise in the air's CO2 content may ultimately provide the solution to the worldwide problem of heat-induced coral bleaching.  This concept originates from research conducted in the terrestrial realm, which reveals, in the words of Ren et al. (2001), that "elevated CO2 can enhance the capacity of plants to resist stress-induced oxidative damage."

In the case of ozone pollution, the primary problems occur in the leaf mesophyll, where ozone dissolves into the wet surfaces of exposed cell walls.  There, reactions of ozone with water and solutes in the apoplasm lead to the formation of several ROS, including hydrogen peroxide (H2O2), hydroperoxide, superoxide, hydroxyl radicals and singlet oxygen (Foyer et al., 1994; Kangasjarvi et al., 1994; Wohlgemuth et al., 2002), all of which substances promote oxygen toxicity (Podila et al., 2001).  However, in a FACE study of this phenomenon in aspen and paper birch seedlings exposed to ambient air, ozone-enriched air, CO2-enriched air or air enriched with both ozone and CO2, Oksanen et al. (2003) found that H2O2 accumulation only occurred "in ozone-exposed leaves and not in the presence of elevated CO2," adding that "CO2 enrichment appears to alleviate chloroplastic oxidative stress."  Similarly, in a study of mature holm and white oak trees that had been growing near natural CO2 springs in central Italy for 30 to 50 years, Schwanze and Polle (1998) found that they exhibited significant reductions in their amounts of lipid peroxidation.

To see if such ROS-fighting properties of elevated CO2 might be operative in the aquatic realm, Yu et al. (2004) grew the marine microalgae Platymonas subcordiformis in the laboratory at ambient levels of atmospheric CO2 and UV-B radiation flux density, as well as at elevated levels of 5000 ppm CO2 and/or UV-B radiation characteristic of what would result from a 25% stratospheric ozone depletion under clear sky conditions in summer.  They found that the elevated UV-B treatment significantly decreased microalgal dry weight and photosynthetic rate, while the elevated CO2 treatment enhanced dry weight and photosynthetic rate.  They also report that elevated UV-B significantly increased the production of the toxic superoxide anion and hydrogen peroxide, as well as malonyldialdehyde, which is an end product of lipid peroxidation, whereas elevated CO2 did just the opposite.  In addition, in the treatment consisting of both elevated UV-B and elevated CO2, the concentrations of these three substances were lower than those observed in the elevated UV-B and ambient CO2 treatment.

Yu et al. say their results suggest that "CO2 enrichment could reduce oxidative stress of reactive oxygen species to P. subcordiformis, and reduce the lipid peroxidation damage of UV-B to P. subcordiformis."  They also say that "CO2 enrichment showed a protective effect against the oxidative damage of UV-B-induced stress," and, therefore, that elevated CO2 can enhance "the capacity of stress resistance."  Put more simply, they say in their concluding paragraph that "algae grown under high CO2 would better overcome the adverse impact of environmental stress factors that act via generation of activated oxygen species."

It is difficult to state the implications of these studies in any clearer language, but we will try.  Since, in the words of Smith et al. (2005), "thermal bleaching of many corals is ultimately the result of the destruction of photosynthetic pigments by ROS," and since, in the words of Oksanen et al. (2003), "CO2 enrichment appears to alleviate chloroplastic oxidative stress," it takes no imagination at all to reach the conclusion that some as-yet-undefined level of atmospheric CO2 enrichment should completely counter coral thermal bleaching.  In addition, since the presence of hydrogen peroxide, in the words of Smith et al. (2005), "may be a signal that triggers a response in the host cell to eject the zooxanthellae or shed the host cell from the coral," and since, in the words of Yu et al. (2004), "CO2 enrichment could reduce ... lipid peroxidation damage," it readily follows that some degree of atmospheric CO2 enrichment should likewise cause host cells to not eject their zooxanthellae.

Clearly, it only remains for someone to do such experiments as those described above on coral itself.  Who will do it first ... and become famous in the process?

Sherwood, Keith and Craig Idso

References


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