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bioscience⏐explained Vol 3 ⏐ No 2 1346 Jarl-Ove Strömberg Kristineberg Marine Research Station Fiskebäckskil, Sweden Climate change and the ocean Climate variability and climate change It may seem like an easy task to distinguish between variability and a more or less permanent trend in a change. However, it is difficult since variability may include cyclic phenomena with long and irregular pulses and our recordings of climate events are often too short to make definite evaluations of their character. We do have a few good examples of recurring events with a periodicity of a few years to a few tens of years. The first may be exemplified by the ENSO events (El Niño/Southern Oscillation) in the equatorial Pacific Ocean and the second by the North Atlantic Oscillation (NAO). Although both have been studied for decades our possibilities to predict when we can expect a change are limited. During an El Niño period a warmer than normal ocean current hits the northern west coast of South America shifting the cold current that normally runs outside this coast away and causing torrential rainfall over land in Peru and Chile where otherwise the climate is dry and we find desert conditions. This in term causes floods and mudslides and has large socio-economic consequences in these countries. One factor behind this is a slow build-up of warm water in the Indonesian ocean region (at times possibly caused by stronger than normal trade winds) and since there is an open communication across the Pacific Ocean this warm water has to flow eastward as an equatorial counter-current. In the mid 1970-ties the effect was thought to be localised to the South American coast and the first person to “predict” an El Niño event was a Peruvian lady scientist who observed the arrival of a planktonic crab, which did not occur in the usually cold waters offshore. In those days females were not allowed onboard Peruvian research vessels. Later the ENSO phenomenon has shown to be much more complicated, being a coupled oceanatmosphere phenomenon and having far-reaching effects also in California, southern Africa, the Indian Ocean and Australia. Predictability is still limited to about half a year and its occurrence varies interannually between 2 to 6-7 years. Also its strength varies considerably (1). CORRESPONDENCE TO Prof. Jarl-Ove Strömberg Kristineberg Marine Research Station, Fiskebäckskil, Sweden e-mail: [email protected] www.bioscience-explained.org The NAO is a shift in winter climate in the north Atlantic and has as its main driving force varying strengths of the atmospheric high over the Azores (the subtropical high) and low over Iceland. With a stronger than normal Azoric high and a deeper than normal Icelandic low we get what is termed a positive NAO, with a dry Mediterranean area and a wet and stormy situation in northCOPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 western Europe and Asia with south-westerly winds dominating. A negative NAO means wet weather over the Mediterranean area and dry and cool weather with mainly northerly wind over western and northern Europe. Then the subtropical high over the Azores is weak as is the Icelandic low. The different phases may last from some years to 20 or more years. At present (2006) we are in a long-lasting positive phase (2). Although these kinds of variability may be affected by more far-reaching climate change, we normally regard them as having “natural” forcing factors – not human induced ones. Figure 1. NAO index is here shown from about 1860 to 2000. A positive value is shown in red and a negative index in blue. Permission by Prof. Dr. Martin Visbeck. (For more information see: http://ldeo.columbia.edu/NAO) Climate change means a long lasting trend (possibly over centuries or millennia) which may or may not be irreversible on a human time-scale. If we look on a geological time-scale the earth has experienced ice ages about every 100 000 years for the last million years which would best fit with a change in solar radiation caused by the earth’s orbit around the sun – going from an almost circular to an oval shape. Other longlasting behaviour of our globe is a change in the tilt of spin axis going from 22.1 to 24.5 degrees and back in about 41 000 years. Finally there is a wobbling in the rotation over periods of 23 000 years. Undoubtedly these changes have influences on the global climate, but these are only partly understood. When looking at relatively short term variations in solar radiation, like the effect of sunspot frequency with an 11 years cycle, these can so far not be accounted for major climate changes (3). Global warming If a change in solar radiation is not the cause for global warming, then we need to look for other influencing factors. There is an almost total agreement among scientists that during the last century there was a global temperature increase of about 0.6oC, most of which, or 0.4oC, occurred during the last 25 years. It is most accentuated on the northern hemisphere (north of 20oN) because of the continents with an increase of close to 0.7oC, while the ocean dominated southern hemisphere (south of 20oS) has had an increase of 0.3oC. There is also an almost total scientific agreement that the main www.bioscience-explained.org 2 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 forcing factor is the concentration of greenhouse gases in the atmosphere, especially that of CO2, although also methane (CH4), nitrous oxide (N2O) and freons (CCl2F2) are major contributors. Measurements of atmospheric CO2 started in a serious way by the end of the 1950-ies on the top of Maona Loa on the island of Hawaii. It was then 315 ppm and has since risen to 380 ppm in less than 60 years. Pre-industrial level has been found to be 280 ppm. A new insight in earlier long-term variation was received from analyses of enclosed air bubbles in continental ice sheets on Antarctica and Greenland, which showed that during the last 450 millennia concentration never reached above 300 ppm and then for most of the time was far below 250 ppm. (4). There is little or no doubt that the dramatic increase in CO2 concentration in the last 100 years is the result of human perturbation and then mainly due to burning of fossil fuels. The increase from 350 to 380 ppm did not take longer than less than 20 years, while during the preindustrial era the quickest build up of 30 ppm took about 1000 years. Estimates of human production of CO2 indicate that only about half of it stays in the atmosphere and that the other half is transferred into the ocean. This is then the major reason for an observed seawater acidification (See more below). The Intergovernmental Panel on Climate Change (IPCC) of the United Nation has investigated various scenarios for the future and estimate that by end of the 21st century the CO2 concentration in the atmosphere could be anywhere between 490 and 1260 ppm corresponding to an increase from pre-industrial level with 75 to 350%. During the industrial era methane concentration in the atmosphere has increased from 750 ppm to about 1600 ppm and corresponding levels for nitrous oxide is a raise from 275 ppm to 315 ppm. Increase in methane is due to human activity but is also resulting from melting permafrost soil of tundra regions and seeps from ocean sediment deposits of methane hydrate. In radiative forcing (in Wm-2) this means an increase by 1.5 for CO2, 0.5 for CH4, and 0.15 for N2O. For meteorologists and oceanographers the above is generally accepted as facts but it has taken a long time to convince politicians and most media that this is bad news and some counteractions are needed. It was therefore a surprise to see the front page of the U.S. Time Magazine in early April 2006:”Be worried. Be very worried. Climate change isn’t some vague future problem – it’s already damaging the planet at an alarming pace” (5). www.bioscience-explained.org 3 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 How will global warming affect the ocean? • Sea level rise 1. Water expansion: When water heats up it expands. A doubling of the atmospheric CO2 concentration has by some models been estimated to give a temperature rise of the oceanic surface water of 3-4oC, and a sea level rise of 40-50 cm. For many low coastal areas and islands this is enough to create serious problems. 2. Melting continental ice sheets: There are two schools of thought: (a) because of increased precipitation on the upper parts of the ice sheets with a build-up of ice, a faster flow of ice towards the periphery, and increased iceberg formation and melting at the edges, the ice mass will not change dramatically and thus the sea level will not be affected in a major way; (b) precipitation will not increase on the upper parts, but the melting at the peripheries of the ice sheets will indeed increase resulting in a loss of ice mass and melting of ice shelves. Sea level will rise depending on degree of melt off. This could mean at least one meter by 2100. Figure 2. The influence on the atmosphere by the various greenhouse gases or particles is very obvious by the steep inclines in all four cases above. Source: Intergovernmental Panel on Climate Change. www.bioscience-explained.org Present investigations do not give a consistent picture. More snowfall has been reported on top of the Greenland ice sheet, but there are also pictures of large “lakes” of melt-water on the top with ice cracks below through which water could drain. In the Antarctic Peninsula area large ice shelves have broken loose and started to drift away and melt. With a large part of the western Antarctic ice sheet being partly under sea water level this part could melt rapidly with higher seawater temperature. If this happens a major sea 4 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 level rise may occur which will flood large low lying coastal areas with catastrophic effects. Most models do not support such a development, but rather high air temperatures in the Antarctic Peninsular region have been recorded recently. 3. Storm surges: Increased sea surface temperature will offer more energy for the development of hurricanes, typhoons, and strengthen monsoons, that will inundate coastal areas hit by these storms. Although they have temporary effects they may be disastrous for the stricken areas both on land and in the shallow waters. In the last few years there are indications of more frequent storms and more violent winds • Changes in ocean circulation and heat transport 1. Change in terrestrial runoff: Warmer air can carry more humidity and increase precipitation and runoff to the adjacent sea areas. North-western Europe and Asia may experience this with increased draining of fresh water into the Arctic Ocean. This may also occur on the North American side of the Arctic. With more fresh water at the surface this will mean that the cold Greenland current along east Greenland will carry less salt than at present. Figure 3. The figure shows the result of various models of global sea level rise by the end of the present century. The uncertainty considering the melt off from the continental ice sheets is also indicated. Source: Intergovernmental Panel on Climate Change. www.bioscience-explained.org 5 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 2. Melting of sea ice: Depending on the rise in the air temperature over the Arctic and possibly warmer surface water entering both from the Pacific and the Atlantic Oceans the extent of the sea ice as well as its thickness will be affected. There are already reports of less and thinner sea ice in the Arctic Ocean. If this development continues and more open water subsists the reflection of solar radiation will decrease and more heat will be absorbed in the surface water. This may accelerate the melting of sea ice and further add to the extent of open water during summer months. During the winter fresh surface water will easily freeze, but not cause deepwater convection to the present extent. Obviously this will have major effects on the upper parts of the Arctic marine ecosystem but also on the transport of oxygen- and nutrient-rich water. Melting and disappearance of sea ice in large areas of the Antarctic waters might occur with dramatic effects on the whole Antarctic marine and terrestrial ecosystems. 3. Surface and deep ocean circulation: There are two major areas for deep ocean water formation; both are in the Atlantic sectors of the polar areas. The one in the north is in the Greenland/Iceland Sea or in the Labrador Sea. In these areas cold water from the Arctic Ocean via the Greenland Current flows south and during winter sea ice is formed, which leaves cold and salty and thus heavy water under the ice. This dense water sinks to form a south flowing deep-water current. It has been said to be the site for the motor or engine for the great ocean conveyor belt. Should this stop or at least be reduced in strength there is the risk that the Gulf Stream and its continuation in the Transatlantic Current will take a more southerly route and thus give colder weather to northern Europe and warmer to the areas to the south. Presently there are indications of a weaker deepwater formation in the Greenland/Iceland Sea and a weaker Transatlantic Current. However Norwegian scientists have shown that although this current transports less water it is warmer than before and thus there is not yet a reduction in the heat transport to the Norwegian and Barents Seas. Computer simulations predict and support a weakening in the heat transport via ocean circulation from the tropics to higher latitudes in the North Atlantic (6). www.bioscience-explained.org 6 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 Figure 4. A very generalized picture of the major ocean cur-rents is given here. Blue currents are in the deep sea and orange are at the ocean surface. Deep-sea water is formed in the North Atlantic and in the Weddell Sea in Antarctica. The deep waters enter the surface in the North Indian and Pacific Oceans. Several things are not shown in the pic-ture, e.g. the way Antarctic deep water penetrates way north in the Atlantic underneath the Arctic deep t In the Antarctic Weddell Sea the second major deep sea water formation occurs. This is denser than the Arctic deep water but joins the eastern deep flow of the conveyor belt. In the Atlantic it reaches a little north of the equator and forms the deepest water of the South Atlantic. In the north regions of the Indian and Pacific Oceans the deep currents come up to the surface and from then on stay at the ocean surface on the way back to the Atlantic. If we speculate that the deep water formation as of the present should stop because of global warming there is the risk of a separation between a shallow and a deep ocean. In the shallow ocean a saturation of CO2 would occur and speed up the increase of this gas in the atmosphere with a further warming effect. A detrimental effect to the deep faunas of the oceans would be the loss of oxygen circulation from the surface. However, it is also a possibility of deep circulation with a strong surface evaporation and thus dense water formation. This is already occurring in the eastern Mediterranean Sea. • www.bioscience-explained.org Ocean biogeochemistry 1. Salinity shifts / haloclines: As mentioned above an excess of freshwater on the surface in the Arctic may have strong effect on the deep water convection in the Greenland/Iceland and Labrador Seas. It is also likely to change the heat radiation budgets in the Arctic. 7 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 Changes in sea ice distribution will certainly have an influence on the marine plankton flora. This might then cause a change in the production of dimethylsulfide, which acts as condensation nucleus and is thus responsible for the Arctic mist, which also affects the radiation budgets. 2. Turbidity: More river water or melt water from continental ice and glaciers reaching into the sea will increase turbidity in coastal and near coastal areas. Effects of this could be e.g. change in algal vertical distribution because of light dependence, excess of sediments which may harm coral reefs or build up unstable sediment packs which will cause turbidity currents affecting benthic faunas over large depth ranges. • Marine biology 1. Some recorded changes in abundance and/or distribution There are relatively few clear examples that can be attributed to global warming. Every species has one or a few centres of its distribution where fluctuations in abundance may occur but where they can always be found. However, the closer one gets to the periphery of its distribution the greater the risk is that it is missing during a season or a time period, which could vary considerably in length before reappearing in the same area. Such fluctuations are common and may often be caused by extreme weather situations – e.g. extra cold or warm temporary seasons, which could affect general survival of any part of the life cycle, availability of food, failure in reproduction for a number of reasons, predation pressure etc. Two examples may be brought up at this point, one dealing with the plankton community of the North Sea and one with a rocky intertidal community on the California coast. a. A certain amount of warming of the North Sea has been recorded during the last decades, which has affected the distribution of two planktonic copepod species, the cold-temperate Calanus finmarchicus and the warm-temperate C. helgolandicus. These species are very closely related but occupy specific thermal niches The former species has a thermal boundary at 10-11oC and the second one at 14oC. Since the late 1980s C. helgolandicus has dominated in the North Sea especially later in the years. However, the total Calanus biomass has declined considerably since the late 1980s (7). www.bioscience-explained.org 8 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 A shift in geographic distribution is what can be expected with a gradual and consistent warming. A possible secondary effect of this is that the European cod, Gadus morhua, which during young stages prefer C. finmarchicus as a food item, may have had its reproductive success influenced by this shift. The decline of cod in the North Sea may thus be the result of overfishing in conjunction with a change of the food resources as a result of global warming. Warming of the sea water does not only mean a possible shift in distribution but also a change in abundance. This has been particularly noticeable in the North Sea and in the North Atlantic when looking at changes from 1960 to 1995. Both in samples taken by the Continuous Plankton Recorder of Sir Alister Hardy Foundation for Ocean Science (SAHFOS) and from satellite observations a rather dramatic increase in phytoplankton biomass has been recorded (8). b. The rocky intertidal invertebrate fauna of the central California coast was studied in detail in a comparison between 1931-33 and 1993-94 (9, 10). Another investigation had shown that during these 60 years the annual mean shoreline ocean temperature increased by 0.75oC and the maximum summer temperature was 2.2oC warmer in 1983-93 than in 1921-31. The net result was that out of 45 species studied eight of nine southern species increased significantly in abundance and of eight northern species five decreased in abundance. Possible causes for such change other than global warming were considered (e.g. ENSO associated effects, change in predator populations, anthropogenic impacts, or random variation) but ruled out. 2. Predicted and possible coming changes in floral and faunal distributions a. in the plankton: There is no doubt that a gradual warming of the sea will have an effect on the distribution of many planktonic organisms with a general northward shift on the northern hemisphere and a similar southward shift on the southern hemisphere. There is a fear that bacteria and virus that can normally not survive in cold or moderately warm water will be able to change their distribution similarly. During warm summers, like we have had in north-eastern Europe in late years, presence of E. coli bacteria in coastal waters has frequently been reported and many popular swimming places have been temporarily closed. Such instances have increased during the last few years. These outbreaks obviously have an anthro- www.bioscience-explained.org 9 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 pogenic background and do not reflect a geographic spread but rather a better survival of the bacteria (e.g. Escherichia coli), because of higher water temperature during summer. However, there are relatively recent reports on mass mortalities in many major marine taxa due to disease outbreaks. In reef corals exposed to high temperatures not only bleaching occurs but their resistance to new diseases is weakened causing a very high mortality. Also marine mammals are victims of new pathogens at an increased rate. It seems that new diseases typically emerge through change of host or distributional range of already known pathogens. Whether the major cause for spread is climatic or due to human activities is hard to decide with our present knowledge, but a combination of the two is very likely (11). The pathogenic agent has rarely been identified but bacteria are commonly found in corals and virus in seals, dolphins and some fish species. Protozoan parasites have been reported to infect oysters in the Gulf of Mexico with prevalence during El Niño events. Harwell et al. conclude ”that a better understanding of the origins of emergent disease and invertebrate immunity is needed before we can evaluate the role of changing environments in host-pathogen interactions. Studies of invertebrate resistance to disease will not only provide important insights for management of commercial and natural populations, but also will yield molecules and compounds with biomedical applications”. The bacterium causing cholera is Vibrio cholerae. It spreads easily around the globe and has resulted in many pandemics. In the present context it is of interest that the bacteria have an association with zooplankton, especially chitinaceous taxa, e.g. copepods, and spreading of the disease can have a cause in ocean currents along coastal areas. The bacterium may also survive in association with aquatic vegetation, e.g. water hyacinths and blue-green bacteria (Anabaena). We have in this bacterium a clear possible connection between global climate, global change and human health (12). Another example is V. parahaemolyticus which causes gastroenteritis. It is found in oysters and since they often are eaten raw the risk for human infection is high. An outbreak of this disease in Alaska in 2004 has been attributed to rising seawater temperature. www.bioscience-explained.org 10 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 Since 1997 it has increased by 0.21oC per year. Before that year the disease was never recorded so far north. (13). b. in grazers and higher predators: In Antarctic waters we find two dominating grazers, Antarctic krill (Euphausia superba) and salps (e.g. Salpa thompsoni). They are normally not found in the same waters. Krill prefer areas with high phytoplankton production like the southwest Atlantic sector, from the Antarctic Peninsula towards South Georgia, while salps tolerate warmer water than krill and are found in areas with lower productivity. Krill abundance also correlates positively with extensive sea ice areas of the previous year, meaning that the larval and sub-adult krill take advantage of the rich flora on the underside of the ice during the winter period. The krill is also largely protected from predation when under the ice. As adults they then feed on the rich planktonic algae in the ice-free water during the summer. Very large parts of the upper Antarctic ecosystem, both in the sea and on land, have krill as the main food source. In the sea it is true for many species of squids and fish and obviously also for the baleen whales that come to these waters in the summer. Most of the Antarctic seal species, all penguins and many other birds also feed rather exclusively on krill while there seem to be very few predators on the gelatinous salps. Thus krill is a key organism in the Antarctic ecosystem and fluctuations in their abundance may have a big influence on the Antarctic food web in general. A recent study (14) indicates that >50% of the krill stocks are found in the Atlantic sector mentioned above, but also that their densities have declined since the 1970s while the salps have increased. Surprisingly enough the western Antarctic Peninsula has been found to be one of the fastest warming areas of the world and the duration of the winter sea ice is becoming shorter and the deep ocean temperatures have increased. Thus we can expect to see effects on the populations of the various predators of these krill stocks. www.bioscience-explained.org 11 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 Figure 5. The krill Euphausia superba is a key species in the Antarctic marine ecosystem. It occurs in large swarms of several metric tons (sometimes in megaswarms of hundreds of tons) although the maximum size of an individual is less than 6 cm. They feed mainly on phytoplankton and are heavily predated on by whales, seals, penguins and other marine birds as well as by fish and squids. They are almost never found in any numbers in the same water masses as salps (Photo by J-O Strömberg). Figure 6. Salps are wholly planktonic and efficient filter-feeding tunicates that live on phytoplankton. They may occur as gelatinous individuals, as in this picture of the Antarctic Salpa thompsoni, or they reproduce rapidly under favourable feeding conditions to form colonies of long chains of connected individuals (Photo by Laurence Madin, Woods Hole Oceanographic Institution). www.bioscience-explained.org 12 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 c. in calcareous organisms: Recently a new threat to the marine biota has been revealed (15). With increased atmospheric carbon dioxide also more and more of this gas is dissolved in the surface waters of the oceans resulting in a gradual acidification. The reason for this is that the predominant ion formed is bicarbonate. The increase in concentration of CO2 in the atmosphere from 280 to 380 ppm since the start of the industrial revolution in early 1800 has had the effect that the average ocean pH has changed from about 8.16 to 8.05 and may by the end of the present century be 7.9. The biota suffering from this acidification are plants and animals having calcified exoskeletons or internal skeletal support in the form of calcite which is most common in shallow waters or aragonite which predominates in deep waters. Coccolithophores are tiny phytoplankton with elaborately shaped calcite covering which when the plants bloom give a turquoise colour to the ocean surface because of reflected light from these organisms. Experiments in mesocosms have shown that increased acidification reduces the calcite covering to about half, if the present carbon dioxide level is tripled. This obviously influences the buoyancy that has secondary effects on the planktonic organisms feeding on these very abundant types of phytoplankton. The risk is that they may never reach the sea bottom and the benthic fauna looses an important food source. Other organisms at risk include echinoderms, especially sea urchins, crustaceans and corals. Deep living corals have their skeletons built up of aragonite, which is more soluble than calcite and thus they ran the risk of having greater difficulties to build them up. Tropical coral reefs may also be heavily influenced, besides the risk that exposure to increased water temperature causes bleaching and the expulsion or death of the symbiotic algae, the zooxanthellae, which are essential for the survival of the hermatypic (reef building) corals. The effect of higher acidity in the water is well documented in the soft-skinned sea urchins and sea cucumbers living at depths of more than about 3500m, where the hydrostatic pressure causes carbonate to change into bicarbonate. Shallow living sea urchins exposed to water with lower than normal pH will have clear difficulties to keep up their hard and pointed spines and thick body covering. www.bioscience-explained.org 13 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 Besides effects on skeletons, respiratory problems have been observed with decreasing pH in many animals, so metabolic and other physiological effects can be expected. We are presently in the beginning of understanding the detrimental effects of a lower pH in the ocean, but it is clear that also small changes may have profound influences on the functioning of marine ecosystems. Obviously there are also experts disagreeing with the notion that acidification will have a major negative influence and they point toward the great buffering capacity in the very large ocean realm and the large ocean bottom areas covered with calcareous sediments. One final point of interest is that ocean acidification may amplify global warming. The reasoning is that coccolithophores when blooming help to reflect light from the ocean surface. If a lower pH reduces the bright calcareous covering or the very number of these plankton and they are replaced by other non-reflecting plankton species, less light will be reflected upwards and thus more heat absorbed in the water. Another effect could be the possible decrease in the production of dimethylsulphide, which functions as condensation seeds for water vapour and thus for cloud formation over extensive ocean areas. A reduction in such cloud formation would certainly affect the global heat budget. Hindcasting and forecasting Hindcasting is a relatively new term for looking back on historical data and try to understand what happened in the past. A very modern case of hindcasting is to investigate air bubbles enclosed in continental ice where analyses can give direct measures of composition of the air at the time of enclosure. This has been very much used in climate research and records going back some 800 000 years are now available. Other means are to be found in deep sea sediments were remains of phytoplankton, foraminiferans, mollusc shells and fish scales can be used to appreciate what has been going on in the upper water layers. Especially in areas with laminated sediments a rather precise dating can be made. A third way is to estimate growth rate in coral heads or tree rings in old or fossil tree trunks. Isotope techniques are then available for dating the age. This in combination with data records from present times give a good background, which can be used in evaluating models to see how well these fit into the past events. Forecasting is obviously more difficult and depending on the development of numerical models. In the beginning they have been very course, but with the addition of more and more factors that have influences on what www.bioscience-explained.org 14 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 we want to model the more robust they become. This is well illustrated in the development of climate models Figure 7. As more and more factors can be included in the models the more reliable they become, but their robustness need to be tested and hindcasting and testing on avail-able data series must be done. The figure gives an indication of the complexity that is gradually achieved when building the models. Source: Intergovernmental Panel on Climate Change. There are almost always factors that have not been considered in enough detail, and even major factors might have been missed. This is shown in cases, where many different models have been applied, that there are relatively large differences between them. The major change in future development, as shown in these climate models, all point in the same direction. Global warming is a fact. Its cause in the effect of greenhouse gases is also clear. How this will influence climate on regional and local levels will clearly vary in different parts of the globe. Its impact on marine biota is understood in a gross view but the details are mostly missing. The influence on the human population will be dramatic with necessary changes in almost all our interactions with nature. Some questions and problems: 1. There are several different greenhouse gases that have an effect on the global climate. Their influence is named radiative forcing and it is very different for the various gases. Find on the web the values for CO2, methane, N2O and some of the CFCs that are active in this case. (Look e.g. on http://www.ipcc.ch) 2. Carbon dioxide is an active part in the atmosphereocean exchange. It is partly dissolved in the surface water but it is also actively taken up by the very large amounts of unicellular algae that dominate in the oce- www.bioscience-explained.org 15 COPYRIGHT © by the Author, 2007 bioscience⏐explained Vol 3 ⏐ No 2 anic waters. They use CO2 during their photosynthesis. By surfing the web, can you find out which parts of the ocean are of most importance for the CO2 dissolving? Where do we have the major concentrations of phytoplankton? Where is the so called biological pump most important? 3. Discuss with your classmates what might happen if we get a separation between a shallow and a deep ocean, and what will the melting of permafrost in the Arctic regions mean for the speed of building up greenhouse gases in the atmosphere? References and useful literature: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. http://www.cdc.noaa.gov/ENSO/enso.description.html, 2006; http://iri.columbia.edu/climate/ENSO/currentinfo/QuickLook.ht ml , 2006 http://www.ldeo.columbia.edu/NAO/, 2006 http://en.wikipedia.org/wiki/Milankovitch_cycles, 2006 J.R. Petit et al. (1999) Climate and atmospheric history of the past 420 000 years from the Vostok ice core, Antrctica. Nature 399, 429-436. TIME, April 3, 2006 Quadfasel, D. (2005) Oceanography: The Atlantic heat conveyor slows. Nature 438: 565-566. SAHFOS, http://192.171.163.165/research.(2006) P.C. Reid et al. (1998) Phytoplankton change in the North Atlantic. Nature 391: 546. J.P. Barry et al. (1995) Climate-related, long-term faunal changes in a California rocky intertidal community.Science 267: 672-675. R.D. Sagarin et al. (1999) Climate-related change in an intertidal community over short and long time scales. Ecological Monographs 69 (4): 465-490. C.D. Harwell et al. (1999) Emerging marine diseases – Climate links and anthropogenic factors. Science 285: 1505-1510. R.R. Colwell (1996) Global climate and infectious disease: The cholera paradigm. Science 274: 2025-2031. J.B. McLaughlin et al. (2005) Outbreak of Vibrio parahaemolyticus gastroenteritis associated with Alaskan oysters. New England Journal of Medicine 353(14): 1463-1470. A. Atkinson et al. (2004) Long-term decline in krill stock and increase in salps within the Southern Ocean. Nature 432: 100103. J. Ruttimann (2006) News Feature: Sick seas. Nature 442: 978980. Acknowledgment The Volvox project is funded by the Sixth Framework Program of the European Commission. www.bioscience-explained.org 16 COPYRIGHT © by the Author, 2007