GLOBAL WARMING


                First direct evidence of greenhouse effect  - Geological Society of London, March 15, 2001
    Scientists from Imperial College, London, have produced the first direct observational evidence that  the Earth’s greenhouse effect increased between 1970 and 1997.
  Writing today in the journal Nature, researchers in Imperial College  Department of Physics show that there has been a significant change in the Earth's greenhouse effect over the last 30 years, a finding consistent  with concerns over so-called radiative forcing of the climate. The Imperial team reached their conclusions after analysing data collected by two different earth-orbiting spacecraft, in 1970 and 1997.
  Comparison between the two data sets has unequivocally established that significant changes in greenhouse gas emissions from the Earth have caused the change to the planet's greenhouse effect over this time period.   Professor John Harries, lead author, says: "These unique satellite spectrometer data collected 27 years apart show for the first time that real spectral differences have been observed and that they can be attributed to changes in greenhouse gases over a long time period."
    The team examined the infrared spectrum of long-wave radiation data from a region over the Pacific Ocean, and also over the whole globe. They discovered significant differences in the levels of atmospheric methane, carbon dioxide, ozone and chlorofluorocarbons (CFCs) 11 and 12 between the data, collected in 1970 and 1997.
   "The scientists found that by taking the difference between the two sets of data for the same region, they observed the change in the outgoing longwave radiation, and therefore a change in  the greenhouse trapping by the atmosphere."
   Although the two experiments were flown on separate spacecraft 27 years apart, the comparison  of  outgoing infrared long-wave radiation spectra is valid. Even allowing for the different spatial and spectral resolutions of the two instruments, there are significant changes in the spectra of the greenhouse gases of the Earth, over this period.
    The team took a number of steps to ensure that their data were reliable. The effects of cloud cover were effectively removed by using a cloud-clearing algorithm. The resulting two datasets were of comparable resolution and representative of clear-sky conditions. To reduce noise in the data, the team selected several regions of the globe and calculated clear-sky average (April & June).
    Dr Helen Brindley, second author on the paper says: "Through our modelling studies using  independent knowledge of the atmospheric state we have shown that the magnitude of the changes  observed can only be explained by long-term changes in the greenhouse gases such as carbon  dioxide, methane, and Chlorofluorocarbons."
     Professor Harries said: "The next step is to assess whether these data can provide information about changes in not only the greenhouse gas forcing, but the cloud feedback, which is a response of the cloud field to that forcing.
    "We must also work to test agreement with the general circulation models used in climate change   experiments. These use basic knowledge of expected changes in climate forcing (for example  changes in greenhouse gas amounts, solar constant) to predict the climate response. "Since these  are the models used to predict future climate and influence policy decisions, it is imperative that  they can accurately simulate measurements of what is considered to be the driving mechanism
behind climate change.
      "We are only at the beginning of making use of these spectral observations. Much more information is locked up in the data that we have. This provides a strong motivation for the launch of similar instruments to monitor the state of our climate."
*************************
    Nature doesn’t need our help to create global warming – bad news, since we’re  giving it anyway…   Geological Society of London, November 7, 2000
        Adverse weather sweeping the UK may not be that unusual, according to fresh evidence from long-term rainfall trends measured using stalagmites.
     A team led by the University of Newcastle upon Tyne has completed the world's first 1,000-year  record of annual rainfall by studying the width of growth rings in cave stalagmites.  The record provides evidence that nature is able to generate recent weather conditions  without the help of global warming.   But this doesn't mean that stalagmites are giving global warming fears the finger. Researchers warn that because predicted global warming-induced change could exaggerate natural variations, it could create even more severe bouts of flooding.
    The research, published in the academic journal Climate Dynamics - by coincidence at a time when storms and floods are wreaking havoc across parts of Britain - suggests that a  number of sustained periods of wet and relatively stormy conditions have occurred over the past 1,000 years.
    'Looking back over the last 1,000 years can give us a real insight into natural climate variability,' said project leader Dr Andy Baker, of the University's Department of Geography. Our research suggests that British rainfall is naturally highly variable. This variability is in addition to any future changes in rainfall or storminess predicted by climate models as a consequence of global warming.
    The thickness of growth rings in stalagmites are determined by rainfall - unlike the rings found in trees, whose  thickness is generally determined by temperature. Dr Baker, working with colleagues from Exeter University, concentrated on caves in the Scottish highlands because the local rainfall there is strongly correlated with the  strength of North Atlantic westerly circulation. This means the results should be valid for a number of other northern European countries.
   While people may take some comfort in the news that the current flood crisis could be part of
natural climate variability, Baker's message is that there is no room for complacency.
     'Certainly I think that politicians and other decision-makers should be aware of both natural and human-induced rainfall variability when planning for the future," he said.  With the help of our longer rainfall record, we have shown that nature is able to repeat current events without the help of global warming, and even more seriously, the addition of predicted global warming-induced change could exaggerate the natural variations and could create even more severe bouts of flooding.'
     The research paper is entitled A Thousand Year Proxy Record of North Atlantic Climate in Scotland, and is  published in the current edition of  Climate Dynamics.
********************************
             Ice Age rain fell mainly on the Altiplano   Geological Society of London, January 26, 2001
     A 25,000-year precipitation record deduced from sediment core samples taken in Lake Titicaca in Bolivia and Peru suggests that tropical South America may have been wet rather than dry during the Ice Age
     Situated on the Altiplano, a 12,000-foot plateau below the  peaks of the Andes in Bolivia and Peru, Titicaca (right -  Landsat 7 image) is South America's largest and deepest freshwater lake. Its location across the high mountain range  from one of Earth's largest sources of water vapour - the Amazon jungle - makes it "an important place in terms of the  present global climate picture," says Paul Baker, a geology  professor at Duke University's Nicholas School of the  Environment and Earth Sciences
     The research carried out by his team in the Bolivian section of the lake is published today in the January 26 edition of the US journal Science. The study's results suggest that the South  American tropics were wet during cold eras when ice was  advancing in the Northern Hemisphere.
     We have a unique record of climate change in tropical South America that shows when global climate conditions cooled and the glaciers advanced, wetter climates prevailed in the Andes," says joint co-author Geoffrey Seltzer, an associate professor of Earth sciences at Syracuse  University.
    Glacial Maximum were arid," Baker says.  However, using the Neecho, a refurbished 38-foot research boat once the property of the U.S. Geological Survey, the research team drew cores as long as 46 feet from the lake bottom at three different   locations under water 121, 498 and 754 feet deep.
     The Peruvian government has monitored lake levels since 1915, but the researchers have extended those   records back another 250 centuries by analysing the core sediments for their remanent magnetism, fossilized   diatoms, (tiny silica-encased aquatic algae) calcium carbonate concentrations and oxygen isotope ratios.
      While all these analyses contributed to the authors' conclusions, studies of fossil diatoms by joint co-author  Sherilyn Fritz, associate geology professor at the University of Nebraska at Lincoln, provided what Baker  describes as “the single most important record".
     Diatoms occur in different assemblages of species depending upon whether the water is deep or shallow and  saltier or fresher. Lake Titicaca currently takes in more water than it loses through evaporation and discharge from its sole outlet, the Rio Desaguadero. But during consistently dry times lake levels drop too low for the river to  discharge any of its water, and salt levels begin to rise.
    Calcium carbonate levels also vary with lake depth and salinity, while magnetic values of the sediment change when upland erosion ceases - another indicator of climatic fluctuations. Oxygen isotopes provide a way for the  researchers to predict the source and temperature of water vapour.
      Using all this evidence, the researchers found that Titicaca's environs were wet - not only during the last glacial  age (25,000 to 15,000 years ago) but also during later cold periods in the North Atlantic Ocean region.  Conversely, warm spells in the North Atlantic were marked by drought on the Altiplano.
     Using additional data from other palaeoclimate studies, the researchers found signs of two mechanisms driving  wet conditions in the South American tropics. The first, operating on a cycle of 20,000 years and more, triggered the last Ice Age when the extreme tilt of Earth's axis delivered less solar radiation to the far Northern Hemisphere.
     The second, operating on a cycle of about 1,000 years, is triggered by low seawater temperatures in both the high-latitude North Atlantic and the northern part of the tropical Atlantic. "When the water is cold in the northern   tropics and warm in the southern tropics, those conditions increase the northeast trade winds that bring moisture  from the Atlantic into the Amazon basin," Baker says.
      "Today, most of the time when you have a really wet year on the Altiplano you also have a wet year in the Amazon  basin; but not every time," added Baker, who acknowledged that the researchers were "stepping out on a limb"  by equating wetness on Titicaca with conditions in the jungles to the east. "But most evidence points that way," he says.
       Baker cautions against forecasting future moisture levels in the tropics based upon past conditions, because of the implications of anthropogenic climate change.
       "Human influence is so dominant now that whatever is going to go on in the tropics has much less to do with sea  surface temperatures and Earth's orbital parameters and much more to do with deforestation, increasing  atmospheric carbon dioxide and global warming," he says.
*************************
        Don’t knock climate change – it may be the reason we’re here   Geological Society of London, January 23, 2001
        Researchers examining deep-sea sediments off the coast of Namibia, West Africa, have found that the Earth cooled off dramatically 3.2 Ma ago. Did climate change really trigger our evolution?

        The world became drastically cooler – by 10°C globally – from about 3.2 Ma ago, according to Dr Jeremy Marlow  (Newcastle University) and a research team of English, American and German scientists.  Marlow says: “There have been arguments for many years about whether the emergence of our ancestors was  linked to climate change. By looking at fossils of marine algae we began to discover evidence of a 10-degree fall  in temperature in the region of Africa where much of the early human fossil evidence has been discovered. “We didn't believe it at first but further tests kept producing similar results until we had to conclude that temperatures really had decreased so dramatically.”  The scientists, from the Universities of Newcastle, Durham, California and Bremen, found that cooling was particularly rapid about 2 Ma ago, at the time when the first ancestors of   modern humans emerged in sub-tropical southern Africa. Global cooling has been   implicated in the landscape change that overtook the cradle of humanity at this time,  changing from lush forest to more open grassland where bipedalism was an advantage for emerging humans.
      Off to buy some thermals.  Global cooling may mean we all evolved from brass monkeys.  Bipedality was, in many ways, the key adaptation of early humans.  Even the most primitive hominid known, Ardipithecus, was to some extent bipedal, anthropologists now believe.  A.  ramicus probably inhabited wooded environments as much as 5 Ma ago.  The Savannah Theory (which links the evolution of bipedalism to environmental change involving more open habitats) has taken some knocks over recent years and many anthropologists believe it to be discredited.  However, evidence of pronounced global cooling will be welcome to it  remaining adherents.   The research also sheds new light on the mechanisms that may cause climate change. By  examining the rate of sediment deposition and the levels of organic carbon within the sediments, the researchers obtained evidence of a well-defined cycle in which a cooling   atmosphere causes increased upwelling of nutrient-rich deep waters in specific parts of the oceans.  This leads to increased biological uptake of carbon dioxide from the atmosphere, which then cools
further, causing more upwelling, further uptake of carbon dioxide, and so on.
     This mechanism took hundreds of thousands, or even millions of years to have an effect on climate but could be  reversed far more rapidly through the burning of this type of locked-up carbon as fossil fuels, said Dr Marlow.
     The research was published in the US journal Science 290: 2288-2291, in a paper entitled Upwelling  intensification as part of the Pliocene-Pleistocene climate transition.  The paper does not discuss the  implications of the discovery for human evolution.
************************
                      In the next 15 years, 80% of the glaciers of the intertropical Andes will have disappeared, say French scientists.
        The conclusion comes after several studies carried out on the glaciers of Chacaltaya (Bolivia) and Antizana   (Ecuador) by researchers from the Institut de Recherche pour le Développement (IRD) and their Bolivian and  Ecuadorian collaborators.  The researchers believe that the recent acceleration of glacier melting is the result of intensified El Niño events during the period.
      Questions of how glaciers respond to climatic fluctuations, especially in a  time of global warming, are  of crucial importance in Andean regions where water supply largely depends on the ice-capped summits of the  Cordillera.  In an attempt to answer these questions, researchers from a  team called ”Great Ice” at IRD, of the Institut d’Hydraulique et d’Hydrologie de Bolivie and the Institut  National de Météorologie et d’Hydrologie d’Equateur conducted detailed studies of two small Andean glaciers: Chacaltaya (5,125 – 5,375m) and Antizana (4800-5760m).
         On these two glaciers, since 1991 and 1995 respectively, the researchers have carried out mass balance
estimates to measure the difference between the amount of water received as snow and that lost by melting
and sublimation (solid to gas without intervening liquid phase).  These “profit and loss” balance sheets were constructed monthly for 12 years in the lower regions of the glaciers where ablation is dominant.  Data for  years before measurements began was obtained using aerial photos and archive documents.
        The results show that the future of these small glaciers is under threat.  In the last 10 years the two glaciers  have lost on average between 0.6 and 1.4 metres thickness each year.  The thickness of Chacalataya, for   example, has been reduced by 40%, and its volume by two thirds in the period studied.  Its surface area fell by more than 40% between 1992 and 1998, and now represents a mere 10% of its extent in 1940.  If this trend  continues, Chacaltaya will have disappeared completely fifteen years from now.
       Has the retreat of glaciers truly been accelerating recently?  Older studies on other Andean tropical glaciers,  for example in Peru, seem to show the rate of retreat has picked up since the 1980s, and these recent studies  confirm that result.  Chacaltaya has lost 0.2m of water per year (m/yr) between 1940 and 1963, 0.6m/yr from  1963 to 1983, and 0.9 m/yr since 1983.  The surface area of Antizana fell three times faster between 1993 and 1998 than between 1956 and 1993.  Altogether, the amount of ablation of the two glaciers has been 3 to 5 times greater in the last 10 years than in previous decades.
        The researchers link this acceleration with El Niño events in the southern Pacific.  The monthly mass balance sheets demonstrate that the maximum ablations occur during or immediately after such events, notably in 1991-1992, 1994-1996 and 1997-1998.
*************************
             Le climat recèle encore de grandes énigmes   Geological Society of London, December 8, 2000
      C'est honteux: les scientifiques ne peuvent pas expliquer pourquoi l'Ordovicien, le Silurien, le Jurassique ou le  Crétacé inférieur étaient apparemment des périodes froides quand, selon l'effet de serre, ils auraient dû être chauds.
       [A l'occasion du sommet européen a Nice, la Société Géologique de Londres souhaite bienvenue a ses visiteurs  francophones. There is an English version below. Rédacteur en chef/Site Editor.]
     Au sortir de la Conférence de La Haye, une étude scientifique publiée cette semaine dans le journal scientifique Nature sème un peu plus le trouble sur nos connaissances réelles du climat. Grâce à une analyse originale des fossiles des brachiopodes, une équipe internationale, comprenant des chercheurs de l'Université de Liège, a pu  obtenir des données nouvelles sur l'histoire du climat terrestre durant tout le Phanérozoïque, c'est à dire pendant les 570 derniers millions d'années. Pour certaines périodes anciennes, ces données contredisent totalement nos connaissances actuelles. Ainsi, l'Ordovicien, le Silurien, le Jurassique ou le Crétacé inférieur  auraient dû être chauds en raison de l''effet de serre' induits par des niveaux élevés de CO2 dans l'atmosphère à ces époques. Eh bien non ! L'analyse des brachiopodes prouve que ces périodes étaient froides et personne ne sait pourquoi. Les scientifiques en concluent que notre climat est conditionné par d'autres facteurs encore inconnus. Beaucoup moins stable qu'on ne le pensait, le climat s'avère capable de répondre de manière inattendue aux perturbations qui l'affectent; Inquiétant pour notre avenir?

     Les brachiopodes sont présents sur Terre depuis 570 millions d'années. L'étude de leurs fossiles permet donc d'obtenir des renseignements sur l'état du milieu dans lequel ils ont toujours vécu : les mers peu profondes. Une des informations cruciales qui peut être obtenue est le rapport 18O/16O des coquilles de ces bivalves. En effet, au  cours de leur vie, ces animaux ont incorporé dans leur coquille calcaire des  éléments de l'eau de mer dans laquelle ils évoluaient, comme le carbone ou  l'oxygène. Ce dernier élément est présent dans l'eau de mer sous la forme de plusieurs isotopes. Les isotopes généralement utilisés sont l'oxygène 18 et l'oxygène 16. Des relations entre la température du milieu et la composition isotopique (18O/16O) des  coquilles de brachiopodes ont été établies. De cette manière, les fossiles de brachiopodes constituent un  paléothermomètre permettant de retracer la température des océans anciens où évoluaient ces organismes.
      Pendant plusieurs années, les équipes du professeur Ján Veizer à l'Université de Bochum en Allemagne, et  d'Ottawa au Canada ont collecté et analysé la composition isotopique d'un grand nombre de brachiopodes fossiles (environ 1500 échantillons) d'âges divers et provenant du monde entier. A ceux-là ont été ajoutés plus de 4000 mesures collectées dans la littérature afin de constituer une base de données couvrant l'ensemble du Phanérozoïque, soit les 570 derniers millions d'années de l'histoire de la Terre.

     Ces données ont été analysées par Yves Goddéris et Louis François, chercheurs au Laboratoire de Physique Atmosphérique et Planétaire de l'Université de Liège, en collaboration avec le professeur Ján Veizer. Les  résultats obtenus montrent d'amples oscillations du rapport 18O/16O au cours des âges. Ces oscillations sont  fortement corrélées avec les fluctuations d'autres types d'indicateurs climatiques, ce qui prouve que le signal 18O/16O conservé par les brachiopodes est un bon signal climatique.

      Les résultats montrent clairement que notre planète a subi des fluctuations climatiques majeures au cours des 570 derniers millions d'années de son histoire, passant de manière récurrente d'un mode froid vers un mode  chaud et inversement. L'existence de ces modes était connue antérieurement. Le fait nouveau est la quantification en termes de température, ce qui permet de mesurer l'importance de ces fluctuations climatiques.
       En outre, les résultats semblent indiquer que la transition entre un mode froid et un mode chaud peut être assez  rapide, du moins à l'échelle des temps géologiques. Il est donc possible que le climat de la Terre soit  relativement instable et fragile. On sait que des changements de l'environnement ont donné lieu à des extinctions  massives d'espèces dans le passé, dont la plus connue; mais pas nécessairement la plus importante - est l'extinction des dinosaures à la fin du Crétacé, il y a 65 millions d'années. On pense qu'un impact  météoritique est à l'origine de cette extinction, probablement via un changement climatique global. Les  changements climatiques majeurs enregistrés dans les fossiles de brachiopodes ont-ils aussi donné lieu à des extinctions massives ? C'est très possible.
      Le Professeur Ján Veizer et les chercheurs liégeois ont également tenté de mettre les fluctuations climatiques  enregistrées dans les fossiles de brachiopodes en relation avec les changements passés de la concentration en  dioxide de carbone (CO2) de l'atmosphère.
       Les variations de cette concentration sont bien connues pour les 400 derniers milliers d'années grâce à l'analyse de l'air piégé dans la glace antarctique. Malheureusement, cette méthode ne peut permettre de remonter  beaucoup plus loin dans le passé, puisque les glaces plus anciennes ont disparu. Il faut donc se tourner vers des  méthodes indirectes pour reconstruire les niveaux anciens du CO2 atmosphérique à l'échelle de plusieurs millions d'années. Plusieurs types de méthodes existent, par exemple basées sur l'abondance de l'isotope 13 du carbone dans les sols fossilisés. De telles reconstructions ont été publiées dans la littérature scientifique récente.
      L'équipe liégeoise a, notamment, utilisé un modèle climatique simple calculant les températures équatoriales à  partir du niveau de CO2.
     C'est là que des situations paradoxales se présentent. En effet, l'évolution de la température équatoriale ainsi  reconstituée sur base des teneurs passées en CO2 est en désaccord flagrant avec celle enregistrée dans les  fossiles de brachiopodes. Ce désaccord est particulièrement marqué à l'Ordovicien et au Silurien (il y a 400 à  450 millions d'années), ainsi qu'au Jurassique et au Crétacé inférieur (il y a 100 à 200 millions d'années).   Conformément aux données des brachiopodes et comme l'indiquent les traces d'anciennes glaciations, ces  périodes sont caractérisées par un climat froid inexplicable en présence des niveaux de CO2 atmosphérique élevés qui régnaient à l'époque.
     Si les reconstructions des anciens niveaux de CO2 sont correctes, ce résultat implique que l'effet de serre accrû  du CO2 a dû être compensé par d'autres facteurs actuellement inconnus, mais dont l'impact climatique fut considérable. Ainsi, le CO2 n'aurait pas été le principal moteur de l'évolution climatique passée de notre planète au moins pendant une partie significative du Phanérozoïque.
     Il est vital d'identifier ces facteurs et de comprendre les mécanismes qu'ils mettent en jeu. Ces facteurs  peuvent-ils influencer en bien ou en mal l'évolution climatique future, en cette période où l'impact de l'homme sur  l'environnement est devenu majeur? Dans quelle mesure sont-ils pris en compte dans les modèles climatiques les plus complexes dont nous disposons à l'heure actuelle?

      L'étude des climats du passé constitue un test pour les modèles climatiques actuels. Elle pousse à tirer la leçon qu'actuellement, nous connaissons encore très mal le fonctionnement du système Terre et que notre climat pourrait être moins stable qu'on ne le pense généralement : il serait susceptible de répondre de manière inattendue aux perturbations que nous avons engendrées. L'espèce humaine serait-elle la prochaine victime d'une future extinction massive?

       Evidence for decoupling of atmospheric CO2 and global climate during the Phanerozoic eon. Ján Veizer, Yves Goddéris et Louis François, Nature 7 décembre 2000
      The international team believes that the climate system appears more complex than we thought and that our  strategies to combat global warming may have to change. In a paper published this week in the UK science journal Nature they look back over the last 550 million years of the earth's history, measuring oxygen isotopes  from fossil marine shells from around the world. These are a key indication of changes in temperature associated  with major climatic events such as ice ages.
    They find that what we know about carbon dioxide concentrations in ancient times does not correlate with what  the palaeotemperatures are telling us about global heat. In other words, when all the indications are that CO2 was  high, and temperatures should have been high too because of the greenhouse effect, they find paradoxically that  palaeotemperatures were often low.
      Trees and soils are often seen as the most important "sinks", where CO2 and water are absorbed from the air and soil. That is why much of the environmental debate that took place in The Hague last month focused on the  world's forests. If we are responsible for warming up the planet by pumping more carbon into the air by burning fossil fuels in our automobiles and elsewhere, then a sufficient amount of forest cover should be able to remove this carbon from the atmosphere.
   Yet Veizer and colleagues suggest that the situation is much more complex. Based on work with his former student K. Telmer, presently at the University of Victoria, he argues that there is a crucial link between the way carbon and water pass through plants, atmosphere and soil. To "fix" one molecule of carbon, a plant has to transpire almost one thousand molecules of water. Yet, the air and soil contain less than one hundred molecules of water for every molecule of carbon dioxide. The system is therefore limited by water, not CO2. With warmer climate, and greater humidity, forests may play an enhanced role in the CO2 budget of the atmosphere.