Bacteria Responsible for Climate Change?

The scientific community is in the midst of one of the strangest controversies. Scientists affirm that climate change is caused by bacteria that use nitrogen and not the carbon dioxide emissions generated by human activities. Did the Intergovernmental Panel on Climate Change (IPCC) fail to take into account a key element in its models?

George V. Chilingar (Department of Civil and Environmental Engineering, University of Southern California) is one of the researchers who support this theory with O. G. Sorokhtin and L. F. Khilyuk. He was an adviser to Ronald Reagan and the United Nations. Moreover, he says that he “advised President George W. Bush not to sign the Kyoto Protocol.” He also states that “George A. Olah, a winner of the Nobel Prize in chemistry, is in agreement with [their] theory.”

O. G. Sorokhtin (Institute of Oceanology of the Russian Academy of Sciences, Moscow)

L. F. Khilyuk (Department of Civil and Environmental Engineering, University of Southern California)

“The hypothesis of current global warming resulting from the increased emission of greenhouse gases into the atmosphere is a myth. Humans are not responsible for the increase in the global surface temperature of 1°F (0.56°C) during the past century and one should explain this increase by natural forces heating the atmosphere,” [1]argue Sorokhtin, Chilingar, and Khilyuk. These authors propose a model that they call the adiabatic theory of the greenhouse effect. According to the latter, “the contemporary global warming, which started in the 17th century (i.e. long before the Industrial Revolution), probably is temporary and determined by the fluctuations in the solar activity.”

This graph, presented by these scientists, is supposed to show the correlation between the temperature change and solar activity.

“Contemporary global warming is developed on the background of general long-term climatic cooling. A new ice age had begun.” In the authors’ opinion, in 400 million years, all continents at moderate latitudes will be covered by glaciers. “At the equatorial belt, the elevated regions will be covered by ice.”This cooling would be caused by bacteria that consume nitrogen, the main constituent of our atmosphere (oxygen represents only 21% of the composition of air). If nitrogen was removed from the atmosphere, this would reduce the pressure of the latter. When the pressure of a gas drops, its temperature decreases—this characteristic of gas is used to generate cold in refrigerators. In our case, this would therefore lead to a cooling of Earth. According to these researchers, past ice ages were also generated by such phenomena related to bacterial activities. Conversely, warmer periods may have been brought about by an increase in atmospheric pressure, for example by an adding of oxygen by plants.

THE END OF LIFE ON EARTH
However, according to this model, in 600 million years, this cold period will come to an end. Oxygen created during the formation of the Earth’s core would no longer be incorporated in the iron contained in our planet’s mantle, the latter being totally “saturated” by this gas. So this oxygen would go in the atmosphere, making its pressure increase. A rise in the pressure of a gas leads to an increase in its temperature (this is the inverse of the case of the cooling of the atmosphere). In this case, the increase in atmospheric pressure would induce our planet’s temperature to rise to 400°C. The situation would continue to worsen: “In 1.5 billion years, the oceans will start boiling.” This would be the end of life on the blue planet.

WHERE IS THE CO2 COMING FROM?
In these authors’ opinion, the rise of the atmospheric carbon dioxide concentration is not the cause of an increase in temperature on Earth but its consequence! According to them, the oceans being the largest CO2 reservoir on Earth—they contain 92 times as much CO2 as the atmosphere—a temperature rise would make carbon dioxide escape from the water and go into the air. The idea is that the warmer a liquid is, the less dissolved gas it can contain. This law can be observed using two glasses and pouring hot water into one and cold water into the other. After a while, bubbles appear on the inner surface of the container that contains the hot water but not on the one with the cold water. These bubbles are made of gas that is “excluded“from the liquid, which can no longer contain it. According to these scientists, in such a situation on Earth, the oceans would therefore release huge quantities of CO2 into the atmosphere.

This graph, created at the Vostok station in Antarctica, charts the parallel change of the temperature and the atmospheric CO2 level. We notice on this chart that the temperature change always precedes the change in atmospheric carbon dioxide concentration.

THE COOLING EFFECT OF CO2
Once this carbon dioxide in the atmosphere, what consequences does it have? According to the Intergovernmental Panel on Climate Change (IPCC) carbon dioxide is a greenhouse gas and therefore induces a warming of the planet. In these researchers’ opinion, this is the contrary: it leads to a decrease in temperature! They state that if our atmosphere were replaced by another one entirely made of carbon dioxide, it would be colder. They reach this surprising conclusion considering that the elements constituting such an atmosphere (the molecules) are 1.5 times as heavy as the ones of air. These ”weighty” molecules have a strong propensity to absorb the sun’s heat by starting to move. These movements of molecules cause the gas to become less dense. This situation can be illustrated by bumper cars; during the night, when they are stationary, it is possible to park them side by side so that they do not take up a lot of room. But during the day, when they move, they use a larger area. It is the same with a gas, which expands once heated. In so doing, it becomes lighter—since it is less dense—and, according to these scientists, rises into the stratosphere, a layer of the atmosphere located between 10 and 50 km. (6-30 miles) above Earth’s surface. It would be a phenomenon similar to that used to operate hot-air balloons. In this case, the air inside the envelope is heated up. The gas expands and so becomes lighter than the one around it. Then it rises up, taking the basket along with it.

In their climate model, once this hot air is in the stratosphere, it cools by radiation, i.e. the heat of the gas changes into waves that go off into space. The hot air, after its ascent into the atmosphere, is replaced by cold air, which is heavier than the surrounding air and therefore goes down. Such movements of air masses are called convection. Thus, in these scientists’ opinion, carbon dioxide has a cooling effect by intensifying these movements.
Another gas that is generally regarded as warming the planet is methane. According to the authors, as in the case of CO2, it would have the effect of cooling the air through the same mechanism.

OTHER SCIENTISTS’ POINT OF VIEW
Regarding the possibility that nitrogen-consuming bacteria could lead to climate changes, Frank Poly, a scientist at the Laboratoire d’Ecologie Microbienne (Laboratory of Microbial Ecology) in Lyon (France), notes that “One must not lose sight of the fact that other theories linking climate to bacteria exist. For example, such microorganisms, also related to nitrogen, produce N2O, a greenhouse gas.” This phenomenon would therefore exert an opposite effect compared to the cooling generated by bacteria according to the mechanism set out by Chilingar, Sorokhtin, and Khilyuk. Bacteria are important in other processes, as in the creation of methane (a greenhouse gas) or dimethyl sulfide, an aerosol that has the curious property of inducing cloud formation. Werner Aeschbach-Hertig (Institute of Environmental Physics at the University of Heidelberg in Germany) works on reconstructions of past climates. He wrote an article in the Journal of Environmental Geology that contradicted the three scientists’ theory. He fears that this has enabled the authors to publish a new article to respond to it. “So I think now that it is better that I ignore these strange theories and concentrate on my scientific work. I don't want to answer questions about these obscure ideas,” he remarks. As for the famous skeptic Willie Wei-Hock Soon, he is also not convinced by the bacterial hypothesis. This astrophysicist at the Solar and Stellar Division of the Harvard-Smithionian Center for Astrophysics in the United States thinks that “The nitrogen-consuming bacteria probably play a role in climate. But is this phenomenon important?” To answer this question, we must go further in understanding the involvement of bacteria in this issue since no assessed estimate is provided in relation to this hypothesis at the present time by the scientists who support it. Nitrogen, carbon, phosphorus, oxygen, and sulfur are necessary for life. Among them, nitrogen has the greatest abundance in the atmosphere and the oceans. The amount of all this nitrogen is larger than that of the four other elements combined. But most of that nitrogen is in the air and cannot be used by the greater part of living beings. That’s where bacteria come in and transform nitrogen that is in the air into other forms that can be incorporated into organisms. For instance, the clover plant hosts such bacteria capable of converting nitrogen into protuberances on its roots.

Clover modifies nitrogen that is in the air. Thanks to this, living creatures like this ladybug can use this element. (Photo: Gius Cescu/http://www.fotocommunity.fr/pc/pc/mypics/979350)

MAN AND THE NITROGEN CYCLE

Since the nitrogen usable by organisms is quite scarce after all, in many environments plants stop developing due to the lack of this precious element. Regarding agriculture, mankind decided to remedy this problem by transforming its useless nitrogen into usable nitrogen in order to give it to cultivated plants so that they can better proliferate. But the quantities of this gas that must be modified through a chemical process (called Haber-Bosch) are such that human beings became a more significant player than nature in this transformation on the continents. This situation has various consequences, notably in terms of pollution. But the one that interests us here is that as the useless nitrogen is taken from the air, 100 million tons of this gas are captured through this process out of the atmosphere each year [2].

“A COMPLETE LACK OF UNDERSTANDING OF THE MECHANISMS”
Does this have an influence on climate according to the model proposed in this theory? It is relatively easy to realize that this is not the case. If we assume that during the past 100 years this amount of nitrogen has been taken out of the atmosphere annually, the total represents only one hundredth of the carbon dioxide added to the atmosphere by the emissions caused by human activities (this is in fact an overestimation for nitrogen since its transformation intensified in the last century). The authors of the theory estimate that the influence of anthropogenic emissions (generated by human activities) of CO2 on temperature is less than 0.03°C. They get this result by calculating the temperature rise according to the change in partial pressure of CO2 due to anthropogenic emissions according to the mechanism described above. Yet they “forget“ to take into account the greenhouse effect! In any event, it is difficult to see how it would be possible for anthropogenic emissions of CO2 to have a negligible effect on climate whereas a quantity of nitrogen at least 100 times smaller can lead to a cooling of Earth by taking into account the same phenomena. When they classify nitrogen-consuming bacteria into the “first-order climate drivers,” which they define as having “an importance 10,000 times greater than anthropogenic emissions of greenhouse gases,” we realize that the mistake is huge. “Changes in partial pressures caused by modifications of the atmosphere composition have a very small effect on climate,” explains Urs Neu, who conducts research on past climates within the Swiss Academy of Sciences. “There is a difference in temperature between the poles and the equator or between day and night even though the average atmospheric pressure between these geographic regions or different times of the day does not change,” continues this scientist, co-author of the book Climate Variability and Extremes during the Past 100 Years. Taking nitrogen up from the atmosphere does not significantly influence the Earth’s temperature, as this element is not a greenhouse gas. Gavin A. Schmidt, a climate modeler at the NASA Goddard Institute in New York City, agrees with this point of view and considers that the scientists who have put forward this hypothesis show “a total lack of understanding of the way the atmosphere works.”

CO2 AND CLIMATE
The bacterial hypothesis is not the only one formulated by Chilinar, Khilyuk, and Sorokhtin. What should we think about the idea that CO2 has the effect of cooling the atmosphere? Is the mechanism set out above real? Let’s recollect the theory: CO2 absorbs heat and so expands, becomes lighter, and rises into the stratosphere, where it cools by radiating out into space. Once cold, it descends in the atmosphere and refreshes it. “One of the problems with this theory is that a heated air parcel rises only if its temperature is higher than the one of the air that is around it,” explains Urs Neu. This is indeed what we saw in the example of the montgolfier: it rises up because the air is hotter inside the envelope than around it. “Because CO2 is relatively evenly distributed throughout the atmosphere, the warming due to the heat absorption of CO2 occurs everywhere.” adds the researcher. Given the fact that for convection phenomena to take place there must be parts of the atmosphere that are warmer than others to have mass differences, in such a case these air movements are nonexistent. Even if the convective processes described by the authors were real, hot air could not go to the stratosphere and cool there. Indeed, one might imagine intuitively that the more one goes up into the atmosphere, the more its temperature decreases. This is in fact not the case. The stratosphere is warmer than the top of the layer beneath it, the troposphere (inside which we are). “Because of that, convection phenomena cannot go through the boundary between these two layers,” underlines Urs Neu. Warm air arriving at this layer is colder than the surrounding air, so it is heavier than the air around it and stops its ascent.

OCEAN DEGASSING
We now come to the last point of this theory: is the rise in the atmospheric level of carbon dioxide caused by the ocean degassing resulting from the increase in temperature? Many factors lead to the refutation of this hypothesis. Techniques (isotopes C12/C13, radiocarbon) permit scientists to determine if the carbon is of natural origin or generated by combustion. One knows, thanks to these studies, that the increase of the atmospheric concentration of carbon dioxide is anthropogenic. The acidification of oceans, which is due to a rise in the quantity of CO2 that they contain, is also an indication pointing in the same direction. Furthermore, reconstructions of past climates carried out at Vostok Station in Antarctica (see graph above) show that in the transitions between glacial and interglacial periods, a temperature increase leads to a rise in atmospheric CO2. There is an 800-year latency between these two events. It is therefore not possible that the warming induces an increase in the atmospheric CO2 level in the current climate change. The authors also do calculations using Henry’s law, a physical law that allows connecting the concentration of a gas dissolved in a liquid and the pressure of this gas in the air. This leads them to the conclusion that CO2 has leaked out of the oceans, which would be consistent with the hypothesis of degassing. Yet only temperature variation is taken into account and not the change in the partial pressure of CO2. By introducing the latter, one can reach the opposite conclusion (depending on the chosen temperature). In addition, Urs Neu draws attention to the fact that Henry’s law is not valid for such considerations. “Many other processes and factors play a role in such a question. For example, there are colder areas in the oceans that can contain a lot of carbon dioxide. This cold water, denser than the one that surrounds it, will then descend into the ocean and therefore remove CO2 from the atmosphere.”

Yet even assuming that the calculations made by the scientists supporting the idea of degassing (using a temperature change of 1°C) are right, their own result contradicts their theory. Thus they come to the conclusion that the CO2 released by the oceans has induced an increase of 13.5 ppm (parts per million, unit of concentration) in the atmosphere. This would only explain a fraction of the actual rise, which is of 100 ppm. Among the first-order climate drivers also appear, according to Sorokthin, Chilingar, and Khilyuk, variations in solar activity. They justify this point of view with the graph correlating solar activity with the temperature on Earth (see above). Two scientists, Eigil Friis-Christensen and Knud Lassen, published a chart similar to the one presented by these researchers in the scientific magazine Science in 1991.

The 1991 graph. In blue: solar activity. In red: the terrestrial temperature.

Part of the scientific community remained skeptical of this paper. The reason for this was that some thought that the statistical treatment used had the effect of distorting the curve of solar activity for the recent periods. In 2000, new information permitted scientists to determine that the graph was wrong.

The corrected chart of 2000. Note that the correlation between solar activity and temperature no longer exists for the recent period of the curve.

Gavin A. Smith, who was named as one of the 50 leaders in science on a global scale by Scientific American magazine, thinks that “These authors’ theory does not make sense. It’s equivalent to writing a book about gravity and assigning all the effects to the sucking of a hypothetical giant turtle.”

                                                               Gaëtan Dübler

[1] The quotations in this part come from the book Global Warming and Global Cooling, Evolution of Climate on Hearth published by Elsevier and authored by the three above-mentioned scientists.

[2] For more information about the nitrogen cycle and man's influence on the latter, see for example Galloway et al., 2003, 1995; Burns and Hardy, 1975; Jaffe, 1992; McElroy et al., 1976; Schlesinger and Hartley, 1992; Stedman and Shetter, 1983; Söderlund and Svensson, 1976; Mackenzie, 1998.

What the Dinosaurs Have to Teach us about Future Climates

This reptile is a Diplodocus. With a length of up to 35 meters (115 feet) and a neck alone measuring up to 9 meters (30 feet), it hatched from an egg measuring 20 to 30 centimeters (8 to 12 inches) in diameter. It is estimated that its heart weighed 1.6 metric tons (1.8 short tons), unless there were auxiliary pumps in its neck. Similar herbivores, even more disproportionate, weighted about 80 metric tons (88 short tons)!

What will Earth look like if the atmospheric concentration of CO2 continues to rise as a result of emissions generated by human activities? The answer lies in a world long gone, the world of the dinosaurs. Indeed, this era was characterized by an atmosphere containing up to 12 times as much carbon dioxide as today and therefore by a considerable greenhouse effect; thus the study of that era is very important for developing realistic scenarios of what can happen in the future. It also makes it possible to test the climatic models used to predict future climates. Climatologists today work with paleontologists. What can we learn about our blue planet’s future from fossils that have been buried under the ground for hundreds of millions of years?

Bettles Airport, Alaska: A U.S. Army CH-47D Chinook helicopter has just landed to fill up with kerosene. The pilots take the opportunity to once again examine the satellite photographs of their destination. The aircraft and B Company, 4th Battalion, 123rd Aviation Regiment, whose soldiers form the crew, prepare for one of the most difficult missions since the Viet Nam war. The objective is to recover a marine reptile fossil, an Ichthyosaur, that lived during the dinosaur era in the Arctic Circle.

Reconstruction of Ichthyosaur.

The stopover complete, the flying machine heads north. Once arriving at the fossil site, the crew sets up camp. There is no road or home within 200 km (124 miles). Army representatives, accompanied by scientists and headed by an expert on polar dinosaurs, Dr. Gangloff, extract the fossil and protect it for transport. Despite difficult weather conditions, on the fifth day the precious stone is hoisted aboard the helicopter under a sun that never sets at these latitudes at this time of year.

The fossil collected during this operation.

Shortly after this expedition is completed, a similar one is arranged.

Members of the second trip.

Chinooks, equipped with skis for landing, flying over the Arctic Ocean toward their new goal.

This time, the expedition brings back different dinosaur fossil specimens, including three Pachyrhinosaurus skulls weighting a ton.

Young Pachyrhinosaurus dinosaur. Once adult, this herbivore was about 5.5 meters (18 feet) long and 2 meters (6.5 feet) high.

Why so much effort to transport the skeletons of creatures extinct since antediluvian times? One reason is that studying them provides indications of the climate that reigned on Earth at the time they lived. For example, it is surprising to realize that dinosaurs lived in the Arctic Circle, which is an inhospitable region today. This suggests to paleontologists that a very different climate existed there than at present. Because CO2 levels during the Mesozoic Era—the period when the dinosaurs lived—were up to 12 time higher than they are today, this period permits study of a world characterized by an important greenhouse effect, perhaps similar to the one created by humans by use of fossil fuels that produce greenhouse gases by combustion.

THE MEMORY OF PLANTS
How do scientists know the atmospheric levels of carbon dioxide existing tens of millions of years ago? One way is the study of magnolias! If these plants are exposed to significant levels of CO2, the shape of their leaves becomes different. Since magnolias existed at the time of the dinosaurs, scientists can look at their fossils and deduce from them the concentration of carbon dioxide when these plants were alive.

A magnolia flower. Because these plants first appeared before bees even existed, their flowers evolved to be pollinated by beetles! (Beetles are insects, such as ladybugs, distinguished by their special hard wings. Today, this is the animal order with the greatest number of species.)

Another way to determine ancient levels of CO2 is also provided by plants. The latter harness this gas and to assimilate it they have microscopic holes in their leaves known as stomata.

This photograph, taken with a microscope, shows a stoma, one of the many tiny ‘’mouths’’ of leaves of plants that permit them to absorb carbon dioxide.

If the concentration of this substance increases in the atmosphere, plants will need less of these orifices to use it and so their number will decrease. Thus, stomata on fossilized leaves can be counted to gauge the level of CO2 at a given time.

GIGANTIC DINOSAURS BECAUSE OF CO2?
This high level of carbon dioxide also had another effect on vegetation. The latter generally grow better in an atmosphere enriched with this gas because plants use it as discussed above, so one can imagine that herbivorous dinosaurs had a lot of food. According to some scientists, that explains why dinosaurs became so big. To test this assumption, Ginkgos biloba, trees that existed at the time of dinosaurs and have persisted to the present day, were placed in an atmosphere enriched with carbon dioxide and oxygen to re-create an atmosphere similar to that of ancient times. The trees grew up to three times faster than they do in current conditions!

A ginkgo tree in Hiroshima in Japan. In 1945, it grew about 1 km (0.6 mile) from the epicenter of the atomic bomb dropped on this city by the United States. The temple that was originally next to it was blown up by the explosion. A new building was built and its stairs were separated to leave a gap for the trunk. Ginkgos biloba appeared hundreds of millions of years ago. They were found throughout the Mesozoic Era (the age of dinosaurs) in vegetation very different from that found at present. Grass, for instance, did not exist. Yet, after this, they gradually started to disappear as other species of trees evolved. They finally came to be located in a region of China where monks patiently grew them for 1 000 years. This tree is now associated with Buddhism, and one can see it around temples. Some of these plants are as much as 3 000 years old!

Not all scientists share this view. For example, Jorn Harald Hurum, a paleontologist at the University of Oslo in Norway, notes that "All dinosaurs were not big. Moreover, huge animals are known throughout the last 200 million years. Even today, such creatures can be found, including whales, elephants, and giraffes.” Christopher R. Noto, a researcher who specializes in dinosaurs at Stony Brook University in the United States, thinks that "We must take into account different phenomena that can, despite higher levels of CO2, lead to decreases in the plants’ production. For example, there are the questions of soil exhaustion, of greater plant sweating due to an increase in temperature, and of difficulty for plants accessing light because of the others around it. Let us also note that an increase in CO2 can cause plants to have less nutritional content, or even to be no longer edible. This is the case for plants that use CO2 to synthesize elements that serve as defense for the plant," continues this scientist. Dr. Lionel Cavin, curator of the Department of Geology and Paleontology at the Museum of Natural History in Geneva, Switzerland, also sees no direct connection between plants that grow faster and big animals: "Today, the areas with the largest quantities of vegetation are found in the tropical forests. Yet it is not there, but in the savannas, where big animals live." One can imagine that it should have been the same during the dinosaur era, because large animals have difficulty moving between the trees in a forest. As we shall see later, these issues play a role in the reconstruction of Mesozoic climate.

THE DINOSAURS’ CLIMATE

In what ways did the dinosaurs’ world differ from ours? The first difference is that Earth was generally warmer than today because of astronger greenhouse effect, so the distribution of climates was not the same.

This map shows Jurassic climates, a period during the era when dinosaurs lived. Yellow: humid climates in summer; pink: deserts; light pink: humid climates in winter; green: temperate climates; blue: cold climates. Note the absence of ice at the poles.

The continents were configured differently than at present. This is because, at the beginning of the Mesozoic, all continents were joined, forming a single supercontinent called Pangaea, before they gradually separated. “Whereas dinosaurs initially all lived on the same continent, due to its breakup, these animals were separated from each other,” says Dr. Lionel Cavin. ”As they evolved to be better adapted to their specific environment, over time they became more and more typical of a certain geographical area." continues this researcher specialized in the Mesozoic fauna. Christopher Noto stresses that this era lasted a very long time, allowing for major evolution. "The Tyrannosaurus rex was more distant in time from the dinosaur Allosaur than it was from man!”

A Tyrannosaur skeleton. At 13 meters (43 feet) long, 5 meters (16 feet) high, and 7 tons in weight, it is one of the largest carnivores that ever lived on this planet. A less gigantic ‘’version’’, Allosaur, existed before Tyrannosaur.

As far as climatology is concerned, the equator today is generally characterized by a climate with warm temperatures and heavy rainfall throughout the year. "At the time of the dinosaurs, the situation was different, because this region [in yellow on the map] was not humid all the time," explains Christopher Noto, who participated in the writing of the article showing this map.“This resulted from a climatology marked by huge monsoons, but the later did not occur in this region of the globe." The tropics are bordered to the north and the south by deserts (in pink on the map). As one advances toward the poles, seasonally wet climates (in light pink) are again encountered, then temperate climates (in green), and finally cool regions near the poles (in blue). How do we know this?

The first map shows plant diversity in the Jurassic era (the bigger the circle, the greater the number of plant species known at this location, as indicated by fossils). The second lists the places where coal (black circles) and evaporates, a type of rock, (white circles) can be found. The last shows where the dinosaurs were located (a larger circle denotes a greater number of species).

"Coal provides an indication about the climate, since it is formed in wet conditions. Evaporites, a type of rock, occur in environments characterized by strong evaporation, indicating dry climates," says Professor Noto. We notice that animals are not necessarily located where there is the most vegetation. This, as we have seen above, can be explained and is a phenomenon also observable today. Regarding flora, some plant species grow in warm climates, others in wet environments, and so on, so their fossils also provide indications about their environment and are included in the map showing climates. Concerning the distribution of dinosaurs, we can see that it was different from present-day distributions of animals. Whereas today the largest concentration of animal species is in the equatorial region, the latter seems to have been little inhabited during the Jurassic. Terrestrial life was found mostly at middle latitudes, with the highest biodiversity in the northern hemisphere.

A LOST WORLD OF TROPICAL FORESTS?
Christopher Noto calls for caution in interpreting such information. "The fact that fossils are scarce in equatorial regions does not necessarily mean that these regions did not support diverse species. Indeed, even assuming that there was a rainforest, we would not necessarily find traces of it." This is because hot, humid forests are not conducive to fossilization. In such an environment, bones rapidly deteriorate, and plants use the minerals leached from bones for their own metabolism. Furthermore, carcasses are not covered, as happens, for example, in a river, where pieces of rock, transported by water, come to rest over them. Another aspect is that dead animals are eaten by carnivores or scavengers. Small bones are eaten and therefore destroyed. As we saw above, forests are populated by small- to medium-sized animals, which are less likely to be fossilized than bigger ones. In addition, a large bone will be more well preserved than a small one since nature needs more time to degrade it. "It is therefore possible to imagine that a world similar to the current tropical forests existed in the equatorial regions but that no indication of them was preserved," concludes Christopher Noto. Concerning tropical regions, another problem may also be the difficulty with which these areas are accessed, which limits possible fossil discoveries. For example, this is the case for the Sahara, the third largest desert after Antarctica and the Arctic, with an area larger than that of the United States! Michael Arthur Paesler, a physicist at North Carolina State University (the United States), is preparing an expedition to search for fossils in this geographical region . . . with a dirigible. This scientist developed a radar system that makes it possible to detect fossils that will be carried by the aircraft. "As we will have to work in an environment where it is difficult to operate computers, the information collected with the radar will be sent to a satellite. The satellite will transmit the data to the United States, where they will be analyzed," explains Professor Paesler, who is delighted at the idea of the potential discoveries that such an enterprise can bring. Indeed, this place was far from lifeless. We know that episodic but significant rains happened, thanks to the signs that such events have left in the ground. The fossils give us information about the fauna that lived here.

For example, herbivores were generally 6 to 15 meters (20 to 50 feet) long. It is therefore possible to imagine this desert as it was 100 million years ago!

THE SAHARA DESERT, 100 MILLION YEARS AGO

This flying reptile, with a wingspan of about 70 cm (2 feet), is a pterodactyl.

One night a pterodactyl put its long beak on the ground. In the calm of the night, it fell asleep, but suddenly it heard a noise. Moving with the help of its wings, the reptile went to the edge of the mound that served as its refuge. It saw a herd of Ouranosaurus nigeriensis dinosaurs moving around down in the plain.

The Ouranosaur was a desert dinosaur that resembled a camel. After sunset, the crest on its back was used to emit excess heat absorbed during the day. It probably also had a mechanism to cool its brain during the day by circulating blood through vessels passing through its nasal region.

The pterodactyl watched them, motionless, from the top of its rock. At each step the dinosaurs were sinking into the sand. They were walking slowly and with a heavy tread. A baby that had certainly hatched not long before was struggling to keep pace. Everything about the Ouranosaurs suggested tiredness. It had not rained for weeks and it was never possible to know when the next rain would happen. The dinosaurs were looking for a watering hole, but these had gradually gone dry. The flying reptile gazed at the landscape bathed in the moonlight, under a starry sky. Already the first light of dawn was appearing. As soon as the sun began to rise in the sky, the air became hot. Soon the temperature reached 50 °C (122°F). The dinosaurs lay down, orienting themselves facing into the sun to minimize exposure. The pterodactyl spread its wings and jumped up and down to leap into the void. Gathering speed, it soared above the sands and the stones. Soon it could feel the effects of hot air currents rising up from the blazing ground on its wings. Its brain, surprisingly large enough to analyze positions and precise balance necessary for flight, allowed it to move with remarkable agility in the air. Starting to soar in circles, it used these movements of the atmosphere to rise up without flapping its wings. Far from the ground, the heat was more tolerable. Large dark clouds were coming up on the horizon; it would finally rain. In anticipation, the pterodactyl landed and found shelter between some rocks. Soon the wind began to blow the sand while the sky darkened. A sheet of rain moved forward, and lighting, intermittently lighting up the plain, could be seen in the far distance. Then a torrential rain started, creating streams. The pterodactyl dipped its beak in a puddle that reached to its feet, then lifted its head to quench its thirst. A few hours after the storm had died down, flowers emerged from the desert soil as far as the eye could see. The Ouranosaurs walked over this carpet of flowers, feeding from it.At the end of the day, the pterodactyl flew off again. It noticed a particular perfume, that of one of the first flowering plants living on the planet. Feeling the warm air of the evening flowing past its wings, it flew over this boundless arid region, which was lying under the orange colors of the sunset.

THE POLAR DINOSAURS

Polar Dinosaurs

Another geographical area that is interesting by virtue of the climate that reined there as well as the solutions that life found for adapting to them are the Polar Regions. These parts of the globe had environments that no longer have an equivalent on Earth. As we have seen above, the poles were colonized by reptiles. In the southernmost latitudes, although they were less cold than today, temperatures fell below 0 °C (32°F) during part of the year, as shown by traces in strata indicating frozen ground at that time. A question then arises: were the dinosaurs cold-blooded animals like the reptiles living today? "It is difficult to imagine that dinosaurs could have survived at such latitudes if this were the case. In the present cold climates, the only animals that are active, such as birds and mammals, are warm-blooded. Besides, [fossils of] dinosaurs of most groups are found in the polar regions," explains Dr. Thomas Hewitt Rich, curator of vertebrate paleontology at Museum Victoria in Melbourne (Australia). He is also one of the world’s most preeminent polar dinosaur specialists. There are indications that certain dinosaurs were actually active year-round, even though the South Pole was plunged into a polar night for three months of the year. For instance, this is the case with Leaellynosaura, a dinosaur with large eyes and very developed optical lobes in its brain. "Thanks to that, it was probably able to discern even small creatures in the darkness of the polar winter,” continues this paleontologist, co-author of the book Dinosaurs of Darkness.

Leaellynosaura, a 60–90 cm (2–3 foot) dinosaur. It was discovered by Thomas Rich and his wife, paleontologist Patricia Vickers-Rich and named after their daughter Leah.

This is not true, however, for all dinosaurs at these latitudes. For example, at least one dinosaur, Timimus hermani, hibernated!

The 3.5 meter (11.5 foot) Timimus dinosaur was also discovered and named by the Riches.

One reaches this conclusion by observing this dinosaur’s bones. "Growth-arrest lines, which reflect periods during which the animal stopped eating, are visible on them," says Dr. Rich. This is a phenomenon similar to the growth rings in cross-sections of tree trunks, which represent a time when the plant no longer grew in the winter. These patterns are nonexistent in other dinosaurs, such as Leaellynosaura, that were active during cold seasons. Reptiles also lived in the Arctic Polar Circle. For example, Svalbard is an island halfway between Norway and the North Pole swept by the winds of the Arctic Ocean. Jorn Hurum is excavating a sea monster’s skeleton, a 15 meter (50-foot)-long Pliosaur with teeth longer than those of a Tyrannosaur, at this place!

The large animal is a Pliosaur, a sea reptile that lived during the dinosaur era.

This island had already given up other secrets; we know that dinosaurs lived here, since their tracks have been found. Although this region was less northward when the footprints were left, it was part of the Arctic Circle. "There was probably snow in the winter," Professor Hurum speculates.

How is this information relevant to the question of present-day climate change? Besides the fact that the climates of the dinosaur age can show us what a world with more CO2 looks like, they also allow testing the models used by climatologists to predict future climates. In this case, one takes into account the different distribution of the continents, the fact that Earth was not spinning at the same speed—so the dinosaurs’ days were half an hour shorter than ours!—and, of course, the higher atmospheric level of carbon dioxide. Yet the result is . . . not correct.

The first map is the one we saw earlier. The second resulted from using a climate model. The color code for both maps is the same (yellow: humid climate in summer; pink: deserts; light pink: humid climate in winter; green: temperate climate; blue: cold climate).

The model predicts the succession of climates that we saw on the first map. Going from the equator to the poles, one finds a tropical zone that is humid during the summer, deserts, temperate climates, and cold climates. The temperate climates (in green) represented in the equatorial region cannot be confirmed or invalidated, since the conditions existing in these areas are unknown. The most blatant error is that too much area shows up as cold climates (in blue) in the high latitudes in the version generated by the model, particularly in the Southern Hemisphere. The problem is that the model’s prediction of heat transfer is too low between the low latitudes and the poles; thus it calculates temperatures that are too cold, for instance, for areas where giant herbivores lived. This could be because the model does not take vegetation into account. Climatologists use this information to improve their models, and more accurate predictions of future climates will most likely be provided.

“CLIMATE CHANGE COULD CAUSE A NEW EXTINCTION”
Beyond the climate change issue, another question is the repercussions of a major increase in the level of carbon dioxide for animal life. As we previously saw, life evolved for 40 million years on this planet in an atmosphere enriched with CO2. Animals adapted to a distribution of climates very different from ours, as we saw in the examples of Ouranosaurus, Leaellynosaurus, and Timimus dinosaurs. Can we thus deduce that life and a lot of CO2 can also coexist in the future? According to Lionel Cavin, "Warmer climates are a normal situation for our planet.” As for Jorn Hurum, he considers that many animals appeared during past global warming events but that these were not the cause of mass extinctions. "These occur in the case of a cooling event. Of course, this does not correspond to the message that one generally hears today,” points out this fossil hunter. Lionel Cavin also believes a correlation exists between temperature and biodiversity: “For instance, we observe in past eras that the warmer the oceans, the higher the fish biodiversity.” Jorn Hurum concludes that the problem essentially concerns humans, since they live in areas that will be flooded if the polar ice melts. For his part, Lionel Cavin stresses the importance of the question of transition from one climate to another: "In the case of a shift to a climate 5 °C [about 9°F] warmer than present, this would not pose any long-term problems. On the other hand, the stage of moving from one equilibrium climate to another could be dangerous.” Thomas Rich shares this point of view by explaining that this change could be disastrous because animals adapted to conditions characterized by an important greenhouse effect are not those that currently exist. "Rapid variations cause problems for living organisms," he adds. Christopher Noto adheres to this idea: "CO2 concentration changes have already occurred in the past, but during much longer periods than what we see today.” According to this scientist, animals evolved, adapted, or disappeared during these events. When they happen in too short a period of time, fauna can’t change. "This leads to widespread extinctions," he adds.

                                                                      Gaëtan Dübler