by Jean Jouzel
Sulfates
The level of atmospheric pollution in the Arctic is sometimes so high that “Arctic fog” is a problem. The term was first used in the 1950s to describe an unusual reduction in visibility that U.S. pilots had observed while flying over the high Arctic latitudes. That fog is seasonal, with a peak in the spring, and comes from anthropogenic sources of emissions located outside the Arctic. The fog aerosols are essentially sulfurated and come from the burning of coal in mid-latitudes.5
The sulfates present in the atmosphere come from both marine aerosols and burning coal and gas. The natural portion can be evaluated by measuring the elements characteristic of an ocean source, such as sodium. That enables the isolation of the component linked to pollution by subtracting the fallout from volcanic eruptions rich in sulfates that have been localized in time and are easily detectable.
At Summit Station (see Figure 17.2) concentrations increased at the beginning of the twentieth century until they peaked in the 1930s; that increase was followed by a slight decrease, no doubt linked to the economic crisis. After World War II a much more rapid increase ensued, but filtration measures for emissions reflected in amounts measured after 1980 indicated a partial return to natural levels.
Figure 17.2. The snow and ice of Greenland: quantity of sulfates during the last centuries. The amounts measured in the snow and ice at Summit Station and in two other sites in Greenland show a remarkable similarity. The natural level, which was stable over the centuries, was greatly perturbed in the last years of the nineteenth century. The impact of human activity culminated before the end of the twentieth century; the decrease subsequently observed was not due to a decrease in industrial activity but to purification through filtration of emissions in our large cities.
As does lead, sulfates of anthropogenic origin behave differently in Antarctica and Greenland. They increased in Greenland from a factor of three to a factor of five in two stages centered on the 1900s and the 1950s. By contrast, in Antarctica, the quantities of sulfates have varied little over the past hundred years, which probably indicates the distance of the sources and the short time (only a few days) that sulfates stay in the atmosphere.
Radioactivity
A striking example of how our atmosphere is connected on a global scale is that of radioactive dust. In the two ice sheets of Antarctica and Greenland, the radioactivity of snow layers has faithfully recorded the calendar and the power of nuclear explosions in the atmosphere. Just as in the case of strong volcanic eruptions, the energy freed during nuclear explosions is sufficient for the radioactive elements to reach the stratosphere and, from there, fall over the entire globe. The profile obtained at the South Pole at the end of the 1970s is typical of the variations observed over the entire continent and is for us a revelation showing the fact that for some pollutants we have only one atmosphere on a global scale.6 The natural beta radioactivity of the layers of snow was at the time around 70 disintegrations per hour and per kilogram of snow (dhp/h); it came principally from lead 210 and from its descendants. Compared to that basic natural noise, the levels of radioactivity are most often much higher. In the spring of 1955 a peak was observed that represented the fallout from the first thermonuclear tests in March 1954. Radioactivity increased by a factor of twenty and remained great until around 1965, during which the fallout from the series of large explosions carried out in the Northern Hemisphere between September 1961 and December 1962 (close to three years earlier) were deposited.
Certain layers of snow containing the fallout of large nuclear explosions were showing radioactive levels up to forty times greater than the natural (in the absence of fallout from nuclear explosion) radioactive level. The suspension of nuclear testing in the atmosphere in 1963–66 was seen in a decrease in radioactivity connected to the depletion of the stratospheric reservoir. Strontium 90 and cesium 137 were the primary causes of beta radioactivity. These are elements whose half-lives are close to twenty years and, with the passing of time, the measurements will be much less impressive.
A series of secondary peaks was observed in the snow deposited between 1969 and 1976; they correspond to a partial resumption of atmospheric tests, whereas the radioactivity returned to values close to the natural level. The particularly high 1955 and 1965 levels enabled the description, over all of Antarctica, of the layers deposited during those years and serve as markers to measure the accumulation of snow. Similarly, the fallout of tritium is also recorded in Antarctic ice.7 A radio-element produced naturally by the action of cosmic radiation over compounds in the atmosphere, it is also formed during thermonuclear explosions; it was a hundred times more concentrated in the snow deposited around the end of 1965 than at the beginning of the 1950s.
The glacial archives thus measure the amount of pollution in our atmosphere far from human sources of emission. They give us a point of reference for the natural “background noise” from which we can evaluate human impact. As for aerosols, the response is clear: humans have marked the atmosphere, from the North Pole to the South Pole. But what about gases?
The Ozone Hole: An Emblematic Pollution
The ozone molecule, formed of three oxygen atoms, is not very abundant in the atmosphere. In the upper atmosphere (stratosphere), where its concentration is higher, only three or four molecules in a million are ozone molecules. Closer to home, in the lower atmosphere (troposphere), the proportion of this component is no more than a few dozen billionths and represents only around 10% of the total mass of ozone in the atmosphere. The ozone of the lower atmosphere is, however, a key component of atmospheric chemistry, ruling in particular the oxidizing capacity of the atmosphere and thus the duration of life and therefore the abundance of many other greenhouse gases, such as methane.
Absorbing infrared radiation emitted by the Earth, ozone is directly responsible, as we have seen, for an additional greenhouse effect of 0.35 Wm–2, or 20% to 25% of the contribution of carbon dioxide. It also controls the thermal structure of the stratosphere within which an absorption of ultraviolet radiation by the ozone constitutes the principal source of warming. Various pollutants can contribute indirectly to the climatic perturbations through photochemical processes that cause, for example, the production of ozone in the troposphere to intervene. This is the case of carbon monoxide (CO) and nitrogen oxides (NOX), 80–90% of which are emitted through the use of fossil fuels (industry, transportation) or by burning the biomass (deforestation, heating wood, bush fires). The emission of these components from the ground or their injection directly into the atmosphere, for example, in the case of NOX emitted by airplanes, leads to the photochemical production of O3. This pollution is limited to the troposphere and is redistributed by winds, increasing the basic level in the atmosphere far from the zones of emission. The ozone molecule has a relatively short life in the troposphere, on the order of a few weeks on average, and the distribution of ozone is thus quite variable in space and in time, with a strong seasonal variation and a heterogeneous geographic distribution.
The concentration of ozone on the surface has been followed at many sites for several dozen years, but measurements before the 1970s are rare. Those done at the observatory of Parc Montsouris in Paris (1876–1909) and Pic du Midi in the Pyrénées (1874–1909) indicate an order of grandeur of ten-billionths, but we had to wait for the measurements taken in the Northern Hemisphere in the 1950s to clearly show an increase in the existing amount. It is now estimated that it has more than tripled during the twentieth century. A maximum ozone reaching more than sixty-billionths in the summer is calculated by the chemical models above polluted regions of the Northern Hemisphere (North America, Europe, Southeast Asia). These models estimate that the global increase in tropospheric ozone has been on the order of 30% since the beginning of the preindustrial era. It is a pity that the ice, which does not retain the memory of these variations, does not allow us to validate that estimate.
Although the ozone in the air that we breathe on the ground is toxic to our health, that which is
more abundant in the stratosphere is more vital. Because it absorbs the solar ultraviolet radiation of short wavelength before it reaches the Earth, ozone protects life on our planet. Amassed together and concentrated in average conditions on the Earth’s surface, it would have a thickness of only three millimeters, or 300 Dobson units in scientific jargon. It is surprising that such a thin layer protects life from ultraviolet radiation that can cause mutations of DNA and skin cancer; without ozone, life would not be possible except in the ocean depths.
The ozone hole in the stratosphere was discovered in Antarctica in 1985.8 The CFCs emitted at the time by the developed and industrialized countries of the Northern Hemisphere were responsible for this, demonstrating the sometimes unpredictable impact of human activity on the entire environment in which we live.
The seasonal depletion of stratospheric ozone first observed above Antarctica at the end of the polar night and more recently above the Arctic is one of the principal problems affecting our environment. The thickness, the surface area, and the duration of the Antarctic ozone hole has continuously increased, reaching an apogee of nearly 30 million km2 in the early 2000s with ozone concentrations about two times less than what they were in the 1960s.
In the Arctic, the ozone hole is less noticeable following a more moderate cooling of the stratosphere, but the mean annual levels of ozone decreased by 10% in the 1990s compared to levels at the end of the 1970s, which increases the risk to populations who live there.
The Montreal Protocol signed in 1987 addressed the protection of the ozone layer; it was a matter of halting its spread and reducing its intensity. This treaty, refined on several occasions, aimed primarily to drastically reduce CFC emissions; when 190 countries gathered again in Montreal in 2007, they noted the effectiveness of the measures proposed. This does not mean the battle has been won; it will certainly require several decades for our atmosphere to regain its natural state, which has been particularly degraded in the polar regions, but we can rejoice at this positive sign for our environment following a concerted action on an international level.
The Anthropocene and Greenhouse Gases
Unlike aerosols, whose concentrations decrease the farther they are from their source, unreactive gases have the same concentration everywhere in our atmosphere, and the industrial period, as we have seen, is strongly marked by a rapid increase in the amount of greenhouse gases. The analysis of air bubbles contained in the ice shows that since 1750 concentrations of CO2 have increased by almost 40% and those of CH4 have more than doubled. These bubbles also teach us that the current amounts are much higher than those of the last hundreds of thousands of years. The industrial period marks the beginning of an era characterized by the impact of humans on the natural environment. It was the increase in concentrations of carbon dioxide and methane starting at the end of the eighteenth century, as is recorded in polar ice, which enabled Paul Crutzen,9 Nobel Prize winner in physics in 1995, to define the beginning of the Anthropocene Era.
CONCLUSION
The Anthropocene Era
Climate warming has become one of the major challenges that our global society must face. The discoveries made in the ice sheets, notably in Antarctica, have proven this to scientists worldwide. In addition, field data and satellite observations, as well as the viability of the models used for analyzing climate change, have shown us that we cannot ignore this phenomenon. For our part, we have wanted to concentrate on our white planet, whose role in this challenge is crucial since the polar ice is both a unique witness and an essential actor.
Homo habilis, which appeared 2.5 million years ago, then Homo erectus and Cro-Magnon Man had to defend themselves against nature to survive. In that long struggle the paths taken in the migrations of our ancestors were the precursors of our highways. The first human beings fed themselves by gathering and hunting, and then, after becoming more sedentary, they cultivated the land and developed an agriculture adapted to their needs. Animal farming succeeded hunting, and to feed those animals they had to cultivate artificial prairies. We thus entered into the Holocene, a new era for the human way of life but also for the climate which, around 10,000 years ago, was already in a warm condition. To warm themselves and cook food, humans burned wood from forests; with the great leap of the conquest of fire began the still undetectable production of greenhouse gas emissions of anthropogenic origin.
Gradually the landscapes changed. Thus through the millennia humans built structures and cities, visibly reducing the extent of natural spaces. In doing so they disturbed natural geochemical cycles and, beyond the land, our atmosphere was also affected. From wood we moved to fossil fuel, coal, oil, and gas to satisfy the energy demands of a population that was growing rapidly at the same time that the industrial era began. We then entered the Anthropocene, characterized by a rise in pollution. Humans thus strongly marked the atmosphere and oceans of the Earth. Humans have become the greatest predator of our environment and a major actor in its destruction, so great is their influence on the evolution of our climate, biodiversity, and, more generally, our living conditions. This destruction cannot be masked by technological and medical progress, which, for example, enables people to live longer.
Among the signs of this destruction, the warning from polar regions, which are practically uninhabited and far from the sources of pollution, is particularly impressive. Two striking examples are the ozone hole, which was discovered by probing the upper atmosphere above Antarctica, and the sudden increase in greenhouse gases. These two symbolic examples plead for a balanced support of research. Although it is necessary to finance projects that demonstrate precise objectives in an aim toward solving social problems, we also need to strongly support basic and quality research already in progress and whose outcome is often unpredictable. This is what happened during the ozone discovery made by the English while they were taking routine measurements, a discovery that seemed unbelievable to the researchers; the first sets of data were even thrown away. This is also the case for research undertaken on glacial ice cores. Long years of observation during winters spent on a base, exploratory fieldwork and extractions, ice core campaigns and measurements in the laboratory by means of sophisticated techniques—all of these efforts have resulted in an awareness of the importance of that ice for the reconstruction of the climate and the composition of the atmosphere. Such research has opened a door onto a critical problem facing our society; we are proud to have helped open this door to the future.
Climate warming and its impacts have become serious realities that foretell of a very different world to which humans and their civilizations will have to adapt, not without damage. In the face of that world and, more generally, of environmental problems, we must clear the path for a more harmonious cohabitation between man and that environment, with a view toward safeguarding the future of generations to come, a notion that the expression “sustainable development” sums up in part.
We have only one planet. The atmosphere and the ocean have no other frontiers. The struggle against climate warming based on controlling greenhouse gas emissions demands a global solidarity involving all human beings, from states to citizens. That solidarity is difficult to achieve, given the differences among those involved, whose behavior too often favors the short term and responds only to their own interests, whether on the level of the individual or on that of industrial, financial, political, or even state groups. And yet it is time to act on an international level through novel initiatives such as those that have been put in place in France like the Grenelle de l’environnement.
Getting people to act will be difficult given budgetary constraints and the fact that right now people are being asked to drastically change their behavior based on events occurring far away. Contemplating the snow on the Belledonne chain or the midnight sun on the ice sheets does not convey the sense that the Earth is in danger or the urgency of the measures that need to be taken.
The control by humans, a living species among so many others, over the global
environment now has a label: the Anthropocene. We have already used this term, which may not have been familiar to the reader, but it is good to bring it up again. The Anthropocene signifies the passage, in the evolution of the environment of our planet, from a balance that depended essentially on natural causes to a state in which the influence of humans becomes the governing factor.
If we go back to the beginning of the Quaternary, around 1.6 million years ago, warming and cooling depended on long periodicities of the Earth’s trajectory around the Sun. During that time, the biosphere, that is, all ecosystems, in which humans then occupied very little space, participated in the saga of the climate. As we have seen, the variation in the composition of the atmosphere modified the radiative levels and through that even the climate. The gases that intervened in these levels depended in large part on geochemical cycles regulated by living species present in the ground, the oceans, and the atmosphere. Among those species, humans, through their activities, imposed their imprint, as is seen in detail in the evolution of the composition of the atmosphere as recorded in the ice.
These data led Paul Crutzen to write: “The Anthropocene could be said to have started in the late eighteenth century, when analyses of air trapped in polar ice showed the beginning of growing global concentrations of carbon dioxide and methane.”1 This statement clearly conveys the message from the ice.
Regarding the climate, the Anthropocene will no doubt mark our future, in any case for the century we are entering and likely the following ones. The climate and the environment are opening the path to many dangers, to many conflicts. In a near future, the rarity and the cost of energy resources will perhaps grant a certain respite to our environment, but they will plunge our world into the social problems born in the Anthropocene. If the Nobel Peace Prize was awarded to Al Gore and the IPCC, it was because beyond the quality of scientific expertise, climate warming creates a state of instability that can lead to migrations and conflicts provoked by unequal access to resources (water, food, energy), by sea-level rise, and by an increase in poverty, not to mention the difficulties linked to religions or to intransigent cultures. Will wars also mark the Anthropocene, or will we be able to find the complex recipes to fashion a peaceful planet?