by Jean Jouzel
In 1987 we demonstrated that the variations in temperature and the amount of greenhouse gases in the atmosphere were connected throughout the last climatic cycle (in the last 150,000 years). With the work of American, Danish, and Swiss researchers, who focused more on Greenland, and the Franco-Russian collaboration centered on Antarctica, the study of glacial archives was well under way. We could henceforth attempt to reconstruct and to understand the mechanisms of climate variations in the past. And from that, it becomes possible to speculate about the future climate and its effects worldwide.
It is the development of this new discipline that we wish to reveal in this work. We are fortunate to have been able to contribute to its inception. But we owe a great deal to the researchers, technicians, administrators, and people on-site who have accompanied us during this amazing scientific adventure. We wish to thank them all.
These glacial archives are of interest not only to the scientific community. They are of huge interest to the broader public because the polar regions in particular remain synonymous with adventure. And at present everyone senses their fragility. Anyone who is interested in the climate, in its history, its future, cannot ignore these regions of extreme conditions.
Several recent films have used the climate as their central theme. One of the two we will mention is a documentary that has become emblematic of the “global warming” concern for the future: An Inconvenient Truth, of which Al Gore is the indisputable star. The other, The Day after Tomorrow, is a work of fiction that quickly departs from the realm of the believable. Both assign a large role to the results obtained from deep glacial core drilling. These two films placed a camera lens on the research undertaken in the polar regions, which have gained new life during the International Geophysical Year, whose fiftieth anniversary we celebrated during the International Polar Year 2007–2008.
We can reconstruct the climates of the past using various methods, and the ice of the ice sheets are a precious memory of our climate. But they above all contain a unique treasure with their air bubbles. As the climate has evolved these bubbles have recorded the composition of our atmosphere, including greenhouse gases. This is the central theme of our book: we will retrace the campaigns of exploration and of core drilling that have reached close to four thousand meters in depth and present the measurements and interpretations that they have allowed. But first we will familiarize the reader with what we scientists call the “cryosphere” and summarize what we know about the “ice of yesteryear,” which has impacted the life of our planet from the time the Earth almost became a snowball up to the heat and the cold of the last two million years.
Our shared enthusiasm for the wealth of results offered by deep core drilling in Antarctica and Greenland comes from the fact that beyond what they teach us about the way in which our climate evolved in the past, they are rich in information on its future evolution. That is why this book also looks at the future while emphasizing the impact of climate warming on the white planet, particularly on the polar regions, which are particularly sensitive to it.
At the end of the journey, we will better understand why, since the beginning of the nineteenth century, we have entered a new era, the Anthropocene, which is characterized by an increase in pollution due to the activities of humankind, which puts its stamp on the environment and on the climate of our planet and thus on our future. This book does not propose a miraculous solution. Its object is to describe the progress of a science that gives us every reason to be concerned and aims to inspire citizens and policymakers to confront the enormous challenge before us.
Let us now look at the icy expanses that will first take us back in time.
Acknowledgments
This work presents scientific results that are the fruit of work carried out by many researchers, engineers, and technicians in areas relating to the history of our climate and of our environment, as well as their future evolution. We wish to thank everyone involved, with special thanks to those we have collaborated with, in France and abroad, during the many years that we have spent deciphering the glacial archives. It has been a fantastic collaborative adventure. In France, since the 1960s, we have enjoyed a close collaboration among the teams from Grenoble, Saclay, and Orsay, and that collaboration has benefited from the unfailing logistical support of the Expéditions polaires, then of the IPEV (Institut Polaire Français Paul Emile Victor), and from that of various departments of the CNRS and the CEA, as well as from European programs (European Union and the European Science Foundation). The adventure has unfolded within a context of remarkably organized and extremely stimulating international collaborations that were enhanced through many friendships. Our thanks go out to everyone. Thanks, too, to Volodia Lipenkov and to Jean-Robert Petit and Valérie Masson-Delmotte for advising on certain chapters in the book.
PART ONE
THE WORLD OF ICE: PAST AND PRESENT
CHAPTER 1
The Ice on Our Planet
The temperature conditions that govern our planet are such that water can exist in three forms (vapor, liquid, and solid) in proportions that vary in different climate conditions. All of the water on the Earth makes up what is called the hydrosphere. Most water exists in liquid form, 97% of which is in the seas and oceans, which cover 360 million km2, or more than 70% of the planet’s surface. Freshwater, a vital resource found in the ground, lakes, rivers, and above all aquifers, represents only a small proportion of the total, a bit more than 0.5%; water vapor in the atmosphere amounts to .001%; and the water of the living world, the biosphere, represents much less.
Low temperatures are found in high altitudes and high latitudes; this is where ice forms. In current climate conditions, this ice represents only around 2% of the hydrosphere. How is that 2% distributed? How is it formed? What surface does it cover? What climatic role does it play? Before looking to the past, we will describe our white planet as it is now. Table 1.1 shows its main characteristics.
Snow and Ice: A Multifaceted World
When we think of ice, we immediately think of 0°C (or 32°F). This is the temperature at which water freezes and ice melts. It is a reference point for the temperature scale that we use in our everyday lives. In nature, it is a bit more complex because that temperature of reference involves only freshwater. In fact, because it contains salt, seawater freezes only below –1.8°C. And in certain circumstances, even very pure water does not easily become solid. This is the case with very small cloud droplets: they form from the condensation of water vapor and can remain in liquid form. Up to temperatures of –20°C, or even below, we then speak of supercooling. We should add that water vapor exists in the atmosphere regardless of the temperature; it can condense on microdroplets that form around condensation nuclei, and it also contributes to the growth of snow crystals by passing directly from the vapor phase to the solid phase.
Table 1.1.
Surface, volume, and contribution to the sea level of the different
components of the cryosphere.
Source: IPCC, Climate Change 2007: Fourth Assessment Report (Cambridge: Cambridge University Press, 2007).
Note: In the case of snow, frozen ground in winter, and the permafrost, the minimum and maximum levels are given. For glaciers and glacial ice caps, the two levels correspond to high and low estimates.
* The melting of one million km3 of continental ice corresponds to a rise in sea level of 2.46 meters; the figures shown in this column take into account the replacement by seawater of the released surfaces below sea level.
There are different types of precipitation that reach the ground in solid form. Two are anecdotal within the framework of this book because, except in unusual cases, they melt quickly. Graupels (much like a fine hail) come from the freezing of raindrops that travel through air that is colder nearer the ground. Hail and hailstones are formed higher up in the atmosphere, within cumulonimbus clouds, which reach an altitude of over 10 kilometers. Snow is formed both through the freezing of small supercooled drops and by direct
condensation of vapor on preexisting crystals. Unlike graupels and hail, a large part of snowfall remains in its frozen state as long as the temperature of the surface on which it falls is below 0°C.
The thickness and extent of the snow cover vary depending on the season. Permanent snow is, of course, found in the mountains, on glacial ice caps, and on sea ice. Outside those zones, snow covers on average 26 million km2, mostly on the continents of the Northern Hemisphere. At the end of January, that surface may reach 45 million km2 but reduces to less than 2 million km2 around the end of August. In the Southern Hemisphere, owing to the unfavorable distribution of the continents, snow fields cover scarcely more than .5 million km2. This snow cover is fairly thin, a fraction of a meter on average. It thus represents a very small volume of ice.
This is the snow that, year after year, over centuries and millennia, feeds our white planet, which we call the cryosphere. On the continents, mountain glaciers, glacial ice caps (a term used when the ice surface is less than 50,000 km2), and the huge ice sheets of Greenland and Antarctica are the main elements of the cryosphere. We must also include frozen ground, which is permanent in some places (permafrost), and other frozen grounds that are frozen only in the winter, such as rivers and lakes. There is also sea ice, which is formed by the freezing of ocean water surfaces; icebergs that float on the edges of ice caps and ice sheets; and ice shelves, fed in some peripheral regions of Antarctica by the ice that flows from the interior of the continent.
Mountain Glaciers and Ice Caps
Outside the high latitudes, it is above all the winter snow and the mountain glaciers that symbolize the white planet. In most regions, when it rains on the plains it snows in high altitudes. The height at which snow is permanent varies between about 3,000 and 4,500 meters depending on the latitude and the site’s orientation to the Sun. The density of the fresh snow cover is very low (0.1 to 0.2) because it contains a lot of air, which occupies the spaces left free between the complex lacy shapes of the snowflakes. The laws of thermodynamics dictate that these flakes will lose their edges through sublimation and assume a more spherical shape. This facilitates the piling of the layers whose density increases (more than 0.5 for the névé [snow that is more than a year old]). With recrystallization the smallest flakes disappear, giving way to the larger ones, and the amount of air captured between the crystals decreases. The ice thus formed has a density close to 0.9, the same as that made in a freezer. Both the névé and the ice then float on water. The amount of time required for these processes can vary considerably; it depends, for example, on the climatic conditions, the temperature, and precipitation. In the mountains, when the winter snow doesn’t completely disappear during the following summer, it becomes névé. The percolation of the melted water can lead to the formation of ice in a few years’ time.
There are approximately 160,000 such glaciers of all sizes. They are found on every continent except Australia. They cover some 430,000 km2, and the largest are found in Alaska, in the Canadian Arctic, in the South American Andes, and in the Himalayas. On the other end of the scale, some African glaciers measure only 15 km2. Among the longest glaciers are those of the Bagley Ice Field in Alaska (185 km), the Siachen in Karakorum (75 km), the Inybtehek in Tian Chan (65 km), the Uppsala in Patagonia (60 km), the Monaco in Spitzberg (60 km), the Tasman in New Zealand (28 km), and the Ngojumba in Nepal (22 km). Alpine glaciers cover around 3,000 km2. Half of them are in Switzerland, including the Aletsch Glacier, which measures 25 km in length; 10% of this surface is in France, including the Mer de Glace (Ice Sea) near Chamonix, which flows over 12 km. Contrary to what the name “mountain glaciers” might suggest, some, depending on the climatic characteristics of their location (precipitation, temperature), can flow as far as the sea: this is the case of the Malaspina (Alaska) and the Darwin (Chile) glaciers. They can become as much as several hundred meters thick.
We generally use the term glacial ice caps for glaciers whose surface can vary from a few thousand to 50,000 km2. They are found in high altitudes in polar and subpolar regions and are relatively flat. In Svalbard (Spitzberg), the largest ice cap found in the North-East Land extends over 8,000 km2 and is 300–400 meters thick. In Iceland, two ice caps (each 1,000 km2) cover the summit of the island, and the Vatnajokull (8,300 km2) is made up of 3,500 km3 of ice. Other ice caps are found in the Arctic, in the northern Canadian archipelago, in Siberia, and in southern Chile. There are approximately seventy of various sizes.
Glaciers and ice caps cover an area that is close to that of France; their volume amounts to between 50,000 and 130,000 km3. The area of the glaciers and ice caps located on the edges of Antarctica and Greenland, not taken into account in Table 1.1, represents 140,000 km2.
Polar Regions: The Omnipresence of the White Planet
Zero degree Celsius (0°C) in the middle of summer on the sea ice of the North Pole. Only nine days a year without frost in Resolute Bay (74° 43´ N, Canada) at sea level. A yearly average of –30°C at the center of Greenland at 3,000 meters in altitude. These figures provide the image of a region, the Arctic, where cold is the rule. On the other side of the planet, –11°C is the average temperature at the coastal base of Dumont of Urville (66° 07´ S) and –55.4°C in Vostok in the heart of Antarctica at 3,488 meters in altitude. And the temperature can plunge as low as –89°C in the winter. The polar regions hold unenviable records. The Sun has little love for them, and the feeling is mutual.
It is primarily the tilt of the Earth’s axis of rotation (23° 27´) compared to the plane of its trajectory around the Sun that is responsible for the fact that the Sun has little love for the polar regions and keeps them among the coldest places on the planet. This tilt, also called the obliquity, determines the length of the presence of the Sun as a function of the latitude and thus the rhythm of the seasons. In the summer, boreal or austral, above 66° 33´ in the north or the south, the Sun can be continuously visible, whereas at the opposite pole it is below the horizon for the six months of winter. In addition, in the polar regions the Sun’s beams never shine perpendicularly. For any given surface, the energy absorbed is that much more reduced. Thus the high latitudes, in terms of solar energy received, are at a disadvantage. As if annoyed by the lack of attention, the white planet that spreads out over the poles has chosen to ignore the Sun since it sends back up to 90% of its incidental rays over a zone covered with fresh snow. This albedo effect varies with the nature of the surface; it can go as low as 50% for old snow and, though it can be around 80% over a large part of the ice sheet, it varies over the sea ice from 80 to 50%, depending on the condition of the surface and how reflective it is. It is thus essential to wear sunglasses in these zones to avoid blinding because the eye knows the difference between an albedo of 80% and that of rocky surfaces (15 to 30%) or of ocean surfaces (5 to 15%). In terms of climate, it is the size of this albedo that is one of the main characteristics of snow and ice. Greatly reducing the absorption of solar rays that are already weak in the high latitudes, it is largely responsible for the extreme cold of these icy regions, both in oceanic and continental regions.
But the Sun and the albedo are not the only players. In high latitudes during the cold seasons the ocean is covered with a lid of ice. Without it, the Arctic Ocean, in the middle of which we find the North Pole (Figure 1.1), and the Southern Ocean, surrounding the Antarctic continent, transfer a large quantity of heat into the atmosphere, maintaining the temperature of the air close to that of the seawater. But when the ice cover is in place, the “ocean radiator” stops and the winter temperatures above the sea ice can reach –30°C or even lower. In the Arctic Ocean and the adjacent seas to the north, as well as in the Southern Ocean, it is common that, following summer, the temperature on the surface of polar waters is lower than –1.8°C, which means that the surface is cold enough to freeze into sea ice. The first ice crystals give birth to “pancake ice,” which, in time, forms sea ice. This process requires rather long periods of freezing because the surface water, when it
is cooled, becomes denser; it sinks and is replaced by warmer water. After reaching a certain thickness, the ice isolates the ocean from the atmosphere and slowly builds up further by freezing of the colder seawater underneath the ice. Waves and swells slow down this formation of sea ice, which can become one to two meters thick in the first year. Over the years, and taking into account summer melting, it can then increase up to three to four meters.
Summer brings melting and partial dislocation but in very different ways in the two hemispheres. In the south, the sea ice attached to the continent is exposed to the whims of the Southern Ocean; it extends up to 17 to 20 million km2 in September—that is, to a surface equivalent to that of the entire Antarctic continent—and five times less in February, or 3 to 4 million km2. In the Arctic, the sea ice is surrounded by continental surfaces that stabilize it; it extends over 14 to 16 million km2 in March with ice that is a bit thicker than that around Antarctica. And, as we will see, it becomes three to four times smaller in September.
On continents with particularly harsh climates without glaciers, frozen ground, or permafrost, forms. When the average temperature goes below 0°C, ice is present at great depths. Mammoths and bison, dating from the last ice age, have been found in these natural freezers in Siberia and Alaska. Depending on the season, this ground can thaw on the surface, but the thickness of the permafrost can reach as deep as six hundred meters. The surface areas are also considerable in these regions: one quarter of the exposed land in the Northern Hemisphere including Alaska, Canada, and Russia but also certain regions in the high mountains are covered by permafrost. However, the zones with a great deal of ice scarcely cover 2 million km2. These permafrost zones can extend under seas and oceans, as well as under glacial ice caps and ice sheets.