The White Planet: The Evolution and Future of Our Frozen World

by Jean Jouzel

  The IPCC’s caution is probably justified; thus the data on a glacier in Greenland show that after a rapid acceleration the glacier slowed considerably the following year whereas in West Antarctica the flow of the Rutford Glacier affected by the rhythm of the tides can vary by 20% over short periods (around fifteen days), which shows how difficult it is to deduce the evolution in the long term from measurements that are generally fixed at a given moment in time.3

  There are uncertainties, then, about sea-level rise from now to the end of the century, which will be greater than the 17 centimeters observed during the twentieth century; the rise could be as much as sixfold if we believe the most alarmist projections. But what was emphasized in the IPCC’s synthesis report was the irreversible nature of that rise beyond the twenty-first century owing to the inertia of the climatic system (Figure 13.4) and of the threat of a partial melting of the Greenland ice cap and possibly of the ice cap of West Antarctica.

  The inertia of the thermal expansion is much greater than a few decades, which is characteristic of the equilibrium of temperatures between the atmosphere and the upper ocean. This last thermal equilibrium concerns only the surface layers of the ocean, whereas dilatation is produced over the entire water column. It takes a lot of time for the heat to be transferred to the ocean depths; one then measures in centuries, even in millennia. Consequently, even if radiative forcing and the temperature are stabilized, the rise in sea level will continue: from 30 to 80 centimeters in 2300 in the hypothesis of the median A1B scenario, followed by a stabilization of the radiative forcing in 2100, then at a lesser rhythm over many centuries.

  The current models, which are still very preliminary, indicate that Greenland will ultimately be eliminated, which would cause a rise in sea level of around seven meters if the average temperature of the atmosphere were, for millennia, maintained above a certain level. That level is not in fact very high since the estimates vary from 1.9 to 4.6°C compared to the preindustrial climate. Another reason to be worried lies in the fact that these temperatures are comparable to those of the last interglacial period, 125,000 years ago, during which the volume of ice in the polar regions was less and the sea level four to six meters higher. Antarctica will remain too cold to melt significantly. However, its mass could decrease, thereby contributing to the sea level, if the flow connected to the dynamics of the ice accelerates; this would affect West Antarctica in particular.

  Figure 13.4. The inertia of the climatic system. The concentration of carbon dioxide, the temperature, and the sea levels continue to increase after emissions have reached maximum levels. Source: IPCC report, 1995.

  Over a few centuries the rise in sea level could thus reach three to four meters, assuming that the volume of Greenland diminishes by a third. Even if this time frame is distant, it should cause us to reflect because great zones would be forever under the sea, and the wealth and beauty of many coastal cities would be lost forever. The situation is all the more urgent because it is our activity in the coming decades that will determine the warming at the end of the century and the sea-level rise in the centuries to come (Figure 13.4).

  The Halt of the Gulf Stream

  There are two reasons to look at the questions raised by the possible halt of the Gulf Stream. The data obtained by glacial ice cores in Greenland have largely been at the origin of the discovery of rapid climatic variations that we believe are connected to the halt then the starting up of the Gulf Stream, with abrupt changes in temperature that could have reached 16°C at the center of the ice sheet in a few decades. Based on these data, the 1995 IPCC introduced the notion of “climatic surprise.” The processes that threaten to lead to a halting of the Gulf Stream in the future differ from those that operated in the past. But the simple fact that rapid and large variations have henceforth been well documented give a certain credibility to the fears that some people—climatologists, writers, filmmakers, politicians, and so forth—have for the future of the Gulf Stream, to which we attribute, even if it is only partially true, the mildness of the climate in regions from Western Europe under the influence of the Atlantic Ocean.

  There is a common characteristic, nevertheless, between the past and present and future operation of the Gulf Stream. Just as it has been in the past, the Gulf Stream is sensitive to the arrival of freshwater into the surface waters of the North Atlantic. That current constitutes the northern extremity of what oceanographers call inverse thermohaline circulation, which goes along the western coasts of the North Atlantic; the term thermohaline indicates that this circulation is affected by both the temperature and the salinity of the surface ocean waters. In almost all climatic models, warming is accompanied by a notable increase in temperature and precipitation in the high latitudes of the Northern Hemisphere. Each of these effects—warming and an additional amount of freshwater (either directly for ocean precipitations or through an increase observed in the contribution of rivers flowing into the sea in these regions)—tends to make the surface waters of high latitudes less dense. They then have increasing difficulty sinking into the deep water.

  None of the simulations that couple general circulation models of the atmosphere and of the ocean (or even less complex models) points to an abrupt stop of the thermohaline circulation during this century. They suggest a slowing instead. But it is important to note that the regions of Europe under the influence of the North Atlantic continue to warm. However, some models, generally those of “intermediary complexity,” suggest that the thermohaline circulation and thus the Gulf Stream could stop in the longer term in response to sufficiently increased warming.

  Simulations using coupled complex ocean-atmosphere models also suggest that in the next five hundred years the thermohaline circulation might indeed completely stop,4 once the contribution of freshwater connected to the melting of Greenland is taken into account, which in the long term threatens to be sufficiently great to have an impact. The same simulation carried out without taking that contribution into account indeed does not lead to a stop in thermohaline circulation.

  Above all we must not imagine that this halt will in any way provoke a planetary cooling. The average warming is scarcely less marked in a simulation leading in the long term to a halt in the thermohaline circulation than in the experiment in which thermohaline circulation remains active, 3.2 compared to 3.5°C, both of which correspond to a doubling of the concentration of carbon dioxide. And in the case of a halt of the thermohaline circulation, the warming would be less in the North Atlantic and in the Arctic, but it would be little affected in Western Europe. Catastrophic scenarios, as in the film The Day after Tomorrow, predicting the beginning of a glacial period resulting from a weakening of the thermohaline circulation are thus mere speculations.

  Let us end this chapter on a more anecdotal note, although it involves a Pentagon report. In 2003, upon the request of the American military, Peter Schwartz and Doug Randall,5 two consultants unknown to the community of climatologists, imagined that an abrupt event similar to that of 8,200 years ago could rapidly occur. The halt in the thermohaline circulation, described in their chapter devoted to the climate of the past 10,000 years, was, in Greenland and in the regions near the North Atlantic, first conveyed by a notable cooling—as much as 5°C—in a few decades. The main idea of this report was that we would be very close to the threshold from which the thermohaline circulation, which is indeed slowing down, threatens to stop—in 2010. With serious droughts in southern China and northern Europe during the following ten years, and, after a decade of cooling, the European climate would be close to that of Siberia. Famine would then spread in a cold and starving China that would jealously covet the energy resources of Russia, and chaos would be unleashed there with civil and border wars between 2020 and 2030. These geopolitical aspects and their consequences for the national security of the United States were at the heart of the report: climate refugees, the risks of war in the Caribbean and in Asia, internal struggles among European countries, new countries developing nuc
lear weapons, and so forth—a world of conflicts that would justify strong diplomatic action on the part of the United States.

  There is nothing really serious in this study, which is without any scientific credibility and whose vision is too apocalyptic. Moreover, at least one of its predictions did not occur: the authors imagined that in 2007 the waters could breach the dams of the Netherlands, rendering The Hague uninhabitable. It is nevertheless true that even in the warmer climate that will prevail in the middle of the next century, a rapid cooling associated with a halt of the Gulf Stream would be extremely destabilizing from an ecological, economic, and geopolitical point of view, even if no country saw its temperatures go below those that it currently is experiencing.

  But this is not the problem our societies will have to face between now and the end of the century or probably beyond that; it is a climate warming toward which we are inexorably headed.

  CHAPTER 14

  A Warming with Multiple Consequences

  It is rather common, sometimes rightfully so, for our community to be criticized for being catastrophists when we broach aspects connected to the consequences of climate change. Alongside our knowledge of the climatic system and its evolution, that of the impacts that a warming would have has progressed greatly in the last twenty years. We now also rely largely on the 2007 IPCC Group II report, which is dedicated to the impacts of climate change and to our adaptation and vulnerability to it.1 Thanks to that synthesis, we will reveal the world toward which we risk evolving if nothing is done to limit greenhouse gas emissions. Before turning to the glaciers and polar regions, we will take a quick look at consequences on a global scale.

  A True Upheaval on a Global Scale

  Intuitively we expect that the consequences of climate change will increase as the temperature rises; they will also depend on the evolution of climatic extremes that contribute in an important way to the damage. This is indeed the case, as is seen at point 1 in table 14.1, which presents a synthesis of the main consequences of climate warming according to large sector: water, ecosystems, food, coastal areas, and health (Table 14.1). Thus the threshold of 1.5 to 2.5°C appears critical for the maintenance of biodiversity—greater warming leads to important changes in the structure and functioning of ecosystems—and in the ability of continental ecosystems to play their role of carbon pumps. In the ranks of particularly vulnerable ecosystems are the tundra, the boreal forest, ecosystems of mountain regions sensitive to warming, and those in the Mediterranean or certain forests in tropical regions as a result of the decrease in precipitation.

  Table 14.1

  Predictions regarding the impacts of climate change in various realms in function of the amount of warming.

  †Based on average rate of sea level rise of 4.2 mm/year from 2000-2080

  Source: IPCC, Climate Change 2007: Fourth Assessment Report (Cambridge: Cambridge University Press, 2007).

  Initially warming would not pose any problem vis-à-vis the potential for food production, which should increase if that warming remains locally inferior to a threshold of 1–3°C. But beyond 3°C agricultural productivity would decrease. In the low latitudes agriculture would also be affected because of a decrease in the availability of water resources, and agricultural production could be severely compromised in many African countries, reducing food security there even more and exacerbating malnutrition.

  The problem of water resources, which even without a modification in our climate is already critical in many regions, risks being seriously exacerbated by warming. Indeed, rain would be less abundant in already dry regions of the mid-latitudes and the tropics. Combined with greater evaporation, this would lead to a decrease of runoff by 10 to 30%. The decrease in water resources due to climate change would also affect the semi-arid zones in the Mediterranean basin, the western United States, South Africa, and northeast Brazil. The regions suffering from droughts would thus extend with impacts on many sectors; the IPCC report anticipates that in Africa in 2020, 75 to 220 million people will be exposed to a hydro-stress due to climate change, and in 2080 the surface of dry and semi-arid land will have increased from 5 to 8%. Inversely, it will rain more where there is already sufficient rain (10 to 40% more in the high latitudes and in certain humid tropical regions), with additional risks of flooding tied also to more intense precipitation, including in regions where the total amount of precipitation will diminish. It is possible that in 2080 as much as 20% of the world’s population will live in regions where the risk of flooding will be greater than it is today.

  Coastal zones are particularly at risk because of the average rise in sea level but also because of an increase in the severity and frequency of storms, resulting in an increase in coastal flooding, especially since in some cases there is an added increase in overflow from rivers that flow into the sea in those regions. One thinks first of all of the consequences on populations of small islands that are particularly vulnerable and on the much larger populations of the megadeltas in Asia from India to Southeast Asia. A sea-level rise of 40 centimeters would cause the number of people whose homes are flooded each year, in particular in India, Bangladesh, Vietnam, and China, to increase from 13 to 94 million. The same is true in Africa, especially the very populated deltas of the Nile and the Niger, but other regions such as Europe and Australia will be affected. The third IPCC report2 indicates that a rise of 40 centimeters would affect around 200 million more people, who would be forced to leave their communities; that number would be half if protections are put into place. In addition, in these regions there would be problems related to the erosion of the coasts, the salinity of water, and the fragility of certain ecosystems, mangroves, and humid zones.

  When we mention “climate refugees,”3 it is logical to turn to the regions that are potentially sensitive to a rise of a few dozen centimeters of elevation in sea level: Bangladesh, the Tuvalu Islands in the Pacific, the Maldives in the Indian Ocean, and the Halligen in the North Sea. But the threat of exceeding 40 centimeters between now and the end of the century is, as we have seen, far from negligible. And within a few centuries, we will be measuring in meters the cumulative effect, very slow but inevitable, of the dilatation of the ocean and the much more uncertain but highly threatening rise that might result from a partial melting of Greenland and even West Antarctica. When Susan Solomon, co-president of the scientific group, presented the results of the fourth report of the IPCC, she added a map showing what would happen to Florida if the sea rose six meters—or rather what would remain of Florida: not more than half, as all the coastal zones would be underwater. Al Gore used this same map in An Inconvenient Truth. Let us repeat: this could only happen within a few centuries, but the more greenhouse gas we emit in the next decades, the greater the risk that a situation of this type might occur. Four or five hundred years is far off, but it is on that scale of time that all these coastal cities with their inestimable architectural wealth that would then be impossible to protect were constructed. This long-term dimension of climate change should also give us pause.

  Another problem that is mentioned more and more vis-à-vis the ocean is that of the coral in warm seas; it is estimated that 30% or more has disappeared in the last twenty years due primarily to an increase in the sea surface temperature. Most corals could die of bleaching as soon as the average temperature becomes warmer by more than 1.5°C, with consequences that are not just aesthetic: coral is indispensable to the survival of very rich ecosystems, including countless other species, many of which have not even been inventoried yet, and consequently, in many regions of the planet, to the survival of local activities with socioeconomic implications, notably tourism and fishing. An increase in temperature is not the only threat to corals. We must also add the risk of an increase in intensity of tropical cyclones and the acidification of the oceans, which also threatens the coral reefs in the cold seas. This acidification, linked to the ocean’s absorption of a portion of the carbon dioxide emitted by human activity, has already been observed and shoul
d increase during the twenty-first century. Independently of the climatic role of CO2, this acidification is a problem, the consequences of which for the marine biosphere have been little studied.

  Warming will also have consequences for human health, including the risks mentioned already of malnutrition and those linked to the geographic modification of zones of influence of some vectors of infectious diseases or to a rise in cardiovascular illnesses resulting from an increase of ozone in the troposphere (itself influenced by climate change). Finally, events such as heat waves but also flooding, droughts, cyclones, and fires can cause death, illness, or injury. Of course, less rigorous winters in our regions can have positive consequences on the health of populations, but globally the negative aspects will dominate.

  No region will be spared from the adverse consequences of climate change, but some are a priori more vulnerable. We have already cited them: areas that are particularly sensitive to the sea level rise, small islands, and megadeltas in Asia and Africa. And the African continent, with its weak capacity for adaptation, is at risk of being affected by other impacts. Another vulnerable region, the Arctic, is also at great risk because of the ever-increasing speed of climate warming. But before looking at the polar regions, let’s turn to the mountain regions, which are also at the forefront of those at risk of being affected by climate warming.