by Al Gore
Ironically, the historic North American drought of 2012 reduced the flow of water from the Mississippi into the Gulf of Mexico so much—and the nitrogen, phosphorus, and other chemicals normally carried with the water—that the large dead zone spreading from the mouth of the Mississippi began to temporarily clear up.
A conference of ocean experts meeting at Oxford University in the summer of 2011 reported their conclusions as a group: “This examination of synergistic threats leads to the conclusion that we have underestimated the overall risks and that the whole of marine degradation is greater than the sum of its parts, and that degradation is now happening at a faster rate than predicted.… When we added it all up, it was clear that we are in a situation that could lead to major extinctions of organisms in the oceans.… It is clear that the traditional economic and consumer values that formerly served society well, when coupled with current rates of population increase, are not sustainable.”
MITIGATION VERSUS ADAPTATION
For at least three decades, there has been a debate in the international community about the relative importance of reducing greenhouse gas emissions to mitigate the climate crisis compared to strategies for adapting to the climate crisis. Some of those who try to minimize the significance of global warming and oppose most of the policies that would mitigate it often speak of adaptation as a substitute for mitigation.
They promote the idea that since humankind has adapted to every environmental niche on the planet, there is no reason to believe that we shouldn’t merely accept the consequences of global warming and get busy adapting to them. For example, the CEO of ExxonMobil, Rex Tillerson, recently said in an exchange provoked by longtime activist David Fenton, “We have spent our entire existence adapting, OK? So we will adapt to this.”
FOR MY OWN part, I used to argue many years ago that resources and effort put into adaptation would divert attention from the all-out push that is necessary to mitigate global warming and quickly build the political will to sharply reduce emissions of global warming pollution. I was wrong—not wrong that deniers would propose adaptation as an alternative to mitigation, but wrong in not immediately grasping the moral imperative of pursuing both policies simultaneously, in spite of the difficulty that poses.
There are two powerful truths that must inform this global discussion about adaptation and mitigation: first, the consequences that are already occurring, let alone those that are already built into the climate system, are particularly devastating to low-income developing countries. Infrastructure repair budgets have already skyrocketed in countries where roads, bridges, and utility systems have been severely damaged by extreme downpours and resulting floods and mud slides. Others have been devastated by the climate-related droughts.
And the disruptions of subsistence agriculture by both the floods and the droughts have led to skyrocketing expenditures for food imports in many developing countries. Also, as noted earlier, some low-lying nations are also already struggling to relocate refugees from coastal areas affected by the early stages of sea level rise, while other nations are struggling to integrate arriving refugee groups into already fast-growing populations.
Since these and other developments will not only continue but worsen, the world does indeed have a moral duty and practical economic necessity to assist these nations with adaptation. Disturbingly, the world has yet to fully realize the effects of the global warming pollution already in the atmosphere. Even if we drastically reduce our emissions today, another degree Fahrenheit of warming is already “in the pipeline” and will manifest itself in the coming years. In other words, so many harmful changes are already built into the climate system by the enormous increase in the emissions, and particularly the increased concentration, of greenhouse gases in the atmosphere that adaptation is absolutely essential—even as we continue building the global political consensus needed to prevent the worst consequences from occurring. We have no choice but to pursue both sets of policies simultaneously.
But the second truth that must inform this debate is still by all odds the most powerful imperative: unless we quickly start reducing global warming pollution, the consequences will be so devastating that adaptation will ultimately prove to be impossible in most regions of the world. For example, higher greenhouse gas emissions are already beginning to cause large-scale changes in atmospheric circulation patterns and are predicted to bring almost unimaginably deep and prolonged drought conditions to a wide swath of highly populated and agriculturally productive regions, including all of Southern and south-central Europe, the Balkans, Turkey, the southern cone of Africa, much of Patagonia, the populated southeastern portion of Australia, the American Southwest and a large portion of the upper Midwest, most of Mexico and Central America, Venezuela and much of the northern Amazon Basin, and significant portions of Central Asia and China.
The scientific reasoning behind this devastating scenario requires some explanation. The basic nature of the global climate system, when viewed holistically, is that it serves as an engine for redistributing heat energy: from the equator toward the poles, between the oceans and the land, and from the lower atmosphere to the upper atmosphere and back again. The large increase in heat energy trapped in the lower atmosphere means—to state the obvious—that the atmospheric system is becoming more energetic.
In the northern hemisphere, this climate engine transfers heat energy from south to north in the Gulf Stream—which is the best known component of the so-called ocean conveyor belt, a Möbius Strip–like loop that connects all of the world’s oceans. Other components include deep currents that travel along the bottom of the ocean, redistributing cold water from the poles back to the equator, where they return to the ocean surface. The largest of these are the Antarctic circumpolar current, which travels around the Antarctic continent and feeds the shallower Humboldt current, which flows from the Southern Ocean northward along the west coast of South America and upwells—laden with nutrients—to nourish the rich concentration of sea life off the coast of Peru; and, less well known, the deep cold current that travels north to south from an area of the North Atlantic in the vicinity of southern Greenland, underneath the Gulf Stream, back to the tropical Atlantic waters.
Energy is also redistributed by cyclones, by thunderstorms, and by multiyear patterns such as the alternating El Niño/La Niña phenomenon (known to scientists as the ENSO, or El Niño/Southern Oscillation). Moreover, all of these energy transfers are affected by the Coriolis effect, which is driven by the spinning of the Earth on its axis, from west to east.
THE HADLEY CELLS
Until recently, relatively less attention has been paid to the relationship between global warming and the atmospheric patterns that move energy vertically up and down in the atmosphere. The so-called Hadley cells spanning the tropics and subtropics are enormous barrel-shaped loops of wind currents that circle the planet on both sides of the equator, like giant pipelines through which the trade winds flow from east to west.
Warm and moist wind currents rise from the ground vertically into the sky in both of these cells at the edge of each respective loop that is adjacent to the equator. When their ascent reaches the top of the troposphere (the top of the lower atmosphere, approximately ten miles high in the tropics), each loop turns poleward—which means northward in the northern hemisphere cell and southward in the other. By the time these currents reach the top of the sky, much of the moisture they carried upward has fallen back to the ground as rain in the tropics.
At the apex of its ascent, each of these air currents starts flowing poleward along the top of the troposphere and travels about 2,000 miles (approximately 30 degrees of latitude), until it has discharged most of its heat. Then it descends vertically as a cooler and much drier downdraft. When each loop reaches the surface again, it turns back toward the equator, recharging itself with heat and moisture as it travels across the surface of the Earth. As it returns to the equator, it completes its loop and repeats the cycle by rising vertically once again,
laden once more with heat and water vapor.
As a result of the dry downdrafts of the Hadley cells, the areas of the Earth 30 degrees north and 30 degrees south of the equator are highly vulnerable to desertification. Most of the driest regions of the Earth, including the largest of the planet’s deserts, the Sahara, are located under these dry downdrafts. (Other factors contributing to the location of deserts include the “rain shadows” of mountain ranges—the areas downwind from mountain peaks—because the prevailing winds rise when they hit the windward side of the mountains and lose their moisture before descending as dry downdrafts on the leeward side. In addition, the location of deserts is influenced by what geographers call continentality—which means that the areas in the middle of large continents typically get much less moisture because they are farther away from the oceans.) But on a global basis, the most powerful desertifying factor is the downdraft of the Hadley cells.
The problem—which climate scientists have long predicted with computer models and are now observing in the real world—is that the massive warming of the atmosphere is changing the locations of these great global downdrafts, moving them farther away from the equator and toward the poles, thus widening the subtropics and intensifying their aridity. Indeed, in the northern hemisphere, the downdraft has already moved northward by as much as 3 degrees latitude—approximately 210 miles—although measurements are still imprecise. The downdraft of the Hadley cell south of the equator has also moved poleward.
There are several theories for why global warming is causing a shift in the Hadley cells, none of which are as yet confirmed. The solar heating of the lower atmosphere in the tropics and subtropics is much greater than anywhere else on the planet for obvious reasons: the sunlight strikes the Earth at a more direct angle all year round. On a percentage basis, surface temperatures are rising faster in the higher latitudes because the melting of ice and snow is dramatically changing the reflectivity of the surface,‡ thereby increasing the absorption of heat energy. This means, among other things, that the difference in average temperatures between the tropics and the polar regions is diminishing over time—which also has consequences for the climate balance.
However, the much larger amounts of overall heat energy absorbed in the mid-latitudes is still much greater, and causes the warmer (and thus less dense) air in the tropics to rise higher. As a result, the extra heat raises the top of the troposphere, where the wind currents deflect at a right angle from their vertical trajectory and begin traveling poleward.
The widening of the Hadley cells moves the downstroke of its circular path farther north in the northern hemisphere and farther south in the southern hemisphere. As with many of the realities connected to global warming, while this one sounds technical and can seem abstract, the real consequences for real people, animals, and plants are extremely severe.
For the areas now subjected to this downdraft, it’s a bit like being under a giant hairdryer in the sky. The results include not just more frequent and more severe droughts, but consistent drought patterns likely leading to desertification in many of the countries in the line of fire. Moreover, most of the areas affected, like Southern Europe, Australia, Southern Africa, the American Southwest, and Mexico—are already on the edge of persistent water shortages anyway.
The word “desert,” by the way, is derived from the relationship of people to the land involved: deserts are deserted by people. Consider the significance of Greece, Italy, and the Fertile Crescent—the cradles of Western civilization—turned into deserts by human alteration of the same natural climate feature that created the Sahara Desert beginning 7,300 years ago.
The jet stream that controls the location of storm tracks in most of North America and Eurasia is also being affected by the impact of global warming on atmospheric circulation patterns and the unusually chaotic weather patterns in these latitudes in recent years. There are actually two jet streams in both hemispheres—a subtropical jet stream flowing from east to west along the poleward margin of the barrel loop of the Hadley cells (the trade winds), and the so-called polar jet stream—which flows from west to east on the poleward side of a second set of barrel loop atmospheric currents known as the Ferrel cells.
The location of the northern polar jet stream (which North Americans and north Eurasians typically call the jet stream) is determined in part by the wall of cold air extending southward from the Arctic Circle. But in recent years, the melting of the Arctic ice cap has led to so much extra heat absorbed there that the northern boundary of the jet stream flowing across North America and Eurasia appears to have been profoundly and radically dislocated—changing storm tracks, pulling cold Arctic air southward in winter, and disrupting precipitation patterns.
All of these energy transfer mechanisms—the wind and ocean currents, storms and cyclones, and atmospheric cells—define the shape and design of the Earth’s climate pattern that has remained relatively stable and constant since shortly before the Agricultural Revolution began. Yet global warming is changing all of the energy balances that have given definition to this climate envelope, and is both intensifying and changing the locations of the weather phenomena we are used to.
Some of these balances are being changed to such a degree that scientists worry that they could be pushed far enough out of the pattern we have always known that they could flip into a very new pattern that would produce weather phenomena with intensity, distribution, and timing that are completely unfamiliar to us and inconsistent with the assumptions upon which we have built our civilization.
By way of illustration, take a leather belt and hold one end in either hand; push your hands together until a loop forms sticking upward. As you move your hands and change the inflection of your wrists, the shape of the belt loop will vary but it will remain in the same basic shape. But if you inflect your wrists a little more, it will suddenly flip into a new basic pattern with the loop pointing downward instead of upward. The variations in climate that we have always known, large as they are, are like the variations in the belt loop pointing upward. There would still be similar variations if the loop pointed downward, but if we push the boundary conditions of the loops to a point that causes it to adopt an entirely new pattern, the consequences for our climate would be extreme indeed.
We have already been confronted by unwelcome surprises in our experimentation with changing the chemical composition of the Earth’s atmosphere. The sudden appearance of a continent-sized stratospheric ozone hole above Antarctica in the 1980s raised the specter of a deadly threat to many forms of life on Earth, because it allowed powerful ultraviolet radiation normally blocked by the stratospheric ozone layer to reach the surface. And except for the fact that the progressive destruction of the stratospheric ozone layer was arrested, scientists say it would have spread to the stratosphere above highly populated areas.
Even though the Antarctic ozone hole lasted each year for only approximately two months, it had already begun to produce a slight thinning of ozone in the stratosphere surrounding the entire planet. Scientists warned at the time that if the concentrations of chemicals causing ozone destruction continued to build, this dangerous thinning process would accelerate, and an even more dangerous ozone hole above the Arctic might form on a more regular basis.
Luckily, almost immediately after this frightening discovery, President Ronald Reagan and Prime Minister Margaret Thatcher helped to organize a global conference in 1987 to negotiate and quickly approve a treaty (the Montreal Protocol) that required the phasing out of the group of industrial chemicals—including the best-known, chlorofluorocarbons (CFCs)—that two scientists, Sherwood Roland and Mario Molina, had proven conclusively in 1974 were interacting with the unique atmospheric conditions in the cold stratosphere above Antarctica to produce this progressive destruction of the protective ozone layer that shields humans and other life-forms from deadly ultraviolet radiation.
EVEN THOUGH THE Montreal Protocol has been a historic success, it is important to understand the pr
ecise mechanism through which these chemicals led to the stratospheric ozone hole in the first place—because of new threats to the ozone layer from global warming. To begin with, there is a third and final set of barrel loop atmospheric cells at both the North Pole and the South Pole, called polar cells, within which the winds form a vortex around each pole.
The south polar vortex is much stronger and more coherent, especially in the austral winter, because Antarctica is land surrounded by ocean—whereas the Arctic is ocean surrounded by land—and while the Arctic Ocean is covered, at least in winter, by a thin layer of ice only several feet thick, Antarctica is covered year-round by two kilometers of ice. That also makes it the continent with the highest average altitude, which means it is closer to the top of the sky and radiates the reflected sunlight back into space more powerfully. Consequently, the air above Antarctica is much colder than anywhere else on Earth, which produces an unusually high concentration of ice crystals in the stratosphere there.
The tight vortex formed by the Antarctic circumpolar wind currents during winter holds the CFCs and ice crystals in place above the continent, almost like a bowl. And it is on the surface of these ice crystals that the CFCs react with stratospheric ozone. One other crucial ingredient must be present before the chemical reaction that destroys the ozone starts taking place: a little bit of sunlight.
At the end of the southern hemisphere winter, around the middle of September, when the first rays of sunlight strike the ice crystals held in this “bowl,” the chemical reaction is ignited. Then it quickly spreads, destroying virtually all of the stratospheric ozone inside the bowl. As the atmosphere absorbs more heat, the vortex formed by the wind currents weakens and the bowl breaks up, signaling the end of the ozone hole for that year. Some large blobs of ozone-free air sometimes move northward, like the blobs in an old lava lamp from the 1960s—exposing populated areas in the southern hemisphere like Australia and Patagonia to high levels of ultraviolet radiation when air with low concentrations of ozone is no longer able to provide a screen for those at the surface.
