Authors: Al Gore
Since the glaciers retreated at the end of the last Ice Age, not long before the first cities were built and the invention of writing preserved the memory of man, we have taken for granted the enduring and relatively stable pattern of jet streams and ocean currents, warm spells and cold snaps, rainy seasons and dry seasons, spring planting and fall harvesting, tadpoles and butterflies, and the other enduring natural phenomena that have characterized our world for almost ten millennia. Just as the proverbial fish doesn’t know it is in water—because it knows nothing
but
water—we have never known anything other than the planetary conditions that have given rise to the flourishing of humankind.
All of those who preceded us added their contributions to the elaborate legacy of the human enterprise bequeathed to us in our time. And each generation in turn has been sustained by gifts from nature itself: the pollination of crops and wild plants by insects and other animals, the natural purification of water by soils, and numerous other ecological benefits that modern economists call “ecosystem services.”
All of this and more we take for granted. All of this and more we are putting at risk. Very large human-caused changes in the long predictable climate pattern we have always known could so radically reorder the nature of nature that it is difficult for us to imagine the challenges our species would confront. When a fish is taken out of the water, it cannot survive. By the same token, if we completely disrupt the conditions on which our civilization is based—not just for a few years, but for many thousands of years—it too would be unlikely to survive in anything resembling its current form.
One of the many consequences of huge disruptions in the climate pattern we have always known would be a much higher risk of political instability. In fact, this risk is one of the principal reasons why military and national security experts in the United States have long expressed
more concern about global warming than most elected officials. In many
regions of the world, governance is already under tremendous stress with several failed states—Somalia, Yemen, and Zimbabwe, for example—creating difficult challenges for their regional neighbors. The increased stress that would accompany large alterations in climate patterns could push many other countries to the breaking point.
After a war game run by the National Defense University in the U.S. to simulate the geopolitical consequences of a mass migration of climate refugees from low-lying areas of Bangladesh, the head of the Bangladesh Institute of Peace and Security Studies, Major General A. N. M. Muniruzzaman, said, “By 2050, millions of displaced people will overwhelm not just our limited land and resources but
our government, our institutions and our borders.”
The few exceptions to the relative climate stability we have always enjoyed prove the rule. A recent study by David Zhang and others of the relationship between relatively small climate fluctuations in the past and civil conflict, published in the
Proceedings of the National Academy of Sciences
, reported, “Climate-driven economic downturn was the
direct cause of large-scale human crises in pre-industrial Europe and the northern hemisphere.” Indeed, our histories record the disruptive effects of comparatively small variations in the prevailing conditions in which we have thrived:
• The medieval warm period was connected to the disappearance of the Mayan civilization in
Central America and the temporary colonization of southern Greenland by farmers from Scandinavia;
• During the Little Ice Age, Eskimos wrapped in fur
paddled their kayaks to Scotland; farther south, millions died in a European famine centered in France;
• The huge downpours in fourteenth-century China triggered
a chain of events leading to the Black Death that wiped out one quarter of the population of Europe;
• The
unusually large eruption of the Tambora volcano in Indonesia in 1815 filled the Earth’s atmosphere with particulates and led to the “year without a summer” in 1816 that caused widespread crop failures around the world, a wave of revolutions in Europe, and mass migrations in many regions by people searching for food and warmth.
All of these events were rare extremes that nevertheless fell within the natural boundaries of variations consistent with the same overarching climate pattern we have always known. And as terrible as the resulting catastrophes were, they were mostly temporary and relatively short-lived. By contrast, the much larger climate disruptions we are now causing threaten to create a planetary emergency lasting for time periods beyond the scope of human imagination.
An estimated 25 percent of the CO
2
we put into the atmosphere this year will still be contributing to higher temperatures at least 10,000 years from now. If we force the melting of giant ice sheets in Antarctica and Greenland, they are not likely to return on a timescale that has any relevance whatsoever to our species.
Nine of the ten hottest years ever recorded since accurate measurements began in the 1880s
have occurred in the last ten years. And the extra heat energy is already disrupting millions of lives. Extreme and destructive weather events that used to occur infrequently are becoming both more common and more destructive. Sometimes described as “once in a thousand year events,” many bring with them enormous economic and human losses. And they are predicted to get much more common and much, much worse.
Among the recent examples: the epic
flooding in Pakistan that displaced 20 million people, further destabilizing a nuclear-armed country;
unprecedented heat waves in Europe in 2003 that killed 70,000 people, and in
Russia in 2010 that led to 55,000 deaths,
massive fires, and crop damage that pushed global food prices to record levels;
the flooding of northeastern Australia in 2011 covering an area the size of France and Germany combined;
the huge droughts in southern China and
southwestern North America in 2011; the even deeper drought in over half of the U.S. in 2012;
Superstorm Sandy in 2012, which devastated portions of New Jersey and New York City; multiple historic windstorms and downpours in many regions of the world.
The global water cycle—in which evaporation from the oceans falls as precipitation on the land and flows back to the oceans through streams that become rivers—is being radically intensified and accelerated by global warming. The warmer oceans allow significantly
more
water vapor to evaporate into the sky. More important still is the fact that
warmer air
holds
more water vapor. If you take a cold shower, the mirror above your sink won’t steam up, but if you take a hot shower it may. With so much
more water in the atmosphere, there is also more energy fueling the size and destructive power of the storms.
Scientists have already measured an extra 4 percent of water vapor in the atmosphere above the oceans, and even though 4 percent doesn’t sound like much, it
has a large effect on the hydrological cycle. Because storms often reach out up to 2,000 kilometers, they gather water vapor from a large area of the sky and
funnel it inward into the regions where storm conditions trigger a downpour.
By analogy, if you pull the drain in a bathtub filled with water, the water rushing down the drain does not come just from the part of the tub directly over the drain, it comes from the whole tub. In the same way, the great basins of water vapor in the sky are funneled to the “drains” opened above the land by rainstorms and snowstorms. When these basins are filled with much more water vapor than in the past, the downpours are more intense. The bigger downpours lead to bigger floods. The floods rush across the land, eroding the soil. And less of the water seeps
down through the soil to recharge the underground aquifers.
Climate change is also driving desertification by altering atmospheric circulation patterns and drying out the land and vegetation. The same extra heat that evaporates more water vapor from the oceans also speeds up the evaporation of soil moisture—leading to longer, deeper, and more widespread droughts. Since the refilling of the atmospheric “basins” of moisture still takes a lot of time, many areas of the world are experiencing longer periods without rain in between the intense downpours. These longer periods of hotter temperatures in between precipitation events lead to more widespread and even deeper droughts. Once it is devoid of vegetation, the surface begins to absorb more heat. When the soil moisture is gone, the ground is baked,
local temperatures rise higher still, and the
topsoil becomes more vulnerable to wind erosion.
The parching and desiccation of the most highly productive agricultural breadbaskets of the world portend a food crisis in the future that could have humanitarian and political consequences too horrific to imagine. A top official with the International Maize and Wheat Improvement Center in Mexico, Marianne Bänziger, said, “There’s just such a tremendous disconnect, with people
not understanding the highly dangerous situation we are in.”
The consequences for food production and water availability are already
extremely harsh. In 2012, largely because of climate-related events that reduced crop yields, the world experienced a
record one-month price increase for food, with additional
record price hikes predicted for 2013.
More than 65 percent of the U.S. suffered from drought conditions in 2012. In addition to the impacts on industrial agriculture in North America, Russia, Ukraine, Australia, and Argentina, subsistence agriculture has been hit hard in many tropical and subtropical countries by large alterations in the timing, duration, and magnitude of precipitation patterns due to global warming’s disruption of the hydrological cycle. As a rice farmer in northeastern India, Ram Khatri Yadav, told Justin Gillis of
The New York Times
, “It will not rain in the rainy season,
but it will rain in the non-rainy season. The cold season is also shrinking.”
Along with the impacts discussed in
Chapter 4
—including the depletion of topsoil and groundwater and the competition that farmers face for land and water from fast-growing cities, industry, and biofuels production—the rising temperatures threaten many food crops with catastrophic yield reductions from heat stress alone. Stanford researcher David Lobell, who recently completed a study of the impact of temperature increases on crop yields with Columbia researcher Wolfram Schlenker, said recently, “I think there’s been
an under-recognition of just how sensitive crops are to heat, and how fast heat exposure is increasing.”
In the last three years, new scientific research has overturned the long-held view by agricultural experts that, in the absence of drought, food crops would be relatively unharmed by rising temperatures. Many had thought that the higher CO
2
levels might fertilize plant growth by enough to counterbalance any yield decreases due to heat stress. But unfortunately, intensive research designed to confirm that hypothesis now shows that food crop yields are likely to decline much more rapidly with higher temperatures than previously believed, and
that the CO
2
fertilization effect is much smaller than predicted. Moreover,
weeds appear to benefit from extra CO
2
much more than food crops.
As temperatures continue to increase, corn (maize)—the most widely grown crop in the world—appears to be the most vulnerable to heat stress. Corn yields start to decrease at a range of temperatures the Earth is already experiencing regularly in summer months. Every day during the growing season (roughly from the beginning of March to the end of August) that temperatures climb
above a threshold of 84 degrees F (29 degrees C), corn yields drop by 0.7 percent.
As temperatures grow hotter than 84 degrees F, the
yield declines plummet further with every degree added. If temperatures in the United States are allowed to rise as much as is now projected as a result of global warming, by the end of this century corn yields could fall by as much as a third from heat stress alone, with the impact of worsening droughts and the
disruption of precipitation patterns taking a larger toll still. Soybeans have a higher threshold for heat stress than corn (86 F/30 degrees C), but the
same accelerated drops in yields begin when temperatures reach and exceed that level.
The warm season is longer;
spring is arriving about a week earlier (and fall about a week later) in both the northern and southern hemispheres. Moreover, the decreasing size of mountain snowpacks and glaciers is adding to the worsening shortages of water for agriculture in several important regions, bringing bigger spring floods earlier in the year and
depriving these regions of water during the hot summer months when it is most needed. And while the focus is normally on daytime high temperatures,
nighttime temperatures are at least as important. Both the computer models and consistent observations confirm that global warming
increases nighttime temperatures more than daytime temperatures.
According to some studies, each degree increase in nighttime temperatures
corresponds with a linear decrease in wheat yields. A large global review of the impact of climate change on crop yields between 1980 and 2010 showed that worldwide wheat production
fell due to climate-related factors by 5.5 percent. A researcher at the International Rice Institute in the Philippines, Shaobing Peng, published findings in the
Proceedings of the National Academy of Sciences
showing that yields of rice
declined by 10 percent with each one degree Celsius increase in nighttime temperatures during the dry part of the growing season, even though there were no significant drops in yield associated with increasing maximum temperatures during the daytime.
Crop diseases and pests are also increasing with global warming. Higher temperatures are leading to a dramatic expansion in the range of insects harmful to food crops, sending them farther north in the northern hemisphere and farther south in the southern hemisphere, and into higher altitudes. A team of crop scientists publishing in
Environmental Research Letters
wrote, “These range expansions could have substantial economic impacts through increased seed and insecticide costs, decreased yields, and the
downstream effects of changes in crop yield variability.”