Which impact of anthropogenic global warming will harm the most people in the coming decades? I believe that the answer is extended or permanent drought over large parts of currently habitable or arable land — a drastic change in climate that will threaten food security and may be irreversible over centuries.
A basic prediction of climate science is that many parts of the world will experience longer and deeper droughts, thanks to the synergistic effects of drying, warming and the melting of snow and ice.
Precipitation patterns are expected to shift, expanding the dry subtropics. What precipitation there is will probably come in extreme deluges, resulting in runoff rather than drought alleviation. Warming causes greater evaporation and, once the ground is dry, the Sun’s energy goes into baking the soil, leading to a further increase in air temp- erature.
That is why, for instance, so many temperature records were set for the United States in the 1930s Dust Bowl; and why, in 2011, drought-stricken Texas saw the hottest summer ever recorded for a US state. Finally, many regions are expected to see earlier snowmelt, so less water will be stored on mountain tops for the summer dry season. Added to natural climatic variation, such as the El Niño–La Niña cycle, these factors will intensify seasonal or decade-long droughts. Although the models don’t all agree on the specifics, the overall drying trends are clear.
I used to call the confluence of these processes ‘desertification’ on my blog, ClimateProgress.org, until some readers pointed out that many deserts are high in biodiversity, which isn’t where we’re heading. ‘Dust- bowlification’ is perhaps a more accurate and vivid term, particularly for Americans — many of whom still believe that climate change will only affect far-away places in far-distant times.
Prolonged drought will strike around the globe, but it is surprising to many that it would hit the US heartland so strongly and so soon.
The coming droughts ought to be a major driver — if not the major driver — of climate policies. Yet few policy-makers and journalists seem to be aware of dust-bowlification and its potentially devastating impact on food security. That’s partly understandable, because much of the key research cited in this article post-dates the 2007 Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). Raising public awareness of, and scientific focus on, the likelihood of severe effects of drought is the first step in prompting action.
I first heard of the risks in a 2005 talk by climatologist Jonathan Overpeck of the Uni- versity of Arizona in Tucson. He pointed to emerging evidence that temperature and annual precipitation were heading in oppo- site directions over many regions and raised the question of whether we are at the “dawn of the super-interglacial drought”.
The idea wasn’t new. As far back as 1990, scientists at NASA’s Goddard Institute for Space Studies in New York projected that severe to extreme drought in the United States, then occurring every 20 years or so, could become an every-other-year phenom- enon by mid-century.
Events are starting to bear out these worrying predictions. Snowpack reduction, early snowmelt and a decrease in dry-season river flow in the American West, forecast more than two decades ago, have now been measured. In much of the northern Rockies, the peak of the annual stream runoff is up to three or four weeks earlier than it was half a century ago. Heat and drought — coupled with the greater impact of destruc- tive species, such as bark beetles, aided by warming — have increased forest die-off and the risk of wildfire.
The palaeoclimate record dating back to the medieval period reveals droughts lasting many decades. But the extreme droughts that the United States faces this century will be far hotter than the worst of those: recent decades have been warmer than the driest decade of the worst drought in the past 1,200 years.
And much warmer conditions are pro- jected. According to a 2009 report of the US Global Change Research Program, warming over mid-latitude land masses, such as the continental United States, is predicted to be higher than the forecast average global warming: much of the inland United States faces a rise of between 5 °C and 6 °C on the current emissions path (that is, ‘business as usual’) by the century’s end, with a substantial fraction of that warming occurring by mid-century.
A 2007 analysis of 19 climate projections estimated that levels of aridity comparable to those in the Dust Bowl could stretch from Kansas to California by mid-century. To make matters worse, the regions at risk of reduced water supply, such as Nevada, have seen a massive population boom in the past decade. Overuse of water in these areas has long been rife, depleting groundwater stores.
Of course, the United States is not alone in facing such problems. Since 1950, the global percentage of dry areas has increased by about 1.74% of global land area per decade. Recent studies have projected ‘extreme drought’ conditions by mid-century over some of the most populated areas on Earth—southern Europe, south-east Asia, Brazil, the US Southwest, and large parts of Australia and Africa. These dust-bowl conditions are projected to worsen for many decades and be “largely irreversible for 1,000 years after emissions stopped”….
In the past six years, the Amazon has seen two droughts of the sort expected once in 100 years, each of which may have released as much carbon dioxide from vegetation die-off as the United States emits from fossil-fuel combustion in a year. More frequent wildfires also threaten to increase carbon emissions
The PDSI [Palmer Drought Severity Index] in the Great Plains during the Dust Bowl apparently spiked very briefly to -6, but otherwise rarely exceeded -3 for the decade (see here).
A very large population will be severely affected in the coming decades over the whole United States, southern Europe, Southeast Asia, Brazil, Chile, Australia, and most of Africa.
The National Center for Atmospheric Research notes “By the end of the century, many populated areas, including parts of the United States, could face readings in the range of -8 to -10, and much of the Mediterranean could fall to -15 to -20. Such readings would be almost unprecedented.”
What will happen to global food security if dust-bowl conditions become the norm for both food-importing and food- exporting countries? Extreme, widespread droughts will be happening at the same time as sea level rise and salt-water intrusion threaten some of the richest agricultural deltas in the world, such as those of the Nile and the Ganges. Meanwhile, ocean acidification, warming and overfishing may severely deplete the food available from the sea….
Human adaptation to prolonged, extreme drought is difficult or impossible. Historically, the primary adaptation to dust-bowlification has been abandonment; the very word ‘desert’ comes from the Latin desertum for ‘an abandoned place’. During the relatively short-lived US Dust-Bowl era, hundreds of thousands of families fled the region. We need to plan how the world will deal with drought-spurred migrations (see page 447) and steadily growing areas of non- arable land in the heart of densely populated countries and global bread-baskets.
Feeding some 9 billion people by mid-century in the face of a rapidly worsening climate may well be the greatest challenge the human race has ever faced.
http://thinkprogress.org/climate/2008/06/19/202806/nature-publishes-my-climate-analysis-and-solution/
Some may believe that stabilizing atmospheric carbon dioxide concentrations below 450 p.p.m. is so difficult that we should seek to stabilize them at 550 p.p.m. or higher. But from a policy perspective, stabilizing at 550 p.p.m. is not much easier to achieve than levelling off at 450 p.p.m. — it still requires employing the vast majority of the wedges described here in under five decades, starting very soon. And yet the scientific evidence suggests that reaching 550 p.p.m. could have much graver consequences, for example destroying a large fraction of the permafrost, which houses a third of the carbon stored in soils globally. Much of this carbon would be released in the form of methane, a far more potent greenhouse gas than carbon dioxide, and could thus trigger more rapid climate change. Delay therefore risks crossing climate thresholds that would make efforts at emissions reduction far harder, if not almost impossible.
In fact, such is the urgent need to reverse emissions trends by deploying a multitude of low-carbon technologies that we must rely on technologies that either are already commercial or will very shortly be so. Fortunately, venture capitalists and public companies have begun to inject many billions of dollars into the development and short-term commercialization of most plausible low-carbon technologies. Governments should now focus their R&D spending on a longer-term eff ort aimed at a new generation of technologies for the emissions reduction eff ort aft er 2040, but the notion that we need a Manhattan Project or Apollo programme for technology development is mistaken. Instead, what is urgently needed is an effort of that scale focused on the deployment of technology.
http://thinkprogress.org/climate/2008/04/26/202588/is-450-ppm-or-less-politically-possible-part-0-the-alternative-is-humanitys-self-destruction/
The idea of stabilizing at, say, 550 or 650 ppm, widely held a decade ago, is becoming increasingly implausible given the likelihood that major carbon cycle feedbacks would go into overdrive, swiftly taking the planet to 800 ppm or more. In particular, the top 11 feet of the tundra would probably not survive 550 ppm (a point I will be blogging about soon) and two other key carbon sinks — land-based vegetation and the oceans — already appear to be saturating. That said, even if stabilizing at 550 ppm were possible, it would probably bring catastrophic impacts and in any case requires implementing some 10 wedges starting now.
At 800 to 1000 ppm, the world faces multiple miseries, including:
-Sea level rise of 80 feet to 250 feet at a rate of 6 inches a decade (or more).
-Desertification of one third the planet and drought over half the planet, plus the loss of all inland glaciers.
-More than 70% of all species going extinct, plus extreme ocean acidification.
Imagine sea level rise of nearly 20 inches a decade lasting centuries — a trend perhaps interrupted occasionally by large chunks of the West Antarctic ice sheet disintegrating, causing huge sea level jumps in a span of a few years. And imagine that by 2100, we lose all the inland glaciers, which Are currently the primary water supply for more than a billion people. Now imagine what future generations will think of us if we let it happen.
A year ago Science published research that “predicted a permanent drought by 2050 throughout the Southwest” — levels of aridity comparable to the 1930s Dust Bowl would stretch from Kansas to California. And they were only looking at a 720 ppm case! The Dust Bowl was a sustained decrease in soil moisture of about 15% (“which is calculated by subtracting evaporation from precipitation”).
Even the one-third desertification of the planet by 2100 scenario by the Hadley Center is only based on 850 ppm (in 2100). Princeton has done an analysis on “Century-scale change in water availability: CO2-quadrupling experiment,” which is to say 1100 ppm. The grim result: Most of the South and Southwest ultimately sees a 20% to 50% (!) decline in soil moisture.
You may be interested in how fast we can hit 1000 ppm. The Hadley Center has one of the few models that incorporates many of the major carbon cycle feedbacks. In a 2003 Geophysical Research Letters paper, “Strong carbon cycle feedbacks in a climate model with interactive CO2 and sulphate aerosols,” the Hadley Center, the U.K.’s official center for climate change research, finds that the world would hit 1000 ppm in 2100 even in a scenario that, absent those feedbacks, we would only have hit 700 ppm in 2100. I would note that the Hadley Center, though more inclusive of carbon cycle feedbacks than most other models, still does not model any feedbacks from the melting of the tundra even though it is probably the most serious of those amplifying feedbacks.
Clearly, 800 to 1000 ppm would be ruinous to the nation and the world, creating unimaginable suffering and misery for billions and billions of people for centuries to come. No one who believes in science and cares about humanity can possibly believe that adaptation is a more rational or moral policy than focusing 99% of our climate efforts on staying far, far below 800 ppm and far away from the tipping points in the carbon cycle.
And that means current CO2 levels are already too high. And that means immediate action is required. So our choice is really to stay below 450 ppm or risk self-destruction.
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