Climate

Unchecked Warming To Dust-Bowlify Southwest, Central Plains, Amazon, Europe For Centuries

CREDIT: AP Photo/Rich Pedroncelli

A warning buoy sits on the dry, cracked bed of Lake Mendocino near Ukiah, Calif. California's ongoing drought was one of the most expensive extreme weather events of 2014.

The unprecedented drought in California will become commonplace for the Southwest, Central Plains, and much of the currently inhabited and arable land around the world in the second half of the century — if humanity stays anywhere near our current path of carbon pollution emissions. Several recent studies spell this out in great detail.

These latest studies confirm a large and growing body of scientific literature that dates back to a 1990 (!) NASA analysis, “Potential evapotranspiration and the likelihood of future drought.”

I spoke to Dr. Benjamin Cook of Columbia, a top drought expert and the lead author of the recent study, “Global warming and 21st century drying.” I first wrote about his work in my post “Climate Change Drying Out Southwest Now, With Worse To Come For A Third Of The Planet.”

Cook warns we are headed into a “fundamental shift in Western hydro-climate.” This drying includes the Central Plains, one of the breadbaskets of the world. Given how rapidly growing the population of the West is, I asked him if there would be enough water for everyone there. He said “we can do it,” but only “if you take agriculture out of the equation.” Ouch!

Cook says his findings match those of the National Center for Atmospheric Research (NCAR). You may recall that an under-reported, 2012 NCAR study by Aiguo Dai “strengthened the case” that, unless we reverse emissions trends soon, we risk having a situation by the end of the century where “most of southern Europe and about half of the United States is gripped by extreme drought” a great deal of the time. Dai said the drying effect of carbon pollution would very likely overwhelm natural variability in the coming decades, warning “the U.S. may never again return to the relatively wet conditions experienced from 1977 to 1999.”

Nature-Dust-Bowl-smallI called this permanent warming and drying, “Dust-Bowlification,” in a 2011 Nature article reviewing the literature, “The Next Dust Bowl.” I used that term simply because the 1930s Dust Bowl was the best analogy to what’s coming. The U.S. Geological Survey does project it will get dustier, but we don’t know yet whether it will get as dusty as it did in the 1930s when deeply flawed agricultural practices worsened the problem.

We do know it will get much, much hotter than the 1930s Dust Bowl. And that the droughts will last much longer than one decade. A study last month found that by failing to curb carbon pollution, humans are dramatically increasing the chances of multi-decade megadroughts that in the past have overturned entire civilizations.

Drought conditions are driven by more than precipitation changes. Indeed, a standard measure of long-term drought developed in 1960s, the Palmer Drought Severity Index (PDSI), measures dryness using “temperature and precipitation data to calculate water supply and demand” and “incorporates soil moisture.”

The whole point of NASA’s 1990 analysis was to examine the impact of warming-driven evaporation on soil moisture and hence on drought. Over the past quarter century, climate scientists have improved their models and refined the areas projected to dry out from a drop in precipitation and/or an increase in evaporation in a warming-driven climate.

The study by Dr. Cohen and his colleagues examined what the “new normal” PDSI would be around the world for the period 2080-2099 — in the business-as-usual warming scenario (i.e. humanity keeps doing very little to combat climate change).

This chart shows their grim results, where PDSI-ALL is what their analysis projects for the future. PDSI-PRE is how the world would look in the future if the only CO2-driven impact on droughts were reduced PREcipitation, and PDSI-PET is how the world would look in the future if the only CO2-driven impact on droughts were reduced PET (potential evapotranspiration):

PDSI

Multi-model mean PDSI-ALL, PDSI-PRE, and PDSI-PET for 2080-2099 in business-as-usual warming. Cross-hatching indicates cells where the Palmer Drought Severity Index anomalies exceed -1 or +1 for at least 12 of the 15 models (80%). Figure shows that PET (potential evapotranspiration) drives many regions into drought that otherwise would still receive adequate precipitation.

If anything like these projections come true — and as noted they are consistent with virtually all of the recent published literature — then large part of the currently populated and arable land around the world will be laid waste. And that will be “largely irreversible for 1,000 years after emissions stop,” as a NOAA-led study explained in 2009.

With such a ruined climate, it would be unimaginably challenging to feed even the current population of 7 billion, let alone the 10 billion people now forecast for the second half of the century. Obviously it would be beyond the immoral for us to let anything close to this happen.

Let me dive further into what this vitally important but complicated graphic means for humanity. Again the top figure, PDSI-ALL, is the new normal we are on track for in the 2080s and 2090s. The crosshatched parts are where at least 80 percent of the models agree.

Here is how the PDSI numbers translate into drought conditions:

-1.0 to -1.99 = mild drought
-2.0 to -2.99 = moderate drought
-3.0 to -3.99 = severe drought
-4.0 to -4.99 = extreme drought
-5.0 or less = exceptional drought

If we look at the U.S. Drought Monitor map of California (top of this post), over 95 percent of California has been in severe drought (PDSI of -3 or worse) for months, and 84 percent has been for over a year.

Here’s one other key point of comparison: In the Great Plains during the Dust Bowl, the PDSI apparently spiked very briefly to -6, but otherwise rarely exceeded -3 for the decade (see here).

So what we are now knowingly risking is putting the U.S. Southwest and Central Plains breadbasket into a new climate where the “normal” is moderate drought and even in places severe drought! Obviously decades comparable to the Dust Bowl (but much hotter) will happen routinely. The new normal for the soil of most of the rest of the country will not be much moister — and what precipitation does occur will increasingly be in the form of superstorms and deluges.

The same new normal will be found over Iraq and Syria and much of the Mideast. What could go wrong there?

The same new normal will be found in the breakbasket of China, and some of the most heavily populated areas of Australia, Africa, and South America.

The normal climate of the Amazon will be much drier than it has been — worse than our Dust Bowl, relatively speaking (compared, that is, to their current baseline climate). Last year, we reported on a study that found the Amazon’s dry season lasts three weeks longer than it did 30 years ago. This alone makes the southern Amazon more susceptible to dieback — from both lack of rain and increased risk of wildfires. The projected post-2050 climate for the Amazon would make die out all but unstoppable, which would release large amounts of CO2 stored there into the atmosphere, an accelerating feedback for climate change.

The normal climate of Southern Europe will much be extreme drought, much worse than our Dust Bowl. All of Europe will be transformed in ways that are difficult to imagine today.

Finally, the normal climate of most of Mexico and Central America will cause soil moisture levels comparable or worse than our Dust Bowl. Fortunately they have a large and friendly neighbor to the north who will no doubt be very accommodating to immigrants — especially from countries whose climate was ruined by that neighbor’s profligate ways. I mean, if you love to smoke in bed — despite numerous warnings — and you start a fire that burns down all of your neighbors’ houses, you’d help them relocate, wouldn’t you?

Obviously, any rational species would take steps to avoid this outcome at any cost, let alone 0.06% of the world’s current economic “growth” rate, which is the currently-projected price tag. Obviously….