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Climate Change Makes Soils Saltier, Forcing Farmers to Find New Livelihoods
By Joyce J. Chen and Valerie Mueller
Salt is essential for cooking, but too much salt in soil can ruin crops and render fields useless. According to legend, Roman general Scipio Aemilianus Africanus sowed the soils of Carthage with salt after conquering the city during the Punic Wars. And after defeating the Italian town of Palestrina in 1298, Pope Boniface VIII is said to have plowed its lands with salt "so that nothing, neither man nor beast be called by that name."
Today it would be very expensive and logistically challenging to gather enough salt to render large swaths of land infertile. But that is precisely what climate change is doing in many parts of the world.
As sea levels rise, low-lying coastal areas are increasingly being inundated with saltwater, gradually contaminating the soil. These salts can be dissipated by rainfall, but climate change is also increasing the frequency and severity of extreme weather events, including droughts and heat waves. This leads to more intensive use of groundwater for drinking and irrigation, which further depletes the water table and allows even more salt to leach into soil.
We have documented this process in Bangladesh, but its impacts are much broader. Our findings show that rising soil salinity is already influencing agricultural production and internal migration in some locations, and could affect many other coastal areas where farming takes place, from Asia to the U.S. Pacific and Gulf coasts.
Sea level rise plus increased groundwater pumping can promote saltwater intrusion into groundwater aquifers, increasing treatment costs or rendering wells unusable.EPA
Growing Crops in Saline Soils
Farming has always been a challenging industry with razor-thin profit margins, even for large-scale farmers. Salt contamination, which leads to stunted and uneven plant growth, is already estimated to affect 20 percent of cultivated land worldwide.
Climate change drives soil salinization in several ways. First, ocean temperatures are rising, and warmer water takes up more space. Ice sheets and glaciers are melting and flowing into the oceans. Scientists currently project that global mean sea levels will rise by at least one-quarter to one-half meter by 2100, even with deep reductions in greenhouse gas emissions. This process pushes salty water onshore along coastlines, from Bangladesh to the Mississippi Delta.
Climate change also causes heat stress, which will deplete groundwater resources and increase saline contamination of soils inland. This process is already affecting parts of Australia, sub-Saharan Africa and California.
Globally, soil salinization will translate into higher food prices and more food shortages. Locally, many farmers are seeing lower yields, which means less income.
Depending on the season and the degree of saline contamination, rice farmers in India can expect to lose anywhere from 7 to 89 percent of their crop. In coastal Bangladesh, we found that households facing moderate saline contamination earn roughly 20 percent less in crop revenue each year than those facing only mild soil salinity.
Taro crops destroyed by encroaching saltwater at Lukunoch Atoll, Chuuk State, MicronesiaUSDA Forest Service / John Quidachay
When Life Gives You Lemons
Large-scale farmers and those in more developed countries have stronger safety nets and more options for coping with salty soils. Millions of subsistence farmers are left searching for ways to make ends meet.
In coastal Bangladesh, farmers are increasingly turning to fish farming as their lands become inundated. We estimate that the share of revenue these farmers derived from aquaculture rose by nearly 60 percent over a period of eight years as their soils became saltier. By diversifying in this way, they could almost entirely offset lost crop revenues.
We also found that converting to aquaculture made farmers less likely to migrate abroad to find work. This may not be a good thing: Competition in the shrimp farming industry is steep and wages are low, so farmers could spend their household savings to convert to aquaculture and then become trapped at the coast. On the other hand, these enterprises offer new job opportunities that may reduce the need to seek opportunities abroad.
But this benefit is probably temporary. Converting farm lands to brackish ponds increases saline contamination of soils. In Bangladesh, it has led to conflict among coastal residents. Some enterprising shrimp farmers even go so far as to dig channels through embankments designed and built—typically by aid agencies and non-government organizations—to prevent saline intrusion.
Seeking New Livelihoods
As the shift towards brackish aquaculture continues, crop cultivation will become even more challenging. Moreover, many households cannot afford to convert to shrimp farming. Instead, some are migrating within Bangladesh in search of new opportunities.
As soil salinity increases, we estimate that internal migration in Bangladesh would increase by 25 percent if all coastal locations had to contend with the highest soil salinity content currently observed. Moves to neighboring countries such as India, Pakistan, Nepal, Sri Lanka and Bhutan would similarly increase. In total, some 200,000 Bangladeshi coastal farmers per year could migrate inland to seek new livelihoods. Two of the most popular destinations—the cities of Chittagong and Khulna—are located near the coast, so people who move there will still be vulnerable to sea level rise.
Many observers have spotlighted the potential for climate change to devastate Bangladesh by increasing river flooding. But as we have shown, river flooding triggers little to no out-migration in Bangladesh and elsewhere, particularly in delta regions where rivers meet the ocean. In fact, riverine flooding supplements soil nutrients, and longtime residents are experienced in weathering "usual" flood events.
Our findings confirm that it is not flooding that threatens livelihoods, but specific types of flooding. Sea level rise will pose unique challenges because of the resultant saline contamination and, eventually, permanent loss of habitable lands.
It is also important to consider broader social impacts of migration, both good and bad. Migrants' mental health and life satisfaction may decline, but the remittances they send home can enable their families to invest in climate-resilient livelihoods. Dispersing household and village members over greater distances may weaken traditional social networks, but women may find greater empowerment as economic opportunities evolve.
Helping Coastal Farmers Cope
Forward-looking adaptation efforts will ease these transitions and reduce the social and economic costs of climate change. Developing salt-tolerant crop varieties and farming methods, and funding infrastructure projects to prevent saltwater flooding, can help coastal farms remain viable as sea levels rise. It will also be important to regulate brackish aquaculture to avoid conflicts between rice farmers and shrimp farmers.
Developing manufacturing and service sectors in secondary towns and cities, particularly those outside the saline belt, can also encourage preemptive migration out of vulnerable areas and provide better job opportunities for subsistence farmers. In highly vulnerable areas worldwide, such as southern Louisiana, governments may also need to consider plans for managed retreat as marginal lands become increasingly hard to protect from the inevitable encroachment of the sea.
Reposted with permission from our media associate The Conversation.
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"Faced with global warming, rising sea levels, and the climate-related extremes they intensify, the question is no longer whether some communities will retreat—moving people and assets out of harm's way—but why, where, when, and how they will retreat," the study begins.
The researchers suggest that it is time to rethink retreat, which is often seen as a last resort and a sign of weakness. Instead, it should be seen as the smart option and an opportunity to build new communities.
"We propose a reconceptualization of retreat as a suite of adaptation options that are both strategic and managed," the paper states. "Strategy integrates retreat into long-term development goals and identifies why retreat should occur and, in doing so, influences where and when."
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"There's a definite rhetoric of, 'We're going to build it back better. We're going to win. We're going to beat this. Something technological is going to come and it's going to save us,'" said A.R. Siders, an assistant professor with the disaster research center at the University of Delaware and lead author of the paper, to the New York Times. "It's like, let's step back and think for a minute. You're in a fight with the ocean. You're fighting to hold the ocean in place. Maybe that's not the battle we want to pick."
Rethinking retreat could make it a strategic, efficient, and equitable way to adapt to the climate crisis, the study says.
Dr. Siders pointed out that it has happened before. She noted that in the 1970s, the small town of Soldiers Grove, Wisconsin moved itself out of the flood plain after one too many floods. The community found and reoriented the business district to take advantage of highway traffic and powered it entirely with solar energy, as the New York Times reported.
That's an important lesson now that rising sea levels pose a catastrophic risk around the world. Nearly 75 percent of the world's cities are along shorelines. In the U.S. alone coastline communities make up nearly 40 percent of the population— more than 123 million people, which is why Siders and her research team are so forthright about the urgency and the complexities of their findings, according to Harvard Magazine.
Some of those complexities include, coordinating moves across city, state or even international lines; cultural and social considerations like the importance of burial grounds or ancestral lands; reparations for losses or damage to historic practices; long-term social and psychological consequences; financial incentives that often contradict environmental imperatives; and the critical importance of managing retreat in a way that protects vulnerable and poor populations and that doesn't exacerbate past injustices, as Harvard Magazine reported.
If communities could practice strategic retreats, the study says, doing so would not only reduce the need for people to choose among bad options, but also improve their circumstances.
"It's a lot to think about," said Siders to Harvard Magazine. "And there are going to be hard choices. It will hurt—I mean, we have to get from here to some new future state, and that transition is going to be hard.…But the longer we put off making these decisions, the worse it will get, and the harder the decisions will become."
To help the transition, the paper recommends improved access to climate-hazard maps so communities can make informed choices about risk. And, the maps need to be improved and updated regularly, the paper said as the New York Times reported.
"It's not that everywhere should retreat," said Dr. Siders to the New York Times. "It's that retreat should be an option. It should be a real viable option on the table that some places will need to use."
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