By Alma Mendoza, Colosio Fellow with the IIASA Ecosystems Services and Management Program
Changes in land use cover can have a crucial impact on the environment in terms of biodiversity and the benefits that ecosystems provide to people. Assessing, quantifying, and identifying where these changes are the most drastic is especially important in countries that have high biodiversity along with high rates of natural vegetation loss. Socioeconomic pressures often drive land use change and the impacts are expected to increase due to population growth and climate change.
To better understand the possible impacts of land use change in Mexico over the short, medium, and long term, my colleagues and I used the Shared Socioeconomic Pathways–a set of pathways that span a wide range of feasible future developments in areas such as agriculture, population, and the economy–together with a set of climatic scenarios known as the Representative Concentration Pathways. We focused on Mexico, because the country is large enough to encompass different ecosystems, socioeconomic characteristics, and climates. In addition, Mexico is characterized by high deforestation rates, huge biodiversity, and a large number of communities with contrasting land management practices. Incorporating all these features, allowed us to take the complexity of socioecological systems into account.
We designed a model to test how socioeconomic and biophysical drivers, like slope or altitude, may unfold under different scenarios and affect land use. Our model includes 13 categories of which eight represent the most important ecosystems in Mexico (temperate forests, cloud forests, mangroves, scrublands, tropical evergreen and -dry forests, natural grasslands, and other vegetation such as desert ecosystems or natural palms), four represent anthropogenic uses (pasture, rainfed and irrigated agriculture, and human settlements), and one constitutes barren lands. We set two plausible scenarios: “Business as usual” and an optimistic scenario called the “green scenario”. We projected the “business as usual” scenario using medium rates of vegetation loss based on historical trends and combined it with a medium population and economic growth with medium increases in climatic conditions. For the “green scenario”, we projected the lowest rates of native vegetation loss and the highest rates of native vegetation recovery with a low population and medium economic growth in a future with low climatic changes.
Our results show that natural vegetation will undergo significant reductions in Mexico and that different types of vegetation will be affected differently. Tropical dry and evergreen forests, followed by ‘other’ vegetation and cloud forests are the most vulnerable ecosystems in the country. For example, according to the “business as usual” scenario, tropical dry forests might decrease in extent by 47% by the end of the century. This is extremely important considering that the most recent rates, for the period 2007 to 2011, were even higher than the medium rates we used in this scenario. In contrast, the “green scenario” allowed us to see that, with feasible changes of rate, this ecosystem could increase their distribution. However, even 80 years of regeneration would not be enough to reach the extent these forests had in 1985, when they accounted for around 12% of land cover in Mexico. Moreover, the expansion of anthropogenic land cover (such as agriculture, pastures, and human settlements) might reach 37% of land cover in the country by 2050 and 43% by 2100 under the same scenario. In terms of CO2 emissions due to land use cover change we found that Mexico was responsible for 1-2% of global emissions that are the result of land use cover change, but by 2100 it could account for as much as 5%.
Our findings show that conservation policies have not been effective enough to avoid land use cover change, especially in tropical evergreen forests and drier ecosystems such as tropical dry forests, natural grasslands, and other vegetation. Cloud forests have also been badly affected. As a biologically and culturally rich country, Mexico is responsible for maintaining its diversity by implementing a sustainable and intelligent management of its territory.
Our study identified hotspots of land use change that can help to prioritize areas for improving environmental performance. Our project is currently linking the hotspots of change with the most threatened and endemic species of Mexican terrestrial vertebrates (mammals, amphibians, reptiles, and birds) to provide useful results that can help prioritize ecosystems, species, or municipalities in Mexico.
Mendoza Ponce A, Corona-Núñez R, Kraxner F, Leduc S, & Patrizio P (2018). Identifying effects of land use cover changes and climate change on terrestrial ecosystems and carbon stocks in Mexico. Global Environmental Change 53: 12-23. [pure.iiasa.ac.at/15462]
Note: This article gives the views of the author, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.
by Rastislav Skalsky, Ecosystems Services and Management Program, International Institute for Applied Systems Analysis
As growers, we know soil is important. It supports plants, and provides nutrients and water for them to grow. But do we all appreciate how crucial the role of soil is in continuously supplying plants with water, even when it hasn’t rained for a few days or even weeks, even without extra water being added via watering?
Soil is like a sponge. It can retain rain water and, if it is not taken up by plants, soil can store it for a long time. We can feel the water in soil as soil moisture. Try it — take and hold a lump (clod) of soil — if it is wet it will leave a spot on your palm. If it’s only moist then it will feel cold — cooler than the air around. And if the soil is dry, it will feel a little warm.
Soil moisture not only can be felt, but it can also be measured — in the lab, or directly in the field with professional or low-cost soil moisture sensors.
Soil moisture in general indicates how much water is contained by the soil. But it is not always the case that soil which feels moist or wet is able to support plants. It could happen that, despite feeling moist, the soil simply does not hold enough water, or holds the water too tightly for the plants to extract it. Or the opposite, soil can sometimes contain too much water. To understand how this works, one has to learn more about how water is stored in the soil.
Water is bound to soil by physical forces. Some forces are too weak to hold water in the plant root zone and water percolates to deeper layers, where plants can no longer reach it. Other forces can be too strong, preventing water from being retrieved by the roots.
If soil moisture is measured at one place over time, it can reveal its seasonal dynamics. Having estimated important soil water content thresholds (FS — full saturation, FC — field capacity, PDA — point of decreased availability, and WP — wilting point) for that particular site, e.g. based on soil texture test or measurement, one can easily interpret if the measured soil moisture and say if there was enough water or not to fully support plants with water and air. In this particular case of sandy 0–30 cm deep topsoil from Slovakia, it was never wet enough to cause oxygen stress for plants, — in fact it never reached state of all capillary voids filled with water (FC). On the other hand, each summer the topsoil moisture dropped below the point of decreased availability (PDA), even got close to the wilting point or went through (WP), which means that during those periods plants suffered drought conditions.
Thresholds In order to describe this behavior in more useful terms, plant ecologists and soil hydrologists came up with couple of important soil water content thresholds (Figure 1). These thresholds, also called “soil moisture ecological intervals”, define how easily plants can get the water out of the soil.
We speak about full saturation of soil when all empty spaces (pores/voids) are completely filled with water. Full saturation of the soil with water prevents air entering into the soil. Yet there is no force holding water in the soil. Roots need air as well as water so, if this situation continues, it eventually causes oxygen stress for most of the common plants because roots simply cannot breathe.
Soil also has different types of pores. Larger ones, which are called “gravitational pores”, are filled with water only when the soil is saturated and otherwise drains freely, and smaller ones called “capillary pores” which are small enough in size to prevent water from percolating down the soil profile by gravitation. These smaller pores can hold water even in well-drained soils and make it available for plants to extract. There are also even smaller pores where the water is held so tightly that plants cannot extract it.
When all gravitational pores/voids are empty of water and it is present only in so called capillary pores/void we speak about the field water capacity — which is considered to be the best soil moisture status of the soil — enabling plants to retrieve the water they need, whilst leaving enough air for roots to breathe. If no new water is added into the soil, the soil dries as water is used by plants or evaporates. As soil dries less water is available to plants until the point of decreased availability when water remains only in the smallest capillary pores/voids. But this water is bound to soil particles so strongly that most plants are not able to extract it suffer from drought. Ultimately, all the available water is used up by plants, and the remaining water is inaccessible. Soil reaches the so-called wilting point and water is not available for the plants anymore. Plants permanently wilt and eventually die.
How Soil Characteristics Relate to Moisture The tricky thing with soil moisture however is that the same amount of water (volumetric percent of the total soil column volume) can, in different soils, represent different amount of water available for plants. How big this difference could be is defined by many soil characteristics.
The most important is the soil texture — a blend of all fine-earth soil mineral constituents (sand, silt, clay) and stones in various rates. In general, the finer the texture is (i.e. more clay, less sand) the more water is bound in the soil too tightly to be retrieved by plants. Even if the soil feels moist, plants can permanently wilt in clay soils. In contrast, those soils with coarse texture (i.e. more sand, less clay) can support plants with nearly all the water they can hold. Although the soil looks dry, plants can still effectively take the water out of it. The drawback here is that in coarse textured, sandy, soil nearly all water drains down the gravitational pores and therefore such a soil cannot support plants for very long time. That is also why medium textured soils (loam, silty loam, clay loam) are considered best for holding and providing the water for plants. Medium textured soils can effectively drain excess water, yet hold much water in capillary pores/voids for a long time, and still, only a relatively small amount of water remains unavailable for the plants.
A practical implication of this behavior of soil with different soil texture could be that one has to apply slightly different strategies to maintain soil moisture in the way that it can effectively supply plants with water. Sandy soils will require more frequent watering with smaller amount of water. It would not make any practical sense to try build-up a storage of water in these soils. All extra water added will simply drain out of the topsoil. Clay rich soils can absorb big amounts of water but a lot is bounded too strongly to the soil particles and thus not available for the plants. Therefore one should water even if the soil looks moist or wet — and if dry a lot of water must be added to recharge the topsoil so that it can support plants effectively. With loamy soils it is possible to be more relaxed with watering frequency, simply because one can build solid storage of water in such soils. Adding a bit more water than is necessary is perfectly fine with these soils because the water is effectively kept in the soil profile and it can be used later on.
Interested in learning more? Why not sign up for GROW Observatory’s next free online course – Citizen Research: From Data to Action – to discover how citizen-generated data on soils, food and a changing climate can create positive change in the world. Starts 5th November.
By Jessie Jeanne Stinnett, Co-Artistic Director of Boston Dance Theater
I recently had the privilege of artistically collaborating on Dancing with the Future, a project spearheaded by Gloria Benedikt and Piotr Magnuszewski of IIASA with Martin Nowak of Harvard University. The process involved five dancers joining two scientists to create an evening-length performance-debate that toured to Harvard University’s Farkas Hall and the United Nations Conference on Sustainable Development at Columbia University this fall. The essence of this interdisciplinary project was a product of Nowak’s published research on altruism and evolution. Nowak proposes: “Evolution is not only a fight. Not mere competition. Also cooperation, cooperation is the master architect of evolution. Now that we have reached the limits of our planet, can you cooperate with the future?”
What can I do to contribute to a global effort to create sustainable practices that yield cooperation with the future? Why do I dance and what kind of impact does my dancing have on my environment and myself? As a co-artistic director, entrepreneur, choreographer, and performing artist of the young and fast-growing contemporary dance company Boston Dance Theater (BDT), I am turning to projects that are on the innovative cross-section between the arts, technology, and other disciplines because they have the most potential to have meaningful impact on the level of the creative team, the audience, and beyond. I too, am searching for practices and partnerships for BDT that yield pathways for collective problem solving, or ‘super-cooperation’. As Nowak notes, “[evolutionarily speaking] humans are super-cooperators.”
Overall, Dancing with the Future has revealed to me that scientists, dancers, and policymakers can successfully sit at the same table (or in the same theater or conference hall), tackle the same issues, and productively collaborate toward unearthing sustainable solutions.
We all had to be open to compromises — this is not an easy task in a room full of expert-leaders. I set a mantra for myself to remember that we were creating something completely new. Each time my choreographer-dancer brain sent up a red flag, I chose selectively when to share my opinion with the group. I elected to practice the Buddhist teachings of Shunryu Suzuki, captured poetically in Zen Mind, Beginner’s Mind, “In the beginner’s mind there are many possibilities, but in the expert’s there are few.” This choice opened others and myself up to creative and peaceful solutions that I otherwise wouldn’t have seen.
Conversely, I was able to offer constructive solutions at moments when working with the scientific material seemed to overwhelm the studio process, for example, dividing the existing text and music into segments and giving each of those segments a specific choreographic task that related to the content of the scientific text. This was a very simple concept that had to do with pacing and sculpting time. Once we counted out the music, it was easy for us to construct the movement score and see the overall arc of the piece.
I learned not to be afraid of using my voice and also listening deeply. It was, at first, very intimidating to be seated across from experts in fields outside of my own. I learned that scientists and policymakers can understand, respect, and respond to the decisions I make through a process of peaceful negotiation, even when we speak different languages, were born on different continents, and may have varying political opinions. My fear was ultimately unnecessary because the very nature of this project appeals to the humanity in us all.
This form of cross-disciplinary collaboration allows participants to see our own work in a new light and to discover new languages that are exciting because we have co-authored them. For the work to be successful, the dance, science, and debate components must all have equal weight and value. Otherwise, the movement and its choreographic structure becomes the visual representation of the science rather than an equal partner. When that happens, the magic of innovative collaboration falls flat into familiar territory.
During the process, we often referred to this Chinese proverb: “Tell me, and I’ll forget. Show me, and I’ll remember. Involve me, and I’ll understand.” Dancers understand this concept in a very concrete and visceral way. For scientists, policymakers, or the general audience to understand too, they must be involved as much as possible in the process of what we are doing. If we cannot for reasons of practicality, have them with us in the studio, then we must bring them into the process in another way. It is only by involving them as collaborators that we can generate large scale, super-cooperation.
Sometimes it feels like my dancer colleagues and I exist in a vacuum: we rehearse in the confines of the studio and historically perform on stages that make us appear as ‘other’ from the people we are performing for. Western concert dance has received criticism for being an inaccessible art form and according to the 2016 report from The Boston Foundation, is the most under-funded of Boston’s performing arts. Dancers aren’t typically trained to speak about their work, and often have a hard time receiving criticism. Contemporary dance in particular, can be challenging to general audience members because the language of the art and its conceptual frameworks are sometimes not evident in the work itself — many choreographers feel creatively stifled when asked to explain their work in language and wonder why the art work can’t speak for itself.
I have come to learn that these problems are not unique to dance. After our premiere of Dancing with the Future at Harvard University, scientists thanked me for helping them to understand new meaning within the scientific research presented through my performance. Their experience of live performance elicited a keen sense of empathy that drew them into deeper understanding of the scientific findings. This collaboration yielded a tri-fold, reciprocal impact for the artists, for the scientists, and for the public.
Our work helped to bridge the traditional gap between creative team and general audience member. It can be that when a member of the public enjoys a performance, they leave the venue with a good feeling and a nice memory as a souvenir. I believe that our art form has the power to do more — to make a greater impact and to be appreciated as an inherent and necessary aspect of our society and culture.
It is our civic responsibility to continue workshopping solutions toward global cooperation and cooperation with future generations. Dancing with the Future has encouraged me, on a micro scale, that this is a reasonable and plausible endeavor. With continued care, attention toward our common goals, compassion, listening, and risk-taking, we can understand one another through the process of creation regardless of what language we speak or where we were born. The next steps may be small, but nonetheless crucial. Next season, Boston Dance Theater will commission new works by three international choreographers with the stipulation that the pieces must speak to pressing global issues, and cross-disciplinary collaboration will be a cornerstone of that production.
Dancing with the Future has revealed to me that partnerships with super-cooperators such the teams at IIASA and Harvard’s Program for Evolutionary Dynamics can bring meaningful potential to catalyze change in me as an individual and in Boston Dance Theater as an organization, while enabling us to reach our extended communities. I can’t wait for the next project!
Note: This article gives the views of the author, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.
By Reinhard Mechler, Deputy Program Director, IIASA Risk and Resilience Program
IPCC Special Report on Global Warming of 1.5°C
The Intergovernmental Panel on Climate Change (IPCC) just approved its Special Report on Global Warming of 1.5°C (SR15). It took long hours of discussions between the body of authors and representatives from about 130 IPCC member states gathered at the approval session in Korea, to get the highly anticipated report accepted. The report was requested by parties to the United Nations Framework Convention on Climate Change (UNFCCC) as set out in the Paris Agreement in 2015, that urged parties to limit warming to “well below” 2°C and pursue efforts towards 1.5°C of warming above pre-industrial levels. Countries that are severely vulnerable to climate change such as small-island states, expressed a particular need for the report. The drafted text of the summary for policymakers (SPM) remained largely intact throughout the approval session and the science was well respected by the parties (as has generally been the case for the IPCC). This bodes well for the IPCC’s process of reporting the most up to date information on climate science to national and international decision makers who closely review and comment on drafts of texts throughout the writing process.
The report, composed of five chapters and the SPM, discusses among other topics whether the Paris target of 1.5°C above pre-industrial temperature is still achievable; what the risks we face are at 1.5°C and 2°C of warming; what this will mean in terms of mitigation and adaptation; and what the synergies are between mitigation, adaptation and the Sustainable Development Goals (SDGs).
Below my take on how the SR15 answers some of these questions:
A stark warning… and indeed half a degree does make a difference
The world is on its way to breaching 1.5°C by around the 2040s, which will lead to further warming if current greenhouse gas emissions trends prevail and current nationally determined contributions (NDCs) are not upgraded. Warming can still be stabilized at 1.5°C, but it is an ambitious target that depends on halving emissions over the next 10 years and becoming carbon-neutral by 2050.
The report shows that we are already seeing serious consequences of a 1°C warming in the form of significant increases in some weather-related extreme events (such as the frequency, intensity, and/or amount of heavy precipitation in several regions), exacerbated sea level rise, and other effects on important terrestrial and oceanic systems. In terms of future warming, the report shows that a half-degree change, which we have actually seen over the last 50 years, indeed makes a difference. Risks will be higher than today at 1.5°C and will further increase at 2°C (and beyond).
Adaptation and its limits: A need for transformation?
In light of the above, adaptation is essential and needs to be ramped up. However, for the first time, the IPCC presents evidence on hard and soft limits to adaptation, of which some would already be reached at 1.5°C. Statement B6 of the SPM reads: “Most adaptation needs will be lower for global warming of 1.5°C compared to 2°C (high confidence). There are a wide range of adaptation options that can reduce the risks of climate change (high confidence). There are limits to adaptation and adaptive capacity for some human and natural systems at global warming of 1.5°C, with associated losses (medium confidence).”
So, what should we do in terms of adaptation in light of pervasive risks becoming increasingly severe and ultimately breaching adaptation limits? Statement A3.3 of the SPM suggests that, “Future climate-related risks would be reduced by the upscaling and acceleration of far-reaching, multi-level, and cross sectoral climate mitigation and by both incremental and transformational adaptation (high confidence).”
Throughout the document, the SR15 discusses what is needed in terms of standard adaptation (incremental) and transformational adaptation. An example of incremental adaptation is to continue building sea walls to manage increasing flooding from sea level rise. Adapting community and regional planning so that people, key assets, and buildings are moved out of harm’s way on the other hand, would be rather transformational–and often have a holistic and systemic component. The report also shows that more effort will be needed to better understand what transformational risk management processes may entail concretely.
Transformation: What does it take?
Transformational adaptation may not always be needed uniformly across the globe, but as the report shows, communities in regions vulnerable to sea-level rise risk, flooding, heat, and drought already clearly need significant support, and in a 1.5°C or 2°C world, much more would be needed. The report also shows that increasing investment in physical and social infrastructure is a key enabler of necessary transformations that enhance the resilience of communities and societies. Upgrading climate adaptation efforts will be fundamental to absorbing some climate change impacts and not critically affecting the achievement of the SDGs. What is more, the SR15 points out that the coordinated pursuit of climate resilience and development is the way forward to achieving the ambitious mitigation and adaptation targets set out, while seeking achievement of development goals such as those formulated in the 17 SGDSs.
Among others, three main implications for adaption (and climate risk) science, policy, and practice can be drawn:
Climate-related risks are becoming pervasive and significant with climatic change: The Paris call for limiting warming to 1.5°C should be heeded and remain the target for ambitious climate mitigation policy in order to avoid some risks from becoming irreversible and hard adaptation limits manifesting themselves.
Climate-related risks are becoming pervasive due to gaps in human, physical, financial, natural, and social capacity/capitals, and increased and targeted investments to strengthen these will be needed to push soft adaptation limits out.
Systemic approaches are needed to tackle high-level risks and consider synergies between adaptation, mitigation, and the SDGs as standard adaptation and disaster risk reduction may not be enough. Transformational approaches requiring large-scale and systemic change are useful in this regard.
The open question…
The final, open question for all of us is of course whether the report can be more than another wake-up call and truly be a game-changer for limiting warming to 1.5°C while ramping up adaptation efforts. The science is there. Broad-based dissemination efforts with policymakers and advisors, experts, the private sector, and civil society are being rolled out. The political will to live up to the massive mitigation and adaptation challenges needs to follow now. Little time remains, and if we truly want to limit warming to 1.5°C and mitigate the associated risks, we need to take decisive and bold steps towards carbon-neutrality and climate-resilience now.
Note: This article gives the views of the author, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.
By Sandra Ortellado, IIASA 2018 Science Communication Fellow
If fashion is the science of appearances, what can beauty and aesthetics tell us about the way we perceive the world, and how it influences us in turn?
From cognitive science research, we know that aesthetics not only influence superficial appearances, but also the deeper ways we think and experience. So, too, do all kinds of creative thinking create change in the same way: as our perceptions of the world around us changes, the world we create changes with them.
From the merchandizing shelves of H&M and Vero Moda to doctoral research at the Faculty of Information Technology at the University of Jyväskylä, Finland, 2018 YSSP participant Laura Mononen has seen product delivery from all angles. Whether dealing with commercialized goods or intellectual knowledge, Mononen knows that creativity is all about a change in thinking, and changing thinking is all about product delivery.
“During my career in the fashion and clothing industry, I saw the different levels of production when we sent designs to factories, received clothing back, and then persuaded customers to buy them. It was all happening very effectively,” says Mononen.
But Mononen saw potential for product delivery beyond selling people things they don’t need. She wanted to transfer the efficiency of the fashion world in creating changes in thinking to the efforts to build a sustainable world.
“Entrepreneurs make change with products and companies, fashion change trends and sell them. I’m really interested in applying this kind of change to science policy and communication,” says Mononen. “We treat these fields as though they are completely different, but the thing that is common is humans and their thinking and behaving.”
Often, change must happen in our thinking first before we can act. That’s why Mononen is getting her doctorate in cognitive science. Her YSSP project involved heavy analysis of systems theories of creativity to find patterns in the way we think about creativity, which has been constantly changing over time.
In the past, creativity was seen as an ability that was characteristic of only certain very gifted individuals. The research focused on traits and psychological factors. Today, the thinking on creativity has shifted towards a more holistic view, incorporating interactions and relationships between larger systems. Instead of being viewed as a lightning bolt of inspiration, creativity is now seen as more of a gradual process.
New understandings of creativity also call on us to embrace paradoxes and chaos, see ourselves as part of nature rather than separate from it, experience the world through aesthetics, pay careful attention to our perception and how we communicate it, and transmit culture to the next generation.
Perhaps most importantly, Mononen found in her research that the understanding of creativity has changed to be seen as part of a process of self-creation as well as co-creation.
“The way we see creativity also influences ourselves. For example if I ask someone if they are creative, it’s the way they see themselves that influences how creative they are,” says Mononen. “I have found that it’s more crucial to us than I thought, creativity is everywhere and it’s everyday and we are sharing our creativity with others who are using that to do something themselves and so on.”
This means on the one hand that we use our creativity to decide who we are and how we see the world around us for ourselves. But it also means that the outcomes and benefits of creativity are now intended for society as a whole rather than purely for individuals, as it was in the past. It may sound like another paradox, but being able to embrace ambiguity and complexity and take charge of our role in a larger system is important for creating a sustainable future.
“From the IIASA perspective this finding brings hope because the more people see themselves as part of systems of creating things, the more we can encourage sustainable thinking, since nature is a part of the resources we use to create,” says Mononen.
Mononen says a systems understanding of creativity is especially important for people in leadership positions. If a large institution needs new and innovative solutions and technology, but doesn’t have the thinking that values and promotes creativity, then the cooperative, open-minded process of building is stifled.
Working in both the fashion industry and academic research, Mononen has encountered narrow-minded attitudes towards art and science firsthand.
“Communicating your research is very difficult coming from my background, because you don’t know how the other person is interpreting what you say,” says Mononen. “People have different ideas of what fashion and aesthetics are, how important they are and what they do. Additionally, scientific concepts are used differently in different fields.”
“We are often thinking that once we get information out there, then people will understand, but there are much more complex things going on to make change and create influence in settings that combine several different fields.” says Mononen.
For Mononen, the biggest lesson is that creativity can enhance the efforts of science towards a sustainable world simply by encouraging us to be aware of our own thinking, how it differs from that of others, and how it affects all of us.
“When you become more aware of your ways of thinking, you become more effective at communicating,” says Mononen. “It’s not always that way and it’s very challenging, but that’s what the research on creativity from a systems perspective is saying.”
By Marcus Thomson, researcher, IIASA Ecosystems Services and Management Program
While living in Cairo in 2010, I witnessed first-hand the human toll of political and environmental disasters that washed over Africa at the end of the last century. Unprecedented numbers of migrants were pressing into North Africa, many pushed out of their homelands by conflict and state-failure, pulled towards safer, richer, less fragile places like Europe. Throughout Sub-Saharan Africa, climate change was driving up competition for scarce land and water, and raising pressure on farmers to maintain the quantity and quality of their crops.
It is a similar story throughout the developing world, where many farmers do without the use of expensive chemical fertilizer and pesticides, complex irrigation, or boutique seed varieties. They rely instead on traditional land management practices that developed over long periods with consistent, predictable conditions. It is difficult to predict how dryland farmers will respond to climate change; so it is challenging to plan for various social, economic, and political problems expected to develop under, or be exacerbated by, climate change. Will it spur innovation or, as has been argued for the Syrian civil war, set up conflict? A major stumbling block is that the dynamics of human social behavior are so difficult to model.
Instead of attempting to predict farmers’ responses to climate change by modelling human behavior, we can look to the responses to environmental changes of farmers from the past as analogues for many subsistence farmers of the future. Methods to fill in historical gaps, and reconstruct the prehistoric record, are valuable because they expand the set of observed cases of societal-scale responses to environmental change. For instance, some 2000 years ago, an expansive maize-growing cultural complex, the Ancestral Puebloans (APs), was well established in the arid American Southwest. By AD 1000, members of this AP complex produced unique and innovative material culture including the famed “Great Houses”, the largest built structures in the United States until the 19th century. However, between AD 1150 and 1350, there was a profound demographic transformation throughout the Southwest linked to climate change. We now know that many APs migrated elsewhere. As a PhD student at the University of California, Los Angeles, I wondered whether a shift to cooler, more variable conditions of the “Little Ice Age” (LIA, roughly AD 1300 to 1850) was linked to the production of their staple crop, maize.
I came to IIASA as a YSSP in 2016 to collaborate with crop modelers on this question, and our work has just been published in the journal Quaternary International. I brought with me high-resolution data from a state-of-the-art climate model to drive the crop simulations, and AP site information collected by archaeologists. Because AP maize was quite different from modern corn, I worked with IIASA soil scientist Juraj Balkovič to modify the crop simulator with parameters derived from heirloom varieties still grown by indigenous peoples in the Southwest. I and IIASA economic geographer Tamás Krisztin developed a statistical technique to analyze the dynamical relationship between AP site occupation and simulated yield outcomes.
We found that for the most climate-stressed high-elevation sites, abandonments were most associated with increased year-to-year yield variability; and for the least stressed low-elevation and well-watered sites, abandonment was more likely due to endogenous stressors, such as soil degradation and population pressure. Crucially, we found that across all regions, populations peaked during periods of the most stable year-to-year crop yields, even though these were also relatively warm and dry periods. In short, we found that AP maize farmers adapted well to gradually rising temperatures and drought, during the MCA, but failed to adapt to increased climate variability after ~AD 1150, during the LIA. Because increased variability is one of the near certainties for dryland farming zones under global warming, the AP experience offers a cautionary example of the limits of low-technology adaptation to climate change, a business-as-usual direction for many sub-Saharan dryland farmers.
This is a lesson from the past that policymakers might take note of.
 Kelley, C. P., Mohtadi, S., Cane, M. A., Seager, R., & Kushnir, Y. (2015). Climate change in the Fertile Crescent and implications of the recent Syrian drought. Proceedings of the National Academy of Sciences, 201421533.
 Thomson, M. J., Balkovič, J., Krisztin, T., MacDonald, G. M. (2018). Simulated crop yield for Zea mays for Fremont Ancestral Puebloan sites in Utah between 850-1499 CE based on temperature dailies from a statistically downscaled climate model. Quaternary International. https://doi.org/10.1016/j.quaint.2018.09.031