How green roofs can protect city streets from flooding

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Spring and summer 2017 have been among the wettest on record in eastern North America, including southern Ontario.

Rainfall amounts in the spring broke records in places like Toronto, where 44.6 millimetres of rain fell in 24 hours.

The relentless downpours caused the stormwater infrastructure in Canada’s biggest city to overflow, leading to flooding of busy downtown streets.

Urbanization in cities like Toronto has led to a rapid loss of permeable surfaces where water can freely drain. Coupled with the growing downtown core population in Toronto, this means that the stormwater and sewer systems in place must manage more water than in previous decades.

Furthermore, global temperature increases have been linked to the rise in extreme weather events worldwide, a trend that could worsen if global warming is not brought under control.

Cities like Toronto are ill-equipped to deal with these unprecedented amounts of precipitation due to their insufficient and outdated stormwater infrastructure.


A tow truck driver walks through flood waters after hooking up a car on the Don Valley Parkway in Toronto after a major rainstorm in July 2013. THE CANADIAN PRESS/Frank Gunn

Twenty three per cent of Toronto’s downtown sewers are combined, meaning that both the city’s stormwater and wastewater flow together within one pipe to a water treatment plant. In periods of heavy rainfall, the amount of stormwater in the sewer can reach capacity and overflow onto Toronto’s streets and into its lake and rivers.

That means to prevent flooding in downtown areas, sewage is released — untreated — into bodies of water that permit swimming and other recreational sports.

With rainfall amounts on the rise globally, it’s a crucial time to examine how cities like Toronto can retrofit their existing building infrastructure to alleviate flood damage and deal with stormwater in a more sustainable manner.

Green infrastructure technologies, such as permeable pavements, bioswales, cisterns and green roofs, are now commonly recommended to confront extreme weather events.

Green roofs for stormwater management

Green roofs are a green infrastructure (GI) option that can be applied to virtually any rooftop given weight load capacity. The benefits of green roofs extend far beyond their obvious aesthetic appeal.

A study done by University of Toronto civil engineer Jenny Hill and co-researchers at the school’s Green Roof Innovation Testing Lab (GRIT Lab) showed that green roofs have the capacity to capture an average of 70 per cent of rainfall over a given time, relieving underground stormwater systems and releasing the rain water back into the atmosphere.


University of Toronto’s GRIT Lab

The study examined four green roof design variables that represent the most common industry practices: Planting type (succulents or grasses and herbaceous flowering plants), soil substitute (mineral, wood compost), planting depth (10 centimetres or 15 centimetres) and irrigation schedule (none, daily or sensor-activated), and how these four factors influenced water capture.

The watering schedule was shown to have the greatest effect, with retention capacity increasing from 50 per cent with daily irrigation to 70 per cent with sensor-activated or no irrigation. In other words, roofs that have not been watered, or are only watered when their soil reaches a predetermined moisture level, have a greater capacity to absorb stormwater.

Furthermore, the study calculated a new peak runoff coefficient — a constant value used to calculate the capacity of a green roof to hold water — for green roofs to be around 0.1-0.15, an 85 to 90 per cent reduction compared to an impermeable surface.

Designers and engineers routinely use a figure of 0.5 (50 per cent reduction) to assess green roof performance. This discrepancy between industry practice and regional evidence-based findings highlights the need for further research.


Rooftop succulents and flowering plants on the GRIT lab’s green roof. University of Toronto’s GRIT Lab

The second most significant variable for stormwater retention was the soil substitute. The most widely used green roof planting material is based on guidelines from the German Landscape Research, Development and Construction Society (FLL).

The FLL recommended a mineral aggregate because it’s thought to be longer-lasting and hardier than biological soil substitutes. But this recommendation has been challenged by research today.

Hill and her team compared the mineral growing material to wood compost. The compost outperformed the mineral by 10 per cent (70 per cent versus 60 per cent rainfall retained) in beds with no irrigation, and had minimal compression or break-down over time.

Another key finding in Hill’s study demonstrated that when already damp, either from watering or rain, the planting material had the biggest influence on water retention. The compost outperformed the mineral soil substitute by as much as three times when fully saturated (83 per cent rainfall retained versus 29 per cent).

Compost a better soil substitute

That means that the compost not only performed better in every season, but it performed a great deal better in rainy seasons and during back-to-back storms.

Planting depth (10 centimetres versus 15 centimetres) and the plant family (succulents versus grass and herbaceous flowering plants) were both shown to have scant impact on stormwater retention compared to the planting material and watering schedule.

And so without compromising stormwater management, plant selection can meet aesthetic goals and environmental benchmarks such as biodiversity and species habitat.


A bee hovers around a flowering plant at the U of T’s GRIT Lab rooftop garden. U of T GRIT Lab

One of the constraints for green roof construction is weight loading, particularly in buildings that were not originally constructed to accommodate the weight of a saturated green roof. Thus, a 10 centimetre planting depth as opposed to 15 would mean more roofs could be eligible for retrofit.

Nonetheless, even though a biodiverse plant palette including grasses and herbaceous plants would be a more aesthetically and ecologically rich green roof option, those plants do require watering in order to survive in cities like Toronto. Since irrigation has a negative effect on stormwater retention, green roof designers can consider drought-resistant succulent plants like sedum.

However, when herbaceous plants are planted in compost rather than mineral planting materials, the decrease in stormwater retention capacity could be prevented.

On-demand irrigation activated by a soil moisture sensor can balance water management with water availability for plant growth. Furthermore, compost weighs significantly less than mineral planting material, opening up more potential for retrofits.

And so Hill and her team’s research into four distinct green roof variables allows us to understand the benefits and limitations of each, and how they can be combined.

Green roofs: Optimal green infrastructure

In our opinion as researchers at the GRIT Lab, green roofs are the optimal urban green infrastructure due to their multi-functionality: They can be retrofitted onto existing buildings, they provide biodiverse space for urban wildlife and they can be enriching public spaces for city-dwellers to enjoy. Additionally, green roofs can make previously inhospitable places pleasant, and provide new outdoor space for office workers.


A butterfly flutters around flowers at the GRIT Lab green roof. U of T GRIT Lab

These recent findings clearly show the potential of green roofs. But thorough scientific studies on green roofs, like those undertaken at the GRIT Lab, are necessary in order to determine the best green roof composition for optimal performance.

For example, though planting type had little effect on stormwater retention, the herbaceous mix of native plants has been shown to be more attractive for native bees and is arguably more attractive. This information is critical; although succulents are currently the industry standard, planting only succulents on roofs could potentially have a negative impact on urban ecology in various regions.

An additional variable to consider when designing a green roof is its location. GRIT Lab researcher Scott MacIvor and co-researchers found that building height matters: There are far fewer bee hives when green roofs are too high, and so designing a roof aimed at helping bees higher than eight storeys would be futile.

As storm events become more frequent and severe for municipalities, cities with aging stormwater infrastructure like Toronto are struggling to find ways to alleviate the impact. Green roofs can be a part of this solution, but all green roofs are not created equal. The proper research and knowledge is essential.

Why is climate change’s 2 degrees Celsius of warming limit so important?

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If you read or listen to almost any article about climate change, it’s likely the story refers in some way to the “2 degrees Celsius limit.” The story often mentions greatly increased risks if the climate exceeds 2°C and even “catastrophic” impacts to our world if we warm more than the target.

Recently a series of scientific papers have come out and stated that we have a 5 percent chance of limiting warming to 2°C, and only one chance in a hundred of keeping man-made global warming to 1.5°C, the aspirational goal of the 2015 Paris United Nations Framework Convention on Climate Change conference. Additionally, recent research shows that we may have already locked in 1.5°C of warming even if we magically reduced our carbon footprint to zero today.

And there’s an additional wrinkle: What is the correct baseline we should use? The Intergovernmental Panel on Climate Change (IPCC) frequently references temperature increases relative to the second half of the 19th century, but the Paris Agreement states the temperature increases should be measured from “preindustrial” levels, or before 1850. Scientists have shown such a baseline effectively pushes us another 0.2°C closer to the upper limits.

That’s a lot of numbers and data – so much that it could make even the most climate-literate head spin. How did the climate, and climate policy community, come to agree that 2°C is the safe limit? What does it mean? And if we can’t meet that target, should we even try and limit climate change?

Fear of ‘tipping points’

The academic literature, popular press and blog sites have all traced out the history of the 2°C limit. Its origin stems not from the climate science community, but from a Yale economist, William Nordhaus.

In his 1975 paper “Can We Control Carbon Dioxide?,” Nordhaus, “thinks out loud” as to what a reasonable limit on CO2 might be. He believed it would be reasonable to keep climatic variations within the “normal range of climatic variation.” He also asserted that science alone cannot set a limit; importantly, it must account for both society’s values and available technologies. He concluded that a reasonable upper limit would be the temperature increase one would observe from a doubling of preindustrial CO2 levels, which he believed equated to a temperature increase of about 2°C.

Nordaus himself stressed how “deeply unsatisfactory” this thought process was. It’s ironic that a back-of-the-envelope, rough guess ultimately became a cornerstone of international climate policy.

The climate science community subsequently attempted to quantify the impacts and recommend limits to climate change, as seen in the 1990 report issued by the Stockholm Environmental Institute. This report argued that limiting climate change to 1°C would be the safest option but recognized even then that 1°C was probably unrealistic, so 2°C would be the next best limit.

During the late 1990s and early 21st century, there was increasing concern that the climate system might encounter catastrophic and nonlinear changes, popularized by Malcolm Gladwell’s “Tipping Points” book. For example, continued carbon emissions could lead to a shutdown of the large ocean circulation systems or massive permafrost melting.

It’s all about risk: Chart from 2014 IPCC report shows how higher temperatures lead to higher risk of problems. UN IPCC, CC BY-NC

This fear of abrupt climate change also drove the political acceptance of a defined temperature limit. The 2°C limit moved into the policy and political world when it was adopted by the European Union’s Council of Ministers in 1996, the G8 in 2008 and the UN in 2010. In 2015 in Paris, negotiators adopted 2°C as the upper limit, with a desire to limit warming to 1.5°C.

This short history makes it clear that the goal evolved from the qualitative but reasonable desire to keep changes to the climate within certain bounds: namely, within what the world had experienced in the relatively recent geological past to avoid catastrophically disrupting both human civilization and natural ecosystems.

Climate scientists subsequently began supporting the idea of a limit of 1°C or 2°C starting over three decades ago. They showed the likely risks increase with temperatures over 1°C, and those risks grow substantially with additional warming.

And if we miss the target?

Perhaps the most powerful aspect about the 2°C threshold is not its scientific veracity, but its simplicity as an organizing principle.

The climate system is vast and has more dynamics, parameters and variations in space and time than is possible to quickly and simply convey. What the 2°C threshold lacks in nuance and depth, it more than makes up as a goal that is understandable, measurable and may still be achievable, although our actions will need to change quickly. Goals and goal-setting are very powerful instruments in effecting change.

While the 2°C threshold is a blunt instrument that has many faults, similar to attempting to judge a quarterback’s value to his team solely by his rating, its ability to rally 195 countries to sign an agreement should not be discounted.

The 2°C threshold is a lot like trying to stop a truck going downhill: The quicker you hit the brakes (on emissions), the easier it will to lower the risk of problems later. Bruno Vanbesien, CC BY-NC

Ultimately, what should we do if we cannot make the 1.5°C or 2°C limit? The most current IPCC report shows the risks, parsed by continent, of a 2°C world, and how they are part of a continuum of risk extending from today’s climate to a 4°C.

Most of these risks are assessed by the IPCC to increase in steady fashion. That is, for most aspects of climate impacts we do not “fall off a cliff” at 2°C, although considerable damage to coral reefs and even agriculture may increase significantly around this threshold.

Like any goal, the 2°C limit should be ambitious but achievable. However, if it is not met, we should do everything we can to meet a 2¼°C or 2.5°C goal.

These goals can be compared to the speed limits for trucks we see on a mountain descent. The speed limit (say 30 mph) will allow trucks of any type to descend with a safety margin to spare. We know that coming down the hill at 70 mph likely results in a crash at the bottom.

In between those two numbers? The risk increases – and that’s where we are with climate change. If we can’t come down the hill at 30 mph, let’s try for 35 or 40 mph. Because we know that at 70 mph – or business as usual – we will have a very bad outcome, and nobody wants that.

Acting on climate change is Africa’s opportunity

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Acting on climate change is Africa’s opportunity Continent is well placed to reap benefits in investment and jobs beyondbrics Read next An Inconvenient Sequel: Truth to Power — a gift for making statistics enthral Part of a wind farm outside Nairobi, Kenya. The country is building Africa’s biggest wind farm, creating 2,000 jobs © AFP Share on Twitter (opens new window) Share on Facebook (opens new window) Share on LinkedIn (opens new window) 3 Save to myFT JULY 25, 2017 by: Ngozi Okonjo-Iweala Acting on the climate remains firmly on the global agenda. It remained a top priority for all but one of the G20 leaders who gathered in Germany this month. That is because it is increasingly clear that strong action is in the economic self-interest of countries at all stages of development.

Climate investment opportunities in emerging markets could be as much as $23tn by 2030. National governments, states, cities and businesses are all seeing the opportunities of climate action, from employment to investment and from smarter growth to a cleaner, healthier future for all.

Take jobs, where climate action could generate a veritable bounty of clean energy employment. Globally, 62 per cent of renewable energy jobs are already in Asia, with 3.6m jobs in China alone, according to the International Renewable Energy Agency. China expects to create 13m jobs in the renewable energy sector over the next four years. Across the African continent, forays into the clean energy industry have been promising, with renewables already providing 62,000 jobs and much potential ahead. beyondbrics Emerging markets guest forum beyondbrics is a forum on emerging markets for contributors from the worlds of business, finance, politics, academia and the third sector.

All views expressed are those of the author(s) and should not be taken as reflecting the views of the Financial Times. Algeria, for example, created 3,500 jobs in the construction of 14 grid-connected solar PV projects in 2015, with 700 permanent jobs expected in operation and management. Kenya is building Africa’s largest wind farm at Lake Turkana, planned to be fully operational later this year. Its construction has created more than 2,000 local jobs since October 2014. Overall investment in sub-Saharan Africa, particularly for clean energy, represents a $783bn opportunity.

We are also particularly well placed to take advantage of cheap and plentiful resources from the sun and wind. The potential for renewables in sub-Saharan Africa stands at about 1,100 gigawatts of solar capacity, 350 gigawatts of hydropower and 109 gigawatts of wind. This would be more than enough to meet future demand. Meanwhile, the cost of utility-scale solar in Africa fell 50 per cent from 2010 to 2014 and continues to fall. Further upstream, African countries could also capitalise on opportunities to get more involved in the production of low-carbon technology. Rather than importing solar panels and wind turbines from elsewhere, Africa can establish itself as a green manufacturing giant. We shouldn’t let people just sell us items that we are well positioned to produce ourselves.

Instead, we can lead in developing and producing the clean energy solutions we need. African cities can leapfrog the urban development challenges that other fast moving economies have faced. The population of Lagos, for instance, is set to reach 25m people by 2030. The city’s traffic congestion is already notorious, costing commuters 3bn hours a year from 2007 to 2009 and — in one memorable case — costing a man his marriage. But recent investment in bus-oriented transport infrastructure, with dedicated lanes for environmentally friendly mass-transit vehicles, has improved the situation considerably and at a fraction of what it has cost elsewhere.

Getting our cities right and, in some cases, building them right in the first place will not only deliver economic benefits but will help us avoid the costs of sprawl, traffic congestion and debilitating air pollution that plague residents of Beijing or Delhi. Rural economies matter just as much as our urban opportunities. And here too, positive actions are yielding solid results. Farmers in Niger, for example, using new agroforestry techniques benefited from increased grain production as well as increased gross annual income, going up by $1,000 per household for more than 1m households. Local communities in northern Ethiopia organised themselves to control livestock grazing and wood cutting on degraded plateaux and mountain slopes, allowing vegetation to regenerate naturally and making the region greener than it has been for well over a century.

Large-scale initiatives are also delivering. AFR100, for instance, was launched in 2015 to bring 100m hectares of deforested and degraded landscapes across Africa into restoration by 2030. Within a year, 21 countries have signed on to committing 63.5m ha into restoration and more than $1bn in development finance and $545m in private investment have been secured. There should be no doubt — in developing countries the world over and especially in Africa — that the new climate economy of the future will bring benefits ranging from jobs in clean energy to improved air quality and more productive land. Staying the course will put us at the forefront of this green economic revolution. That’s a good place to be. Ngozi Okonjo-Iweala is co-chair of the Global Commission on the Economy and Climate and chair of the Global Alliance for Vaccines and Immunization. She was previously finance minister of Nigeria and managing director of the World Bank

Global Water Shortage Risk Is Worse Than Scientists Thought

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Global Water Shortage Risk Is Worse Than Scientists Thought

About two-thirds of the world’s population faces water scarcity for at least one month during the year.

By Kim Bellware

FOTO24 VIA GETTY IMAGES
Sheep seen on Manie van Rooys farm on November 6, 2015 near Frankfort, South Africa. Free State farmers have been severely affected by what is considered as the worst drought since 1992.

The growing risk of worldwide water shortages is worse than scientists previously thought, according to a new study.

About 66 percent, which is 4 billion people, of the world’s population lives without sufficient access to fresh water for at least one month of the year, according to a new paper published Friday in the journal Science Advances.

Previous studies calculated a lower number, estimating that between 1.7 and 3.1 billion people lived with moderate to severe water scarcity for at least a month out of the year.

Scientists, led by Dr. Arjen Hoekstra of the Netherlands’ University of Twente, used a computer model that is both more precise and comprehensive than previous studies have used to analyze how widespread water scarcity is across the globe. Their model considers multiple variables including: climate records, population density, irrigation and industry.

“Up to now, this type of research concentrated solely on the scarcity of water on an annual basis, and had only been carried out in the largest river basins,” Hoekstra said in a statement. “That paints a more rosy and misleading picture, because water scarcity occurs during the dry period of the year.”

“The fact that the scarcity of water is being regarded as a global problem is confirmed by our research,” Hoekstra added. “For some time now, the World Economic Forum has placed the world water crisis in the top three of global problems, alongside climate change and terrorism.”

SCIENCE JOURNALS
About two-thirds of the world’s population faces water scarcity for at least one month out of the year.

Severe water scarcity happens when consumption is twice as high as available resources, according to the study’s researchers. Consequently, half of those suffering from water scarcity are in the world’s two most populous countries — India and China — where demand is high.

High-scarcity levels are also widespread in areas with significant irrigated agriculture (like the Great Plains in the United States) or low natural availability of fresh water (like the Arabian Desert) where populations are also relatively dense, according to the study. Similar patterns exist in the south and western United States where heavily populated states like California have been in a drought for years. 

The consequences of water scarcity can result in economic losses due to crop failure, limited food availability and poor business viability, and can threaten environmental biodiversity. When faced with scarcity, areas in need of water often resort to pumping groundwater, which can permanently deplete the supply.

Water shortages have also precipitated or heightened the potential for global conflicts in places like the Middle East and Africa.

“Freshwater scarcity is a major risk to the global economy, affecting four billion people directly,” Hoekstra told The New York Times. “But since the remaining people in the world receive part of their food from the affected areas, it involves us all.”

Despite the grim findings, the study recommends ways to reduce scarcity, such as increasing reliance on rain-fed rather than irrigated agriculture, improving the efficiency of water usage and — perhaps the most challenging for humans — sharing what’s available. The researchers point out that for these solutions to be effective, governments, corporations and investors will need to cooperate.

How To Feed the World After Climate Change

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How To Feed the World After Climate Change

Seeds.
There are limits to how technology can help post-climate change agriculture.

Photograph courtesy San Luis Obispo County, Calif., Department of Agriculture

On Thursday, April 12, Future Tense, a partnership of Slate, the New America Foundation, and Arizona State, will host a live event in Washington, D.C., on the future of food. “Feeding the World While the Earth Cooks” will examine post-climate-change agriculture, the rising demand for meat, and more. Click here for a full agenda and to RSVP.

When my daughter turned 7 last week, we celebrated with a homemade chocolate cake. I wonder whether she’ll be able to do that with her own child someday. Scientists are already warning that chocolate and wheat (the raw material for flour) will become harder to grow as temperature and rainfall patterns are disrupted.

Over the next 50 years, climate change will transform the world in ways we have only begun to imagine. Humans have changed the weather on this planet, and that will change everything, especially how we grow food.

Consider corn. The major crop (by volume) grown in the United States, corn does not reproduce at temperatures higher than 95 degrees. During the 20thcentury, Iowa experienced three straight days of 95 only once a decade. But by 2040, if greenhouse gas emissions remain on their current high trajectory, Iowa will experience three straight days of 95-degree heat in three summers out of four, professors Katharine Hayhoe of Texas Tech University and Donald Wuebbles of the University of Illinois have calculated.

John Beddington, the chief science adviser to the British government, has warned that by 2030 the interlocking trends of climate change, population growth, and resource scarcity may result in “major destabilization,” including street riots and mass migrations as people flee shortages of food and water.

But that nightmare scenario need not come to pass. We already know what works—and what doesn’t—to feed a post-climate-change world. In fact, many of the practices and technologies we need are already in use, in the United States and abroad.

What’s needed is to bring these isolated success stories to scale, to make them the rule rather than the exception. But that’s not an easy task when the agricultural approaches that actually improve people’s lives can be overshadowed by inferior alternatives propped up by large PR budgets or government support.

Take the argument that more heat- and drought-resistant seeds are what’s needed to cope with climate change. The good people at Monsanto have spent lots of advertising money to spread this message.  And joined by two other high-profile backers of genetically modified organisms—the Bill and Melinda Gates Foundation and the Warren Buffet Foundation—Monsanto has claimed to have already increased corn yields in Africa by 25 percent to 35 percent. There’s a catch, though: The only documentation for those results was found on Monsanto’s own website and was later removed.

Most peer-reviewed research has found little reason for optimism that GMO seeds will revolutionize yields in the face of climate change. The most authoritative analysis is found in Agriculture at a Crossroads, the landmark report issued by the International Assessment of Agricultural Knowledge, Science and Technology for Development in 2009. Testifying before Congress, Robert Watson, the scientist who directed the assessment, explained in the gentlest possible terms that GMO crops are an unproven technology whose benefits remain highly uncertain: “[I]t is likely to be several years at least before these [GMO] traits might reach possible commercial application [my emphasis].”

So better seeds alone won’t save us. Instead, feeding the world under climate change will require a broader strategy, grounded in two imperatives. On the one hand, we must rapidly reduce the amount of greenhouse gases in the atmosphere, to avoid facing unmanageable amounts of future climate change. On the other, we must prepare our agricultural sectors for the climate impacts already “in the pipeline,” which will be severe enough.

The currently dominant system of industrial agriculture is a loser on both fronts. It emits enormous amounts of greenhouse gases, partly because it consumes huge quantities of oil—to power farm equipment, manufacture fertilizer, and ship food through global networks. Meanwhile, its preference for monoculture rather than diversity makes it extremely vulnerable to hot and volatile weather, as well as to the uptick in pests and diseases such weather will bring.

“We absolutely have to develop seeds for improved and climate-adapted varieties, but we also need to increase the diversity of seeds,” says Sara Scherr, the president of Ecoagriculture Partners, an NGO in Washington, D.C. (Scherr will also be speaking at the upcoming Future Tense event “Feeding the World While the Earth Cooks.’) “A lot of the focus is on, ‘Let’s get a few seeds that are drought-resistant that can be used on millions of hectares.’ The current business model in agriculture is based on maximizing volume, which militates against diversity.”

More and more agricultural experts are saying we need a shift to ecological agriculture, sometimes known as agro-ecology. Ecological agriculture eschews applying chemical fertilizers to soil; rather, it favors compost and manure, which increase the soil’s fertility and ability to retain water—key advantages against hot, dry weather. And rather than monocultures, agro-ecology fosters a diverse agricultural landscape where nature’s processes are utilized not only to grow food but to maintain the health of the soil, water, and biodiversity that make agriculture possible in the first place.

In western Africa, for example, thousands of the poorest farmers on earth are capturing scarce rainfall and rejuvenating soil fertility by growing trees amid their fields of millet and sorghum. Despite enduring some of the hottest, driest weather on earth, these farmers have returned greenery to 12.5 million acres of land—enough to see from outer space, courtesy of satellite imagery from the U.S. Geological Survey. More important, underground water tables have been replenished, and crop yields have doubled and tripled.

Mixing forests and farmland is also being explored in China, where Lin Erda, a senior government scientist, has joined with Greenpeace to endorse ecological agriculture as the best way to cope with climate change. Raising ducks and fish in rice paddies, for example, reduces both greenhouse gas emissions and the need for chemical fertilizers; the fish decrease the methane that the paddies would otherwise emit, while the ducks control pests.

But how does ecological agriculture compare against industrial agriculture’s greatest strength—its ability to produce prodigious amounts of food? That’s a vital question on a planet where, even today, one in seven people goes hungry.

In Africa, extensive field studies show ecological agriculture matching the yields of conventional agriculture, while also boosting water supply and soil fertility. But Africa is a special case. Bypassed by the Green Revolution of the 1970s, it never got used to the inflated yields that industrial agriculture made possib–le.

In the United States and Europe, switching from industrial to ecological agriculture has invariably caused an initial decline in yields. However, after a brief transition period of three to five years, ecological agriculture’s yields rebound to equal those of industrial agriculture, according to a 30-year studyconducted by the Rodale Institute.

And ecological agriculture’s advantages promise to be even greater under climate change.  In drought years, Rodale found, its yields were 31 percent higher than conventional yields. Ecological agriculture also built rather than depleted soil fertility while recharging groundwater supplies. Finally, it produced 40 percent fewer greenhouse gases than industrial agriculture.

My daughter was born into what I call Generation Hot—the 2 billion young people worldwide who will spend the rest of their lifetimes coping with the hottest, most volatile climate human civilization has ever known. Agriculture, it turns out, is one of the few tricks humanity still has up its sleeve to avoid the unmanageable and manage the unavoidable of climate change. Let’s not squander it.