San Diego Press Club 2019 Excellence in Journalism Award Winner
Carbon is getting a bad rap these days as the main pollutant responsible for climate change. On the other hand, carbon is, quite literally, the stuff that life is made of. All living things—plants, animals, bacteria, and all other life forms—are built out of carbon. Considering this basic fact offers a window into how we might harness the elegance of biology to slow down and even possibly reverse climate change.We’ll return to this later, after a short exploration of how climate change might be affecting nutrition in the food we eat.
Everything Starts With PhotosynthesisFirst, a crash course on the basics of plant biology that are key to understanding how plants might be affected by climate change, and also how they might help us solve it.Plants take in carbon dioxide gas (CO2) from the atmosphere, and use water and sunlight in a chemical process called photosynthesis to convert that CO2 into carbohydrates. These carbohydrates are of two types: structural, that is, the fiber that makes up the leaves, stems, roots, fruits, seeds, and other parts; and non-structural, sugars and starches contained in those tissues, which is where much of the caloric content comes from. Healthy Food Depends on Healthy SoilPlants contain more than just carbs, though, so while the carbohydrate building block comes from CO2 in the air, other elements like nitrogen (the main ingredient in protein), phosphorus, calcium, iron, zinc, and many others originate in the soil. This means that the nutrients we get from plants come to us from the earth beneath our feet.Soils rich in nutrients produce more nutritious plants, and depleted soils produce less nutritious plants. According to Dr. Ratan Lal, director of the Carbon Management and Sequestration Center at Ohio State University, not only do healthy soils produce higher crop yields, they also produce healthier foods. We obtain 24 essential elements exclusively through plants, which obtain them from the soil. Over time, our conventional agricultural practices such as frequent soil tilling, excessive grazing, and heavy reliance on agrochemicals, including synthetic fertilizer, have depleted agricultural soils of the carbon-rich organic layer and the diverse life forms in them. In fact, conservative estimates are that global agricultural lands lose a total of 75 billion tons of fertile soil every year. In addition to eroding soils and the nutrients they contain, we now know that our current agricultural practices are responsible for around 20% of global greenhouse gas emissions causing climate change.
Climate Change Is Altering Plant NutritionFor several decades we have known that CO2 in the atmosphere is increasing due to human activity. Scientists working in agriculture and other plant science fields have found, in study after study, that plants actually photosynthesize faster and produce more carbohydrates in conditions of elevated CO2. This is sometimes referred to as the “CO2 fertilization effect.” It turns out that the added carbs are actually the non-structural kind. That is, under conditions of elevated CO2, plants add more starch and sugar to their tissues than they do under current CO2 conditions, in some cases up to 45% higher.If starches and sugars are more abundant in plants grown in higher CO2 conditions, how might nutrients, which originate in the soil, be affected? Are they able to keep up with the added carbohydrate production by plants?Scientist Irakli Loladze, a mathematician with a keen interest in plants and climate change, set about asking these questions. He conducted a giant meta-analysis of almost 8,000 scientific observations on the levels of various soil-based elements in plants that had been grown under conditions of experimentally elevated levels of CO2. Loladze’s expertise in mathematics allowed him to correct for the differences in sample size and other factors that varied between studies. Sure enough, when he controlled the statistical noise, he found a signal: Nitrogen, iron, zinc, calcium, and several other important nutrients all dropped in concentration—on average by 8%—as the levels of starches and sugars rose. In other words, Loladze found that regardless of plant type, geographic region, or which nutritional element he looked at, levels of important nutrients are not keeping pace with increasing levels of sugars and starch, a foreboding phenomenon that has been described elsewhere as “growing junk food". Those are findings from experiments in which future conditions were simulated, but what about the more recent past?As CO2 levels have risen over the last two centuries, have plants already undergone a similar shift? Scientists analyzing archived plant collections have found that in both crops and wild plants, mineral levels have indeed been decreasing. Some scientists attribute the change in crops to changes in selectively bred traits, but the parallel change in wild plants has led Loladze to speculate that elevated CO2 may be the more important agent of change.
Nutritionists speculate about the effects additional sugar and reduced protein could have, for example, on diabetes and obesity rates, but they caution that the research simply isn’t there yet to know exactly what the effects could be. The findings could certainly help target important traits to select for in future crop breeding and selection.Summing up all of the above paints a discouraging picture. Our current practices of food production lead to soil degradation, which means we produce less food per unit of land area, with fewer nutrients.We usually attempt to solve this by clearing more land, tilling more soil, and using more fertilizers—further degrading the soil and contributing one-fifth of all greenhouse gases emitted by human activities. This exacerbates climate change, which we have learned is shifting our crops toward higher sugars and lower nutrients, thus exacerbating food insecurity. And so on and so forth—a sobering set of runaway challenges.
Turning the Problem into the SolutionDespite this grim outlook, there actually exists a simple solution: rebuilding soil carbon through a set of practices known as carbon farming.By partnering with plants, bacteria, and fungi (and earthworms and numerous other soil dwellers), we can actually convert some of the excess CO2 that’s in our atmosphere to rebuild the amount of organic material in the soil, over half of which we have lost. Carbon in our soils helps conserve and retain water and rebuild soil fertility. Over time, when paired with the right practices, the soils actually sequester that carbon deep underground, locking it up in substances such as soil humus, where it can stay for hundreds and even thousands of years.Carbon farming practices include practices familiar to permaculture, organic agriculture, and regenerative farming. They include compost application, riparian restoration, agroforestry, cover cropping, no-till farming, and several other methods that increase organic soil matter. This additional organic matter can increase the productivity of croplands as it also restores the availability of nutrients so dramatically depleted over the last century from our conventional agriculture practices.By increasing the water-holding capacity of the soil, carbon farming will help us adapt to drought, changing precipitation patterns, and other climate challenges ahead. Once soil carbon buildup starts, if the practices are maintained, the process of carbon sequestration continues for several decades. Expert contributors to the book Drawdown maintain that if we commit to investing in building soil carbon on a large scale while also decreasing our energy, transportation, and other emissions, we can actually begin to draw down atmospheric greenhouse gases and reverse climate change through the same practices that help us attain global food security.
It may turn out that rebuilding soil fertility might not impact the relative amounts of nutrients and carbs in plants growing under higher CO2 levels, and the effect that Loladze found will continue as long as we have elevated levels of CO2. We have yet to learn enough about this topic to theorize, but enhanced soil fertility will at least ensure the availability of key nutritional elements in the soils, and most importantly, rebuilding the soils could finally shift our atmosphere back to one in which elevated CO2 is a thing of the past.Sometimes the fight against climate change seems like a bitter pill that we must swallow sooner or later. But if we work with tried and tested practices and the biodiversity of the soil, getting that carbon out of the atmosphere and into the soil can make combating climate change a life-affirming call to action. Here in San Diego County, several organizations are working to build policy and programs that bring climate action together with carbon farming incentives that support agricultural livelihoods.Learn MoreFor more information on how carbon farming can help our county’s climate mitigation targets, climate resilience efforts, and agricultural economy, you can download the technical report, Linking Climate-Friendly Farming Practices to San Diego County’s Climate Action Plan: An Opportunity Analysis of Carbon Farming in the Unincorporated County, or the summarized version, Building a Climate Friendly San Diego From the Ground Up, from the San Diego County Farm Bureau or San Diego Food System Alliance websites.