Agriculture – humanity’s most spatially expansive activity – is under stress. From semi-arid rangelands to humid tropical rice paddies to the USA’s corn belt, agriculture is vulnerable to increased weather variability across the planet. Yes, current commodity prices are low as recent seasonal conditions have ‘averaged out’, but increasing weather variability is and will continue negatively impacting production. Agriculture - our food supply - performs best without extreme weather conditions during the growing season. Yield impacting events, including weather that is too hot, too cold, too wet, or too dry, are already occurring more frequently all across the planet. Unfortunately, agriculture needs approximately 70 to 150 continuous days without extreme weather events to support crop production. While seasonal crops can be adapted to better perform in changing conditions, such as drought tolerant seed varieties, a single extreme event still has the potential to damage an entire production season. As our atmosphere continues to warm, the energy increases, and the odds of an extreme weather event grow.
The Impact of a Warmer Atmosphere
Atmospheric physics tells us that it takes an enormous amount of energy to warm the atmosphere by 1°C. We can calculate this amount of energy in joules. We have observed an approximately 1°C warming of our atmosphere since the mid-1800’s (officially 0.85°C), which translates to about 5.53 x 1023 joules of additional energy available in our atmosphere. In a conversation with Axel Kleidon, research scientist at the Max-Planck-Institute for Biogeochemistry, the impact of a 1°C warming of our atmosphere disproportionally affects the earth’s heat engine, as there are what he calls “non-linearities in the power equation, also known by the Carnot limit.” Adding heat to the atmosphere disproportionately increases the amount of work the atmosphere can do, and “the work” of our atmosphere is the weather we witness every day. With 1°C of warming, research has shown that thunderstorms are 15 percent more powerful and hurricanes are 25 percent more powerful. This response is much stronger than the intensification of the hydrologic cycle, and can be understood by the warmer atmosphere having greater temperature gradients to work with and more moisture, which disproportionally fuels these extreme events.
This additional energy in the atmosphere is driving our climate to become more volatile and extreme weather events to become more frequent and severe. The Guardian, quoting a study from Nature Climate Change, reported in April 2015 that, “[r]esearchers say heatwaves that previously occurred once every three years are now happening every 200 days thanks to global warming.” The relation to agriculture is simple: an abnormal and extreme weather event, such as a heat wave or a too much precipitation, during a sensitive crop growth stage can have a lasting negative impact on yield, regardless of whether the rest of the season’s conditions were ideal. The estimation that such episodes will occur once every 200 days as opposed to once every 1000 days predicts a 500 percent increase in the frequency of these weather events – an increase that is linked to atmospheric warming. Furthermore, the researchers suggest that the probability ratio of 5-day, 15-day, and 31-day extremes increases even faster than the daily frequency just referenced. Agriculture is, of course, vulnerable to 5, 15, and 31-day temperature and precipitation extremes.
For example, hail can destroy a crop in a brief explosion of energy lasting between 5 and 20 minutes. Similarly, a powerful downdraft can knock over maize stalks, while tornados can do substantial local damage. Further examples include a frost, for which many agricultural crops have little or no tolerance and the frequency of which might actually increase as the atmosphere warms, as well as excessive rainfall, which can drown crops. With larger storms occurring and expected to grow even larger, the footprint of extreme event damage is sure to increase both spatially (over a larger area) and temporally, as more events occur. Some events such as drought can be widespread, regional, or ‘pocket droughts’, all with significant consequences for agriculture and farmers.
Subtle Weather Effects
It’s clear that extreme weather events can negatively impact agriculture, but it’s critical to note that not all of these events have to be extreme to inflict damage. More insidious than extreme events, warmer and more humid nights create conditions in which foliar diseases, including viral, bacterial, and fungal diseases, can thrive. For perennial crops, like coffee and cacao, persistently higher nighttime temperatures can kill the trees. These warmer nights are currently negatively impacting coffee trees in Vietnam, where 40 percent of the world’s Robusta coffee is produced, and elsewhere including Guatemala and Tanzania, leading to a tremendous human impact as poor farmers and workers lose their cash earnings.
Do you enjoy chocolate? Over the last 10 years we’ve seen a systematic degradation in conditions for cacao tree health in both Cote d’Ivoire and Ghana, important cacao producers. Hotter weather, more persistent dry spells, and stronger winds are all challenges to cacao production. As the weather systems change, where can we find areas suitable for the crop? For cacao, this will be a challenge in the future, as conditions for current cacao production appear to be degrading in a prime production region.
Coffee and cacao may just be the ‘canary in a coal mine,’ for agriculturally impacted weather changes. The struggle of these perennial plants to thrive in their traditional areas is analogous to the increased stress also faced by our seasonal crops. This sets the stage for what is likely a more concerning conversation; what will happen to our food crops in the face of climate change? Corn (maize), soybean, rice, and wheat are the staple crops that feed the planet. While we currently have a glut of these crops, it was only 4 years ago in 2012 that a widespread drought impacted global production so significantly that prices of maize soared from around $3.25/bushel to over $8.00/bushel. The conclusion in front of us is that our food supply becomes more vulnerable as weather variability increases.
In January of 2016, the journal Nature reported that, “Extreme weather is damaging to crop production and threatens food safety worldwide.” Weather variability creeps into all facets of agriculture, and our risk and uncertainty grow as weather conditions become less predictable. Unfortunately, there are a number of examples of food causing conflict and uncertainty around the world
Consider the ongoing conflict in Syria. Proceeding the conflict that began in 2012, analysts report, was the worst drought in Syria in 900 years. Farmers left their farms and migrated towards the cities. In 2008, the failure of the Ukraine’s wheat crop triggered a spike in global wheat prices to historic levels. This surge in food prices contributed to discontent that, in part, spurred calls for change in many MENA nations (the ‘Arab Spring’). Today, the USA is the recipient of refugees from Central America that are no longer able to earn a living as laborers on coffee plantations. In Africa, increasing rainfall variability across the Sahel will continue to displace people. ‘Pocket droughts’ and other localized rainy season failures leads to conflict as resources grow short when people and animals move from too-dry areas to nearby areas that received rain.
India has faced climate-related challenges in recent years with its monsoon becoming less predictable. The country’s annual monsoon, which supplies three-quarters of the sub-continent’s annual rainfall, is becoming more erratic in both location and timing. High temperatures, heavy rain spells and humid-hot conditions are following each other in rapid succession. In the last half year alone, the weather has touched on two extremes, with six weeks of unprecedented scorching heat in May and June, alongside untimely and heavy rains in upper Punjab in late October. Similar to other parts of the world, erratic weather patterns in India have left farmers struggling when agriculture suffers, as it has in the last two years following poor monsoon seasons.
Climate in the US
The United States is not immune from such atmospheric pressures. Here in the US, the growing season has been getting longer (ranging from 32°F in the Spring until 32°F in the Fall) each year since 1985. On the surface, this may appear to be a benefit, but the drawback is that pests and diseases can flourish with a longer growing season. Gene Tackle, Director of Iowa State’s Climate Science program, explained a simple plant physiological truth: when it’s extremely humid and hot at night, the plant transpires and gives back the carbon to the atmosphere it gathered during the day. That lost carbon represents lost grain weight opportunity.
In general, longer and warmer growing seasons means more generations of insect pests to wreak havoc on crops during the growing season, in addition to more pests surviving the shorter and warmer winters.
Across the USA, extreme weather events are costly. October 2016’s Hurricane Matthew is just one example. According to Erin Auel of the Center for American Progress, “As global temperatures continue to climb, these events are going to become more frequent, more powerful, more deadly, and costlier.” 
Meanwhile, weather variability characterized the 2016 growing season in the USA. Some US corn and soybean growing areas experienced a rainfall deficit early in the 2016 growing season, and on July 11, 2016, the National Weather Service in Des Moines announced that part of south central Iowa had received 8 to 10 inches below-normal rainfall (for the year - see Figure 1). This was followed by a rainfall surplus from August through September. The USDA, meanwhile, predicted record yields for these crops in mid-August. aWhere monitors localized daily weather conditions, and saw tremendous variability in the agriculture weather for some areas of the corn belt (see Figure 2). Solely examining seasonal totals would obscure this in-season variability. Growth stage specific stresses were observed (too dry then too wet), and this variability in agriculture-weather during the season can negatively impact yields. As a result, good yields are expected in total, but specific weather conditions make it unlikely that this year’s yields will beat records.
In the above figure, the US Weather service shows a pocket drought forming in Iowa. Rains later in the season alleviated the drought – but the impact on yield did not fully disappear.
The above figure shows that areas of the US corn belt (outlined) colored in orange to red received significantly less rainfall than expected in June, while areas in blue received significantly more than usual in August and September.
Protecting the future of agriculture and farmers in the face of a changing climate is a challenge. Here at aWhere, we continue to track, closely and in real-time across the planet, the agricultural weather. Agile and adaptive agricultural systems are needed, with farmers requiring real-time agriculture-weather information to cope with the variability. Across the agricultural value chain, from input providers and researchers to markets, all need to know what farmers are facing, what they need (ranging from crop and seed type to crop protection), and how things are going. Agriculture and food security have become another ‘big data’ information challenge and one that will increase in importance with increasing weather variability.
 Kleidon has a new book entitled, ‘Thermodynamic Foundations of the Earth System’ which delves into the fundamental thinking of the physics of our atmosphere. See https://thermodynamicearth.org/
 See, for example, https://agfundernews.com/how-ag-big-data-can-provide-the-early-warning-signals-of-global-conflict5708.html
 Punjab received over 60mm of rains in a few hours in October. http://www.dawn.com/news/1267389
 As compared to the 1895-2015 average.
 An interactive web-site highlighting the most recent billion-dollar weather events in the USA can be found here: http://www.c2es.org/science-impacts/maps/extreme-weather