By Andrea Calderon Irazoque
The agricultural sector today is facing the daunting challenges of adapting to increasing impacts from climate change while minimizing greenhouse gas emissions and meeting ever-growing food demand. Crop-producing regions will be required to respond to these issues in the coming decades and their ability to do so will potentially affect all of humanity – even those living in highly urbanized areas. To put things into perspective, according to the United Nations, food demand is predicted to double by 2030.
In response to these concerns Nature Climate Change recently published a web focus collection “A new climate for farming”. The collection includes sixteen recent publications by AgMIP and other authors, including research articles, letters and opinion pieces addressing three essential topics: climate change impacts on agriculture, the influence of agriculture on the climate and our capacity to adapt to these challenges. Highlights of the contributions are succinctly summarized below.
Climate Change Impacts On Agriculture
The editorial of the collection, “Yields and more,” is an overview of topics included in the web focus. The editors highlight the importance of crop models as the best tool available to simulate future climate change impacts on yields. The Agricultural Model Intercomparison and Improvement Project (AgMIP) is named as one of the leading efforts to improve these crop models and evaluate their relative performance, addressing some of the challenges and general lessons regarding the potential impacts of climate change on crops and agricultural yields.
The letter “Uncertainty in simulating wheat yields under climate change” by Asseng and others (2013) presented the largest standardized model intercomparison for climate change impacts on wheat yields. The authors conclude that projections from individual crop models fail to represent uncertainties known to exist in crop responses to climate change. However, model ensembles have the potential to quantify the significant crop component of uncertainty.
In the commentary “Crop–climate models need an overhaul” by Rötter and others (2011), AgMIP scientists state the urgency of focusing research on rigorous multi-model ensembles that can lead to more accurate estimates of the amount of food that can be grown in a warmer world. This approach has the potential to provide robust and useful information for farmers and policymakers in the coming decades.
In the commentary “Fertilizing hidden hunger,” AgMIP researchers Müller, Elliott and Levermann (2014) analyze the evidence of negative impacts of high CO2 levels on crops. They explain that even if CO2 fertilization could compensate for the impact of climate change on crop yields, it comes at the expense of decreasing the nutritional value of food. A more detailed analysis of this commentary was made in the AgMIP blog post: Are increasing CO2 emissions causing hidden hunger?
The role of how extreme weather will affect crop yields still needs further investigation. The majority of crop impact studies focused on changes in the average state of the climate rather than in adverse weather events. Trnka M. and others (2014) in the article “Adverse weather conditions for European wheat production will become more frequent with climate change” analyze how the rising number of extreme events will increase crop failure. The authors studied fourteen sites across thirteen European countries representing the main wheat-growing areas in the continent. They showed that occurrence of adverse events might substantially increase by 2060 compared to the present (1981-2010). This could lead to global repercussions, since Europe produces around 30% of worldwide wheat supply.
Adaptation strategies reduce the risks of climate change are imperative. In “Europe’s diminishing bread basket is included in the collection” Meinke (2014) suggests that a potential limitation of the (2014) study by Trnka and others is that they only analyze wheat grown on free-draining soils with high water-holding capacity, yet soil type differences will likely have an impact on risk profiles such as frequency and severity of water stress or water logging.
Lobell and others (2012) report studies on “Extreme heat effects on wheat senescence in India.” Using nine years of satellite measurements to monitor rates of wheat senescence or aging with exposure to temperatures greater than 34°C. The authors detected a statistically significant acceleration of senescence from extreme heat. With simulations they also showed that existing models underestimate the effects of heat on senescence. They imply that warming presents an even greater challenge to wheat (the most widely grown crop in the world) than previously thought. The effectiveness of adaptation strategies will depend on how well they reduce crop sensitivity to extreme temperature events.
Influence Of Agriculture On The Climate
Climate and Land Use
The growing demand of food exacerbated by a population that is expected to rise to 9.6 billion in 2050, will catalyze the need to increase yields in the coming decades. This challenge is also exacerbated by the demand to guarantee energy security leading to proliferation of biofuel crops instead of fossil fuels. In this area of research Mello and others (2014) quantified the soil carbon balance for land use change for sugarcane expansion in Brazil in the letter “Payback time for soil carbon and sugar-cane ethanol.” Half of the 721 million tonnes of this crop harvested in Brazil in 2012 was destined for ethanol production. This makes sugarcane the main source of renewable energy in that country, ranking Brazil as the second largest producer of bioethanol in the world. The authors show evidence that soil carbon decreases after land use change from native vegetation (like savannahs) and pastures, and increases where croplands are converted to sugarcane. The payback time for the soil carbon net loss was eight years for native vegetation and two years for pastures. A commentary of this article by Maced and Davidson (2014) entitled “Forgive us our carbon debts” gives further observations on the topic.
The letter “Carbon emissions from forest conversion by Kalimantan oil palm plantations” by Carlson and others (2012), also studies the effect of land use but from another perspective, their focus is on the carbon emissions from forest conversion to oil palm plantation in Kalimantan, Indonesia. Sumatra and Kalimantra produce around half of the palm oil worldwide. The authors show that from 1990 to 2010, 90% of lands converted to oil palm were forested, leading to a palm oil expansion over the region of 278% from 2000 to 2010. They also give evidence that plantation expansion is projected to contribute to 18-22% of Indonesia’s 2020 CO2-equivalent emissions. Indonesia ranks among the top 20 greenhouse gas emitters largely due to deforestation and forest degradation.
“Effects of double cropping on summer climate of the North China Plain and neighbouring regions” by Jeong and others (2014) is also included in the collection. This letter studies intensification, which is one of the two ways in which increase in agricultural yield can be achieved globally. It consists in improving the average yield of land already under cultivation. The other alternative is extensification, where the area under agricultural cultivation is increased. The region of study, the North China Plain, produces up to 50% of the cereal consumed in China each year and has switched from single to double cropping to meet the increasing food demands without expanding croplands. The authors conclude that double cropping in the region can amplify the magnitude of summertime climate changes over East Asia.
Quantitative estimates of how much climate impacts can be avoided through adaptation of farm systems are difficult to evaluate. In a letter, Moore and Lobell (2014) study the “Adaptation potential of European agriculture in response to climate change” using an empirical approach. The authors found high adaptation potential for maize to future warming (87%) but large negative effects and limited adaptation potential for wheat and barley (7% and 31%, respectively). They claim that agricultural profits could increase slightly under climate change if farmers adapt but could decrease in many areas if there is no adaptation, concluding that studies that attempt to quantify uncertainty using an ensemble of climate models but only a single adaptation scenario or a single yield response model could be significantly underestimating the uncertainty of climate change impact.
In the letter “Crop yields in a geoengineered climate” Pongratz and others (2012) examine possible effects on global crop yields under a high-CO2, geoengineered scenario. They show that these conditions generally cause crop yields to increase, largely because temperature stresses are diminished while the benefits of CO2 fertilization are retained. However, they mentioned that there could possibly be losses locally. In addition to this they argue that the known and unknown side effects and risks associated with geo-engineering mean that the safest option to reduce climate risks to food security is to reduce emissions of greenhouse gases.
Evidently, the world is facing an enormous challenge, we have to address the stress on the agricultural sector caused by the changing climate, avoid the harrowing impacts of climate change, implement mitigation strategies, supply enough food to eliminate hunger and satisfy the rapidly growing population. The high-quality research presented in the 2014 Nature Climate Change focus collection will be vital to take the next steps forward involving a science driven global view of the problem by farmers and policy makers.