Climate Change Impacts on Agriculture and Food Security

Introduction: Weather, Climate, and Agricultural Dependence

Weather — and the related variables of temperature, light, and water — determines to a large extent human society's ability to feed itself and the animals it cares for. When weather changes due to climate variations or long-term shifts in climate, there are very serious impacts on agricultural production, reductions in crop output, and pressures on farmers to adopt new methods in order to cope with the new situation. The world's food security is thus directly affected by the prevailing climate. The changes in climate directly affect agriculture through both their effect on agricultural processes and their impact on agricultural production. It is not yet fully understood how all of this occurs or how agricultural practices can be altered to minimize those impacts. Human civilization has depended on agriculture since its inception, and farming has always been one of the fundamental means by which humans have survived.

The methods and output of agriculture remain the main contributors to the economies of developing countries. In certain cases, agricultural processes themselves may contribute to climate change — through arable farming, burning and clearing of forests, cultivation of rice in wetlands, raising livestock, and the use of nitrogenous fertilizers — resulting in increased carbon dioxide in the atmosphere and the development of methane and nitrous oxide. At the same time, when global climate changes occur, they reduce the availability of arable land, decrease crop yields, and threaten food security. This affects developing countries disproportionately.

Most of these threats are being ignored: climate change, soil erosion, depletion of water aquifers, and the expansion of deserts. These changes collectively threaten the livelihoods and food availability of hundreds of millions of people worldwide. Many national governments do not even acknowledge these problems. It is therefore important to inform the global public about the changes being caused to agriculture by climate change, and the changes in climate caused by agricultural processes. The correct application of technology and sound government policies is essential to reduce these changes. The people who live in local areas are often most aware of their own environment, and adaptation strategies can emerge from that human capacity to respond.

Rising Temperatures and Falling Water Tables

Growth in population and rising incomes have tripled the world's demand for grain over the past fifty years — from 640 million tons in 1950 to 1,855 million tons in 2000. A critical question now is whether the farming community can increase production by 100 million tons per year to feed the 70 million people added to the world annually, while also building global food stocks to a secure level. The main challenges facing farmers are rising temperatures and falling groundwater levels. Temperatures have risen sharply since agriculture was first practiced by humans approximately 11,000 years ago, and farmers are increasingly watching the water in the aquifers they depend upon disappear, with a resultant loss of irrigation capacity.

Temperature recording began in 1880, and 16 of the hottest years on record have occurred since 1980. The three hottest years came within the most recent five-year period, and crops are now regularly facing temperatures they have not previously encountered. High temperatures reduce crop yields through their impact on photosynthesis, moisture balance, and fertilization. Research has shown that photosynthesis slows when temperatures exceed 94°F (34°C), and many crops cannot photosynthesize at all above 100°F (38°C). In the United States, corn plants enter thermal shock and dehydrate when temperatures in the corn belt exceed 100°F. At those temperatures, every additional hot day reduces the harvest. High temperatures also impair the fertilization process necessary for seed development.

The widely accepted rule of thumb among researchers at the United States Department of Agriculture and the International Rice Research Institute in the Philippines is that a rise of one degree Celsius above the optimum temperature during the growing season will reduce grain yield by 10%. The second major challenge facing farmers is the rapidly falling water table. In earlier times, water was lifted from underground sources by devices powered by human or animal labor, which lacked the capacity to significantly draw down aquifer levels. Over the past fifty years, diesel and electric pumps have enabled far greater extraction of groundwater, leading to a steady and dangerous increase in water demand. This affects the three largest grain-producing countries — China, India, and the United States — which together supply 50% of the world's grain. Falling water levels in these and other countries make cutbacks in grain production virtually inevitable, and this is occurring simultaneously with a population growth rate of 70 million per year.

It is nearly impossible to predict exactly when growth in food production will fall below the growth in demand driven by population increase, but when it does, it will drive up food prices significantly. A slowdown in harvest growth, dropping water levels, and rising temperatures all point toward a future in which food becomes a matter of national security. The last time grain prices rose sharply — in 1972–74 — a politics of food scarcity emerged almost immediately. Countries that were then exporting grain began restricting exports to prevent domestic price increases. The poorest people in the world currently spend approximately 70% of their income on food grains. If food prices were to double in a short period, these populations would be impoverished almost immediately. They would naturally blame their governments, and the governments of low-income, grain-importing countries would face serious political destabilization.

Food Insecurity, Prices, and Political Consequences

There has always been a natural variation in rainfall, temperature, and related conditions in certain parts of the world — such as the Sahel, northeast Brazil, central Asia, and Mexico — leading to food insecurity through variable agricultural production. Extreme climate events such as floods, droughts, and storms, while having high visual impact, actually have a lesser effect on agricultural production than slow, persistent climate variability. Both types of effects may intensify as a result of global warming. These long-term climate changes could affect agricultural production in multiple ways, all of which would increase food insecurity for the world's most vulnerable populations. Planning for agriculture would become more difficult as weather and climate become increasingly unpredictable.

Climate variability will increase, making farming in difficult terrain even more challenging. Extreme climate events will become harder to prepare for. Agricultural land near coastlines will be submerged by rising seas, as will nearby low-lying islands. Mangroves and tropical forests would be lost, destroying fragile ecosystems. The geographic distribution of climates suitable for agriculture will shift, threatening natural vegetation and wildlife. The existing imbalance between food production in cool and temperate regions versus tropical and subtropical regions will become even more pronounced. Beyond direct impacts on farming, the fishing and seafood industries will also be disrupted. Climate change will introduce pests and vector-borne diseases into regions where they were previously unknown.

One of the documented effects of climate change has been damage to the fish and prawn breeding grounds of Vietnam, Indonesia, Malaysia, and Thailand, as reported in "The Potential Socio-economic Effects of Climate Change" by Parry, Magalhaes, and Nih (1992) under a United Nations Environment Programme (UNEP) study. Research by Godden and Adams (1991), in "The Enhanced Greenhouse Effect and Australian Agriculture," found that while some sectors of Australian agriculture had experienced productivity declines, there had been overall agricultural growth driven by increased foreign demand for Australian produce — illustrating how socioeconomic effects can be uneven and can sometimes outpace the environmental changes that cause them. An estimate of the effects of climate change using two alternative crop strategies, made by Kane, Raelly, and Tobey (1992), projected changes in agricultural commodity prices due to yield changes and shifts in global patterns of consumption and production.