Global Warming Has Pros and Cons for Agriculture around the World

Editor’s Note: “2020 Views” seeks to generate dialogue and discussion through interviews with participants in the 2020 Vision initiative. For this issue, NEWS & VIEWS interviewed Cynthia Rosenzweig, a research scientist and head of the Climate Impacts Group at the National Aeronautics and Space Administration’s Goddard Institute for Space Studies and Columbia University. She is coauthor, with Daniel Hillel, of Climate Change and the Global Harvest: Potential Impacts of the Greenhouse Effect on Agriculture (Oxford University Press, 1998).

NEWS & VIEWS: How would you describe the likely effects of climate change on global food production?

On the positive side, first and foremost, we have increasing levels of carbon dioxide, which is, all else being equal, good for crops because it increases photosynthesis. Also on the positive side are warming temperatures in regions where length of growing season is limited by cold. Finally, there is the potential for increasing precipitation in some currently water-stressed places.

On the negative side, increasing temperature is a primary concern in both tropical and temperate regions. Here we have several important effects. First, there is heat stress, especially the direct effect of high temperature at the time of crop pollination. Second, high temperatures speed annual crops through their life cycle, allowing less time for grain production. Third, high temperatures increase the atmospheric demand for water, thus increasing the potential for water stress on crops. Additionally, plant respiration rates increase, constraining net photosynthesis.

In a warmer world, we may expect all weather phenomena to be intensified, thus exacerbating instability. Extreme events such as storms, floods, droughts, and heat spells may well increase in frequency, duration, and severity.

Impacts on forests, fisheries, and livestock also are potentially important. In forestry, there may be changes in species toward those more adapted to the changing climate. There will have to be long-term planning to factor in adaptation of species to climate change. For fisheries, the key point is that water temperatures will rise, which will affect species composition and production in both marine fisheries and aquaculture. Range-fed livestock will be affected by changes in grassland. Some grasslands could benefit from a longer growing season. On the other hand, high temperatures could have direct effects on livestock in terms of heat stress and, potentially, calving rates. For feedlot cattle, the key point is what climate change does to grain production, and thus grain prices, since grain is a key input in this industry.

NEWS & VIEWS: On balance then, is the impact of climate change on global food production expected to be positive or negative?

Our simulations show that there is the potential for initially positive but eventually negative effects on global food production. In the shorter term, over the next couple of decades, carbon dioxide is beneficial and temperature effects are likely to be relatively small. In the longer term, beyond the next several decades, the effects could become negative.

NEWS & VIEWS: What relationship, if any, exists between climate change and El Niño?

Initial warming of oceans may be affecting El Niño, which is a specific cycle of ocean-atmospheric interaction in the Pacific. The warming of the oceans caused by the greenhouse effect is global. Understanding the interaction between this global pheonomenon and the specific El Niño phenomenon is an active area of research. In the current decade, the pattern of El Niño seems to be changing. Why? That is part of the science we don’t know yet.

NEWS & VIEWS: What do we know about the impacts of climate change on different regions, particularly in the developing world? What don’t we know about these regional impacts?

Studies show that the developing countries appear to be more vulnerable to climate change in at least two ways. First, there is the direct impact of climate change. Developing countries tend to be in low latitudes, where it’s warmer already. This in a sense will put more places “over the top,” in terms of high temperatures. The second point concerns adaptation. The agricultural reasearch infrastructure tends to be weaker in developing countries, yet these are the regions where research is going to be most needed.

We don’t know exactly how the climate is going to change in any given region. Therefore, what we need to do as we prepare is to take a range of possible climates into account. Testing a range of climates improves our flexibility. We no longer will be judging our future climate by our past. We need to move from static perception to dynamic reality, and the reality is that the future climate is likely to be different from the present climate.

NEWS & VIEWS: How might climate change affect small-scale farming, particularly rain-fed agriculture in Sub-Saharan Africa?

By most measures, many of the countries in Sub-Saharan Africa appear to be most vulnerable to climate change. The region is home to many low-income populations who depend on isolated farming systems. The climate of the region is already hot, and large areas are arid or semi-arid. Average per capita income is among the lowest in the world. Further factors adding to the region’s vulnerability are that a large proportion of the population depends directly on farming, and agriculture accounts for a large portion of the GDP of countries in the region.

NEWS & VIEWS: What will be the effect of climate change on hunger and malnutrition, particularly in the developing world?

When there is a potential for a decrease in global production, there is an increase in the risk of hunger. With climate change, we have the potential for long-term declines, so there is potential for increased risk of hunger. Reducing vulnerability to the impacts of climate change on agriculture requires maintaining regional productivity and improving access to food. Enhancing the capacity of vulnerable groups to adapt their farming systems or economic livelihoods to changing agroclimatic and market conditions should be the goal.

NEWS & VIEWS: Will climate change alter the current relationship between major food exporters, such as Canada and the United States, and major food importers among developing countries?

What we see is a widening split between the major food exporters and the major food importers. We see climate change putting additional pressure on developing countries to develop marketable goods and services in order to buy food, because with climate change they may be producing less food. The major food exporters, which are primarily in the mid- and high latitudes, may benefit from climate change.

NEWS & VIEWS: How should countries prepare to tackle the effects of climate change?

We have to develop appropriate adaptations, so there can be flexible systems in place to react to the changes. First, we need to maintain existing species and varieties—so regions can switch easily from corn to sorghum, for example, since sorghum is more drought-resistant. Next is the development of heat- and drought-tolerant varieties— development of these varieties makes sense today. Third, we need to maintain flexible agricultural policies. For example, commodity support programs that make it harder for farmers to switch from one crop to another may inhibit flexible responses to climate change.

NEWS & VIEWS: In December 1997 the parties to the international climate convention in Kyoto agreed on several binding targets for limiting carbon dioxide emissions. How might the Kyoto agreement alter the outlook for climate change and agriculture—assuming it is ratified and implemented?

Kyoto is a modest first step toward modifying long-term emissions of greenhouse gases. As part of this global effort, we need policies and measures that can engage both the developed and the developing world. To the extent that the global society succeeds in reducing emissions and the threat of climate change, we can then return our focus to our “normal” challenge of feeding the approximately 10 billion people that we’re going to have in the future without environmental degradation. So we have enough on our plate even without climate change.

While some people in the farm industry are concerned that responding to the Kyoto accords will impose restrictions on energy use in agriculture, I think that appropriate responses may be found that both improve energy efficiency and are cost-effective. Climate change is not unmitigated gloom and doom. It is very serious, but it also is an opportunity for enhancing environmental sustainability and global cooperation.

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