Gains, losses as climate changes
Marco Bindi, of the Department of Agronomy and Land Management at the University of Florence, Italy, has participated in EU-funded projects on the impact of climate change on natural and agricultural ecosystems, and is a lead author of the Fourth Assessment Report, Climate Change 2007, of the Intergovernmental Panel on Climate Change (IPCC)
How does the build-up of atmospheric greenhouse gases affect potato production?
"In C3 plants, such as potato, an increase in atmospheric concentrations of carbon dioxide leads to a higher rate of photosynthesis. Currently, the level of CO2 is about 385 parts per million [ppm] and the latest IPCC emission scenarios project levels by the year 2100 ranging from 540 to 970 ppm. Experiments on potato have shown that increasing CO2 concentrations have little effect on production of biomass above ground, but below ground biomass is significantly enhanced, through higher numbers of tubers and bigger tuber size. The yield increases by about 10 percent for every extra 100 ppm. As for the effects of increasing levels of ozone, experiments indicate an overall reduction of photosynthetic efficiency and a significant decrease in tuber starch content, but an increase in the ascorbic acid concentration."
What effect will global warming have on the potato?
"This century could see a rise in average global surface temperature of from 1.8° to 4°C. Since potato's tuberization rate declines above a temperature of 17°C, increasing temperature may lead to reduced yields in potato varieties now cultivated close to the upper climatic limits of the crop that would not be recovered by higher levels of carbon dioxide. On the other hand, a simulation study has shown that in northern European countries a warmer climate would bring a longer growing season and big increases in yields. Areas that are now too cold for potato - for example, parts of Canada, Siberia and Scandinavia - may become viable, as would highland areas such as the altopiano in Peru and Bolivia. But the global picture is worrying: worldwide research shows that, without adaptation, higher temperatures reduce yield by 10 to 19 percent in 2010-2039 and 18 to 32 percent in 2040-2069. The most vulnerable area is the tropical belt, where the loss could be more than 50 percent."
Potato is highly sensitive to water stresses. How will climate change affect water availability?
"The change in temperature will be uniform, but not that of rainfall. There will be an increase in rainfall in mid- to high latitudes - areas with no water shortages - and problems instead for the Mediterranean and subtropical zones, where we will see rainfall on fewer days but with greater intensity. A crop growth simulation experiment on an EU scale reported that, under the present climate change scenario, yields under rain-fed conditions were strongly affected by water shortages, with reductions of 50 percent. In arid regions, where drought is expected to become more frequent and more intense, there will clearly be a drop in productivity."
Could climate change also lead to an increase in potato pests and diseases?
"Given the thermal limit for late blight - 22°C - increases above that temperature threshold in Europe may prevent infections. At the present northern limit of potato cultivation in the USA, Canada and central Russia, late blight could increase significantly as temperature increases, but at the same time, warming further north may open up new zones for potato production, with minimal late blight risk. Increasing quantity and frequency of rainfall would also create conditions more favourable to viral disease vectors. Other researchers have predicted an increase in the Colorado potato beetle's area of diffusion in Europe, as well as in the area infested by potato cyst nematode."
How can potato cultivation adapt to climate change?
"Anticipating the planting date, using different potato varieties and improving soil water supply, especially in dry regions, might be useful - by one calculation, those strategies could cut by half the expected decrease in global yields. In southern Europe, earlier planting increases potato yields and reduces water requirements in both present and future climate scenarios. But, in practice, adaptation options may be not so simple. The planting season also depends on factors such as the preceding crop, water availability, pests and diseases, and markets. Cultivars better adapted to a changed climate exist, but may not be available to farmers in some regions. Another strategy is shifting potato production towards areas of higher productivity or areas where there is currently no potato production. In some tropical highland regions, cultivation could expand into higher altitudes. At high latitudes, there could be considerable potential for expansion of the potato area."