Science Briefs

Olive Oil, Sun-dried Tomatoes, and Global Warming

The Mediterranean basin provides a good case study for analyzing regional differences in vulnerability to climate change. Mediterranean agriculture accounts for virtually all olive oil produced worldwide, 60% of wine production, 45% of grape production, 25% of dried nuts (mostly almonds, chestnuts, and walnuts), 20% of citrus production, and about 12% of total cereal production. The comparatively more temperate and humid northern countries (Spain, France, Monaco, Italy, Former Yugoslavia, Albania, and Greece) are more productive than the warmer and drier southern countries (Turkey, Cyprus, Syria, Lebanon, Israel, Egypt, Libya, Malta, Tunisia, Algeria, Morocco). The increased temperatures and lower precipitation simulated for this region by the NASA GISS global climate model driven by a scenario with rapidly increasing greenhouse gases (see top figure) would adversely affect crops and water availability, critically influencing the patterns of future agricultural production.


Summer seasonal mean temperature and precipitation changes for the Mediterranean region corresponding to a doubling of CO2, as simulated by the GISS GCM. This climate might occur in the 2050s, if greenhouse gases increase very rapidly.

An international research team, including Cynthia Rosenzweig, Francesco Tubiello, and Daniel Hillel from GISS; Ana Iglesias and M.I. Minguez from Spain; G. Kapetanaki from Greece, and H.M. El-Shaer and M.H. Eid from Egypt conducted coordinated studies to analyze potential agricultural impacts and adaptations to climate change in Spain, Greece, and Egypt. Computer crop models were used to predict yield changes caused by climate change. These models include the beneficial effects of increasing CO2 levels on crop growth and water use.

Global climate change scenario experiments in Spain show that wheat yields generally increase, but maize yields significantly decrease. These reductions, along with exacerbated problems of irrigation water availability, may force the maize crop out of production in some regions by 2050. In Greece, the climate change scenarios generally resulted in decreases in maize yield of up to 15% for the 2050s, due to reduced duration of the growing period at all sites. In Egypt, simulated studies show dramatic decreases in yield for wheat (bottom figure) and maize at four sites along the Nile in the 2050s. Egypt is particularly vulnerable to global warming because of its dependence on the Nile River, its large traditional agricultural base, and its long coastline, where sea-level rise may inundate crops.

Current trends in Mediterranean population growth, land and water use, and food supply and demand reveal significant differences between the Northern and Southern Mediterranean countries. Over the past 30 years, population growth in the Mediterranean region has increased by 50% to a current estimated total of 400 million. Growth rates were four times higher in the southern basin (3.2% /yr) than in the northern countries (0.8% /yr), with the gap in growth rates currently widening. Thirty years ago both northern and southern countries satisfied about 90% of their internal demand for food. However, today while the northern basin is self- sufficient, the southern countries produce less than 60% of their food.


Simulated changes in wheat yield (percent of current yield) with three climate change scenarios for the 2050s. Wheat is rainfed at Matruh on the Mediterranean coast and irrigated at the other three sites on the Nile River. Scenario simulations include the direct effects of CO2 on crop photosynthesis and water use. CF indicates crop failure.

Our research shows that climate change could further exacerbate these trends, especially in the southern basin where agricultural production is increasingly unable to satisfy internal food demand, and soil quality and water availability continue to deteriorate. While the northern countries may fare better in the short run, production is still likely to decline with global warming. Water management could become a problem in semi-arid areas of the northern basin, especially in parts of Spain, Greece, and southern Italy where irrigation water for vegetable crops (such as tomatoes) may be in shorter supply. In the southern basin, more than a third of irrigated land is in Egypt where special problems arise due to salinization, water logging, and salt-water intrusion.

The Mediterranean studies demonstrate the advantage of collaboration between local scientists and experts in climate change impact studies. Local scientists have an intimate knowledge of the agricultural systems, an invaluable aid to proper crop model validation and evaluation of results. Collaborative studies expand the cadre of scientists informed about the climate change issue and help to build research capability. Finally, because climate change is a long-term global environmental issue, assessing adaptation and mitigation strategies helps to encourage responsible sustainable development.


El-Shaer, H.M., C. Rosenzweig, A. Iglesias, M.H. Eid, and D. Hillel 1997. Impact of climate change on possible scenarios for Egyptian agriculture in the future. Mitig. Adapt. Strategies Global Change 1, 233-250.

Iglesias, A., and M.I. Minguez 1997. Modelling crop-climate interactions in Spain: Vulnerability and adaptation of different agricultural systems to climate change. Mitig. Adapt. Strategies Global Change 1, 273-288.

Kapetanaki, G., and C. Rosenzweig 1997. Impact of climate change on maize yield in central and northern Greece: A simulation study with CERES-Maize. Mitig. Adapt. Strategies Global Change 1, 251-271.

Rosenzweig, C. and F.N. Tubiello 1997. Impacts of global climate change on Mediterranean agriculture: Current methodologies and future directions. Mitig. Adapt. Strategies Global Change 1, 219-232.


Please address all inquiries about this research to Dr. Cynthia Rosenzweig.