Warming: Famine or feast?

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Mass famine and starvation due to a collapse of agricultural production ranks high among myriad catastrophes environmentalists claim human-induced global warming will cause. Fortunately, this is one global warming bogeyman that's easy to slay.

Regardless of the cause of the current warming, the best available evidence indicates a warmer planet should result in bountiful crops. The modest warming many scientists expect should result in longer growing seasons, more sunshine and rainfall, while summertime high temperatures change little. And a warmer planet means milder winters and fewer crop-killing frosts. History shows the Earth's climate is less stormy and more stable in relatively warm eras.

The present warming trend has not resulted in agricultural water shortages. Indeed, rainfall is increasing moderately over most of the world because global warming evaporates more water from the oceans, where it falls back down to earth in a reinvigorated hydrological cycle.

Thanks partly to increased rainfall, infrared satellite readings show worldwide vegetative activity generally increased 6.17 percent between 1982 and 1999. The world is getting greener. Continued warming should increase, rather than reduce, rainfall.

In addition, global warming also increases carbon dioxide (CO2), which acts like fertilizer for plants. As the planet warms, oceans naturally release huge tonnages of additional CO2. (Cold water can hold much more of a gas than warmer water).

CO2 in the atmosphere has increased more than 30 percent in the past half-century. CO2 is a critical component of photosynthesis, the process by which plants use sunlight to create carbohydrates -- the material that makes up their root and body structures. Increasing CO2 levels not only speeds the growth of plants, it improves their water use efficiency. More CO2 also decreases water loss in plants, which is beneficial in arid climates or during droughts.

Botanists pump large volumes of CO2 into their greenhouses to enhance plant growth. A series of 55 experiments by research scientist Sherwood Idso, formerly of the Agriculture Department, support botanists' faith in CO2's beneficial effects. For example, when Mr. Idso increased CO2 by 300 parts per million (ppm) above the current atmospheric level of more than 370 ppm, plant growth increased 31 percent under optimal water conditions, and 63 percent under water scarcity. With a 600 ppm CO2 increase, plant growth was enhanced 51 percent under optimal water conditions and an astonishing 219 percent under conditions of water shortage.

CO2 enrichment causes plants to develop more extensive root systems that allow plants to reach additional pockets of both water and nutrients in the soil, reducing the metabolic energy required to capture vital nutrients. More extensive, active roots also stimulate and enhance the activity of bacteria and other organisms in the soil that are beneficial to plants.

Since many of today's plants evolved when CO2 levels were much higher, some scientists fear today's plants are literally starving from CO2 deprivation.

Based on nearly 800 scientific observations around the world, a doubling of CO2 from present levels -- would improve plant productivity on average by 32 percent across species.

Controlled experiments have shown that, that under elevated CO2 levels, average yields of cereal grains, including rice, wheat and oats are 25 percent to 64 percent higher. Tubers and root crops, including potatoes, and cassava, yield 18 to 75 percent more under high CO2 conditions. And yields of legumes, including peas, beans and soybeans, increase between 28 percent and 46 percent.

So far, since 1950, in a period of global warming, these factors have helped the world's grain production soar from 700 million more than 2 billion tons last year.

Humans can help nature along. Recently, Egypt genetically engineered a drought-tolerant wheat plant -- containing a gene from the barley plant -- that needs to be irrigated only once, rather than eight times per season. The new wheat is expected to dramatically increase food production in semi-arid climates. In addition, constantly improving trans-portation systems help reduce localized food shortages.

The real famine threat will come not in the present warming, but rather the next Ice Age when huge ice sheets will once again cover Canada and Russia, and the Northern Plains will be too cold to farm. Fortunately, that test may not come for another 10,000 years. By then, unless regulations interfere, the world should have genetically engineered a set of even higher-yielding and still more stress-tolerant crop varieties to feed humanity on dramatically reduced acreage.

Dennis Avery is director of the Center for Global Food Issues and an adjunct scholar at the National Center for Policy Analysis (NCPA). H. Sterling Burnett is a senior fellow at the NCPA.