The evidence shows neither that a modest warming will threaten human life through environmental catastrophe nor that the recent rise in CO2 levels is responsible for the measured rise in global temperature.

Carbon dioxide is not a pollutant. It is tasteless, colorless, nontoxic to humans at concentrations up to 13 times present levels and is essential to life. Plants breathe CO2, and as they grow and reproduce they exhale oxygen, making the earth habitable for humans. Instead of a disaster, the expected doubling of CO2 due to human activities will produce a number of benefits over the next century.

The Role of CO2. CO2 is a "greenhouse gas," one of several that partially trap solar radiation in the atmosphere. Without these gases the earth would be uninhabitable - at least by humans. CO2 occurs naturally and accounts for 2 to 4 percent of the greenhouse effect (water vapor is responsible for virtually all of the rest). Most of this CO2 is used by or stored in oceans, plants and animals. However, over the past 150 years atmospheric CO2 concentrations have increased approximately 30 percent, rising from 280 to 360 parts per million (ppm).  

CO2 and Global Warming. Ground-level temperature measurements indicate that the earth has warmed about 1 degree Fahrenheit since 1850, but human-generated carbon dioxide could have been only a small factor because most of the warming occurred before 1940 - preceding the vast majority of human-caused CO2 emissions. Historically, increases in atmospheric CO2 concentrations have often followed rather than preceded warm periods.  

Plants Need CO2. Most of the earth's plant life evolved in an atmosphere of much more concentrated CO2. Indeed, some scientists have argued that, until quite recently, many plants were starving for CO2.

CO2 is essential to photosynthesis, the process by which plants use sunlight to produce carbohydrates - the material of which their roots and body consist. Increasing CO2 levels speeds the time in which plants mature and improves their growth efficiency and water use. Botanists have long realized that CO2 enhances plant growth, which is why they pump CO2 into greenhouses.

In addition, higher CO2 levels decrease water loss in plants, giving them an advantage in arid climates and during droughts. In 55 experiments conducted by U. S. Department of Agriculture research scientist Sherwood Idso, increased levels of CO2 dramatically enhanced plant growth. For example, Idso found:

• With a CO2 increase of 300 ppm, plant growth increased 31 percent under optimal water conditions and 63 percent when water was less plentiful.

• With a 600 ppm CO2 increase, plant growth increased 51 percent under optimal water conditions and an astonishing 219 percent under conditions of water shortage (see Figure II).

Farmers Need CO2. Based on nearly 800 scientific observations around the world, a doubling of CO2 from present levels would improve plant productivity on average 32 percent across species. Controlled experiments have shown that:

• Tomatoes, cucumbers and lettuce average between 20 and 50 percent higher yields under elevated CO2 conditions.

• Cereal grains including rice, wheat, barley, oats and rye average between 25 and 64 percent higher yields under elevated CO2 levels.

• Food crops such as corn, sorghum, millet and sugar cane average yield increases from 10 to 55 percent at elevated CO2 levels.

• Root crops including potatoes, yams and cassava show average yield increases of 18 to 75 percent under elevated CO2 conditions.

• Legumes including peas, beans and soybeans post increased yields of between 28 and 46 percent when CO2 levels are increased. 

• Since 1890, high-altitude conifers in the Cascade Mountains of Washington have increased in mass approximately 60 percent from previous growth trends.

• In New England, a study of 10 tree species showed an average growth enhancement of 24 percent from 1950 to 1980, a period when CO2 levels were rising.

• Stands of Scotch pine in northern Finland have experienced growth increases of 15 to 43 percent since 1950.

• Forest growth rates in Baden-Wurttemberg, Germany, have increased 20 percent in the past 20 years.

Ecosystems Need CO2. The earth's ecosystems should benefit from higher levels of CO2. Increased crop yields mean that humans will not have to convert more fragile forests, savannas and deserts into crop lands to feed growing populations. Wildlife will get a respite from the development of their habitats. As forests increase, many currently fragmented ecosystems will regenerate - as many already have in Europe and the eastern United States. Since trees will put on more mass under higher CO2 conditions, fewer trees will have to be cut to supply humanity's demand for timber.

Finally, many scientists contend that outside of human society the availability of food is a primary inhibitor of population growth. Therefore, as plants increase in size and number, so should animals - more herbivores due to increased edible vegetation and more omnivores and carnivores due to increased herbivore populations.

Conclusion. According to government mine safety regulations, atmospheric CO2 would have to rise as high as 5000 ppm before it posed a direct threat to human health. Since no scientist predicts a rise of this magnitude in the next century, the anticipated rise in CO2 levels should be viewed as beneficial. Even if temperatures increase slightly, life on earth will thrive.

This Brief Analysis was prepared by NCPA environmental analyst H. Sterling Burnett and NCPA vice president of domestic policy Merrill Matthews, Jr.