The increase in carbon dioxide (CO₂) in the atmosphere, now exceeding 400 parts per million (A 50 percent increase) and still rising rapidly, is having numerous effects on the Earth and its biosphere. The biosphere includes all the living things on Earth, including humans. Nearly all of these effects are negative, as living things are not well adapted to the new warmer regime that has not been experienced on Earth for millions of years. That the increase in carbon dioxide is causing the surface of the Earth to heat up is not debatable among scientists. What to do about it, of course, is debated.

This lecture will outline the history of atmospheric CO₂ on Earth, and then deal with the effects of the increase in atmospheric CO₂ on forest vegetation. CO₂ rise has two major effects on forest vegetation: it increases the rate of photosynthesis and hence productivity, and it may cause increased drying due to increasing temperature. Both of these processes are occurring, and which one will be dominant depends on latitude and location. An increase in warming will also increase rainfall in many places, which may or may not counter the increase in evaporation and drying of soil. Climate change may also affect forest tree species by affecting the biological community, which includes herbivores, pollinators, and seed dispersers. These may be long-term effects.

The lecturer has been involved with the study of forest ecology for many years in Khao Yai National Park, where he established a large, long-term forest study site around 2000. This is now the 30-hectare, Mo Singto ForestGEO Plot, which is part of the international network of large forest research plots coordinated by the Center for Tropical Forest Science of the Smithsonian Tropical Research Institute (check the Smithsonian’s ForestGEO website online). Studies are being conducted on the approximately 265 species of trees and at least 135 species of lianas on the plot, including their growth rates, survival, reproduction, and seed dispersal by animals. An attempt is being made to correlate changes in forest condition with climate change. A major finding is that tropical forests such as Khao Yai are not unchanging and stable, as was often assumed in the past, but are dynamic and changing in response to climatic variation and change. Uncovering the long-term signal of the trend of forest condition is challenging and requires decades of monitoring. This is an important priority for researchers and policymakers because forests are a major store, and possible source or sink, for atmospheric carbon.