All of the statements are true. 300 ppm 56. The annual flux in carbon dioxide concentrations in the Northern Hemisphere is caused by seasonal changes in photosynthesis. Carbon dioxide concentrations in the Northern Hemisphere are higher during the winter. Some greenhouse gases such as CFC's and methane are more potent than carbon dioxide.
Carbon dioxide is the most important single greenhouse agent produced by human activities.
The slight overall crop benefit from elevated CO2 levels is not enough to compensate for the loss of agricultural lands. Commercial timber production will not benefit from increased CO2 levels, unless the trees are provided with fertilizers. A marked improvement in growth of C4 plants supplied with abundant fertilizer, light and water occurs under conditions of doubled CO2 b. C3 plants supplied with abundant fertilizer, light and water will occur under conditions of doubled CO2. Plants using the C4 photosynthetic pathways will stand to gain more from an atmosphere enriched in CO2 than plants using the C3 pathway 59. Deserts will spread as many areas become drier.