Answer
The productivity of the Amazonian forests will increase in starting and then decrease later with the increasing concentration of carbon dioxide.
Work Step by Step
The burning of fossil fuels is the biggest reason for increasing CO2 in the atmosphere. The green plants require CO2 for photosynthesis. Thus, an elevated level of CO2 will lead to an increased growth of the plants in the Amazonian forests. As a result, the primary productivity of the Amazonian forests will increase.
The elevated levels of CO2 will raise the temperature of the Earth and will cause excessive evaporation from the plants and the soil. The dry plants in the forests are more likely to catch fire. As a result of drought and forest fires, the forests will get destroyed and will decrease the productivity of the Amazonian forests at a later stage.
