Final answer:
The most disproportionate factor contributing to CO2 emissions in the nations ranked 3rd and 4th is the use of fossil fuels, with tropical deforestation and coal consumption being significant contributors.
Step-by-step explanation:
The factor disproportionately responsible for the total CO2 emissions in the nations ranked 3rd and 4th in 2000 is the reliance on and consumption of fossil fuels, particularly coal. As these nations industrialize, they rely on more carbon-intensive energy sources.
For instance, Indonesia, which is ranked 3rd, is significantly impacted by tropical deforestation, which plays a substantial role in their emissions. Conversely, the 4th ranked country's emissions may be driven by coal consumption, as indicated by the fact that coal has historically been the dominant CO2 producer globally. Additionally, per capita emissions are important to consider, as they account for differences in population size when assessing environmental impact.