Figures 1 and 2 reveal the trend of the nine independent variables and CO2 emissions. Urban population, GDP per capita, energy consumption, and gas all have an approximately monotonically increasing trend similar to CO2 emissions. This phenomenon may affect the forecast accuracy of the RF method, and we will discuss this problem in the Results and discussion section later. Table 2 also summarizes some descriptive statistics of each variable.
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Table 2
Descriptive statistics of non-normalized data
| Variable | Count | Min | Max | Mean | SD | CV |
|---|---|---|---|---|---|---|
| CO2 emissions (million tons) | 144 | 495.59 | 2,675.07 | 1,432.60 | 782.79 | 0.545 |
| Foreign direct investment (%) | 144 | 0.13 | 1.69 | 0.74 | 0.39 | 0.635 |
| Industry, value added (%) | 144 | 9.44 | 11.92 | 11.03 | 0.68 | 0.416 |
| Trade (%) | 144 | 4.85 | 16.18 | 9.92 | 2.97 | 0.584 |
| Urban population (%) | 144 | 5.69 | 15.41 | 10.11 | 3.01 | 0.679 |
| GDP per capita (current US$) | 144 | 62.06 | 2,624.95 | 787.73 | 849.54 | 1.172 |
| Energy consumption (10,000 tons of standard coal) | 144 | 19,022.43 | 124,913.29 | 61,547.91 | 35,913.87 | 0.844 |
| Coal (%) | 144 | 14.17 | 19.07 | 17.54 | 1.37 | 0.393 |
| Oil (%) | 144 | 4.06 | 5.53 | 4.58 | 0.39 | 0.764 |
| Gas (%) | 144 | 0.44 | 2.12 | 0.86 | 0.49 | 1.194 |
| Variable | Count | Min | Max | Mean | SD | CV |
|---|---|---|---|---|---|---|
| CO2 emissions (million tons) | 144 | 495.59 | 2,675.07 | 1,432.60 | 782.79 | 0.545 |
| Foreign direct investment (%) | 144 | 0.13 | 1.69 | 0.74 | 0.39 | 0.635 |
| Industry, value added (%) | 144 | 9.44 | 11.92 | 11.03 | 0.68 | 0.416 |
| Trade (%) | 144 | 4.85 | 16.18 | 9.92 | 2.97 | 0.584 |
| Urban population (%) | 144 | 5.69 | 15.41 | 10.11 | 3.01 | 0.679 |
| GDP per capita (current US$) | 144 | 62.06 | 2,624.95 | 787.73 | 849.54 | 1.172 |
| Energy consumption (10,000 tons of standard coal) | 144 | 19,022.43 | 124,913.29 | 61,547.91 | 35,913.87 | 0.844 |
| Coal (%) | 144 | 14.17 | 19.07 | 17.54 | 1.37 | 0.393 |
| Oil (%) | 144 | 4.06 | 5.53 | 4.58 | 0.39 | 0.764 |
| Gas (%) | 144 | 0.44 | 2.12 | 0.86 | 0.49 | 1.194 |
SD, standard deviation; CV, coefficient of variation.
Figure 1
Trends of nine independent variables. The shared x-axis represents the year ranging from 1985 to 2020, and the shared y-axis denotes the normalized values of nine independent variables.
Figure 1
Trends of nine independent variables. The shared x-axis represents the year ranging from 1985 to 2020, and the shared y-axis denotes the normalized values of nine independent variables.
Figure 2
Trend of CO2 emissions. The y-axis denotes the normalized values of CO2 emissions.
Figure 2
Trend of CO2 emissions. The y-axis denotes the normalized values of CO2 emissions.