| Region | P-value | |
| CO2 equation | SO2 equation | |
| Africa | 0.000 | 0.0472 |
| Asia | 0.000 | 0.1634 |
| Central America & the Caribbean | 0.247 | 0.4544 |
| Former USSR & Eastern Europe | 0.029 | 0.437 |
| MENA | 0.000 | 0.001 |
| OECD | 0.000 | 0.040 |
| South America | 0.001 | 0.000 |