| Country | 2000 | 2015 | 2030 | 2045 |
| USA | 20.9 | 24.7 | 36.8 | 39.1 |
| Finland | 24.7 | 35.4 | 47.8 | 48 |
| Germany | 26.2 | 35.3 | 52.1 | 63 |
| Norway | 25.8 | 27.9 | 36.1 | 41.8 |
| Japan | 27.6 | 47.2 | 58.2 | 75.3 |