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Number of studies by GEO-3 region. Sums to 242 because one reference described studies from two regions.
| Region | Number of references |
|---|---|
| Polar | 13 |
| Asia and Pacific | 20 |
| Europe | 76 |
| Latin America and Caribbean | 6 |
| North America | 60 |
| West Asia (Middle East) | 0 |
| Africa | 67 |
