In 2008, for example, 20 million people were displaced as a result of sudden-onset climate-related weather events, compared to 4.6 million internally displaced by conflict and violence.126 There is, however, no global database on migratory movements related to natural disasters. At best, there are estimates that can be derived from displacement data relating to particular crises. Although the number of disasters has increased significantly over the last two decades (see map 8 showing the change in the number of natural disasters between 1990 and 2009), there has not been a major impact on international migratory flows, as much displacement is short-lived and temporary, and those who are displaced do not have the resources or networks to migrate abroad.127 This is why it is often asserted that environmental change is likely to contribute to more internal rather than international migration. For example, environmental degradation may be the result of changes in average annual temperatures or rainfall levels, but it may equally be the result of deforestation or poor land management - or a combination of these factors.