According to Bogumil Terminski it seems reasonable to distinguish the general category of environmental migrants from the more specific (subordinate to it) category of environmental refugees.

Environmental migrants, therefore, are persons making a short-lived, cyclical, or longerterm change of residence, of a voluntary or forced character, due to specific environmental factors. Environmental refugees form a specific type of environmental migrant.

Environmental refugees, therefore, are persons compelled to spontaneous, short-lived, cyclical, or longer-term changes of residence due to sudden or gradually worsening changes in environmental factors important to their living, which may be of either a short-term or an irreversible character

There have been a number of attempts over the decades to enumerate ‘environmental migrants/ refugees’. Jodi Jacobson (1988) is cited as the first researcher to enumerate the issue, stating that there were already up to 10 million ‘Environmental Refugees’. Drawing on ‘worst case scenarios’ about sea-level rise, she argued that all forms of ‘Environmental Refugees’ would be six times as numerous as political refugees. (1988: 38).[5] By 1989, Mustafa Tolba, Executive Director of UNEP, was claiming that ‘as many as 50 million people could become environmental refugees’ if the world did not act to support sustainable development (Tolba 1989: 25).In 1990, the Intergovernmental Panel on Climate Change (IPCC 1990: 20) declared that the greatest single consequence of climate change could be migration, ‘with millions of people displaced by shoreline erosion, coastal flooding and severe drought’ (Warner & Laczko: 2008: 235). In the mid-1990s, Norman Myers became the most prominent proponent of this ‘maximalist’ school (Suhrke 1993), stating that there were 25 million environmental refugees in the mid-1990s, and claiming that this figure could double by 2010, with an upper limit of 200 million by 2050 (Myers 1997).[8] Myers argued that the causes of environmental displacement would include desertification, lack of water, salination of irrigated lands and the depletion of bio-diversity. He also hypothesised that displacement would amount to 30m in China, 30m in India, 15m in Bangladesh, 14m in Egypt, 10m in other delta areas and coastal zones, 1m in island states, and with otherwise agriculturally displaced people totalling 50m (Myers & Kent 1995) by 2050. More recently, Myers has suggested that the figure by 2050 might be as high as 250 million (Christian Aid 2007: 6)