I dipped a toe into climate skeptics' blogland this morning. There goes the morning. Starting here with Derek Tipp, who I found a while back via the Freedom Association. He links to a story in the Asian Correspondent asking, ‘what happened to the climate refugees?’
Of course, WUWT got onto this as well – “the UN ‘disappears’ 50 million climate refugees, then botches the disappearing attempt.” (We’ll come back to the disappearance in a moment.) The internets eats them both up: forty thousand results for the original, six thousand for WUWT’s take on it.
The claim from the original Asian Correspondent article: “In 2005, the United Nations Environment Programme predicted that climate change would create 50 million climate refugees by 2010.” This is supposedly refuted by claiming that four islands – the Bahamas, St. Lucia, Seychelles and the Solomon Islands – have seen their populations increase. To spare the suspense: (1) based on the references the article is pointing to, no, UNEP did not predict that at all. (2) Census data from four tropical islands is not a good way to check, especially when you haven't checked what it is you're checking.
Let's start with the original source. The Asian Correspondent doesn't have any. There's a map but, as we'll see, it's not relevant. Watts, however, does respond to a commenter by giving a reference. He doesn’t actually link to it – here’s the original PDF report. There are some links provided, but none point to any page making the “fifty million climate refugees by 2050” claim. All I’ve managed to find is what appears to be a graphic screendump by Probe International, one of the many organisations devoted to revealing the terrible environmental damage being inflicted by foreign aid. (I promised myself I’d get through this post without snark. Fail #1.)
Perhaps that’s a genuine screendump, and someone at UNEP did make that headline claim – I don’t know. But on reading the report, you quickly find the first major blunder: the subject is environmental refugees, not climate refugees. I’ll spare paraphrasing and go straight to the source, Professor Norman Myers:
As far back as 1995 (latest date for a comprehensive assessment), these environmental refugees totalled at least 25 million people, compared with 27 million traditional refugees (people fleeing political oppression, religious persecution and ethnic troubles). The environmental refugees total could well double between 1995 and 2010. Moreover, it could increase steadily for a good while thereafter as growing numbers of impoverished people press ever harder on over-loaded environments. When global warming takes hold, there could be as many as 200 million people overtaken by disruptions of monsoon systems and other rainfall regimes, by droughts of unprecedented severity and duration, and by sea-level rise and coastal flooding. 
So Professor Myers is saying there were already 25 million environmental refugees by 1995. I’ll come back to this report, but let’s just take a diversion into the earlier 1995 study that forms the basis for this later little overview. Again by Norman Myers, it was commissioned by the Climate institute: that page says it was -
the first-ever rigorous assessment of the plight of a growing number of people displaced as a result of environmental problems such as drought, soil erosion, desertification and deforestation.
Here’s the scanned PDF. I’ve transribed some key sections from it - those are at the bottom of this post, and well worth reading. Some bullet points:
But the main points: we’re talking about environmental refugees, not climate refugees. By the 1995 report assessment, there were already 25 million by Myers’ definition. I don’t know what current assessments are, but I’m guessing they probably go some way beyond looking at census data for four tropical islands. I will try and find out the current state of play and update. Snark #2: should I be reading anything into the fact that the ‘skeptics’ I’ve quoted here have got ‘environmental’ and ‘climate change’ muddled up? The mistake could lie with someone at UNEP: perhaps they did the muddling. At the moment, though, I'm not sure I want to trust one screen dump as evidence of this, given that the reports are entirely clear on the matter. Linking to the original report would have helped.
Going back to the more recent report, it concludes:
A prime way to tackle desertification, salinization, in fact several sorts of land degradation, is through planting trees for shelter belts, to retain soil moisture, and to resist soil erosion. Certain types of trees offer additional benefits, e.g. leguminous species add nitrogen to infertile soils, or they supply built-in insecticides, or they offer industrial timber. Probably the biggest benefit lies with reforestation in montane areas, in order to rehabilitate hydrological systems and watershed functions, and thus avoiding floods and drying-outs for river systems downstream. All in all, and in whatever part of the world, restoring tree cover almost always presents an exceptional win-win outcome. 
So: tree planting and leguminous vegetables. Myers notes in passing, “on top of all these sub-problems is the lack of official recognition, whether on the part of governments or international agencies, that there is an environmental refugee problem at all.” I suspect that an organisation like Probe International would certainly take issue with the term.
Just to finish on that ‘disappearance’. Watts, I think, is referring to the ‘disappearance’ of a map, which you can see here. It makes no reference to any date or number that I can see.
From Norman Myers, ‘Environmental Exodus: an Emergent Crisis in the Global Arena’ (1995)
The position today: there are at least 25 million environmental refugees today, the total to be compared with 22 million refugees of traditional kind. They are mainly located in sub Saharan Africa (notably the Sahel and the Horn), the Indian subcontinent, China, Mexico and Central America. The total may well double by the year 2010 if not before, has increasing numbers of impoverished people press ever harder on overloaded environments. Their numbers seem likely to grow still more rapidly if predictions of global warming are borne out, whereupon sea level rise of selling of many coastal communities, plus agricultural dislocations through droughts and disruption of monsoon and other rainfall systems, could eventually cause as many as 200 million people to be put at risk of displacement.
[Footnote] These findings are based on an 18 month research projects carried out in consultation with representatives of governments, intergovernmental bodies, United Nations agencies, the world bank, and dozens of ngos including refugee organisations. The findings also reflect a broad spectrum of expert opinion on the part of leading scientists and policy analysts in all major parts of the world. In particular, the research report draws heavily on the experience of field workers with their extensive and firsthand knowledge. Further, overall assessment is illustrated by six regional case studies with detailed documentation. All individual findings and conclusions are supported by specific references, 1000 of which can be found in the main text.
These estimates constitute no more and no less than a first cut assessment. They are advanced with the sole purpose of enabling those to ‘get a handle’, however preliminary and exploratory, on an emergent problem of exceptional significance. Moreover, the estimates are cautious and conservative. Note that, for instance, there are already 135 million people threatened by severe desertification, and 550 million people subject to chronic water shortages. While certain of these people will have been included in the 25 million figure, many could well have been driven to migrate without being counted as environmental refugees.
From all those factors we get: “the 25 million environmental refugees in 1995 have mostly become obliged to migrate since roughly 1980, when the numbers first started to climb rapidly. In light of patterns and trends of environmental decline and associated problems such as population increase, it is probable that by 2010 i.e. within another 15 years, there will be at least another 25 million refugees, if only because the impelling factors will continue to be at least as prominent as during the past 15 years. (this supposes that there will be very few preventative measures of sufficient scope.) In fact, the total could well be a good deal larger than 25 million acres of increasingly degraded environments coupled with growing numbers of people in absolute poverty.”