Brooks, Nichols and Hall carried out a detailed study of the consequences of sea level rise from global warming [1]. The predicted rise in sea level fro expanding seas is scenario-dependent and the effect of melting ice and snow is highly uncertain for short-term predictions. Nonetheless, for the high-end global warming scenario and making allowances for snow and ice melt contributions, a 1 m sea level rise by 2100 is a possible scenario. A rise of 1 m would affect 23 million people in five European countries and would displace the population of vulnerable coastal cities. The estimated cost of coastal protection against a 1-m rise in sea level ranges between $13 billion and $47 billion.
Twilley and Doyle illustrate the delayed effects of global warming on sea level rise in the figure below [2]. The figure shows that even if greenhouse gas emissions peak and decline during this century, the sea level will continue to rise, for centuries, well above the level reached by 2100. For a sea level rise of 10 m, Brooks et al. predict that the displaced population could range from 900 million to 2.6 billion people. The study also showed that saline intrusion from rising sea levels could impact fresh water resources and the composition of ecosystems.

Wikipedia

enumerates major potential consequences of global warming:

1. Global warming is a threat to food security and water supply. Climate change will affect crop yields. The decrease of agricultural productivity in tropical and sub-tropical zones particularly will endanger food security.
2. Climate change could lead to mass migrations leaving lands at risk. Rising sea levels damaging coastal regions through flooding and erosion, desertification and shrinking freshwater supplies displaced up to 10 million people in year 2006, and will create up to 50 million environmental refugees by the end of the decade. The Red Cross says environmental disasters already displace more people than war. Environment-related migration has been most acute in sub-Saharan Africa, but also affects millions of people in Asia and India. Europe and the US face increased pressure from people driven from North Africa and Latin America by deteriorating soil and water conditions. Small island states like Tuvalu are facing the immediate consequences of climate change. New Zealand has already agreed to accept the 11,600 inhabitants of the low-lying Pacific island state if rising sea levels swamp the country.
3. Elsewhere, as many as 100 million people live in areas that are below sea level or liable to storm surge. A total of 213 communities in Alaska are threatened by tides that creep 3 m further inland each year.
Climate change will exacerbate vulnerabilities and has a bigger impact in poor countries
Climate change has a bigger impact on poor communities, which are the most vulnerable. Developing countries are more vulnerable, due to the economic importance of climatic sensitive sectors (agriculture, fisheries) and their limited human, institutional and financial capacity to anticipate and respond to the direct and indirect effects of climate change. It is likely that this vulnerability is higher for the least developed countries located in the tropical and sub-tropical areas. Often extreme weather events set back the development process for decades.

References:
1. Brooks, N, Nicholls, R., and Hall, J., "Sea Level Rise: Costal Impacts and Responses, WBGU, Berlin, 2006.

2. Twilley, RR and Doyle, T, "Is it Doable? Rising Sea Level and the Challenges of Restoring Costal Louisiana, March 5, 2001.

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