Tenth of humanity vulnerable
to sea level rise

David McAlary

A new global population study has identified the regions and people at greatest risk from rising sea levels and more intense storms connected to global warming. More areas are potentially vulnerable than commonly thought.
   Census figures and satellite imagery tell a story of swelling populations along coastal regions that are expected to flood and experience more violent cyclones because of climate change.
   Study says areas in red are at risk from rising sea levels in Bangladesh. Using the data, the International Institute for Environment and Development in London has released a study showing that exposed low lying coastal zones 10 meters or less above sea level contain 10 percent of all humanity, 634 million people, although they make up just two percent of the world's land area. "Coastal areas are disproportionately urban and coastal areas are disproportionately dense," said demographer Deborah Balk of the City University of New York, a co-author of the study.
   "The urban areas in those coastal systems are both larger and more of the system is dedicated to urban areas than we would find in dry lands or in forests, for example," she said.
   Balk says the 16 island nations are not the only places threatened by predicted sea-level rise. The study shows that nearly two-thirds of all cities with more than five million people are at least partly in the 10 meter coastal zone, including Shanghai, China; Mumbai (Bombay), India; Dhaka, Bangladesh; and Cotonou, Benin. In fact, 75 percent of people in the zone are Asians because of the nature of the continent's geography and its large population, but parts of every inhabited continent are affected.
   Balk says the population in this coastal zone will continue to increase, especially in Asia. "Most of the growth we will see in Asia is not going to be in rural areas, but will be in urban areas. So that will further exacerbate this issue because the cities are already located in these low elevation coastal zones," she said.
   The study appears in the April issue of the journal "Environment and Urbanization" and is unique in the way it defines coastal zones. Its focus on regions 10 meters or less above sea level contrasts with previous research that looked at areas within certain distances from the coast. The authors say their standard is a more accurate way to measure who is most at risk from rising oceans and stronger cyclones.
   The study says easing climate change is the best means to deal with the problem, but adds there is not enough time for that to be the only solution. Migration away from the lowest elevation coastal zones is part of their answer. They recognize how costly, difficult, and disruptive this would be, but point out that small population shifts to higher ground can be important.
   They also recommend coastal management that avoids policies, like China's, which favor coastal development to encourage exports. "This is a call to policymakers to be more active in thinking about settlement incentives or local planning to protect certain systems," she said.
   Global warming causes sea level to rise by thermal expansion of the ocean waters and the melting of land-based ice, producing a range of impacts. With unmitigated emissions, writes Robert Nicholls, sea level will be about 40 cm higher than today by the 2080s, and this is estimated to increase the annual number of people flooded from 13 million to 94 million. 60 per cent of this increase will occur in southern Asia (along coasts from Pakistan, through India, Sri Lanka and Bangladesh to Burma), and 20 per cent will occur in South East Asia (from Thailand to Vietnam including Indonesia and the Philippines).
   The flood impacts of sea-level rise are reduced by the emissions scenarios leading to stabilisation of CO2; by the 2080s, the annual number of people flooded is estimated to be 34 million under the 750 ppm scenario and 19 million under the 550 ppm scenario. Again, most of those flooded will be in southern and South East Asia.
   Humanity's greenhouse gas emissions are expected to lead to climatic changes in the 21st century and beyond. These changes will potentially have wide-ranging effects on the natural environment as well as on human societies and economies. Scientists have made estimates of the potential direct impacts on various socio-economic sectors, but in reality the full consequences would be more complicated because impacts on one sector can also affect other sectors indirectly. To assess potential impacts, it is necessary to estimate the extent and magnitude of climate change, especially at the national and local levels. Although much progress has been made in understanding the climate system and climate change, projections of climate change and its impacts still contain many uncertainties, particularly at the regional and local levels.
   Human health
   Spread of major tropical vector-borne diseases
   Climate change and altered weather patters would affect the range (both altitude and latitude), intensity, and seasonality of many vector-borne and other infectious diseases.
   
   Dengue and Malaria
   Potential dengue transmission in case of temperature rise
   A warmer climate increases occasions of vector borne tropical diseases. The figure depicts weeks of potential dengue transmission under current temperature and 2°C and 4 °C warming.
   Plasmodium vivax, with the Anopheles mosquito as a vector, is an organism causing malaria. The main climate factors that have bearing on the malarial transmission potential of the mosquito population are temperature and precipitation.
   Source: VOA, UNEP

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