Climate change-induced sea-level rise in small island nations continues to be most pressing threat to their environment and socio-economic development, with losses of trillions of dollars incurred every year, says a new report released Thursday by the United Nations Environment Programme ( UNEP).

The report, launched here to mark the World Environment Day, called for an immediate shift in policies and investment towards renewable energy and green economic growth to avoid exacerbating these impacts.

The vulnerability of the Small Island Developing States (SIDS) to climate change and seal-level rise -- estimated to be up to four times the global average -- is magnified due to their relatively small land masses, population concentrations, and high dependence on coastal ecosystems for food, livelihood, security and protection against extreme events, says the SIDS Foresight Report.

The report says increased flooding and shoreline erosion pose direct challenges for the 52 small island nations across the world.

In all SIDS regions, coral reefs, the frontline for adaptation, are already severely impacted by rising sea surface temperatures. The global net loss of coral cover -- around 34 million hectares over two decades -- will cost international economy an estimated 11.9 trillion U.S. dollars, with SIDS especially impacted by the loss, says the report.

The report also warns that the magnitude and frequency of many weather and climate-related hazards will increase as climate warming accelerates, especially in small islands. This will lead to disproportionate and compounded climate change impacts, which will adversely affect multiple sectors -- from tourism, agriculture and fisheries to energy, freshwater, health and infrastructure.

For example, fisheries play a significant role in economy, livelihoods and food security in SIDS, estimated at 12 percent of total Gross Domestic Product (GDP) in some nations. In Pacific SIDS, fish accounts for up to 90 percent of animal protein in the diet of coastal communities.

Yet climate change is expected to negatively impact fisheries, posing a clear challenge to meeting the nutritional needs of growing populations, damaging livelihoods and hampering efforts to lift people out of poverty.

However, the report demonstrates that SIDS can transition to an inclusive green economy and ensure a sustainable prosperous future by taking advantage of opportunities in areas such as renewable energy, sustainable exploration of unexploited resources, developing an ocean-based green economy and leading the world in the development of inclusive indicators that go beyond GDP.

The report says it is necessary to develop appropriate growth indicators that take into account climate change, poverty, natural resource depletion and human health, and the new indicators need to enter into widespread use.

On the day, the UNEP also launched a report on the green economy study of Barbados, providing a practical roadmap for policymakers and businesses on the greening of tourism, agriculture, fisheries, buildings and transportation in Barbados -- lessons that can also be applied in other SIDS.

The World Environment Day is celebrated every year on June 5 to encourage worldwide awareness and action for the environment.