The effects of climate change on small island countries are affecting people in coastal areas through sea level rise, increasing heavy rain events, tropical cyclones and storm surges. These effects of climate change threaten the existence of many island countries, their peoples and cultures. They also alter ecosystems and natural environments in those countries. Small island developing states (SIDS) are a heterogenous group of countries but many of them are particularly at risk due to climate change. Those countries have been quite vocal in calling attention to the challenges they face from climate change. For example, the Maldives and nations of the Caribbean and Pacific Islands are already experiencing considerable impacts of climate change. It is critical for them to implement climate change adaptation measures fast.

Some small and low population islands do not have the resources to protect their islands and natural resources. They experience climate hazards which impact on human health, livelihoods, and inhabitable space. This can lead to pressure to leave these islands but resources to do so are often lacking as well.

Efforts to combat these challenges are ongoing and multinational. Many of the small island developing countries have a high vulnerability to climate change, whilst having contributed very little to global greenhouse gas emissions. Therefore, some small island countries have made advocacy for global cooperation on climate change mitigation a key aspect of their foreign policy.

Sea level was much lower during the last ice age when glaciers covered a third of Earth's land mass.

Small island developing states (SIDS) are identified as a group of 38 United Nations (UN) Member States and 20 Non-UN Member/Associate Members that are located in three regions: the Caribbean; the Pacific; and the Atlantic, Indian Ocean, Mediterranean and South China Seas (AIMS) and are home to approximately 65 million people. These nations are far from homogeneous but they do share numerous features, including narrow resource bases, dominance of economic sectors that are reliant on the natural environment, limited industrial activity, physical remoteness, and limited economies of scale.

Due to close connections between human communities and coastal environments, SIDS are particularly exposed to hazards associated with the ocean and cryosphere, including sea level rise, extreme sea levels, tropical cyclones, marine heatwaves, and ocean acidification. A common feature of SIDS is a high ratio of coastline-to-land area, with large portions of populations, infrastructure, and assets being located along the coast.

Patterns of increasing hazards, high levels of exposure, and acute vulnerability interact to result in high risk of small island developing states (SIDS) to climate change.

Small island developing states (SIDS) have long been recognized as being particularly at risk to climate change. These nations are often described as being on the "frontlines of climate change", as "hot spots of climate change", or as being "canaries in the coalmine". The Intergovernmental Panel on Climate Change warned already in 2001 that small island countries will experience considerable economic and social consequences due to climate change.