Flooding, famine and rising sea levels will put hundreds of millions at risk in one of the world's most vulnerable regions

People in coastal regions of Asia, particularly those living in cities, could face some of the worst effects of global warming, climate experts will warn this week. Hundreds of millions of people are likely to lose their homes as flooding, famine and rising sea levels sweep the region, one of the most vulnerable on Earth to the impact of global warming, the UN states.

The report – Climate Change 2014: Impacts, Adaptation and Vulnerability – makes it clear that for the first half of this century countries such as the UK will avoid the worst impacts of climate change, triggered by rising carbon dioxide levels in the atmosphere. By contrast, people living in developing countries in low altitudes, particularly those along the coast of Asia, will suffer the most, especially those living in crowded cities.

A final draft of the report, seen by the Observer, will be debated by a panel of scientists set up by the Intergovernmental Panel on Climate Change (IPCC) this week at a meeting in Yokohama, Japan, and will form a key part of the IPCC's fifth assessment report on global warming, whose other sections will be published later this year.

According to the scientists who have written the draft report, hundreds of millions of people will be affected by coastal flooding and land loss as global temperatures rise, ice caps melt and sea levels rise. "The majority of it will be in east, south-east and south Asia. Some small island states are expected to face very high impacts."

In addition, the report warns that cities also face particular problems. "Heat stress, extreme precipitation, inland and coastal flooding, as well as drought and water scarcity, pose risks in urban areas with risks amplified for those lacking essential infrastructure and services or living in exposed areas." The report adds that this latter forecast is made with very high confidence.

In addition, climate change will slow down economic growth, further erode food security and trigger new poverty traps, particularly "in urban areas and emerging hot spots of hunger," it is argued.

This combination of a high-risk region and the special vulnerability of cities make coastal Asian urban centres likely flashpoints for future conflict and hardship as the planet warms up this century. Acrid plumes of smoke – produced by forest fires triggered by drought and other factors –are already choking cities across south-east Asia. In future, this problem is likely to get worse, say scientists.

The authors warn that some other climate change effects will be global. "Climate change throughout the 21st century will lead to increases in ill-health in many regions, as compared to a baseline without climate change," the report states. "Examples include greater likelihood of injury, disease, and death due to more intense heatwaves and fires; increased likelihood of under-nutrition resulting from diminished food production in poor regions; and increased risks from food-borne and water-borne disease."

Other potential crises highlighted by the report include the likelihood that yields of major crops such as wheat, rice and maize are likely to decline at rates of up to 2% a decade, at a time when demands for these crops – triggered by world population increases – are likely to rise by 14%. At the same time, coral reefs face devastating destruction triggered by increasing amounts of carbon dioxide dissolving in sea water and acidifying Earth's oceans.

The report makes grim reading. "This comprehensive scientific assessment makes clear that climate change is having a growing impact in the UK and around the world, and that the risks of catastrophic consequences increase every day as more greenhouse gas pollution is pumped into the atmosphere. I hope David Cameron will read this report and understand the huge dangers of delaying the bigger cuts in emissions that are required to protect our children, grandchildren and future generations against this devastating threat," said Bob Ward, policy and communications director at the Grantham Research Institute on Climate Change.