The warning will be part of the latest report, to be released on Friday, from the Intergovernmental Panel on Climate Change, a body of more than 2,000 international scientists assessing global warming.
The report will also address what it terms as a "climate divide", with wealthy nations far from the equator experiencing fewer effects of climate change.
The report states that, for the rest of the world, destructive patterns seen in the last decade will accelerate in the next 40 years.
The scientists claim the warnings are clear; storms and floods have become more severe, coastlines have eroded and deserts have expanded. Meanwhile, diseases common in the Tropics have spread.
In the northern hemisphere, spring is coming earlier, disrupting bird migrations and causing flowers and trees to bloom too early.
Within 25 years, hunger and death from diarrhoea will threaten poor countries.
The report states that, later in the 21st century, warmer seas may destroy coral reefs and fish feeding on them, and may lead to the poisoning of shellfish. Cities on the coast and in river basins may be hit by flooding, and fresh water supplies could be polluted with salt water from sea surges.
Small islands will probably be submerged by rising sea levels. Meanwhile, forest and wild fires will become more widespread.
However, the scientists say not all of these dire consequences are inevitable.
A report to be released next month will outline possible ways to slow the effects of global warming.