The UN says about 8.2m people need emergency food aid in Ethiopia, nearly double the number six months ago.
The UN has warned that children are the worst affected by climate change.
It estimates that nearly 700 million of them live in areas at the highest risk of severe drought and flooding.
In southern China alone, as many as 57 million children are at risk of flooding. But the most at-risk are those in the South Asia region, including Bangladesh, India and Pakistan, where 340 million children are in danger.
The report was issued in advance of a climate change summit in Paris next week.
The UN has urged nations to take immediate action, pointing out that most of the affected areas are also among the poorest in the world.
Al Jazeera’s Gerald Tan explains.