For climate scientists reviewing a Pacific Ocean temperature forecast map in November, a bright red, sideways “V”, thousands of kilometres long signalled disaster, Reuters reported.

Combined with La Nina cooling in the central and eastern Pacific, the V-shaped pattern of warm sea water, stretching from Australia’s east coast to the Philippines and back over the ocean north of Hawaii, indicated that halfway around the world in the Horn of Africa the upcoming March-May rainy season would likely fail.

The scientists’ organization, called Famine Early Warning System Network or FEWS Net, sent out an alert with U.N., EU and African institutions, saying the “unprecedented” drought would likely “cause a perilous and disruptive humanitarian disaster”.

If the warning is born out, it could push the region into its worst drought on record. Millions of people would struggle to feed themselves.

Such warning systems are becoming increasingly essential as climate change puts food security at increasing risk. “Our work is to save lives and livelihoods,” said FEWS Net agricultural meteorologist Gideon Galu said in Kenya.

On Monday, a report by the U.N.’s Intergovernmental Panel on Climate Change, the top global climate science authority, warned heatwaves, droughts and extreme rainfall would become more frequent in coming decades as temperatures continue to climb.

Already, “increasing weather and climate extreme events have exposed millions of people to acute food insecurity and reduced water security,” it said.