Last month, floods struck the coasts of West Africa, drowning dozens, requiring hundreds of rescues, and displacing thousands. Now scientists have concluded that the rains that caused the floods were supercharged by climate breakdown. Global heating, they say, turned what should have been a routine weather event into a climate catastrophe.

They also warn that the affected countries must adapt to a frightening new reality. “The climate is changing faster than most nations can adapt,” said Friederike Otto, a professor of climate science at Imperial College London. “Adapting to these now common events is critical, but so is reducing emissions much further and faster, to allow us time to keep up with the changes we’ve already put into motion. Quite simply, until emissions stop these extremes will only grow worse.”

Residents on the Gulf of Guinea coast expect rain this time of year - rainy season runs from May until the end of July. Granted, this year it had been particularly heavy, but what began on 20 June caught people by surprise. Over 72 hours, intense rainfall drenched the densely populated coastal regions of Côte d’Ivoire, Ghana, Togo, and Nigeria. More than 140mm of rain fell in some cities in less than a day. The deluge overwhelmed drainage systems, triggering flash floods.

From Lagos to Monrovia in Liberia, the overflow inundated neighborhoods and washed away markets. It submerged roads and swamped infrastructure. At least 34 people died in Ghana, five in Togo, and 59 in Côte d’Ivoire since May.

On Thursday, Otto and the World Weather Attribution team said such a deluge was five times more likely in today’s climate. Heavy, three-day downpours in the region had increased in intensity by roughly 23% since record-keeping began. It will not be long until something similar occurs again, they warned. With the climate 1.4°C hotter than before the industrial use of fossil fuels, they expect rainfall of a similar scale to explode above the Gulf of Guinea every two to four years.

To quantify the role of the climate crisis, scientists compared historical weather observations with climate model simulations, focusing on the three most extreme days of rainfall. Despite climate models often struggling to recreate similar events in the global south, they showed climate change had caused a 4% increase in intensity. The researchers said this made them confident that greenhouse gas emissions had intensified the event.

Joyce Kimutai, who researches extreme weather and climate change at Imperial College London and was the lead author on the study, said: “Climate models typically struggle to capture the full scale of tropical precipitation trends when we look at extreme events like this one. As such, the fact that we found such a role for climate change is significant. Combined with the very wetter trend in the observational-based data, it’s clear that human-caused warming made this event worse, and wetter, with devastating impacts.

“This study is a clear example of the need for international cooperation on climate justice. Industrialised nations have a responsibility to help nations like Togo, Côte d’Ivoire and Ghana to adapt to a worsening problem that they didn’t cause.”