Hot Cities travels the world from Lagos to Los Angeles, from Shanghai to Surat, from Dhaka to Durban to analyse one of the significant threats facing the planet.

Talking to the experts, the politicians and some of the millions of new migrants to the world’s biggest cities, the series assesses not just the threat from climate change but our response.

In 2008 the world reached an important milestone when, for the first time in history, more people lived in cities than the countryside. Homo sapiens had become homo urbanus.

All this has led to a vicious circle. Cities are one of the big drivers of climate change. As cities get even bigger, they drive climate change even harder. And that makes many of these massive urban areas more vulnerable to rising sea levels, violent storms and dramatic changes in temperature.

In December the most important climate change conference in over a decade will be held in Copenhagen. That is where world leaders and their advisors must hammer out a blueprint for survival. Hot Cities shows how important their decisions will be.

Half the world’s population face severe food shortages by the end of the century as climate change takes its toll on the global harvest. It has become so desperate in some countries riots have broken out in protest at the lack of food.

Senegal is one of them, a country where one of the government’s biggest challenges is making sure there is enough food to go round.

Drought in the Sahal, which runs through Senegal, means many climate migrants are flocking to the capital, Dakar, to find work to feed their families.

Hot Cities follows migrants from their villages, where farming has almost been wiped out, to the city. Feed the World also looks at what is being done to feed Senegal in the future.