Witness

Things started to go wrong at the Windscale nuclear plant in October 1957. A reactor was overheating and workers were rushed in to help. In 2011 Chris Vallance spoke to Vic Goodwin and John Harris, two of the men who helped bring things under control during Britain's worst nuclear accident. Photo: the Windscale nuclear plant. Credit: Getty Images.

In 1970 the American scientist, Norman Borlaug, was awarded the Nobel Peace Prize for his pioneering work developing disease-resistant crops. At the time famine and malnutrition were claiming millions of lives across the world, particularly in South Asia. Dr Borlaug’s work meant countries like India were able to become self-sufficient. Critics said the new grain varieties were too reliant on chemical fertilizers, but it’s thought millions of lives were saved. Rebecca Kesby has been speaking to Professor Ronnie Coffman, student and friend of Norman Borlaug. (Photo: Dr Norman Borlaug in a field of wheat. Credit CIMMYT International Maize and Wheat Improvement Centre)

By the 1980s a deadly cocktail of factory fumes and car exhausts had turned Mexico City into the world's most polluted city. Hundreds of thousands of people were falling ill each month, many of them children. The Mexican authorities came up with an ambitious plan to curb the use of each of the city's two million cars for one day a week. The scheme was an immediate success and has been copied in other major cities around the world. Ramon Ojeda Mestre, the environmentalist behind the Mexican initiative spoke to Mike Lanchin about overcoming fierce opposition to the plan. Photo: Cars driving through Mexico City. Credit: Alamy

How a young American scientist began the work that would show how our climate is changing. His name was Charles Keeling and he meticulously recorded levels of CO2 in the atmosphere. His wife Louise and son Ralph spoke to Louise Hidalgo about him in 2013. (Photo: Thick black smoke blowing out of an industrial chimney. Credit: John Giles/PA)

The US first began sending troops to the UK in 1942 to help in the war effort. It is estimated that at least two million American servicemen passed through the UK during World War Two and tens of thousands of them were black. The African-American GIs stationed in Britain were forced by the American military to abide by the racial segregation laws that applied in the deep south of the US. But that didn't stop relationships developing between British women and the black soldiers, some of whom went on to have children. Babs Gibson-Ward was one those children. She has been speaking to Farhana Haider about the stigma of growing up as mixed raced child in post-war Britain. (Photo: Hoinicote House children, c.1948. Boys and girls whose parents of mixed ancestry met during WWII. Credit: Lesley York)