John Harries obituary

Physicist who designed and developed innovative instruments that provided evidence of changes in the Earth's atmosphere

The consensus on how human activity is changing our climate is now so comprehensive that it is easy to forget that crucial to building the scientific understanding has been the acquisition over decades of many careful environmental measurements. John Harries, who has died aged 76, was involved in designing, developing and deploying instruments that were placed on aeroplanes, balloons and satellites to measure the heat radiation emitted by the Earth. His work resulted in the first direct observational evidence of an increase in the carbon dioxide greenhouse effect.

Visible light is radiation with a spectrum of colours from blue at short wavelengths to red at long wavelengths. Radiation at even longer wavelengths is invisible, but the spectrum continues with heat radiation in the infrared and far-infrared. Each gas in the atmosphere absorbs and emits radiation uniquely, having its own characteristic spectrum, and, knowing this, we can interpret measurements of radiation to reveal the concentration of that gas.