COP21: Rallies mark start of Paris climate summit
Rallies have been held around the world, calling for a global agreement to combat climate change, as nearly 150 world leaders gather in Paris for a critical UN meeting on the subject.
The conference, known as COP21, will attempt to craft a long-term deal to limit carbon emissions.
The demonstration in Paris was marred by a small number of protesters who clashed with police.
Science Editor David Shukman reports.