When it comes to the global response to the climate change emergency, it pays to differentiate between words and deeds. At the Cop26 summit in Glasgow the chorus of concern from world leaders was deafening, but tough decisions on deeper emissions cuts were put off until next year.

Stephen Sackur speaks to US special envoy for climate John Kerry. His mission remains to restore American leadership on the biggest existential challenge facing our planet. Is that mission impossible? Show less