After a 12-month delay due to the Covid pandemic, COP26 finally got underway at the weekend. Hosted by the UK and Italy, world leaders and climate negotiators gathering in Glasgow have just two weeks to thrash out an agreement for what many believe to be the last chance to save the planet from the irreversible consequences of climate change. But, as John Barwise explains, reducing greenhouse gas emissions, the main cause of climate change, remains the biggest challenge.