If you're reading this, you're emitting carbon. A single online search uses about as much electricity as a lightbulb left on for 35 minutes. Sending an email with a large attachment? That lightbulb will last about an hour. And if digital technology were a country, it would be the third-largest consumer of electricity in the world, after China and the United States. These are some of the findings in a new book by French journalist and documentary filmmaker Guillaume Pitron. The Dark Cloud: How the digital world is costing the earth. At a time when many of us are trying to be as environmentally friendly as possible – using reusable shopping bags, bringing our own cups to the cafe – it’s easy to forget that part of our carbon footprint comes from the devices we use every day. But how did we get here – and what can we do about it?