In this talk, I will discuss the need for low carbon and sustainable computing. The current emissions from computing are almost 4% of the world total. This is already more than emissions from the airline industry and ICT emissions are projected to rise steeply over the next two decades. By 2040 emissions from computing alone will account for more than half of the emissions budget to keep global warming below 1.5°C. Consequently, this growth in computing emissions is unsustainable. The emissions from production of computing devices exceed the emissions from operating them, so even if devices are more energy efficient producing more of them will make the emissions problem worse. Therefore we must extend the useful life of our computing devices. As a society we need to start treating computational resources as finite and precious, to be utilized only when necessary, and as effectively as possible. We need frugal computing: achieving our aims with less energy and material.