There are three types of solar geoengineering to allow more heat to escape the Earth’s atmosphere: injecting tiny reflective particles into the stratosphere to block sunlight; using the particles to make low-lying clouds over the oceans more reflective; and thinning high-altitude cirrus clouds. This idea is to accelerate research into these options and start to deploy the best of them, if warranted and only with the endorsement of the United Nations - before we reach tipping points where global warming will have run away, completely out of our control. Not after. Nobody wants it, but we are now in a position where we have to make difficult choices. So lets get on with making them.