A team of US climate scientists using computer models has determined that there is no flexibility in how much greenhouse gas emissions we can continue to emit if we want to stop warming. The only viable goal is zero emissions. The value of this is that it gives us an unsullied goal, one that is easy to measure but very difficult to achieve. In fact I suspect the target we really have to shoot for is a negative emissions goal, one in which sequestration is an equally important part of the total number. This will be necessary to offset the growing demand for and use of energy worldwide by a rapidly growing global population. Those of us in the Western world have a responsibility to go beyond zero in our carbon emissions.