The concept of net zero is very simple: our greenhouse gas emissions need to be balanced by removing CO2 from the atmosphere. Many countries are setting a target to reach net zero by the middle of this century. There is no doubt that global commitments to reach net zero would be a step forward but there are a couple of points to bear in mind. The first point relates to the rate of decline in emissions. For example, countries around the world might continue to pump massive volumes of CO2 into the atmosphere for the next 30 years and then suddenly, cut emissions dramatically so that they are net zero by around 2050. This would meet the target of net zero, but total levels of CO2 in the atmosphere could be so high that temperature would be well above the maximum target of 2°C. Setting a target of net zero does not set any limits on the total level of emissions. The second problem with net zero is that it is based on assumptions that we can capture carbon from the atmosphere. In practice this is difficult. For example, planting billions of trees will not achieve net zero because trees only capture 25% of CO2 in the atmosphere. The oceans capture another 25% and the remaining 50% will remain in the atmosphere for many hundreds of years. The only solution to global warming is to reduce carbon emissions dramatically and this needs to happen now. We can’t wait until the middle of the century. By setting a goal of ‘net zero’ we could be deluding ourselves that this will solve the problem. Unfortunately, it won’t.