In March, the United Nations took the first meaningful step to hold investors, businesses, cities and regions accountable for reducing greenhouse gas emissions, when UN Secretary-General António Guterres asked a group of experts to develop standards for "net zero" pledges to the group . The challenge now is how to count emissions coherently. Nations, societies and scientists each use different, disparate methods to measure greenhouse gas emissions. These numbers cannot be easily compared or combined. The current patchwork of greenhouse gas stocks is woefully inadequate. From governments to businesses, information about these emissions is inconsistent, incomplete and unreliable. In order to design effective carbon taxes, border tariffs and other zero-carbon policies or investments, the numbers must be reconciled at all levels, from product supply chains to the global scale. The sum of national emissions should match the increase in atmospheric carbon dioxide and carbon sequestration estimates. (Amy Luers)