While atmospheric carbon dioxide (CO2) levels are higher than ever before, an estimated 2.5 billion additional people are expected to integrate into urban areas worldwide by 2050, making reduced urban CO2 emissions a priority. A group of scientists investigated the effects of urban form, specifically at the building and street level, on urban carbon emissions using detailed assessment methods in three different U.S. cities. The results demonstrate that the relationship between urban form and CO2 emissions is complex and dynamic. Patterns could be different depending on the context and factors such as climatic conditions and size and function of the city. This means that one-size-fits-all approaches cannot be applied to determine optimized urban forms.