It is possible to delimit the areas of the North, Central, and South America that are most susceptible to fire and would have been most affected by burning practices of early Americans. Areas amounting to approximately 155 x 105 km² are here designated as the most burnable part of the New World. Using estimates of burnable biomass, burning frequency, and burning efficiency, the authors determine the amount of biomass burned annually in an environment in which anthropogenic fires were at a hypothesized maximum. The amount of carbon released annually approximates estimates for present-day burning. Changes in carbon sinks may have been the most significant aspect of a shift to a low-biomass state. Decreases in stored biomass, soil carbon, and charcoal production may have had effects on a global scale. Likewise, the shift to a higher biomass/lower fire-frequency state over the last 400-500 years may be one component of an increased mid- to high-latitude carbon sink. The assessment made here is preliminary but may aid in clarifying the state of the climate system during the pre-industrial period.