Carbon Flux of an Urban System in México

We estimated vertical and lateral fluxes of carbon for the isolated coastal city of Ensenada (Baja California, México). In 2005, the city had a resident population of about 261,000, with tourism adding about 1.5%; it occupied an area of roughly 68 square kilometers (km²). Carbon (C) export was estimated at 400 gigagrams of carbon per year (Gg C/yr); notable sources to the atmosphere were combustion engines (42%), cement production (38%), water heating and cooking (7%), and human respiration (6%). Solid waste (6%) was exported for burial, but efflux to the bay was minor (about 0.1 Gg C/yr). Local deposition was limited to sewage sludge (about 2 Gg C/yr), asphalt, and extremely low primary production. Remote fluxes driven by local demand could be estimated only for electricity (61 Gg C/yr), but local flux from cement and other industrial production might be attributed largely to external demand. The urban system output to the atmosphere was about 6.4 kilograms of carbon per square meter per year (kg C/m²/yr), or roughly 23.6 kg/m²/yr in CO₂ equivalence. By comparison, net ecosystem productivity in the surrounding watershed has been estimated at 0.04 kg C/m²/yr, so the city's atmospheric output of C might be balanced by productivity over about 11,000 km² of the surrounding ecosystems. Between 2000 and 2005, C output increased faster than population growth, particularly from engine fuels.