Rain water running through soils and wetlands will leach decomposing plant organic matter into streams and lakes in the form of dissolved organic carbon (DOC). In streams, lakes and eventually estuaries, DOC can be mineralized to CO2, precipitated to sediments or taken up in biological matter, and is thus an important part of many aquatic ecosystems. Using hydrological, climatological and geographical data from 32 sites located in Canada, we developed a neural network model which allowed us to estimate DOC export from the Canadian land mass. We reapplied the model to the 32 sites plus a further 43 basins to estimate area normalized exports for various regions of the country. We estimated that 14.3¿106t of DOC are currently exported from Canadian terrestrial ecosystems. We then modified climatological inputs to the model to reflect the predicted temperature and precipitation conditions under a doubled atmospheric CO2 regime. Our model suggests that DOC exports will increase by approximately 14% under a doubled CO2 atmosphere, mostly owing to increases in runoff. Our analysis also shows that DOC export is greatest in the spring in southern Canada and summer in the north. ¿ 1999 American Geophysical Union