Convenience and cost savings have fueled unprecedented growth of online banking and bill payment over the past several years. But as growth flags, environmentalists are urging consumers to put away their checkbooks and fire up their computers in the name of conservation.

The fact that online banking and bill payment saves trees is a no-brainer. Less obvious is the reduction of resources required to make, ship and ultimately discard paper, according to a report by Javelin Strategy & Research.

Some 53 percent of all U.S. households (61 million) now do their banking online; nearly half of those also pay their bills via computer. But the report says that a whopping 16.5 million trees, roughly 2.3 million tons of wood, could be spared annually in the unlikely event that all U.S. households made the switch to paperless payments. Such a move would also reduce fuel consumption by 26 million BTUs, enough energy to provide residential power to a city the size of San Francisco for a year.

Other major pluses: toxic air pollutants would be cut by 3.9 billion pounds of carbon dioxide equivalents, which is comparable to taking 355,015 cars off the road; waste water would drop by an estimated 13 billion gallons (enough to fill 19,846 swimming pools), and 1.6 billion pounds of solid waste (equal to 56,000 fully loaded garbage trucks) would be eliminated. In addition, the report says, there would be 8.5 million fewer particulates and 12.6 million fewer nitrogen oxides in the air, on par with getting 763,000 buses and 48,000 18-wheelers off the streets.

Alas, it seems the days of double-digit growth in online banking and bill payment are a thing of the past. Javelin projects that the number of online bank service users will grow to 82 million households by 2012, a compound annual growth rate of just 6.1 percent.

Javelin conducted the study to get to the root of the downturn and determine its consequences, says James Van Dyke, founder and president of Javelin. "The green message is an important new message that people need to get," Van Dyke says. "My thinking was first, 'okay, you'll save some trees,' but we found that this was fairly significant."