(Update: The cash raised was $5.8 million, according to a regulatory filing at the SEC)

terrapass.jpgTerrapass, a Menlo Park, Calif. company that lets people calculate the greenhouse gas emissions caused by daily activities such as driving, and then pay to offset them, has raised another round of funding.

Despite no prior backing, the company is growing very quickly, now boasting 50,000 adherents. It has become a leader of the movement to go “carbon neutral,” a trend is gaining adherents elsewhere, including big companies. Both Google and Yahoo, for example want to be carbon neutral. Google is installing a solar power grid to reach that goal. Yahoo recently launched Yahoo Green as part of a similar initiative.

TerraPass charges individuals $29.95 per year or more for “Terrapasses,” depending on their lifestyle. Maveron, of Seattle, led the round, Nth Power, of San Francisco. It also brought on a new chief executive, Erik Blachford, the former CEO of Expedia, and who has also invested in TerrPass. John Cook, of the Seattle PI, has more on Blachford’s move. He is just the latest in a trickle of executives moving to clean-tech (See Amy Vernetti’s VentureBeat column today about this trend).

Terrapass is a six-person startup. The 50,000 number is up from 30,000 earlier this year, and 2,000 last year, when we first mentioned the company. It is making more than $1 million a year. Jay Parkhill most recently mentioned the company in a VentureBeat column about the sector.

Terrapass says it reduces emissions in a number of ways, such as helping with landfill capping and supporting wind power projects. It says that its audited to make sure its methods are sounds. Here’s more about how it works.

Competing services include NativeEnergy and Carbon Fund.

Some critics have emerged, however, saying that these services are essentially offering a license for people to pollute more. They cite examples of carbon neutral companies buying up emissions created by oil extraction projects, thus seemingly making more oil pumping more palatable — but ironically, justifying more of it.