Last month, I summarized the best tally of green-collar jobs in Cascadia. It surveyed more than 9,500 private businesses in Washington and found 47,194 people working in renewable energy, energy efficiency, waste management and recycling, and pollution reduction, clean-up, and mitigation. It pointed out, furthermore, that it would have found even more had it included public employees and people who toil in the conservation and restoration of our natural heritage, bicycling and transit, or real-estate development for compact communities.

Last week, Eric Hess summarized the best tally of green-collar jobs in the United States. This new study, published by the Pew Charitable Trusts (pdf), mined and combined a set of commercial databases, some of them enormous, to identify clean-energy companies (and businesses with other environmental aims such as water conservation and pollution reduction) in one of the United States. It then confirmed the categorization with a custom-designed web-search tool. The activities these companies perform were similar to those in last month’s Washington study: energy efficiency, renewables, water conservation, waste recycling, pollution mitigation. This methodology yielded a ten-year time series of counts of green businesses and employees.

Unfortunately, the two studies diverge sharply about how many green jobs Washington has. The first study found 47,194; the second found 17,013.

Obviously, the varying counts stem from varying methods. The Washington study surveyed businesses, described certain activities such as energy efficiency retrofitting, and asked how many of their workers did those activities for a large share of their workday. The national study sorted databases to find whole companies that specialized in green activities. Consequently, the national study only counts pure green businesses, such as solar energy companies and waste recycling companies. It doesn’t cover construction firms that, for example, employ green building practices in half their projects.

What can we conclude? Sigh. Not much. There’s much in each study to inform policymakers, but the grail of a definitive green-collar job count remains elusive. In fact, the divergence between the two studies makes me unsure whether to believe the trends reported in the Pew study. It suggested rapid growth in Idaho and Oregon’s clean-energy jobs, but slow growth in Washington’s.

The value of the Pew study, it seems to me, is that it tracks growth among businesses that are focused rather narrowly on clean energy. The Washington study sets a baseline for green-collar jobs (still narrowly defined) across a wide range of companies.