Welcome to another installment of “What’s Schipper Saying?”, a collection of comments about sustainable transport, cities and fuel efficiency made by Lee Schipper, a senior research engineer at the Precourt Energy Efficiency Center of Stanford University and the founder of EMBARQ, the nonprofit that produces this blog.

Schipper, a.k.a. Mr. Meter, leaves a trail of commentary on popular blogs across cyberspace. We track him down — so you don’t have to — and offer a round-up of his latest responses to hot topics in the world of sustainable cities.

This week, he talks about how a recently reported decline in U.S. carbon emissions is not necessarily reason to celebrate…because of unreliable data.Andrew Revkin of the New York Times Dot Earth blog wrote a post last week asking whether the dip in CO2 emissions – which exceeded the drop in gross domestic product – was a “blip or a trend.” He included a note from Schipper, who responded by saying the government’s efforts to track emissions data is like “the blind leading the blind”:

If there is one lesson, it is that in times of rapid growth or recession, different parts of the economy change at different rates, and that differential alone can cause significant changes in the ratio of energy to G.D.P. Since a big recession might hit coal-burning utilities’ customers more than other utility customers (to name one example) or hit coal-using industries like cement and steel more than others, one has to look carefully not only at CO2 emissions changes but at underlying economic activity or personal activity changes and how those are tied to emissions in a disaggregated way.

Some countries can do this roughly 18 months to two years after the end of each year. We can’t….

It’s hard to imagine how the U.S. will enact any sensible policies in this foggy atmosphere.

Read more about why the government’s attempt to collect is “foggy” here.