For a company whose business depends on sending fleets of new cars out onto the road, Uber's environmental proposition is a strong one.

The theory is quite simple: Uber, along with other ride-hailing startups, will decrease carbon emissions in cities where it operates by lessening people's reliance on personal automobiles, minimizing traffic congestion on roads, and eventually disincentivizing the perks of owning a vehicle in the first place.

"A city that welcomes Uber onto its roads will be a city where people spend less time stuck in traffic or looking for a parking space," Uber CEO Travis Kalanick once said. "It will be a cleaner city, where fewer cars on the road will mean less carbon pollution—especially since more and more Uber vehicles are low-emission hybrid vehicles."

But so far, we've seen a staggeringly small amount of meaningful data to verify any of Uber's grand claims about its ability to reduce the transportation industry's carbon footprint. When nearly every other aspect of the gig economy has been quantified, why are we left clueless when it comes to the issue of Uber's environmental impact?

"Nobody had ever studied the environmental impact of ride-hailing companies before."

Uber has a long history of holding its user and driver information close, especially when it entails valuable and potentially proprietary activity data. Because of the startup industry's brutally competitive nature, young and successful companies such as Uber often err toward secrecy, which can hurt their transparency in the short term. Earlier this year, the California Public Utilities Commission issued the company a $7.6 million fine for failing to report accessibility and driver safety data back in 2014.

"Believe it or not, if you had a big data set and started to crunch the numbers, you'd be able to see an awful lot about their business—when and where they're most successful. Information abstracted from data like this could inform new or existing competitors," Dr. Susan Shaheen, co-director of the University of California, Berkeley's Transportation Sustainability Research Center, told me.

Some of Uber's unwillingness to open parts of its API to researchers and stakeholders can also be interpreted as due diligence, or perhaps just paranoia. Over the last couple of years, the company's security credentials have been patchy at best. Multiple data breaches, accidental leaks of customers' personally identifiable information, and deeply troubling evidence that Uber employees were able to track riders through its "God Mode" tool might have influenced the company's hush-hush attitude.

Instead, Uber has decided to periodically released its own in-house reports on ridership, sustainability, and emissions—all of which are provided with unclear methodology, and inherent bias.