Emissions factors are a metric used by the U.S. Environmental Protection Agency to gauge the effect that power plants, oil refineries, and other sites of industry are having on the atmosphere. The problem? The numbers are far from accurate. Worse, they’re being used in ways that were never intended.

As per Scientific American:

The original aim had been to paint a broad-brush picture of pollution. Instead, the numbers—meant to represent average emissions from industrial activities—were incorporated into permits stipulating how much pollution individual facilities could release. This happened despite EPA warnings that about half of these sites would discharge more than the models predicted.

Here are some of the stomach-churning substances that are tracked by emissions factors: ammonia, a cause of algal blooms capable of killing off marine life; methane, a potent greenhouse gas; and benzene, a known carcinogen.

Emissions factors can be a good compass when we just need a broad estimate of what’s in the fumes our chimneys belch out. However, we’ve already seen how things can go pear-shaped when they’re used for other purposes.

Scientists believe that many metropolitan areas in the U.S. may have overshot their ozone targets because they were measuring them against emissions factors. For example, when the city of Houston ditched those metrics in favor of direct monitoring, it found that levels of organic compounds in the air were 10 to 100 times higher than expected.

In light of this new information, Houston’s ozone production rates dropped by 50 percent in just six years. Emissions factors were, essentially, leading the city on a wild goose chase.

As cities throughout the U.S. begin setting targets to reduce their footprint, imagine what would happen if emissions factors were used to set greenhouse gas emissions limits. The new policies would be way off the mark from the outset. Relying on these metrics means we’re firing blind, and with our future on the line.