Hyundai-Kia is now the greenest automaker in the world, at least according to the Union of Concerned Scientists, and Honda (the winner in 2010) is now playing second fiddle. Personally, I think Tesla is probably the greenest automaker — not a tailpipe in the whole company — but UCS’s rules measure only the top eight global automakers.

With those criteria, Hyundai beat not only Honda but Toyota (third), Nissan (fourth), VW, Ford, GM and Chrysler (which also measured last in other fuel economy measures). Dr. David Cooke, UCS’ vehicles analyst and the new report’s author, said the jointly operated Korean companies triumphed “thanks to a concerted effort to green the fleet, using turbocharging, downsizing and hybridizing.” Honda, he said, “will need to step up its innovation.”

Kia Soul EV

The Kia Soul EV is headed for the market this fall. (Photo: Kia)

Considering the terms of the rankings, automakers don’t gain much by having electric cars in their fleets. Hyundai-Kia didn’t have one in 2013, and is only now gearing up to produce the Kia Soul EV. Because plug-ins are such a small part of the mix — just 0.6 percent of the 2013 fleet — they’re relatively insignificant as a factor, though I’d like to see carmakers (especially pioneer Nissan) getting credit for starting early and pushing the technology.

“Tesla sells only one vehicle, and if we just weighted our findings on the Model S, it’s true that Tesla would be the greenest,” Cooke told me. “And if Nissan was measured only by the Leaf, it would also be the greenest. But we focused on the eight largest automakers, which account for 90 percent of all the light-duty vehicles sold in the U.S. — and also 90 percent of all emissions.”

The rankings are for the 2013 model year. There is good news in the findings for the entire industry. All eight companies reduced their global warming emissions compared to the 1998 average. On emissions per mile, Hyundai was tops at 86.4 grams (combined), and Honda second with 90.2; tied for third were Toyota (92.2), Nissan (92.6) and VW (92.6). Compared to '98, Hyundai is down 11.4 percent, Honda down 2.9 percent, Toyota down 11.6 percent and Nissan down 15.3 percent.

Fuel economy suffered in the 2000s, thanks to (relatively) cheap gas and Americans’ continuing (and inexplicable) fixation on SUVs. But now all the companies are squeezing out mileage as they try to reach the 2025 federal fleet target of 54.5 mpg.

In 2010, Honda was first, beating Toyota and Hyundai. American companies aren’t really in the running for the top spots yet, though the Chevrolet Volt and Spark EV, the Focus Electric and Ford Energi plug-in hybrids, plus the Fiat 500e electric and Chrysler battery minivan show they’re working on it. “There are signs that the U.S. automakers are improving,” UCS says. “Ford had the biggest drop in smog-forming emissions of any automaker.” But Chrysler got the “dirty tailpipe” award for improving the least among the top eight.

Here's a closer look, on video, at Kia's electric car:

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