green car sales graphic

So, the good news in December for green-car advocates as that Nissan Leaf sales continued their gangbuster climb. And Honda picked up some proverbial steam. But that's about it.

In all, Americans bought 48,553 hybrids, plug-in hybrids, battery-electrics and diesels last month.

US green car sales for December 2013 were 12 percent lower than 2012 figures, easily making last month the largest year-over-year sales drop all year. By that measure, September was second-worst, with a 1.8 percent decline. In all, Americans bought 48,553 hybrids, plug-in hybrids, battery-electrics and diesels last month.

For the "glass half full" folks, Nissan had its best-ever month with the battery-electric Leaf, with sales surging 70 percent from the year before to 2,529 units. The Japanese automaker beat its previous record, set in August 2013, by 109 cars.

Sales of the Civic Hybrid, CR-Z and Insight all jumped at least 35 percent.

Honda also continues to turn around its fortunes, with all of its advanced-powertrain models, save the Acura ILX Hybrid, posting year-over-year increases. Sales of the Civic Hybrid, CR-Z and Insight all jumped at least 35 percent from December 2012 numbers, while Honda moved 426 and 38 units of its new Accord Hybrid and Accord Plug-in Hybrid, respectively. Overall, Honda's green-car sales rose 73 percent from a year earlier to 2,077 units. Also coming up on the positive side of the ledger was Audi, which more than doubled diesel sales from a year earlier, to 1,955 units.

All four Prius variants had year-over-year declines.

And that's where the fun stops and the hangover begins. Toyota couldn't keep up with surging sales in late 2012, with December green-car sales falling 19 percent from the year before to 24,922 units. All four Prius variants had year-over-year declines of between 11 percent and 32 percent. Camry Hybrid sales plunged 39 percent to 2,726 units, while Highlander Hybrid sales fell 54 percent. And Lexus hybrid sales were down 4.5 percent to 4,696 units. Only the Avalon Hybrid showed promise, almost doubling December 2012 sales to 1,480 units.

Ford had a similar drop-off as big sales in late 2012 hurt year-over-year comparisons. Ford's green-car sales fell 20 percent from a year earlier to 6,499 units. C-Max Hybrid sales were hit particularly hard, plunging 64 percent from a year earlier to 1,201 units. C-Max Energi Plug-in Hybrid sales and Fusion Hybrid sales each declined 15 percent. The doubling of Lincoln MKZ Hybrid sales, to 754 units, wasn't nearly enough to offset the difference.

Chevrolet Volt sales dropped 9.2 percent to 2,392 units.

General Motors also had issues, with mild-hybrid models such as the Buick LaCrosse and Regal and Chevrolet Malibu eAssist versions all having year-over-year sales declines of between 38 percent and 81 percent. And while the newer Cruze Diesel and Spark Electric Vehicle moved 495 and 126 units, respectively, Chevrolet Volt sales dropped 9.2 percent to 2,392 units.

Additionally, Volkswagen's green-car sales dropped 13 percent from a year earlier to 6,409 units, as the 360 units sold of the newer Jetta Hybrid couldn't offset the effects of an 18 percent decline in VW diesel sales. And, while Daimler's Smart division sold 167 of its Smart ED all-electric vehicles, other lower-volume green-car makers such as Mitsubishi and Porsche saw year-over-year declines.

Whether December's weak numbers (compared to a strong December 2012) are a sign of some sort of Prius fatigue is anyone's guess, as the falling gas prices usually associated with declining green-car sales didn't materialize. In fact, regular gas was selling at an average of about $3.33 a gallon at the end of the year, up almost a dime from a month earlier, according to AAA.

Annual figures for 2013 put things in a slightly rosier light.

Annual figures for 2013 put things in a slightly rosier light, as green-car sales for all of 2013 rose 17 percent from compared to 2012 to 641,925 units, not including the approximately 21,000 Tesla Model S vehicles likely sold (Tesla doesn't break out monthly sales figures). If we count only plug-in vehicles, the numbers get even better, as Americans bought 77,530 battery-electrics and plug-in hybrids (again, not including Teslas), up 55 percent from a year earlier. Of course, those year-to-date plug-in vehicle numbers were up as much as 90 percent in August before tapering off towards the end of the year.