Every year, as Earth Day rolls around, we survey the automotive landscape looking for progress in the industry's efforts to reduce emissions and limit global warming.

We've identified a lot of progress recently. More than a dozen new electric models are set to go on sale in the coming year, and sales of plug-in models more than doubled in the past year, primarily as production of the Tesla Model 3 ramped up.

CONSIDER THIS: An Earth Day question: When will we see 'tailpipes' on cars as morally wrong?

Yet there are troubling signs as well. Plug-in car sales dropped by almost half in the first quarter of 2019 after federal tax credits in the U.S. began to wind down on the most-popular models. California's zero-emission vehicle mandate, which gave rise to production and sales of electric cars, is under attack by the EPA. The Trump administration has also begun the process of pulling the U.S. out of the Paris Climate Accord and overturned the Obama administration's Clean Power Plan. The latter called for electric utilities to reduce emissions, and thus had the secondary effect of making electric cars even cleaner.

A pessimist might conclude that progress has started to backslide. Yet, given the importance of clean air and the threat of global warming, getting more electric cars on the road can be viewed as a moral imperative.

CHECK OUT: Poll: When will it be unacceptable to drive a car with a tailpipe?

So on this Earth Day, we revisit a question we first asked for Earth Day in 2014: "When will it be unacceptable to drive a car with a tailpipe?"

Our options include, "It already is," as we hear from readers almost every day in our comments section; "2030," which, according to the most optimistic experts is when most new car sales in many developed countries will be electric; "2040," according to less optimistic projections, and "Never," for those readers who may not see electric cars as a moral issue or may have other opinions on the subject.

We've asked the question before, and we frequently run the answers. For example, we ran them after Norway announced a plan to make all new car sales in the country electric by 2025.

READ ALSO: Norway's Goal: All New Cars Will Be Emission-Free By 2025 To Cut Carbon

The landscape has changed significantly since the last time our readers weighed in on the question. Lots more electric cars are on the road, of many more types, and there are a lot more places to charge them.

With that context, it's time to update our understanding of readers' thoughts on the question.

As always, remember that our Twitter poll questions do not aim to reach a scientific conclusion, such as on climate change. We generally get too few responses, and our respondents are self-selected.

Green Car Reports respectfully reminds its readers that the scientific validity of climate change is not a topic for debate in our comments. We ask that any comments by climate-change denialists be flagged for moderation. Thank you in advance for helping us keep our comments on topic, civil, respectful, and fact-based.