Reaction to the decision by Carnival Cruise Lines to leave the Port of Baltimore next year because the U.S. Environmental Protection Agency has not agreed to its proposal to use scrubbers, instead of cleaner fuel, to meet air quality requirements breaks down like this: Those who hate government regulation blame the EPA; those suspicious of polluters blame Carnival; and those caught in the middle just want to see jobs restored.

Indeed, it’s difficult to know who to blame. Has Miami-based Carnival been a good corporate citizen, and is its proposal an honest effort to clean the air? If so, then perhaps the EPA is at fault for not approving its plans faster. But is it possible Carnival is just trying to skirt the rules as long as possible, minimize its cost and pressure politicians like Gov. Martin O’Malley to convince persuade the EPA to loosen its standards?

In that case, Carnival’s customers ought to be appalled. Cruises aren’t usually billed as an opportunity to ride the dirtiest form of transportation in the world, but that’s what most ships are. By one estimate, a mere 16 of the world’s largest freighters or oil tankers can pump out as much polluting sulfur into the air as all the world’s automobiles put together.

Cruise ships aren’t much better. When they are at sea, they burn a fuel called “bunker,” but closer to land they are required to burn a more refined diesel (although it’s still more noxious than what’s burned by trucks). By cruising to the Caribbean from Baltimore, Carnival’s Pride is required to burn that cleaner, more expensive fuel longer. New, tougher requirements might add as much as $140 to the cost of a round-trip ticket.

That reality is what strikes us as the most confusing aspect of all. The chief reason the cruise ship business came to Baltimore in the first place was the opportunity to capture customers from the affluent Baltimore-Washington market. Local cruisers can simply drive to the terminal at South Locust Point rather than book a plane ticket to Florida or elsewhere.

The Pride’s relocation to Tampa makes it a far more expensive option for Mid-Atlantic customers. A round-trip ticket to Tampa from Baltimore-Washington International Thurgood Marshall Airport runs in the neighborhood of $300 and can be a lot more. Wouldn’t raising ticket prices have been a much more sensible solution to retain customers who have sold out every cruise the Pride has offered from Maryland?

Still, no matter what is at work here — bean-counting or bureaucracy — it behooves the Maryland Port Administration to focus its efforts now on replacing the Pride after its last departure on Nov. 30 of next year. By some accounts, that may not be that difficult a chore. Baltimore is already home to another cruise ship, Royal Caribbean’s Grandeur of the Seas, and future growth at the port’s passenger terminal had been limited. Now, Royal Caribbean or another carrier has an opportunity to expand into what has been a profitable market with growth potential.

In the meantime, it’s clear that more attention must be paid to the pollution caused by oceangoing ships. Carbon dioxide emissions from shipping represent an estimated 5 percent of the world total, and that’s far from the only pollution its exhaust contains. Oil spills, sewage dumping at sea, bilge water and solid waste have all been issues, too.

Friends of the Earth maintains a report card on cruise lines, and those thinking about booking a getaway ought to take a look at that organization’s findings first. Some carriers, like Disney Cruise Lines (top of the list with an A-) fare quite well, while others — Carnival, unfortunately, among them with an overall D+ grade in 2012 — have not.

The loss of economic activity and jobs is unfortunate, but it would also be wrong to allow one oceangoing industry to pollute as it pleases while those of us on dry land are left to deal with the consequences of dirty air and water. The Maryland Port Administration has done an outstanding job attracting cruise ships to Baltimore over the last decade, and now it will be its task to find at least one more in the next 18 months.