What do glaciers, maple syrup and lobsters have in common?

They’re all symptoms of global warming — the worldwide process of climate change that has become our major environmental challenge.

Glaciers are a well-known symptom, with the astonishing retreat of ice around the North Pole providing shipping lanes through the Arctic. And no, the addition of ice to some parts of Antarctica will not compensate, though this aspect is frequently cited by climate change skeptics.

Maple syrup is not at the top of most lists. But it’s an extraordinarily well-documented change. Through records kept by generations of New Englanders, we can plot the epicenter of peak production from Connecticut in the 1800s through Massachusetts and southern Vermont by the 1900s. Some still imagine that Vermont remains the center of syrup production, but the best territory has long since shifted north, to northern Maine and, now, the even higher latitudes of Quebec.

About lobsters we have less data, but what we do know is troubling. As recently as the 1990s, there was a fishable population of lobsters in Long Island Sound. Then it disappeared, almost overnight. The well-known abundance of Maine lobster in recent years has been matched by sharp declines off southern New England. Could our turn be next?

We do know that lobsters reproduce best in cold ocean water. The early shedding seen this year — producing a glut of lobsters before the tourists arrived — could be the first sign that Maine waters are no longer cold enough.

We’ve experienced dramatic storms, droughts and wildfires of ever-increasing severity. But it may be these subtle, gradual changes that provide the strongest evidence that we should admit the obvious — we’re tampering with the Earth’s climate in a way that puts thousands of species, including ourselves, in peril.

As a nation, we’ve responded to environmental crises before. The toxic waste and foul odors that once plagued every major river system in the east have been largely abated by the 1972 Clean Water Act championed by Maine’s Sen. Edmund Muskie. The acid rain that was devastating forests and lakes from pollution by coal-burning power plants was substantially reduced by the 1990 Clean Air Act amendments, authored by Sen. George Mitchell.

Recently, Mitchell reminded us that there was plenty of opposition back then. At an international conference in Northport last month, he said, “Then, as now, there are those who sought to deny science, who called acid rain a hoax, who imagined a conspiracy where none existed.”

The difference was that we managed to act 22 years ago. Our response to the broader challenge of global warming has instead been a mix of inattention, denial and inaction.

The last major national figure to call attention to the topic was Al Gore, who, by the end of the 2000 presidential campaign, was hardly mentioning it, so fierce was the opposition to doing anything, or even acknowledging the problem.

Mitchell had raised the alarm a year earlier in “World of Fire,” a book that plowed much of the same ground as Gore’s best-selling “Earth in the Balance.”

As we look toward the mid-21st century, it’s clear that denial isn’t serving us well. No one can infallibly predict the future, but there’s really no doubt that human contributions to global warming are significant and growing, and that any prudent species would at least be looking to reduce those contributions.

Think what our political debate would look like, if, as Mitchell urges, we adopted “the soundest, most current science” as our benchmark.

We have been doing some things right. Maine adopted tax credits for historic buildings that refocus development on our compact downtowns, which also happen to be the most beautiful, livable parts of our urban areas. We’ve encouraged the investment of $1 billion in windpower here, and the first major tidal power project will soon begin operation.

Unfortunately, we don’t often see these projects as investments in our future well-being that can’t solely be measured in dollars and cents. There are plenty of ways to make money. But not all of them contribute equally to a sustainable future.

Issues like sprawl and energy production inevitably require us to confront flaws in the status quo, which isn’t easy or comfortable. But the consequences of not doing so are becoming incalculable.

Again, Mitchell provides a timely summary. “How do we balance the need for continuity, and for change, in society?” he asked. “How can we ensure that future generations have more opportunities than we’ve had, not fewer?”

We can start by being honest and attentive. It might get us a lot farther than we think.

Douglas Rooks has contributed to Maine editorial pages for 25 years and writes for a variety of state, regional and national publications. He’s served as editor of Maine Times and editorial page editor for the Kennebec Journal in Augusta, and lives in West Gardiner.