A beacon of hope in a changing climate.

On a clear hot August day you can take a ferry to Spectacle Island and walk a winding path up to its northern summit, admiring wildflowers and eating blackberries. The summit is the highest point of land on Boston Harbor, with low wooded islands scattered around.

Off to the east you can spot a windmill near the huge sludge-digesting eggs of Deer Island, and a second windmill a few miles south at the tip of the Hull peninsula. These two points of land bracket the entrance from Massachusetts Bay to the harbor’s inner archipelago.

One distant day, Deer Island and Hull also may anchor a massive sea barrier, holding off an ocean that’s now projected to climb as much as eight feet by 2100.

Today it’s hard to imagine how we might start to build such a Big Dike, given our current politics.

But you can also see hopeful signs on this Spectacle for our ability to clean up our own messes.

The first time I sailed past the island it was a garbage dump, with the remnants of a horse-rendering plant buried under many feet of still-smoldering refuse.

Now that’s all taken away and replaced by fill from the Big Dig. The island was reengineered and replanted. Rich ecosystems began to reappear. On summer days like this, children swim a stone’s throw away from the site of the old factories.

In wildness is the preservation of the world, as Thoreau said. But not just in wildness.