From a discussion of climactic provinces in the distribution of intertidal species, Rachel Carson (remember her from Silent Spring?) describes a growing awareness of global warming already becoming obvious to marine biologists early in the last century. Again, note the sensitivity of the arctic regions to climate change. The canary in the coal mine…

Although these basic zones are still convenient and well-founded divisions of the American coast, it
became clear by about the third decade of the twentieth century that Cape Cod was not the absolute barrier it had once been for warm-water species attempting to round it from the south. Curious changes have been taking place, with many animals invading this cold-temperate zone from the south and pushing up through Maine and even into Canada. This new distribution is, of course, related to the widespread change of climate that seems to have set in about the beginning of the [twentieth] century and is now well recognized–a general warming-up noticed first in arctic regions, then in subarctic, and now in the temperate areas of northern states. [Emphasis my own--ER.] With warmer ocean waters north of Cape Cod, not only the adults but the critically important young stages of various southern animals have been able to survive.

from “Patterns of Shore Life” in

“The Edge of the Sea”

Rachel Carson (1955)

She then goes on to describe instances of animals found outside their normal ranges, and changes in historical fisheries resulting from these migrations. Those lines were written over sixty years ago.