I was standing on the beach the other day, just beyond the reach of the waves, looking out over the blue, blue water of Monterey Bay. A friend and I had been talking about sea level rise, and I was interested in learning what it might mean—in practical, real-world terms. I decided to begin with a trip to the shore. There, I planted myself in the sand and imagined the water creeping up my legs: one foot, two feet, three feet—on me, almost navel high. Scientists predict that a one- to three-foot rise in sea level is quite likely by the year 2100—not very long from now, in the grand scheme of things.

It was a calm day, and the water was barely moving. But I threw some huge, lashing waves and heavy surge into my imaginary scenario—because scientists also predict that along with sea level rise, we will be experiencing more extreme weather events, with heavier seas battering the shore.

That was enough to get started. And once I set to imagining, I was shocked at how vulnerable this coast seems, even to one extra foot of water, much less three. All along the shore are buildings and roads. Already riprap is piled on Monterey Beach, protecting a condominium development that marches from high land directly onto the sand—and every year the beach suffers a bit more in skirmishes with the superior forces of nature. At my back was a sturdy concrete wall that protects a beachfront hotel. Sturdy now, but it already feels the splash of high tides; more water would leave it not long for this world. The beach would vanish under the waves, and the dunes would likely be undercut and washed out to sea. Farther along, the shore is built up: there are wharves full of tourist shops and fish-processing plants; more hotels, restaurants, shops; the Monterey Bay Aquarium. All now out of reach of the sea, but how soon before they fall victim to higher water and fiercer waves?

Rising Tides

Rising seas; extreme weather; bigger waves—these things are not simply predicted, they are already happening. ... Global warming is causing the sea not only to rise, but also to warm. And that has an impact on the critters living in it—not just in theory, but in fact. In the early 1990s Rafe Sagarin, a graduate student at Hopkins Marine Station in Pacific Grove, launched a telling study driven by two key sets of data. One was an inventory carried out 60 years before by another Hopkins grad student, W. G. Hewatt. Between 1931 and 1933, Hewatt counted every invertebrate animal he found along a 108-yard transect stretching out to sea from the high tide to the low tide mark. The second data set was a temperature log, kept at Hopkins since 1917. This log revealed that the average temperature in 1993 was three-fourths of a degree warmer than it had been when Hewatt conducted his study—and two full degrees warmer during the warmest part of the season, in late summer.

Suspecting that warmer waters would affect the intertidal community, Sagarin repeated Hewatt’s inventory, sampling along the same transect during 1993–1994. “When the results began to come in,” Sagarin said, “it was incredibly exciting. I never expected any changes to be so obvious.” Obvious, but also startling: of 45 invertebrate species selected for close analysis, fully 32 showed statistically significant changes in abundance. Moreover, a northward population shift was clear: whereas eight of nine southern species had increased markedly in abundance, five of eight northern species had decreased. Several snail species that Hewatt had not even seen are now among the most common gastropods on the rocky reef off Hopkins.

Sagarin (now a professor in the Department of Environmental Health Sciences at UCLA) attributes these changes to global warming, and is adamant that we should be concerned. “People may not be interested in the fate of a few invertebrates in tide pools,” he says, “but consider that mosquitoes, which bear some of the world’s deadliest diseases, are also invertebrates, and they are expected to respond to climate change in a similar fashion, and quite quickly at that. Cities that have been spared malaria and other diseases solely as a geographical consequence of being far enough north, or high enough in altitude, may be infested as climate warms. Likewise, ideal conditions for crops may move northward, and since plants don’t care about political or economic borders, some farmers may end up hurting a lot.”

The Future

The issue of global warming raises many questions, especially with regard to the particulars: how it will make itself felt, how it will influence other processes on Earth. For example, we all know that El Niños have a strong impact on California’s weather patterns—causing landslides, floods, power outages, extreme tides, and dramatic changes in ocean fisheries—and they will certainly do so in the future. How will global warming affect this climatic phenomenon? Nobody really knows, though two studies reported within the last decade in Nature suggest that El Niños could become the norm, with the California climate of the future looking like an amplified version of the last few decades (remember those El Niños of 1982–83 and 1997–98?). General storminess—frequency as well as location—likewise is difficult to predict. One thing does seem sure, however: a warmer global climate will increase evaporation from the oceans, increase moisture in the atmosphere (because warmer air can hold more water), and increase precipitation worldwide. These changes in the global water cycle are likely to bring more rain to the western edges of the continents in major frontal storms and to increase the number and/or intensity of thunderstorms bringing brief bursts of heavy rainfall. And the temperature is likely to continue rising—and with it, sea level.

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