Few people embody scientific glamour more than my friend Jeff, who dropped in two weeks ago on his way home from a two-month research mission in Antarctica. Aboard Swedish and American ships, Jeff towed an underwater camera recording footage of the Southern Ocean sea floor. So, in addition to de rigueur snapshots of Adelie penguins and towering icebergs, Jeff has a collection of king crab portraits.
The problem is that the crabs aren’t supposed to be there.
The hefty claws of the king crab are more familiar to your dinner plate than they are to animals on the Antarctic sea floor, which have evolved thinner shells and exposed juicy body parts over 40 million years in the absence of crabs. Now, warming ocean temperatures (increased by nearly two degrees Fahrenheit in recent years) have allowed crab populations to creep pole-ward into waters once too cold for their metabolisms, nearing shelf waters where they can decimate the local community.
Most of us are more familiar with invasive species introduced directly by humans, like cane toads, zebra mussels or, here in California, the mighty eucalyptus. Indeed, the most worrisome predictor of the Southern Ocean’s future comes from Norway, where scientists introduced the red king crab (hoping to produce a fishery rivaling Alaska’s “deadliest catch”). Today, the crabs expand their range by 50 km per year — the distance between Stanford and San Francisco — clear-cutting the seabed as they advance.
But today, climate change — whether you ascribe to its anthropogenic drivers or not (hint: you should) — is boosting temperatures and shifting rainfall patterns, producing dramatic changes in “natural” communities as plants and animals adjust ranges and behaviors to compensate.
Biological responses come in several forms. First, as Jeff and the Antarctic crab team observed, warming temperatures can drive species invasion. Second, climate change can shrink habitat. That’s the hypothesis behind worries over polar bears, which hunt on dwindling ice pack, and emperor penguins, whose mortality spikes during low-ice years. Third, climate change can alter an organism’s phenology — the timing of its life history events, like mating or flowering — by shifting environmental cues relative to the calendar year.
Such changes decouple delicate ecological balances fine-tuned over millennia. Spring arrives earlier and autumn later. Birds, whose migrations are often timed to capture a rich spring insect boom, are among the hardest hit: a recent study of 100 European migrant birds found that birds that weren’t heading north sooner had declining populations. But some species, able to jump-start their clocks with the shifting season, were doing better than ever.
Closer to home in North America, vast tracts of dying trees herald the climatic release of native insect pests. The spruce beetle can now complete its life cycle in one year instead of two, so its population boom is decimating Alaskan forestry stands. The mountain pine beetle, which has devastated 25 million hectares of trees in Canada and the U.S. Rocky Mountains in the last decade, is also enjoying warmer, drier conditions which weaken the defenses of the trees it drills.
Of course, the relationships between these shifts and climate change are not always clean. Yes, in the lab we can show that many organisms grow faster under higher temperatures. And the changes we’re witnessing are generally consistent with the predictions we’d make based on climate factors. But, as any scientist will tell you, in the real world biology is messy.
As with Europe’s birds, different species can adapt — and shift ranges — at different rates. Some will benefit from the new conditions — at least for now. Others will be left behind, or not be affected at all. All, of course, still face a multitude of other threats: habitat loss, overfishing, pollution, ocean acidification, and so forth.
How do these issues compare to climate change? In combination, they are certainly wreaking havoc on the world as we know it. In my mind, the more pressing worry is this: How fast can humanity adapt, and what critical parts of our earthly life support system will we succeed in saving?
On Jeff’s last day in California, we drive north to Muir Woods, trailing carbon dioxide emissions behind us, to the place where the redwoods stand hundreds of feet tall and hundreds of years old. Here, in this cathedral of light and shadow, the world stands still for just a moment. I try to forget that fog feeds these forests during the dry months (providing 40 percent of the trees’ annual water supply) and that fog frequency is down 30 percent in the last half-century (most likely due to climate change). Because these forests are part of my life support system, and I cannot imagine a world without them.
Holly welcomes reader feedback — especially from fellow redwood communers — via email at [email protected]