The second installment of the IPCC's 4th Assessment on Climate Change, titled "Impacts, Adaptation and Vulnerability", was released on April 6, 2007. In recognition of this report, I'm doing a weekly series called "Climate Dangers You May Not Know About".
Spring is finally here, and lifecycles are on display all around us — flowers are blooming, birds are migrating, eggs are hatching. The signs of spring may seem simple, but actually they're intricately choreographed. Flowers bloom when insects are around to pollinate them; migrating birds and newborns normally arrive when there is food for them to eat. Life's fragile choreography is based on signals from the environment, such as light or warmth. As global temperatures rise, what happens to all those cues?
One of the most obvious effects of global warming is that spring is starting earlier. Frogs are calling earlier. Birds are migrating and breeding earlier. Butterflies are emerging earlier. All good things, right?
Unfortunately, not all plants and animals are flexible enough to take part in the early spring. Scientists are finding that as temperature cues change, some species are getting out of sync others, disrupting the coordination necessary for survival. There are already documented cases:
A cute little European bird called the pied flycatcher depends on caterpillars to feed its chicks. Over the past 20 years, as temperatures have risen, caterpillars have emerged earlier and earlier, but the flycatchers' egg-laying dates have not advanced as much as the caterpillars. When chicks hatch after the caterpillar population has peaked, adult birds can't find enough food to feed their young. In some areas, flycatcher numbers have plummeted 90 percent . (We also have to wonder about the consequences of all those caterpillars that are no longer bird food.)
The flycatcher's story is fairly well known, but there are other examples, too:
- In Europe and North America, migrating birds such as swans, buzzards, warblers and robins are arriving at their feeding and breeding grounds earlier, which is not always the same time their food sources are available .
- In the ocean, different parts of the marine food chain are getting out of sync .
- In Colorado, yellow-bellied marmots emerge from hibernation three weeks earlier than they did 30 years ago, but the plants they eat haven’t changed their timing .
- In California, the rare bay checkerspot butterfly has started mistiming its emergence date relative to its host plants .
Today's rapid global warming is disrupting the delicate timing that evolved over thousands of generations. Some species are adapting; others are clearly in trouble. How will these changes filter up the food chain to our food supply? Hard to say, but it could be surprising and unpleasant. Consider what is now happening to bee colonies. For reasons that are not yet understood, bees are disappearing throughout the United States (registration required). Unfortunate but no big deal, you think? Well, it is a big deal because we depend on bees to pollinate the crops we eat. Their disappearance may undermine our food production system.
There is no evidence that global warming is implicated in the bee disappearance, but the phenomenon reminds us that we are critically dependent on the services provided by species and ecosystems. The fact is that global warming is upsetting ecosystems in both subtle and profound ways. We allow these warming trends to continue unabated at our own risk.
1 Christiaan Both et al., published in Nature.
2 Marcel Visser and Christiaan Both, published in Proceedings of the Royal Society.
3 Martin Edwards and Anthony Richardson, published in Nature [PDF]
4 Camille Parmesan, published in Annual Review of Ecology, Evolution, and Systematics [PDF]