Chapter Introduction
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CHAPTER 21
CLIMATE CHANGE
WHEN THE TREES LEAVE
Scientists grapple with a shifting climate
CORE MESSAGE
One of the biggest environmental problems facing humanity today is climate change. Evidence overwhelmingly points to the fact that climate is rapidly changing and that human activity is responsible for the changes. Climate change is impacting species, ecosystems, and the health and well-being of people around the globe, with more changes to come. Science can help us evaluate the changes that are happening, investigate causes, and provide information to help make sound policy for dealing with changing climate.
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AFTER READING THIS CHAPTER, YOU SHOULD BE ABLE TO ANSWER THE FOLLOWING GUIDING QUESTIONS
1 What is the difference between climate and weather? Why is a change of a few degrees in average global temperatures more concerning than day-to-day weather changes of a few degrees?
2 What is the physical and biological evidence that climate change is currently occurring?
3 What natural and anthropogenic factors affect climate, and which are implicated in the climate change we are experiencing now? How might positive feedback loops affect climate?
4 How do scientists determine past and present temperatures and CO2 concentrations? What evidence suggests that climate change is due to human impact?
5 What are the current and potential future impacts of climate change? What actions can we take to respond to a world with a changing climate?
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Lee Frelich was examining a 700-year-old cedar tree when he first noticed the smoke curling up into the sky over Minnesota’s great North Woods. Within an hour, his entire view was filled, so Frelich, an ecologist with the University of Minnesota, and his companions—a photographer and a journalist who had cajoled him into taking them on a tour of the iconic boreal forest—trekked up to the north end of Ham Lake, away from the calamity. They would remain trapped there, amid dense, ancient stands of spruce and fir, for 3 full days, as fire claimed some 30,000 hectares (75,000 acres) around them.
The fire’s magnitude was not surprising. Neither, really, was the fact that the flames laid bare a patch of forest that had not burned since 1801.
What was surprising was the timing. It was the first weekend in May—unusually early in the year for such a tremendous fire, especially given that the foot-thick ice had just broken apart on the lake a few days before. Frelich’s hiking companions, who knew that such fires tended to come in late summer, were surprised. Frelich wasn’t. To him it was just one more not-so-subtle reminder that climate change was rapidly throwing this ancient landscape into flux.
climate change
Alteration in the long-term patterns and statistical averages of meteorological events.
Other reminders have become commonplace: earlier springs, later winters, some tree species dying off, others popping up in unexpected places. Frelich and his colleagues worry that if current projections hold true, the forests themselves could vanish—converted by stress and time into scrubland or savanna.
Minnesota is not alone. In fact, the great North Woods are but one example of a whole planet in distress. In Africa and the American West, prairies are giving way to deserts (see LaunchPad Chapter 27). Ocean ecosystems are being affected by the twin problems of warmer temperatures and acidic waters. (See LaunchPad Chapter 29 for more on ocean acidification.) At the poles and higher altitudes, ice is melting at unprecedented rates, causing flooding in some areas and diminishing freshwater supplies in others. Precipitation patterns are shifting, with some areas getting drier and others wetter. In many places around the world, heat waves are becoming more frequent and more extreme. Wildfires like the one that scorched the North Woods are increasing in many areas around the globe due to hot, dry conditions turning forests into tinderboxes. Declining crop yields linked to temperatures or precipitation changes are evidence that agriculture is also being negatively affected. And all over the world, biodiversity is being threatened on a scale not seen since the last mass extinction 65 million years ago (see Chapter 13). Scientists say that all these changes are occurring as global climate warms with unprecedented speed. What this might mean for the future of our planet is something they are still trying to figure out.