Latest predictions for life in North America's changing climate
Considering how much trouble two people have deciding what movie to see, the most remarkable thing about a new set of global-climate predictions may be that it exists at all. More than one hundred nations belong to the Intergovernmental Panel on Climate Change (IPCC), and for the panel to speak, the representatives of all those nations have to agree.
Over the course of this year, the panel will issue a comprehensive report on the state of science concerning climate change, updating the panel's 2001 analysis. The new report, the IPCC's fourth, divides climate science into three areas: the physical processes, their effects, and what people could do about it. Three working groups of hundreds of scientists specializing in the relevant topics have been laboring for 5 years to draft the technical chapters for the epic document.
In April, the panel convened in Brussels to weigh the results from the working group on Impacts, Adaptation and Vulnerability, which considers how global warming has affected people and ecosystems and what is yet to come. The 451 scientists who created the technical chapters had squeezed them down to 1,572 pages. In Brussels, the national representatives had a week to agree on a summary22 pages, in the endthat they could all accept.
"They [went] over it sentence by sentence," explains one of the working group scientists, Chris Field of the Carnegie Institution in Stanford, Calif. Four days of debate stretched into wrangles that lasted throughout the final night, and IPCC Chair Rajendra Pachauri of the Energy Research Institute in New Delhi, India, confided at the concluding press conference that he was wearing the same clothes he'd put on the morning before.
Yet the parties finally agreed on a summary and accepted the report. It includes more details about regional effects than any IPCC report has had so far. In North America, as in the rest of the world, the panel says, climate change already shows effects. On the politically explosive topic of agriculture, the panel notes predictions of rising yields for some crops, such as grains in middle latitudes. But the report warns of "major challenges" for crops growing near the warm end of their ranges.
The report also highlights concerns over the availability of water for all uses, and over the greater likelihood of damage from sporadic but huge natural disasters. The world is woefully underprepared for the effects of climate change, says the IPCC. One of the biggest themes to emerge from the report is an urgent need to think about adapting to the risks that are already upon us.
Climate change isn't just about the future anymore. The summary begins by emphasizing a flood of new evidence documenting the effects that climate change has already produced.
That's evidence "from all continents and most oceans," says the summary. Numerous studies show glaciers melting, permafrost warming, birds nesting earlier in the year, leaf buds popping sooner, fish migrations changing, animals shifting their ranges, and many more events in nature going askew. The summary highlights 75 long-term studies documenting significant biological and physical changes in nature. Of the 29,000 sets of observations in those studies, 89 percent show a shift in the direction predicted for the effects of global warming. "We're no longer hand-waving with models," said Martin Parry of the United Kingdom's Department for Environment, Food and Rural Affairs, cochair of the IPCC impacts group, as he unveiled the consensus summary.
"There are some good examples from North America now," says Linda Mortsch of Environment Canada in Waterloo, Ontario. She and Field worked as coordinating authors for the technical chapter on climate impacts in North America. This chapter is now getting its final editing, with release currently scheduled for this summer. But Mortsch and Field are already talking about its contents.
Like the summary, the North American chapter starts with what's already happened. For example, daily observations from satellites starting in 1981 show that spring has been turning Canada and the continental United States green earlier and earlier. By 2000, the region was greening up 10 to 14 days earlier than it had 19 years before then.
Ground-level data, meanwhile, show that lilacs advanced their first blooms by about a week between 1959 and 1993. Honeysuckle in the western United States has started blooming 3.8 days earlier per decade, while in the northeastern United States, apples and grapes have been opening their leaves about 2 days earlier per decade.
Animals furnish many more such examples. Fifteen out of 23 butterfly species in lowland California are taking off for their first flight of spring an average of 24 days earlier than they did 31 years ago. In northern Canada, red foxes have pushed north, driving back Arctic foxes.
Having established that changes are already under way, the IPCC impacts group went on to consider what will probably happen if people don't curb greenhouse-gas emissions. Debate has burned especially hot over agriculture. Seizing on predictions that crop yields will rise, at least under certain scenarios, some political factions and business interests have touted the benefits of climate change.
It's probably not going to be that simple. In North America, the IPCC says, "moderate change in the early decades of the century is projected to increase aggregate yields of rain-fed agriculture by 5 to 20 percent but with important variability among regions." But the summary warns that results will vary by region, especially for crops that depend on fought-over water supplies.
That mixed message is for mid-and-higher latitudes only. The summary says that nearer the equator, rises of even 1° to 2°C are expected to decrease crop productivity.
Within North America, climate change will push different crops in different directions. For the early decades of this century, most studies predict that warming will boost yields of major cereal crops, such as corn, rice, soybeans, and wheat, some 5 to 20 percent. On the other hand, a study of 12 crops in California hasn't shown a consistent trend one way or the other, says Field. He and Carnegie Institution colleagues David Lobell and Kimberly Cahill have shown that temperature rises can explain some improvements in yield among the state's orange groves. Avocado yields, on the other hand, have trended downward.
The IPCC report likewise refers to a complex story in the wine grapes of California, citing work by Ramakrishna Nemani of the University of Montana in Missoula and his colleagues. During the period from 1951 to 1997, the average annual temperature in the Napa-Sonoma region rose a modest 1.13°C. Most of that change came from warmer nights and earlier spring warming. Those tweaks lengthened the growing season by 65 frostfree days. The humidity increased, too, and the summer temperatures turned milder and more grape friendly. Thus far, the researchers conclude, warming trends in the coastal region have brought good fortune to premium-wine vineyards.
Further warming may not be so kind. Some grapes already grow under optimal conditions, and more climate change will probably undermine their performance. For example, bringing just a little more humidity to the California coast raises the risk for grapevine diseases. Growers are already fighting an intensifying wave of Pierce's disease, a bacterial vine killer spread by the glassy-winged sharpshooter, a highly mobile insect typically killed by frost.
Field sums up the situation by saying that many tree and vine crops may not fare as well as the big cereal crops will. Grain farmers can choose from a range of varieties, and the plants' short life span, just a season from seed to harvest, allows flexibility in tailoring crops to changing climate. But grapes and other woody plants can take years to yield, so growers can't rip them out and replace them in one season. And these crops rarely come in alternative varieties that would better tolerate changed conditions. "I'm more worried about our iconic crops, like maple sugar or California wine," says Field.
The future of crops in North America depends in large part on the future of water, and that's worrisome, says the IPCC report. Across the region, farmers, developers, shippers, conservationists, and others already wrangle over water. Climate change and drying regions will put these antagonists' interests into even sharper conflict.
Picking highlights from all climate-change impacts on North America, the IPCC panel chose to comment first on water supplies in the continent's western mountains. With "very high confidence," says the report, scientists predict that warming will decrease the snowpack blanketing the mountains in the winter, increase the flooding in winter and spring as precipitation shifts from snow to rain, and reduce the water flows out of the mountains in the summer.
For land and people sustained by water from these mountains, the report predicts shrinking snowpacks "exacerbating competition for over-allocated water resources." Taking the Columbia River as a case study, the report cites studies predicting that water flows will swell in winter and spring but dwindle in summer and fall. At the same time, a rising population is dependent on the river's water. Current projections for Portland, Ore., say that by the 2040s, population growth alone will raise the city's thirst for the Columbia's water by 20.8 million cubic meters per year. On top of that, a 2°C temperature rise translates into an extra 5.7 million m3 a year of water use by residents, while shrinking the supply by some 4.9 million m3 a year.
Changes in river flow could stymie well-intentioned efforts to solve environmental problems, warns Mortsch. Energy planners call for switching to more hydropower to reduce carbon emissions, but that energy source will dwindle if river flows weaken. Lower water flow also means less dilution of pollutants. Research at the Bay of Quinte in Lake Ontario suggests that a drop in flow could increase a river's average phosphorus concentration 25 to 35 percent.
Water temperatures will rise, too, with repercussions for fish that need cool water. The report notes that Lake Ontario is both warming and falling in volume, changes that have already shrunk the habitat for the lake's cherished walleye. Brook trout in Canada will also suffer as water warms, and they may disappear from half of their current habitats by the year 2050, according to work by Cindy Chu of the Great Lakes Laboratory for Fisheries and Aquatic Sciences in Ontario and her colleagues.
And don't ignore frozen water. The IPCC report notes that natural snowpacks will shrink but that snowmaking could cushion the shock for the ski industry in western North America. The $27-billion-per-year snowmobiling industry, however, remains at the mercy of natural flakes.
Big bad blips
One of the big changes in thinking that the new IPCC report captures, says Field, is "an increased appreciation" of extreme events. It's not enough to talk about climate change in terms of upticks and downturns in average conditions, he says: "Hurricane Katrina occurred halfway through our writing." Much of the impact from climate change will come not from average conditions but from disasters that exact sudden and huge tolls on people, property, and ecosystems.
Field clarifies that he's not laying the blame for Katrina or any other specific coastal storm on global warming. Still, these calamities show vividly how much damage extreme events can bring.
A warming climate means dry horrors as well as wet ones. For example, "it's clear that risks from wildfires are sharply rising and very, very sensitive to climate change," says Field.
As the climate warms, summer lingers and gives potential wildfire fuel an extra toasting, the new report says. It notes calculations that the wildfire season in the western United States during the past 30 years has expanded some 78 days. Substantial firesthose that scorch more than 1,000 hectareshave gone from burning an average of nearly 8 days to burning for 37 days. Between 1987 and 2003, fires burned nearly seven times the area of westernU.S. forests as they did from 1970 to 1986.
Even if the world doesn't burst into flames, heat still kills. "It's really striking how many people die of heat-related causes," says Field. The European heat wave of 2003 killed tens of thousands of people, and North America is far from immune to such disasters. The new report cites estimates that by the end of the century, the frequency of heat waves in Chicago will have increased by 25 percent. Los Angeles' current dozen-or-so typical heat wave days will grow as to as many as 95 a year.
The emphasis on disasters raises another big point, says Field. "Doing something" about climate change has typically meant reducing carbon emissions. That's vital, but it's not enough, he says. Disasters are already on the way, and preparations for themwhat the new report lumps into the term adaptationhave been spotty and weak.
"People look at their portfolio of protection, and they say, 'Well we have reasonable building codes, and we have reasonable distribution of insurance,'" says Field. That kind of thinking, he warns, relies on preparations for disasters past, and won't necessarily address disasters of the future. He also predicts that insurance will become less consoling as people face the magnitude of impending risks. "Until disaster strikes, you feel like insurance is a good way to protect yourself. After it strikes, you say, 'You know, a stronger levee would have been a good idea.'"
The main problem, though, is to get people thinking about what to do, he says. "As we look at the history of adaptation in North America, in some ways, the biggest risk is complacency."