MEREDITH — "The climate is changing and we can read the signature of change in our own backyard," said Lindsey Rustad, an ecologist with the United States Forest Service who studies the effects of rising temperatures on the northern forest at the Hubbard Brook Experimental Forest in Woodstock.
As the keynote speaker at the annual meeting of the Lakes Region Planning Commission on Monday night, Rustad tackled what she called the "the conundrum of climate" , or "what we know, don't know and need to know" from both a global and local perspective. She began by tracking the rising levels of carbon dioxide in the atmosphere since 1800, which after reaching unprecedented levels have continued to rise at a quickening pace. As the concentration of carbon dioxide and increased, temperatures have climbed. "Ten of the hottest years on record occurred in the last 15 years," Rustad said, "and the hottest year ever was 2104."
Rustad recalled that the changing climate began to catch the attention of scientists in the late 1950s and 30 years later the International Panel on Climate Change (IPCC) was convened. The first report of the IPCC, issued in 1990, she described as "wishy-washy" but its fourth report found that "warming of the climate system is unequivocal" and "very likely" is the result of man-made greenhouse gas emissions. The most recent report of the IPCC concluded that "human influence has been the dominant cause of observed warming since 1950" and warned that longer the reduction of greenhouse gas emissions is delayed, the greater the costs will be. "The language of the IPCC has changed dramatically," Rustad remarked.
Warming temperatures, Rustad said, have hastened the melting of sea ice leading to rising sea levels. At the same time, the warming world has been marked by changing patterns of precipitation levels as well as altered the patterns of precipitation and greater frequency of what she called "extreme events," like heavy precipitation, severe droughts and heat waves.
Rustad said that the changing climate has left its marks at the Hubbard Brook Experimental Forest. Established in 1956 , the 8,000 wooded acres riven by Hubbard Brook was originally a venue for studying the impact of acid rain, but since 1996 has been a center for measuring the effects of climate change on the northern forest. She said that since 1955 the average annual temperature in the forest has risen 2.9 degrees Fahrenheit, more than the global average. She noted that temperatures have risen relatively more at the higher latitudes. Precipitation has increased 12 percent, with more rainfall than snowfall. Both the amount of snowfall and days of snow cover have dropped 25 percent.
Rustad explained that because of the diminished snow cover, the soil freezes to greater depths in the winter, which impairs the capacity of the roots of trees and shrubs to absorb nutrients, chiefly nitrates and phosphorus, stunting the growth of their root systems. Instead, elevated levels of nitrates and phosphorus leach into ground and surface water. At Hubbard Brook, Rustad said, the ice storm of 1998 was simulated by spraying trees with a fire hose amid freezing temperatures. The experiment confirmed that when the capacity of trees to absorb nutrients is impaired, elevated levels of nitrates and phosphorus are found in nearby surface water after the icing event.
Rustad herself is interested in extreme events, which she defined as precipitation of two inches or more. She said that as the climate has changed wet and dry periods, which once alternated, have begun to coincide with greater frequency. "We have drier soils in a wetter world," she remarked. Likewise, warmer temperatures prompts trees to leaf and flowers to blossom earlier in the spring while a late spring frost, which counts as an extreme event, may destroy a significant share of the forest canopy opened by the early warming.
Asked what aspect of climate change should most concern municipal Planning Departments in New Hampshire, without hesitation Rustad replied "heavy precipitation".
Although Rustad acknowledged some have questioned the findings and ignored the warnings of the scientific community, she said that more and more people, especially those whose livelihoods and life styles are affected, understand from experience that the climate is changing. "People are beginning to care," she said.