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WASHINGTON — Climatic changes — and the results of those changes — could occur within decades or even sooner, and they are becoming a greater concern for scientists, according to a new paper from the National Academy of Sciences.

“The most challenging changes are the abrupt ones,” said James White, a professor of geological sciences at the University of Colorado in Boulder and chair of the report committee. White and several coauthors of the paper spoke at a press conference Tuesday morning.

The paper focuses on those impacts due to climate change that can happen most quickly. Among these are the rapid decline in Arctic sea ice that scientists have seen in the last decade and increased extinction pressure on plants and animals caused by the rapidly warming climate.

Many such changes, according to Tony Barnosky, a professor in the Department of Integrative Biology at the University of California, Berkeley, are “things that people in this room will be around to see.” He emphasized that scientists are “really worried about what’s going to happen in the next several years or decades.”

“The planet is going to be warmer than most species living on Earth today have seen it, including humans,” said Barnosky. “The pace of change is orders of magnitude higher than what species have experienced in the last tens of millions of years.”

Other, more gradually occurring changes can still have abrupt impacts on the ecosystem and human systems, such as the loss of fisheries or shifts in where certain crops can be cultivated. Rapid loss of ice, for example, would mean that sea levels rise at a much faster rate than the current trend, which would have a significant effect on coastal regions. A 3-foot rise in the seas is easier to prepare for if it happens on a 100-year horizon than if it happens within 30 years.