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Measuring Climate Change

Weather extremes and their consequences captured headlines this year. From March temperatures in the 90s, to the Southwest’s most severe drought in a century, to the calving of massive icebergs in the most serious Antarctic thaw in 12,000 years, indications of global climate change are mounting. Yet our national capability for assessing, forecasting, and planning for climate change remains inadequate, largely because the United States has no integrated, comprehensive system for long-term climate observations. Recent input requested by the Cabinet-level working group on the President’s US Climate Change Research Initiative highlights the problem. Climate scientists have to “make do with an eclectic mix of observations mostly taken for other purposes, such as weather forecasting,” decried Kevin Trenberth of the National Center for Atmospheric Research (NCAR), Thomas Karl of NOAA’s National Climatic Data Center, and Thomas Spence of the National Science Foundation in a position paper titled “The Need for a Systems Approach to Climate Observations.” Likewise, Climate Change Science: An Analysis of Some Key Questions, a report issued by the National Research Council (NRC) in 2001 (see www.nap.edu/ books/0309075742/html/), points at the paucity of useful data as a major limitation to climate models, which depend on real-world measurements to decipher climate processes. Unfortunately, current real-world observations provide neither “the information nor the continuity of data needed,” the report states. Edward Sarachik, University of Washington atmospheric scientist and contributor to the report, describes the problem as twofold. “We don’t have measurements of key variables such as soil moisture, ice thickness, the states of the upper ocean and vegetation around the earth,” he says. “But also, the measurements we do take aren’t calibrated for climate.” Climate data are not simply compiled and averaged weather data, nor are they the findings of researchers studying climate processes; rather, such data are the product of continuous, precise measurements over extended time periods. NCAR’s Trenberth explains: “In weather observations, you’re concerned with large fluctuations, and differences of less than a degree don’t matter, whereas in climate it matters a lot.” When weather station locations are changed, or mercury thermometers are switched to thermistors, for example, effects that are negligible to weather forecasting significantly affect the climate record and befuddle climate models. “You end up with records that have jumps in them that might be interpreted as climate change when they mostly come from operational changes,” Sarachik says. Satellite data are another case in point. Although NASA’s Earth Observing System (EOS) was originally conceived with the aim of collecting longterm consistent measurements, most satellites are “one-shot deals,” says Trenberth. “Each EOS instrument has its own team of investigators responsible for its data stream, but there’s no integration between them.” Satellite-based instrumentation often goes in and out of commission with little continuity of data collection. So what would a robust climate observing system look like? At hearings held in April by the House of Representatives’ Committee on Science, chaired by Sherwood Boehlert (R–NY), Eric Barron of Pennsylvania State University listed the essential features. Long referred to as the “ten commandments” by the climate community, these rules include overlapping measurements, systems documentation, data quality and homogeneity, data maintenance and exchange, links between operational providers and users, and the assessment of proposed changes in observing systems in terms of their effects on climate time series. “The investment required to adhere to these rules is often small and will reap many benefits,” Barron testified. Chairman Boehlert stated that “there is no doubt that we need a more broadly based, better coordinated, more fully funded climate observing system.” The nature of the global change issue, he believes, dictates that research on the subject be the responsibility of many agencies; nonetheless, he added, “We need to set up a system... that has a clear set of goals and specific deliverables and guarantees coordination among the various players.” Although Sarachik and others advocate the creation of a new climate service that would take charge of climate observations, Trenberth and Barron speak more cautiously of a “new capability,” with several potential models for making observations synergistic and accessible. The cost of arriving at this new capability, Trenberth’s team calculates, is about $450 million. Given the potential social, environmental, and economic consequences of global climate change, further delay in establishing a scientifically strong observation system could drive costs much higher. As Sarachik ruefully noted, “In a hundred years, people will look back and ask, why didn’t those guys who could have done it put in a climate observation system?”