Interior Department scientists define climate change projection limits

A new report from the U.S. Geological Survey—the indispensable source of portland cement, crushed stone and sand & gravel shipment data—stresses the need to factor uncertainties attending climate change predictions, especially as models link present greenhouse gas emission levels to earth temperature trajectories through the year 2100.

USGS is tasked with providing objective scientific information about the effects of past, present, and potential future climate change to decision makers within and outside the Interior Department. The just-released “Using Information From Global Climate Models to Inform Policymaking—The Role of the U.S. Geological Survey” report, posted at, offers Interior and peer agencies, lawmakers and the public an overview of model-based climate science in a risk management context.

Natural climate variability is the largest source of uncertainty in climate projections in the near term, or up to 20 years out, authors contend, adding, “For time periods approximately 30 to 50 years out, scientific uncertainty about the climate system is the largest source of uncertainty in climate projections. Beyond 50 years, human decisions that affect global greenhouse gas emissions are the largest source of uncertainty. Examining a range of projected climate outcomes based on multiple scenarios is a recommended best practice because it allows decision makers to better consider both short- and long-term risks and opportunities.”

“Global climate models are increasingly sophisticated numerical representations of the Earth’s climate system. The[y] are able to simulate or replicate many important aspects of Earth’s climate, including observed changes in global mean air temperature and ocean heat content attributed to rising atmospheric greenhouse gas concentrations,” authors explain. “Research groups from institutions around the world regularly participate in a coordinated effort to produce a suite of climate models. The resulting outputs from the various climate models are compared to each other and to observations. This global effort provides a test bed to assess model performance, structural uncertainty, and projections of future change under various prescribed climate scenarios.”

“A scenario describes a plausible future outcome associated with a specific set of societal actions that captures the relationships between human choices, greenhouse gas and particulate matter emissions, greenhouse gas concentrations in the atmosphere, and consequent climate change as simulated by global climate models,” they continue. “Because scenarios are developed in a risk-based framework with a high degree of uncertainty about future societal developments, the primary scenarios used in policymaking contexts are usually not assigned a formal likelihood of occurrence, [hence], each scenario is considered to be a ‘plausible’ outcome without assuming [its] ‘likelihood’.”