Climate change where we live

Whether or not they could be definitively linked to a changing climate, weather crises in the first years of the 2000s added regional exclamation points to the global possibilities raised by modeling and theory. A relentless 2003 heat wave in normally temperate Europe took tens of thousands of lives. Hurricane after hurricane battered the U.S. coast, with Katrina the worst of a bad bunch. And the Arctic Ocean’s year-round coating of sea ice showed new fragility, accenting the potential for ice-free summer conditions that could arrive sooner than almost anyone had expected.

Society’s hunger for region-by-region projections of global warming’s impact pushed the climate research community into new territory. At NCAR, two projects were among many worldwide that worked with both global and regional models, trying to gain much-needed detail using computers and code already available.

The multiagency North American Regional Climate Change Assessment Program (NARCCAP) drew on an international array of four global and six regional models, including the Community Climate System Model (CCSM) and a research-oriented version of the Weather Research and Forecasting model (WRF). Investigators hailed from universities and national laboratories across the United States, Canada, Italy, and the United Kingdom. In one NARCCAP phase, regional climate models picked up where the four global models left off, providing finer-scale detail on precipitation and other variables for the periods 1971–2000 and 2040–2070.

Visualization by computer model of a hurricane, swirls of red, orange yellow and blue
In a simulation of hurricanes for the decade 2045–2055, the NRCM produced realistic depictions, such as this one of a major hurricane striking the central Gulf Coast (not a literal forecast of any particular hurricane). (Visualization courtesy NRCM.)

“This is the largest and most complex regional modeling activity ever created in the United States in support of climate assessment,” says project director Linda Mearns (NCAR). The program’s value, she adds, lies in using multiple global and regional models to more fully explore the uncertainties of regional climate change: “The multimodel approach is crucial.” The U.S. Environmental Protection Program is using NARCCAP scenarios for its water quality program, and other U.S. agencies are expected to follow suit.

What about running a global and a regional model at the same time, in order to understand and improve the treatment of fine-scale processes? That’s the strategy behind the Nested Regional Climate Model, led by NCAR’s James Hurrell and Greg Holland. The NRCM brought together WRF and the high-resolution Regional Ocean Modeling System (which originated at Rutgers University) within the CCSM.

Through a special allocation of NCAR supercomputing time, the NRCM team simulated the periods 1995–2005, 2020–2030, and 2040–55 at resolutions reaching as fine a scale as 4 kilometers (2.5 miles) for specific cases and areas. When it zoomed into the genesis areas for Atlantic hurricanes, NRCM output hinted at the possibility of tropical cyclones by the 2050s that could be, on average, smaller but stronger and longer lasting.

Much of the NRCM’s support is drawn from the insurance industry through the Willis Research Network, and from the U.S. Department of Energy and the offshore oil industry through the Research Partnership to Secure Energy for America. Both sets of users are interested in how hurricane tracks and intensities might evolve in a changing climate. Other NRCM projects will examine climate in the U.S. Midwest and Intermountain West as well as in Antarctica.

By decade’s end, the demand for locally relevant climate guidance had spurred NCAR to create a unit aimed at producing it. The Climate Science and Applications Program emerged from the Research Applications Laboratory, the same NCAR unit that, for years, had crafted specialized weather forecasting tools for aviation, transportation, and other high-value needs.

“After the IPCC report in 2007, many people’s interest went from, Is climate change happening? to What will be the impacts?” says the program’s director, Lawrence Buja. Adhering to NCAR founder Walt Roberts’s precept that science should serve society, this new group was using GIS-based tools to make climate model output more accessible to broader groups, including water utilities. They also aimed to complement the work of NOAA’s National Climate Service, which was officially proposed in 2010.


Today — Scenarios and pathways: Mapping the route to tomorrow's climate

Photo of Kathy Hibbard

"This collaboration is leading us down new paths of scientific and human understanding of the Earth system."

—Kathy Hibbard, Pacific Northwest National Laboratory

"It’s not just a number—it’s how we reach it.” That was the pithy summation of Anand Patwardhan (Indian Institute of Technology) at an event sponsored by NCAR in Copenhagen, Denmark, during the 2009 United Nations climate summit.

Patwardhan referred to the growing realization that setting a single target for global emissions or carbon dioxide concentrations wasn’t enough, just as knowing your destination on a road trip doesn’t tell you how the journey will unfold. Researchers at NCAR and elsewhere are paying closer attention to the possible paths by which greenhouse gases might accumulate over coming decades.

Since the earliest days of the Intergovernmental Panel on Climate Change, the IPCC has relied on “scenarios”—plausible depictions of how greenhouse gases might change in the future, based on assumptions about population, development, and other human variables. In turn, climate models depicted how the atmosphere would respond to any given scenario. A set of four scenarios, including “business as usual” (no policy intervention), were laid out in 1990; these were joined in 2000 by a larger, more varied set. But the steps required to get from scenario to model meant that not all scenarios were used by climate models for the IPCC’s 2007 assessment. Moreover, none of the scenarios considered what might happen if society began to reduce emissions.

Photo of an urban landscape with visible pollution, river in foreground
The breakneck growth in greenhouse gas emissions from China is just one of many variables that scenario planners consider in portraying possible 21st-century futures. (Photo courtesy William Bradford.)

Now a third set of scenarios is in the works—this time produced in tandem with climate modeling through a new parallel approach. One critical early step in designing the next round of modeling was a 2006 workshop coordinated by NCAR’s Kathy Hibbard (now at Pacific Northwest National Laboratory) and Gerald Meehl. Three communities of researchers—one focused on integrated assessment; another on impacts, adaptation, and vulnerability; and a third on global climate models—have begun identifying a family of scenarios consistent with four representative concentration pathways (RCPs) for greenhouse gases.

Meanwhile, in early 2010, climate modelers began simulations based on each RCP. Through this simultaneous work, both the RCPs and scenarios will inform the fifth IPCC assessment report, scheduled for release in 2013–14.

“The RCPs provide a starting point for new and wide-ranging research,” noted Richard Moss (Joint Global Change Research Institute) in a 2010 Nature overview cowritten by Hibbard and Meehl.

Even before the new RCPs were available, researchers were learning more about the importance of the emissions journey versus the destination. In a 2010 study published in Proceedings of the National Academy of Sciences, NCAR’s Brian O’Neill and coauthors found that a year-2050 emissions goal is critical to ensure that a year-2100 target remains within reach. As O’Neill observed, “Setting mid-century targets can help preserve long-term policy options while managing the risks and costs that come with long-term goals.”