"To get the kinds of climatic conditions we have today, you need that increase in carbon dioxide. For anyone doubtful about the effect of human activity on global warming, that finding really is a 'smoking gun.'"
-- Warren Washington
Warren Washington could probably allay the concerns of even the last holdouts denying climate change who complain about climate scientists' heavy reliance on computer modeling. Washington, a senior scientist at the National Center for Atmospheric Research (NCAR), has devoted his life to creating increasingly precise and accurate computer models of Earth's climate. And the results of his labors have been phenomenal by any measure. It is not an exaggeration to say that Washington, a former head of the American Meteorological Society and an adviser to every president—Republican and Democrat alike—since Jimmy Carter, wrote the book on climate modeling: he is the coauthor of Introduction to Three-Dimensional Climate Modeling, the classic graduate-level text in the field.
"What people need to understand," he says, "is that these are not untested models scientists have dreamed up. They are based on actual meteorological data and known physics of the atmosphere and oceans. And we have spent many years refining the models by comparing them with observed data."
The process started decades ago, he explains, when scientists had only bulky mainframe computers to test their models for weather prediction. After entering several days' worth of weather measurements into their large mainframes, scientists would compare predictions against observed weather outcomes a few days later.
In that work, as in almost every facet of his life, Washington was a pioneer. As a boy he was fascinated by science, devouring biographies of Thomas Edison and George Washington Carver the way some kids read adventure stories. But as an African American, Washington had to fight against entrenched segregation throughout his early life. Despite his aptitude and passion for science, his high school guidance counselor steered him away from attending college, but Washington went anyway—one of only ten black students out of 4,000 enrolled at Oregon State. When he continued his studies, he was just the second African American in the United States to receive a Ph.D. in meteorology.
Washington's undaunted perseverance showed up pretty early on. Back in high school, for instance, when his science teacher wouldn't (or couldn't) tell him what made an egg yolk yellow, young Washington set about on his own to find out everything he could about chickens' diets until he traced the yolk's color to the sulfur they ingested in corn and seeds.
That rare blend of initiative and inquisitiveness was a requirement in a field as complex, uncharted, and exacting as the one Washington chose. When he started out, for instance, the room-sized computer he worked on, called the ALWAC, had to be painstakingly programmed using paper tape. Since then the computing power and the details built into climate models have increased exponentially, but the basic technique remains the same: first Earth, its oceans, and the atmosphere around it are divided into a grid of boxes. Into each box scientists enter real-world data about temperature, pressure, and other variables. These are then fed into complex equations based on many factors, including the physics of fluid dynamics, the chemistry of reactions, and various biological processes in such a way that the myriad data points interact with one another to simulate the movements of the atmosphere and oceans that create climate patterns.
Washington was a pioneer again in 1978, on a project with the U.S. Department of Energy, as one of the first scientists to use computer models to study the effects of carbon dioxide concentrations on global temperatures. By that time the computer models of weather were becoming so accurate that Washington and others realized they could use them to project climatic conditions many years into the future, looking not just at changes in weather patterns but at larger-scale changes in the climate. What they soon saw, with the buildup of greenhouse gases in the atmosphere, he says, "was the threat of a dramatic warming trend."
Soon Washington's team at NCAR became one of the first to practice parallel computing, in which researchers use multiple computer processors simultaneously to break the program into modules so they can include more information about variables such as the effect of sunspots and volcanic eruptions as well as human factors, including greenhouse-gas emissions from fossil-fuel burning and from the tiny atmospheric particles that scientists call aerosols.
Today's supercomputers routinely have hundreds of processors to handle the billions of computations involved in running the latest versions of climate models. That change is also reflected in the burgeoning of the field itself. In the early days, Washington says, there were only a handful of groups making climate models, with five or six scientists in each group. Today more than 350 scientists might attend a meeting on some highly specialized aspect of the ever-evolving climate models, such as refining treatment of ocean processes or more accurately accounting for changes in soils, vegetation, and permafrost.
Washington stresses that today's climate models have been subjected to so many tests and trials over such a long period that scientists have a high level of confidence in their ability to project how the climate is likely to change when subjected to a range of highly specific scenarios. One such key test scientists have performed, he explains, is the so-called twentieth-century reconstruction, in which researchers start the computer model with data from 1850 and run it to the present, accounting for changes in heat-trapping emissions, volcanic activity, and a host of other variables. Only when the model is accurate enough to reproduce the climate features of the twentieth century will scientists use it to estimate possible future climate change.
As Washington explains, "The most important thing is not just that we can reproduce twentieth-century changes—which we can. It is that we can go back and rerun the calculations, changing just one thing at a time. In this way the model becomes useful not only for future projections but also for understanding what factors have the most influence on changes in the climate."
What comes out most clearly, Washington says, is that the model simply cannot reproduce today's temperature record when scientists remove the increase in atmospheric carbon dioxide from fossil-fuel burning. "To get the kinds of climatic conditions we have today, you need that increase in carbon dioxide. For anyone doubtful about the effect of human activity on global warming, that finding really is a 'smoking gun.'"