PHYSICS

The release of the movie "The Day After Tomorrow" is spurring discussion about global climate change, with its depiction of giant storms and plummeting temperatures abruptly menacing the planet. But are the movie's climate scenarios plausible? At the National Center for Atmospheric Research (NCAR), scientists who study the impact of rising industrial emissions on the world's climate say it is impossible for an ice age to strike within days, as happens in the movie. They warn, however, that climate change may have significant consequences for society in coming decades. Humans are affecting global climate through emissions of carbon dioxide, methane, and other greenhouse gases that trap sunlight in the atmosphere and warm the planet. Emitted from the burning of fossil fuels and other sources, many greenhouse gases remain in the atmosphere for decades or even centuries. Sulfates and other pollutants that comprise tiny particles can have a different effect--often blocking sunlight and cooling temperatures--but their impacts are more localized and shorter-lasting. Researchers at NCAR and other institutions have found that global temperatures are likely to rise by 3.1 to 8.9 degrees Fahrenheit (1.7 to 4.9 degrees Celsius) between 1990 and 2100. Such an increase in temperatures may spur droughts, extreme storms, and related events, including wildfires, vegetation changes, and a rise in sea levels. As dramatic as real-world climate change is likely to be, it would differ from the climate change depicted in "The Day After Tomorrow" in several important ways: MOVIE SCENARIO. Temperatures in New York City plummet from sweltering to freezing in hours. ACTUAL CLIMATE CHANGE. Temperatures in parts of the world could drop, but not nearly as rapidly or dramatically as portrayed in the movie. In a warmer world, additional rain at middle and high latitudes, plus meltwater from glaciers, will add more fresh water to the oceans. This could affect currents such as the Gulf Stream that transport heat north from the tropics and might result in parts of North America and Europe becoming relatively cooler. Even if this were to occur, it would take many years or decades because oceans move heat and cold much more slowly than the atmosphere. (Some ocean changes, however, such as the periodic warming of Pacific Ocean waters known as El Niño, can affect regional weather patterns within weeks.) MOVIE SCENARIO. A massive snowstorm batters New Delhi as an ice age advances south. ACTUAL CLIMATE CHANGE. Although human-related emissions might cool some parts of Earth by affecting ocean currents, they cannot trigger a widespread ice age. That is because increased levels of greenhouse gases will increase temperatures across much of the planet. In addition, Earth's orbit is in a different phase than during the peak of the last major ice age 20,000 years ago, and the Northern Hemisphere is thus receiving more solar energy in the summer than would be associated with another ice age. MOVIE SCENARIO. Tornadoes strike Los Angeles and grapefruit-sized hail falls on Tokyo. ACTUAL CLIMATE CHANGE. Research has shown that climate change may lead to more intense hurricanes and certain other types of storms. In a hotter world, evaporation will happen more quickly, providing the atmosphere with more fuel for storms. In fact, scientists have found this is already happening with rain and snowfall in the United States. But even when scientists run scenarios on the world's most powerful supercomputers, they cannot pinpoint how climate will change in specific places or predict whether Los Angeles or other cities will face violent weather. EXPERTS NCAR has several experts on past climate shifts and future climate change: -- Lisa Dilling, 303-497-2885; ldilling@ucar.edu Specialties: As a member of NCAR's Environmental and Societal Impacts Group, Dilling focuses on how policy makers can better incorporate scientific research into their decisions-especially when it comes to climate. She is an expert on the movement of carbon dioxide between Earth and the atmosphere. -- Carrie Morrill, 303-497-1375; morrill@ucar.edu Specialties: A paleoclimatologist, Morrill researches eras when the climate of a large region or the entire planet shifted within a few decades or centuries. She is particularly interested in the mid-Holocene climate change, when rainfall lessened across parts of Africa and Asia about 4,000 years ago and possibly contributed to the demise of some civilizations. -- Susanne Moser, 303-497-8132; smoser@ucar.edu Specialties: Moser is an expert in the human dimensions of climate change, including the potential impacts of climate on society and how policymaking can reduce the risks from climate change to society. Much of her work focuses on climate change impacts on coastal communities and ecosystems and the potential for environmental degradation. -- Bette Otto-Bliesner, 303-497-1723; ottobli@ucar.edu Specialties: The head of NCAR's paleoclimate group, Otto-Bliesner investigates past climates and climate variability, with special emphasis on the current interglacial period; the Last Glacial Maximum, which occurred about 21,000 years ago; and the Last Interglacial, which occurred about 125,000 years ago. She is particularly interested in comparing climate models and paleoclimate data to interpret climate responses to changes in solar radiation and greenhouse gases. -- Kevin Trenberth, 303-497-1318; trenbert@ucar.edu Specialties: An internationally recognized authority on climate change and climate variability, including El Niño, Trenberth was a lead author of the 2001 climate change report by the Intergovernmental Panel on Climate Change (IPCC). He studies the likely impact of climate change on storms and other types of severe weather, and he also analyzes global weather observations and tracks the cycle of water between the atmosphere, land, and oceans. -- Tom Wigley, 303-497-2690; wigley@ucar.edu Specialties: One of the world's foremost experts on using computer models to study climate change, Wigley has served as lead author in each of the six major IPCC scientific reviews of the greenhouse problem. He has published on a diverse collection of topics, including data analysis; climate impacts on agriculture and water resources; paleoclimatology; and modeling of climate, sea level, and the carbon cycle.