Many who see the global warming disaster movie "The Day After Tomorrow" will want to sift the science from the fiction around climate change. With that in mind, two well-known climate change research groups have prepared responses that MSNBC.com presents below.
The National Center for Atmospheric Research, a federal lab, looks at three of the movie's key scenarios.
The Pew Center for Climate Change, a nonprofit alliance of major businesses seeking strategies to counter warming, answers some commonly asked questions via its director, Eileen Claussen, who previously has held senior science policy positions at the State Department and National Security Council.
The responses are followed by a list of online resources on climate change.
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NCAR's response
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 melt 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, may 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 of carbon dioxide and other greenhouse gases 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 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 might 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.
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Q & A on climate change
What is an abrupt climate change?
Claussen: When scientists talk about climate change, they are usually referring to “gradual climate change.” In other words, if the planet warms steadily, the climate changes steadily. But there's evidence that some parts of the climate system work more like a switch than a dial: if a certain temperature level is reached, there may be an abrupt and large change in the climate. That’s why some scientists worry about a catastrophic event — like the breakup of the West Antarctic ice sheet or the collapse of the Atlantic thermohaline circulation.
Could an abrupt climate change really happen?
Claussen: Scientists have just begun to study the possibility of an abrupt climate change. But when scientists talk about abrupt climate change, they mean climate change that occurs over decades, rather than centuries. It’s too soon to know for certain whether abrupt climate change could occur, but if it does, it’s not expected to happen within the next several decades.
Should we worry about global warming?
Claussen: Global temperatures have increased by 1degree Fahrenheit over the past 100 years. Although this may seem like a small change, it is enough to harm important ecosystems, change rainfall patterns and raise the sea level. Climate models project additional warming of about 2-10 F over the next 100 years. The overwhelming consensus of scientists who study the atmosphere is that this warming is caused primarily by the build-up of greenhouse gases in the atmosphere, mostly from the burning of fossil fuels like coal and oil.
The good news is that there are many ways to reduce emissions inexpensively. Many states and businesses are already taking action. Senators John McCain, R-Ariz., and Joe Lieberman, D-Conn., plan to reintroduce their Climate Stewardship Act this year. A companion bill is now being considered by the House.
Do scientists agree about global warming?
Claussen: Although scientists still argue about how fast and how much the atmosphere will warm, the mainstream scientific community agrees on three key points: the earth is warming; the warming can only be explained by the build-up of greenhouse gases in the atmosphere; and that the warming will continue if we don’t reduce emissions.
What is the Atlantic thermohaline circulation?
Claussen: The Atlantic thermohaline circulation, which includes the Gulf Stream, acts like an oceanic conveyer belt that carries heat from the tropics to the North Atlantic region. Warm surface water from the tropics travels northward by the Gulf Stream. As the warm water cools in the North Atlantic, it sinks to the ocean floor, and then slowly moves southward until it returns once again to the tropics. This ocean circulation pattern is caused by differences in water temperature and salinity in the ocean.
Could climate change shut down the thermohaline circulation?
Claussen: Global warming is expected to increase ocean temperatures and to increase the flow of freshwater into the ocean through precipitation, run-off, and melting of glaciers. Many climate models have projected that increased surface ocean temperatures and reduced salinity could slow or completely “shut down” the thermohaline circulation.
What are the chances of the thermohaline circulation shutting down?
Claussen: We don’t yet know the probability of the thermohaline circulation shutting down. It depends on how much and how quickly the atmosphere warms. In general, it is considered possible but not very likely. If it were to occur, it would probably not happen within the next 100 years, and circulation would eventually recover, after decades or centuries.
How can global warming cause cold weather?
Claussen: Without the thermohaline circulation, not as much heat would be transported from the tropics to the North Atlantic region. Eastern North America and Western Europe would cool, while the rest of the world continues to warm. We don’t know how much of this cooling would be balanced by the simultaneous warming in the atmosphere.
If “The Day After Tomorrow” is fiction, what is the truth about global warming?
Claussen: The truth is that global warming is happening and that it is already too late to avoid some of the effects. Even under the most optimistic circumstances, atmospheric scientists expect global climate change to result in increased flooding and droughts, more severe storms, and a loss of plant and animal species. These events will occur, even if climate change is gradual.
What can be done about global climate change?
Claussen: There is no single cause of global climate change and there is no single solution. Most experts believe that technology will provide solutions. Technologies that reduce emissions (energy efficiency, hydrogen fuels, carbon storage, nuclear energy and renewable energy) and technologies that remove carbon from the atmosphere may all play a role. Government policies that encourage businesses to develop and use these and other technologies are also very important. Many states and businesses have already found they can reduce emissions while saving money.
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Online resources
NCAR: A primer on weather and climate is at www.ncar.ucar.edu/eo/basics/index.html.
Pew Center on Climate Change: Resources include global warming basics at www.pewclimate.org/global-warming-basics.
Intergovernmental Panel on Climate Change: This U.N. agency brings together hundreds of scientists from around the world for periodic reports on the science so that policymakers can make decisions. Full reports, summaries and press releases are online at www.ipcc.ch.
U.N. Framework Convention on Climate Change: Delegates to a 1997 conference in Kyoto, Japan, hammered out a draft treaty, dubbed the Kyoto protocol, for mandatory actions to combat warming. The treaty has yet to gain enough signatories to enter into force, but this site includes treaty details and climate change basics at unfccc.int/press/dossiers.