If you think of an automobile enginewhen you step on the accelerator, the engine speeds up because you're putting more energy into it by increasing the fuel flow, so everything runs harder and hotter and faster. The extremes get more extreme.
That's what's happening with the climate. We're stepping on the accelerator by adding greenhouse gases to the climate and increasing heat energy in the system.
How does climate change manifest itself?
Ocean levels are rising, because water expands as it heats up. Since there is more energy in the system, storms may become more frequent and more violent. Increased incidents of flooding create heavier runoffs and soil erosion. Indirect effects of climate change can also cause entire species to go extinct.
How realistic is this movie?
It has a kernel of truth, although it has been "Hollywoodized." There is evidence that abrupt climate change has happened a couple of times in the last 13,000 years, but it's never happened in a few days, as it does in the movie. That's completely impossible.
What is the ocean conveyor belt referred to in the movie, and what is its importance to the Earth's climate?
It's the system of currents that flows around the oceans of the world and carries heat from the tropics to the northern latitudes. There is evidence that the North Atlantic branch of the current has failed in the distant past8,200 and 12,700 years agocausing a great cooling of the climate.
In the movie, the influx of fresh water, caused by the melting of a massive ice sheet, changes the salinity of the oceans, shutting down the Gulf Stream. Could that happen?
In theory, that is realistic. Salty water is heavier than fresh water. When the cold, salty current reaches the northern latitudes and gives out its heat, the current actually sinks and flows back along the bottom of the ocean toward the tropics.
When then there's a lot of fresh water added to that current, it may stop flowing, because it's not dense enough to sink anymore. In the past, retreating glaciers dumped enormous amounts of fresh water very suddenly into the North Atlantic, and the currents stopped.
What about the superstorms depicted in the movie, which form like hurricanes over North America, Europe, and Asia? Are they realistic?
No. Hurricanes form over waters and tend to break up and dissipate when they reach shore. They can't get the energy to keep going anymore.
One of the effects created by the superstorms in the movie is the pulling down of supercool air from the troposphere that freezes people in a matter of seconds. There is nothing that suggests this could happen.
Could another ice age happen?
It's unlikely. Even if there were a continued influx of fresh water that weakened or stopped the North Atlantic current, any cooling effect that might create would be swamped by the warming that would continue to happen in the meantime.
But if abrupt climate change has happened in the past, before the industrial revolution, isn't this just part of a natural cycle that is, in a sense, inevitable?
Certainly the climate has, to some extent, a mind of its own. But that's not to say we're not having an influence on what the climate is, what it does, and how it behaves.
We've taken a great deal of carbon that used to be locked up in the Earth in the form of coal and undisturbed oil and natural gas and released it into the atmosphere. That carbon hadn't been there in the atmosphere for millions and millions of years.
It's simply naive to think that's not going to have an effect on the climate.
So what do you say to skeptics who dispute the seriousness of global warming?
Most don't dispute that the climate is warming and that human activity has a great deal to do with that. Even the most vociferous of the climate skeptics have pretty much stopped saying that global warming is not happening.
Actually, science benefits from having skeptics. They challenge assumptions and arguments and force people to go back and get more data.
Do you think the catastrophic events in the film may be so extreme that audiences may not take the climate change issue seriously?
I hope people will come away with the lesson that we need to be more careful with the climate that we're fooling around withnot that they need to worry about buying property in Mexico because the Northern Hemisphere is going to be locked up in an icebox.
People should have a good time, but I don't think they should take this as a reason to laugh off climate change. I hope this becomes a teachable moment for people and shows that we are doing serious damage to the climate.
Any particular aspects about the film that you liked?
I liked how it used shots from space to give you a sense of how huge and powerful the climate really is. One of the key lessons of the film is that this is a very big, very complex system that we don't understand very well. Since we're conducting a giant experiment with this huge, complicated, poorly understood system, weird and unexpected stuff is probably going to happen.
I don't think anyone thinks abrupt climate change is likely any time soon, but the probability is not zero.
Do you think the general public appreciates and fully understands the threats that global warming pose?
I hope they understand that climate change is happening now. It's affecting everyone who is alive on the planet, and it will inevitably affect their children and their children's children. I have a ten-year-old son, and I want to do everything that I can do to ensure that the world he grows up in is as wonderful and pleasant as the world we got now.
So what can people do about this problem?
They can do a great deal. If millions of people turn off the lights when they leave the room, it makes an enormous difference on how much carbon winds up in the air. Most people believe their electricity comes from renewable or nuclear power or hydroelectric power, but more than half of the electricity generated in the United States comes from coal.
When you leave the light on all night long, that one act is directly responsible for putting a couple of more pounds of carbon into the atmosphere.
I would urge people to go see the movie. I thought it was a lot of fun. I would also urge them to drive to the movie theater together with a few friends [to conserve gasoline and put less exhaust into the atmosphere] and turn out all the lights in the house before they leave.
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