Allegra LeGrande

In a nutshell, what is global warming and why should we care?

"Climate change" is a better term. Sometimes people ask me if I "believe" in climate change. I say no. Does ice float on water? I do not "believe" this—it's not a question of faith, it's a matter of fact. Climate change has happened throughout earth's history, but what's unusual about the future is that there will be—,as there is now—,human-caused change, resulting from our daily emissions of these gases. We are moving into a world unseen by human eyes: Greenhouse gases haven't been this high in more than 850,000 years. The difference between the Ice Age (the last one was 20,000 years ago) and pre-industrial times (around 1850) is a 40% increase in carbon dioxide and only around 9°F warming. We've already eclipsed this carbon-dioxide difference in the brief 150 years since pre-industrial times. If we continue business as usual, we're likely to see a 2.5 to 9°F increase. That may not sound like much, but a similar increase in temperature caused major changes in the past: That temperature change meant the difference between a massive ice sheet covering Canada and parts of the US, and none.

So how do you address naysayers, those who don't think global warming exists?

Naysayers are a tough one. Well, without any greenhouse gases at all, the earth would be a frozen ice ball: These gases warm the earth's surface. But greenhouse gas concentrations over the past million years were never greater than they are today, and never before in the entire history of man has the earth had so much of the greenhouse gas carbon dioxide. The last time this was so high, it was before we even existed. We're pushing the world into a regime that was last realized millions to tens of millions of years ago. The earth and many creatures thrived during that time, but humans did not.

What's your personal "eco-sin"?

Oh, I love sherry, especially this Hidalgo Amontillado (eek! Like Poe!), and Spanish wines in general. They all have to be flown over!

What can geologic evidence tell us about the future?

We can see geologic evidence in our own backyard. Just walking around a local park on the banks of the Hudson River, I can see striations in the ground, the incremental markings of the movement of ice sheets through the years. We can't actually see the ice sheets melting, but we can look to this pattern of how they melted before and draw evidence-based conclusions. Shakespeare said, "the past is prologue." Well, we look to the past for a hint of the future. For instance, we can look at the disappearance of ice sheets from thousands of years ago and draw our best conclusions as to the fate of our remaining ice sheets like Greenland and Antarctica. In other words, say you have a sick patient—in this case, a "sick" ice sheet. As humans have never seen a sick ice sheet before, you don't know how the illness will develop, but you try to find a similar "patient" in recorded history to draw parallels. We can infer what happened to a sick ice sheet from 9,000 years ago, and try to determine what will happen to the ice sheets today. But instrumental records, like the readings from a thermometer, date back only some 150 years. We try to predict the future with these climate models, but are challenged by the relatively short period of recorded data. In short, we use geologic evidence to help us meet the challenge of predicting climate beyond the range of this data.

For folks to get a better sense of what you do, they can look to the Dennis Quaid character—who studied ancient climate patterns and applied them to today—in the movie The Day After Tomorrow. Describe your work, and incidentally, how realistic is the "doomsday" scenario in that movie?

The NASA Goddard Institute for Space Studies has a collaborative climate research effort with Columbia University called the Center for Climate Systems Research. This is where I work. I test a climate model's ability to reproduce past climates, before our 150 years of observational data. Past climate was much more variable than today: Think of disappearing ice sheets, or the warm tropics in the Arctic region during the time of the dinosaurs. If the model performs well with reproducing past climate, we can have confidence in its ability to perform in the future. The work I do refines the model for long-term predictions. As for the movie, the scenario is that the melting of ice sheets, due to climate change, causes the Gulf Stream—the warm current of water that flows north along the southeastern US coastline to North Carolina and then shoots off toward northern Europe—to stop, sending the earth into a deep chill. I've modeled the exact scenario that Quaid's character did in the movie and the idea just doesn't pan out. But in terms of more realistic scenarios, we think that what's on our horizon are higher intensity hurricanes, rising sea levels, scarcity of fresh water supplies, increased extreme heat and drought frequency, and an increased intensity of storms.

So the alarming natural disasters in recent years—the 2004 Asian Tsunami, Hurricane Katrina—are these due to climate change and if so, can we expect more or worse of the same?

Even though the 2004 Asian Tsunami was not the result of climate change, it points to the vulnerability of low-lying areas to abrupt rises in sea level. Keep in mind, it's not only the absolute change in sea level that matters, since even small changes can translate into relatively large ones in areas prone to storm surges. As for Katrina, a powerful hurricane is like a race car. There are many components required to get the car going fast: good engine, proper air-fuel mixture, racing fuel, etc. Hot sea surface temps are the "racing fuel" of hurricanes, but, like a car, there are many other things required to get it started and to keep it from stopping. If we continue on our path of warming sea surface temperatures, however, the intensity of hurricanes could increase since we are essentially providing lots of racing fuel for hurricanes.

From unusually warm winters to really hot summers, we seem to be seeing an increase in temperatures overall. People make jokes about enjoying global-warming's benefits, but is this really climate change?

Weather and climate are not exactly the same thing. Day to day, there can be huge changes in the weather; climate is the mean. Listening to your weather forecast, you sometimes hear things like "the hundred-year flood" or "heat-wave of the century." These kinds of phrases will completely lose their meaning if we continue along our "business as usual" path. What kind of "heat-wave of the century" comes every ten years? Last year tied as the warmest year in recorded history. And eight of the last ten years have been one of the top 10 warmest. Overall, past climate reconstructions for the last 1,000 years indicate that we're warmer today. Going back even further, around 130,000 years ago, to the previous "warm" period, the Eemian—before ice sheets covered North America and parts of Europe—global temps were a bit warmer, by two to four degrees, but then, greenhouse gas concentrations were not as high as they are now. So if we go on like we've been, we'll match, and maybe exceed the warmth of the Eemian. Why hasn't it happened yet? Because so much of the Earth's surface is water, it takes awhile for warming to occur: Even after you turn on the gas under a pot of water, it still takes time for it to boil. If we can reduce our greenhouse gas emissions—turn down the gas on the stove—we can avoid this kind of warming. But time is of the essence. When preparing to send your kids off to college, you start saving from day one; it would be very difficult to scrape the funds together from scratch when they’re seniors in high school. In the same way, we need to make "carbon savings" today, to avoid huge climate changes tomorrow. If we wait another 30 years, when even today's naysayers recognize that humans are causing climate change, it will be too late—we'll be committed to a significantly larger degree of climate change. The glaciers for example: They're melting faster than ever, and once they're gone, they're gone.

What are some steps each of us can take in our day-to-day lives to help reduce carbon emissions? There are many organizations that work with carbon offset programs. How effective are they really?

To start, ask yourself these questions: What is the carbon footprint of the product I'm buying? What amount of energy went into producing it? And how much energy went into transporting it? If I buy this, how much energy will go into maintaining it? And does the product itself consume energy? If so, how much, and can I find an energy-saving alternative [with, for example, an Energy Star appliance: http://www.energystar.gov/]? But while it's great to keep these things in mind and switch to using compact fluorescent lightbulbs, hybrid/electric cars, and energy-efficient appliances, even this is not enough. After all, electric cars use energy. We need to think top to bottom, to see wide-scale public policy changes. Contact your legislators—local, state, and federal—about things like building power plants with low greenhouse-gas emissions (or even better, renewable-power plants using solar, wind, or tide energy), increased mass transportation, and funding incentives for research into carbon-neutral technologies. And buy local as much as possible! As for carbon-offset organizations, well, it feels good to be doing somethingabout climate change. But you have to be aware of your carbon footprint: You can't absolve yourself from burning carbon by donating to one of these funds. If you have a big gaping wound and put a band-aid on it, it looks nicer, but is it really better? These programs offer to "offset" your emissions (from flying, commuting, etc.); what we really need to focus on is (1) reducing carbon emissions and (2) removing and permanently storing carbon with carbon-sequestration technology. This is being developed, but it's still in infancy. The trick is to find a technology that's carbon neutral, one that can pull carbon from the atmosphere, but doesn't emit much carbon in the process. And then, there is the question of storing it. Trees are great: They take in carbon and store it, but when they die, they decompose and release it back into the atmosphere. So planting more trees is not a permanent solution. We need to offer financial incentives for the development of this technology. If people can make money by removing and permanently storing carbon, they will. Same with renewable energy: We should proactively invest in green energy sources now to be prepared for the future. We have a finite amount of natural resources.