Heidi B. Hammel joined The Planetary Society's Board of Directors in 2005. A Senior Research Scientist with the Space Science Institute in Boulder, Colorado, Hammel herself lives in Ridgefield, Connecticut.
She received her undergraduate degree from the Massachusetts Institute of Technology in 1982 and her Ph.D. in physics and astronomy from the University of Hawaii in 1988. After a post-doctoral position at the Jet Propulsion Laboratory (Pasadena, California), Hammel returned to MIT, where she spent nearly nine years as a Principal Research Scientist in the Department of Earth, Atmospheric, and Planetary Sciences.
Hammel primarily studies outer planets and their satellites, with a focus on observational techniques. Hammel received the 2002 American Astronomical Society's Division for Planetary Sciences (AAS/DPS) Sagan Medal for outstanding communication by an active planetary scientist to the general public .
Question: What can Neptune tell us about climate change?
Heide Hammel: Yeah. I had an interesting experience a few years ago. Now, I’ve been studying Neptune for over 20 years now. And one of my colleagues at Lowell Observatory Wes Lockwood, has been measuring the brightness of Neptune. Every year he does this. He measures it sort of all summer and fall. That’s when it’s up in the sky. And then he comes up with a number for Neptune’s brightness for that year. And for a couple of, for a decade or so, it looked like Neptune was getting brighter and fainter kind of along with the solar cycle. But then in about 1986, that changed, and Neptune started getting brighter and brighter and brighter and brighter and brighter. And I remember about like 1994, I said to Wes, I said, “You know, let me know. I get this nervous feeling when I look at this Neptune light curve, like what’s going to happen to Neptune? It’s just brighter and brighter and brighter, you know. What’s going on here? What’s it doing? What happened?” So, you know, we’ve been keeping a really close eye on it and looking at it very carefully. And so there are some theories. Some people had a theory that it was a seasonal variability, you know, that it was just like Uranus has the seasons. The earth has seasons. Well, Neptune has seasons. Now, Neptune takes 165 years to go around the sun. So to watch the seasons, you know, is longer than one astronomer can do. But there have been people at Lowell watching for like 50 years now. So we have this 50-year record of Neptune. And the seasonal model that people had didn’t fit the older data, like from the ‘50s and ‘60s. And they said, ah, well, it’s old data. Well, Wes, you know, went back and the guy who actually did that, Mike Justicavich, was still around. He was working in Russia. And they reanalyzed all the data. It was good. It was good data, and they reanalyzed it. So there was not a problem with the data. So one day I was sitting in my kitchen, reading a journal, flipping through the pages while I ate lunch. And I saw this graph go by, and I said, “Oh, there’s Neptune.” And I kept going, and then wait a minute. That wasn’t Neptune. I went back and I looked. And what is this graph? And the graph was the earth’s temperature over the last 50 years. And I just looked at it. That looks just like Neptune. Well, that’s really odd. I mean, it wasn’t that it was rising, it was these bumps or wiggles. And I thought, well, there’s a challenge here. So I talked to Wes about it, and I said, “Look at this. What do you think?” He’s like, “Ah, people find correlations all the time, you know.” I’m like, “I know. But it just really, really looks a lot alike.” And so I tried to publish it in this paper that Wes and I had about the long term variability of Uranus and Neptune, and the referees just said, “This can’t possibly be true. There can’t be a correlation. Do not publish this.” And that kind of made me kind of take a step back. I thought, you know what? I don’t know if it’s true or not, but its’ very interesting, and I don’t think that a referee should just say it can’t be true. So I worked for several years on that data, did a lot of statistical analyses on it, and eventually did publish it with the title “Suggested Correlations between Neptune’s Brightness, Earth’s Temperature, and Solar Irradiation, Sunlight.” And when you do hard core statistics, the correlation is not statistically significant. But, you know, we would have to do probably 500 years of observations before we would know if it was statistically significant. Being insignificant statistically doesn’t mean it’s right or wrong. It just means you don’t have enough data to show yes or no. That’s really what it means. So I published this, and what I think the important thing about it is that it shows that there is a role of sunlight in changing the climate of planetary atmospheres. I mean, that sounds like a kind of an obvious no brainer, but sometimes you need to have actual data to show you what that role can be, and if you only have earth’s atmosphere, you know, you don’t want to be messing with earth’s atmosphere to do tests. So the only way to find out how planets really respond to differing amounts of sunlight, is to look at planets that get different amounts of sunlight, because the physics on Jupiter or Neptune or earth is the same physics. It’s the same chemistry. It’s got different chemical compounds, but the physics and the chemistry that one does, it should be the same. And so if you had things going on another planet that don’t work, don’t fit your theories, that makes me nervous that we’re missing some kind of component in the theories that we’re working with here on earth. So another piece of the Neptune puzzle was observations that I and other astronomers have put together about its temperature over the last couple of decades. And we have found that Neptune’s atmosphere is steadily warming. And is that a seasonal effect on Neptune, or is there something else playing a role here? The answer is we don’t know, but we sure would like to know, wouldn’t we? Because if there are effects that are causing temperature rises across the solar system, that means that our planetary atmospheres are much more sensitive than we had anticipated. And because we don’t know the answers to these questions, I get really nervous when I hear scientists talk about geo-engineering, injecting dust into the earth’s atmosphere to cool it, to counteract global warming, global climate change, makes me very nervous, because as a planetary scientist, as someone who studies climates on other planets in the solar system, my sense is that we don’t understand earth’s whole climate system well enough to be taking proactive steps in changing it. I really worry about that. I think we need to be very careful if we want to do things like further modify our atmosphere. And similarly, I think we need to be very worried about unintentional modification, which is basically what’s been going on. What do we do then about climate change on earth?
Question: Is Climate Change New?
Heidi Hammel: It’s very clear that global climate change is occurring on earth, but it’s also been very clear that that has always happened on earth. We’ve always had a changing climate on earth. We all know about ice ages. We know when our continent was covered with ice sheets. We know glaciers come and they go. It puzzles me that people forget that. They talk about climate change as if it’s something new. Climates always change. The question is, how are we going to adapt to climate change? Now, it may be true that we are accelerating it inadvertently by messing with our atmosphere, but regardless of that, the climate will change. And so, okay, so maybe we have a shorter time to adapt to it than we otherwise would have had, but we would have had to adapt anyway, because the climate will change with time. So I get very frustrated. We do need to adapt to climate change. We can either do it intentionally, thoughtfully, or climate change will happen and we’ll just be dealing with it. And so I think most of our efforts need to be on how we can adapt to changing climate thoughtfully. How can we set up our population systems in cities so that they can react to a changing climate, you know, whether it’s getting hotter or colder. Mother nature will always throw surprises at us, and so here we are planning for this global warming. Well, 30 years ago we were planning for global cooling. It just goes to point out that we’re never really quite sure what we’re going to deal with. We need to be ready to deal. And like I said before, geo-engineering I don’t think is the right way to do it. I think we really need to be working with our governments and our population systems, and finding ways to be prepared for a climate change, whichever way it goes.