- Email: [email protected]
Professor Alan Robock
Professor Alan Robock Department of Meteorology, University of Maryland, College Park Interviewed by Prof. R. Bornstein Department of Meteorology, San Jose State University, San Jose, California, USA.
Q: Could you give us some background on the work you've done in the area of climate modeling? A: I have used an energy-balance climate model to look at the effects of volcanic dust, changes in the solar constant, and changes in the concentration of atmospheric carbon dioxide on global climate. Recently, I have used this model to investigate the nuclear winter phenomenon - the climatic effects of a large-scale nuclear war. Q: How did the research on nuclear winter first originate? A: Nuclear weapons have been around since 1945, but only in the last decade did we realize that an environmental effect of the use of nuclear weapons might be to partially destroythe ozone layer in the stratosphere, which would have the effect of increasing the ultraviolet radiation reaching the surface. It was thought that this was the worst environmental effect of nuclear war, but in 1982, the Swedish journal Ambio commissioned a study of the various global effects of nuclear war. Paul Crutzen and John Birks wrote an article on the effects of nuclear war on the atmosphere. In particular they were interested in the effects on ozone near the surface of the earth produced by photochemical reactions with pollutants put into the atmosphere from the bombing of cities. In order to do this, they had to calculate the amount of sunlight that would reach the surface.A quick calculation showed that there would be so much smoke from the fires that virtually no sunlight would reach the surface, and therefore there would not be enhanced ozone production. Climate scientists spent the next year using these results to estimate the global climatic effects of this enormous amount of atmospheric smoke.The first papers were published in the fall of 1983 by an American group, which goes by the acronym 'TRAPS', for Turco, Toon, Ackerman, Pollack and Sagan, and by a Russian group, Aleksandrov and Stenchikov. Q: How did you get interested in this problem? A: The results were presented on October 31 and November 1, 1983, in Washington, D.C., at the Conference on the Long-Term Worldwide Biological Consequences of Nuclear War. I attended the conference and realized that the climate model I had been using could be applied to this problem in order to investigate some of the interactions in the climate system that had not been studied by the other groups. Q: How can we investigate the potential climatic effects of a nuclear war? A: This is not an experiment that we can perform in the real world. And we cannot bring the atmosphere into the laboratory. One way is to look at past occurrences in the climate system that would let us learn about the global climate response, and we need not confine the search to our planet. The extinction of the dinosaurs 65 million years ago by an asteroid impact, forest fire smoke plumes, volcanic eruptions, dust storms on Mars, and World War II firestorms as cities burned all suggest that a nuclear winter could occur. Another way is to use the theory of the global climate system that has been incorporated into global climate models that have already been used successfully to investigate other causes of climate change. Q: Could you describe your climate model and compare it to the other climate models that have been used? A: The first study of ]-I-APS used a one-dimensional model that looks at the atmosphere in detail in the vertical. It calculates the solar and terrestrial radiation at different heights in the atmosphere, but does not look at the horizontal distribution of climate change. The first Soviet study used a three-dimensional model (general circulation model, or GCM), which looked at both vertical and horizontal climate changes. My model is intermediate between these two. It looks at the earth in 132
Environmental Software, 1986, Vol. 1, No. 2
he North/South direction, while in the vertical I do a lot of averaging, so there is not really any ,ertical resolution. [In the East/West direction I have only two grid points,- one for all the land, and me for all the oceans.] This type of model has been called a 11/2-dimensional model. All models ~implify certain parts of the climate system in order to look in detail at other parts. The climate ~ystem is so complex that there is no model which includes all the important physics that could run ast enough on even the fastest computers to give a solution. ~: Could you describe the computer software aspects of these global climate models? ~,: -irst of all, they are all written in FORTRAN. Although by today's standards FORTRAN is a rather )rimitive language, a great deal of software has been developed in FORTRAN. This includes the ~raphics package developed at the National Center for Atmospheric Research (NCAR). In ~ddition, FORTRAN codes run quite rapidly. The one-dimensional TRAPS model is very fast. My ~odel takes about one second of computer time to simulate one year of real time on the Amdahl ~,70V6 at the Goddard Space Flight Center in Greenbelt, Maryland, which is equivalent to a small BM mainframe computer. It takes more than the model run time to do the graphics and the ~tatistical analysis afterwards. The three-dimensional GCMs take much much longer, i.e., at least )ne minute of computer time to simulate one day on a Cray computer. This limits the number of ;alculations that can be done with GCMs. The longest nuclear winter runs with this type of model ~ave simulated only 40 days of real time, whereas my model has simulated several years. And I ~ave done many different multiyear simulations. 3: How many lines of code does your model have, and also how much core does it require? t takes a bit more than one megabyte of storage, although it could easily be rewritten to take less :han a megabyte. As far as lines of code, it has several thousand; however, the model itself doesn't :ake very much. I have also developed a great deal of analytical software to diagnose the different :lows of heat and radiation in the model and to do-statistical and graphic analysis of the output. 3: What results do all of the models agree on, and what are some areas where they disagree? l-he greatest uncertainty in the theory is in the amount of smoke and dust that would be put into :he atmosphere from the fires. Given a certain scenario, say 180 Tg (million metric tons) of soot put nto the atmosphere, all of the models agree that there is so much smoke that it virtually blocks out Ihe sun, and it gets very cold and dark at the earth's surface. They disagree on how cold it would get and on how long it would remain cold. This depends not 3nly on how much smoke is put in, but how fast it is transported around in the atmosphere and on ~ow fast it is removed from the atmosphere. We do not have a very good understanding of the removal processes, i.e., when it rains, how much smoke might be washed out by the rain. The most recent results from the Los Alamos National Laboratory, one of the two U.S. weapons laboratories where nuclear weapons are made, show that about a third of the smoke would be heated by the sun and lofted above the region of the atmosphere where the weather occurs. So although about two-thirds of the smoke would be washed out fairly rapidly in a summertime case, about a third ~vould remain in the stratosphere for quite a long time, which would prolong the cold surface temperatures. My model looks at feedbacks between snow and sea ice in the climate system which are kept ~,onstant in the other calculations. When it gets cold more snow and ice are produced which act to make it colder still, by reflecting sunlight from this bright surfaces and insulating the ocean from the atmosphere. This mechanism produces still more snow and ice, and is called a "positive feedback." I found that the initial atmospheric cooling might be prolonged for one or two years. Although most of the model results suggest that agriculture would be virtually impossible after a spring or summertime conflict because of the large climatic effects, my model suggests that even in the next year, agriculture could be quite difficult because it still might be very cold at the earth's surface. Q: For some of the problem areas that have yet to be formulated satisfactorily, what approaches might be taken in the next year or two in order to get a better understanding of these processes ? What new software might have to be developed in order to implement these new ideas? A: There are two main problem areas. The first, which I mentioned, is the source function. If you drop a certain number of weapons on a certain number of cities, how much smoke is generated? You need to know what the number of grams of burnable fuel are per square centimeter in each city is; what fraction of that turns into smoke; and what fraction of the smoke remains in the atmosphere. In order to do this calculation, we need to do detailed smoke-source inventories. Microscale or mesoscale weather models can calculate on the scale of a smoke cloud in three dimensions.They can compute how the smoke is lofted up into the atmosphere, and how raindrops and ice crystals Environmental Software, 1986, Vol. 1, No. 2
133
are formed to remove the smoke. Some detailed calculations have been done in this area, but more remains to be done. In one simulation, Dr. Bill Cotton at the Colorado State University, simulated the burning of Denver. Using the Cray I computer at NCAR, it took two hours to simulate a half hour of burning. We found that a large fraction of the smoke would end up high in the atmosphere and would not be washed out. On the larger climatic scale, there has already been extensive model development. The first three-dimensional models kept the smoke fixed in height and horizontal extent and did not calculate the transport and removal of the smoke. In the last two years, new code has been developed to keep track of the distribution of the smoke as it moves with the wind, its radiative impact, and the processes which remove it from the atmosphere. We have also discovered that because we are working in a climate regime so different from that for which the models were developed, that certain parts of the model probably do not do a very good job of simulating the system. In particular, at the surface of the earth, the model predicts a very cold surface above which the atmosphere is very warm - a regime which does not exist in the real world. Thus, one area in which models are being developed is to do more detailed calculation of the flux of heat and temperature between the surface of the earth and the atmosphere, including fog formation. Another area is the vertical distribution of smoke in the upper part of the atmosphere, in the stratosphere. The most detailed models only consider the stratosphere in a few layers, and we have discovered that the models remove smoke from the atmosphere faster than occurs in reality. We can look at volcanic eruptions or radiactive fallout from atmospheric bomb tests in the 60's and measure residence times which are about 1 1 or 12 months. But the models have enhanced the vertical diffusion process which produces an unrealistically large amount of smoothing between the different layers in the model. This acts to mix the smoke down in the atmosphere and remove it after only one to four months. The solution is to put in more model layers, but this requires additional computer time. This is being done at the Lawrence Livermore and Los Alamos national laboratories and at the National Center for-Atmospheric Research in Boulder, Colorado, which have Cray XMP computers. Q: What has the government's reaction been to the results showing the dire cfimate consequences of nuclear war? A: The first reaction, especially from the Defense Department which has the mandate to control nuclear weapons and to calculate their effects, was embarrassment, as the first studies were carried out by university scientists without any support from the Defense Department. The Defense Department was ordered by Congress to write a report on the policy and science implications of nuclear war. A very short report was published in March 1985. It glossed over many of the details. It basically, said that "our policy is to prevent nuclear war, and if we prevent nuclear war, we'll prevent duclear winter." In June 1 986, two months late, they released this year's report, which was 5 pages long! They say that the results are so uncertain that we can not really make policy decisions because we can not be sure that it would actually happen. This is opposite to their response to many other problems, in which they take a worst-case scenario. Q: Has the government supported research within their own laboratories and within the university community? A: The National Climate Program Office submitted a plan to the President to spend $10 million dollars a year for five years on nuclear winter research two years ago. The recommendation was not approved. The current national research budget for nuclear winter research - is about $51/2 million dollars. All money reprogrammed from that already existing in the various agencies. $21/2 million dollars a year is being spent by the Department of Energy, mainly at Los Alamos and Livermore. $21/2 million is also being spent by-the Defense Department, the Defense Nuclear Agency, with much of the work done at universities. In addition, half a million dollars is supposed to be spent by the National Science Foundation, but it is not clear that all of it will actually be spent on nuclear winter research. All of this money is being spent on the climatic effects, with virtually none at all being spent on biological impacts. Congressman Tim Wirth (D - Colorado), frustrated at the Pentagon's response to Congress, has recently introduced a bill to mandate substantially more funding for nuclear winter research. Q: Could you summarize the implications of nuclear winter for human life and the biosphere in general? A: The climatic effects are that following a large scale nuclear war, there would be a great deal of smoke generated by burning cities. This black city smoke would rise up into the atmosphere and produce cold and dark conditions for weeks or months. Biological systems would not be able to 134
Environmental Software, 1986, Vol. 1, No. 2
~ustain themselves, and agriculture would be virtually impossible for the first year. The main effect )n the people who would not be killed outright by the blast, fire and radioactivity, would be ~tarvation, because food could not be produced. Countries like the Soviet Union and the United ~tates, which would be hit by the weapons, would suffer so much anyway that nuclear winter .~ffects would not have a significant effect. However, for countries away from the conflict, such as ndia or Kenya or Brazil, there might be large climatic consequences. ~: If nuclear war is limited to the Northern Hemisphere, what climate effects would the Southern Hemisphere suffer? ~,: t would suffer smaller effects for two reasons: one is that the Southern Hemisphere has a lot more )cean than the Northern Hemisphere, which acts to buffer the climate change. In addition, most of :he smoke would be generated in the Northern Hemisphere. Some of it would blow into the 3outhern Hemisphere by the changed atmospheric circulation arising from the heating of the ~tmosphere by the absorption of sunlight by the smoke. If a war took place in summer in the ~lorthern Hemisphere, there would be a lot of absorbed sunlight and a large shift in the ]tmospheric circulation. If it took place in the Northern Hemisphere winter, there would be less ~unlight and so the changed circulation might not take place. The Southern Hemisphere effect Nould then be much less. 3: How has the media covered this issue and how has the public responded to what has been in the media? ~,: 3arl Sagan wrote an article in Parade Magazine on nuclear winter which received a great deal of 3ress coverage. The term "nuclear winter" was coined by Rich Turco, the lead author of the first 3aper. It has been a catalyst to get people to think more about all the horrible effects of nuclear war. The uncertainties involved in the theory have not been described that well by the media Oecause it is easier to write about the catastrophic effects, and some scientists have not been sareful enough to point out the uncertainties in their work. In general I think the coverage has been rather fair, although its political implications frequently depended on people's previous political biases. For instance, nuclear winter has been used to argue both for and against Star Wars. Q: Where do you see the research in nuclear winter developing in the next year or two and, in particular, what implication might this have for the development of new software techniques? A:
It has already produced much better climate models that can be used for other problems, e.g. Arctic haze, the transport of volcanic dust, and transport of dust from desert storms. I expect that there will be further developments in large scale climate models, and also in the mesoscale cloud models. These models will be quite useful in the future for many other climate problems. There will also be studies not involving computers, eg. observations of actual fires. There will be a controlled brush burn in Los Angeles during this summer, which will be studied by airplanes and by satellites. Q: Can you say that we might know for sure in several years that the climatic implications will be certain, or will there always be significant uncertainties given the nature of the problem? A:
We will never be able to know what combination of bombs might be used on which targets, at what time of year, or what the weather will be that day. I hope we will never find out. As far as the response of the climate system, these are also uncertainties, but we will narrow them down. Some of the things which we have to know better concern the optical properties of smoke, the amount of sunlight it absorbs, and how much terrestrial radiation is absorbed and emitted. It is the job of scientists to communicate their results to the public so that informed decisions can be made on arms control. I hope that by studying nuclear winter, we will learn enough about the dangers of nuclear war to reduce the changes of it ever happening.
Environmental Software, 1986, Vol. 1, No. 2
135
Q: Could you give us some background on the work you've done in the area of climate modeling? A: I have used an energy-balance climate model to look at the effects of volcanic dust, changes in the solar constant, and changes in the concentration of atmospheric carbon dioxide on global climate. Recently, I have used this model to investigate the nuclear winter phenomenon - the climatic effects of a large-scale nuclear war. Q: How did the research on nuclear winter first originate? A: Nuclear weapons have been around since 1945, but only in the last decade did we realize that an environmental effect of the use of nuclear weapons might be to partially destroythe ozone layer in the stratosphere, which would have the effect of increasing the ultraviolet radiation reaching the surface. It was thought that this was the worst environmental effect of nuclear war, but in 1982, the Swedish journal Ambio commissioned a study of the various global effects of nuclear war. Paul Crutzen and John Birks wrote an article on the effects of nuclear war on the atmosphere. In particular they were interested in the effects on ozone near the surface of the earth produced by photochemical reactions with pollutants put into the atmosphere from the bombing of cities. In order to do this, they had to calculate the amount of sunlight that would reach the surface.A quick calculation showed that there would be so much smoke from the fires that virtually no sunlight would reach the surface, and therefore there would not be enhanced ozone production. Climate scientists spent the next year using these results to estimate the global climatic effects of this enormous amount of atmospheric smoke.The first papers were published in the fall of 1983 by an American group, which goes by the acronym 'TRAPS', for Turco, Toon, Ackerman, Pollack and Sagan, and by a Russian group, Aleksandrov and Stenchikov. Q: How did you get interested in this problem? A: The results were presented on October 31 and November 1, 1983, in Washington, D.C., at the Conference on the Long-Term Worldwide Biological Consequences of Nuclear War. I attended the conference and realized that the climate model I had been using could be applied to this problem in order to investigate some of the interactions in the climate system that had not been studied by the other groups. Q: How can we investigate the potential climatic effects of a nuclear war? A: This is not an experiment that we can perform in the real world. And we cannot bring the atmosphere into the laboratory. One way is to look at past occurrences in the climate system that would let us learn about the global climate response, and we need not confine the search to our planet. The extinction of the dinosaurs 65 million years ago by an asteroid impact, forest fire smoke plumes, volcanic eruptions, dust storms on Mars, and World War II firestorms as cities burned all suggest that a nuclear winter could occur. Another way is to use the theory of the global climate system that has been incorporated into global climate models that have already been used successfully to investigate other causes of climate change. Q: Could you describe your climate model and compare it to the other climate models that have been used? A: The first study of ]-I-APS used a one-dimensional model that looks at the atmosphere in detail in the vertical. It calculates the solar and terrestrial radiation at different heights in the atmosphere, but does not look at the horizontal distribution of climate change. The first Soviet study used a three-dimensional model (general circulation model, or GCM), which looked at both vertical and horizontal climate changes. My model is intermediate between these two. It looks at the earth in 132
Environmental Software, 1986, Vol. 1, No. 2
he North/South direction, while in the vertical I do a lot of averaging, so there is not really any ,ertical resolution. [In the East/West direction I have only two grid points,- one for all the land, and me for all the oceans.] This type of model has been called a 11/2-dimensional model. All models ~implify certain parts of the climate system in order to look in detail at other parts. The climate ~ystem is so complex that there is no model which includes all the important physics that could run ast enough on even the fastest computers to give a solution. ~: Could you describe the computer software aspects of these global climate models? ~,: -irst of all, they are all written in FORTRAN. Although by today's standards FORTRAN is a rather )rimitive language, a great deal of software has been developed in FORTRAN. This includes the ~raphics package developed at the National Center for Atmospheric Research (NCAR). In ~ddition, FORTRAN codes run quite rapidly. The one-dimensional TRAPS model is very fast. My ~odel takes about one second of computer time to simulate one year of real time on the Amdahl ~,70V6 at the Goddard Space Flight Center in Greenbelt, Maryland, which is equivalent to a small BM mainframe computer. It takes more than the model run time to do the graphics and the ~tatistical analysis afterwards. The three-dimensional GCMs take much much longer, i.e., at least )ne minute of computer time to simulate one day on a Cray computer. This limits the number of ;alculations that can be done with GCMs. The longest nuclear winter runs with this type of model ~ave simulated only 40 days of real time, whereas my model has simulated several years. And I ~ave done many different multiyear simulations. 3: How many lines of code does your model have, and also how much core does it require? t takes a bit more than one megabyte of storage, although it could easily be rewritten to take less :han a megabyte. As far as lines of code, it has several thousand; however, the model itself doesn't :ake very much. I have also developed a great deal of analytical software to diagnose the different :lows of heat and radiation in the model and to do-statistical and graphic analysis of the output. 3: What results do all of the models agree on, and what are some areas where they disagree? l-he greatest uncertainty in the theory is in the amount of smoke and dust that would be put into :he atmosphere from the fires. Given a certain scenario, say 180 Tg (million metric tons) of soot put nto the atmosphere, all of the models agree that there is so much smoke that it virtually blocks out Ihe sun, and it gets very cold and dark at the earth's surface. They disagree on how cold it would get and on how long it would remain cold. This depends not 3nly on how much smoke is put in, but how fast it is transported around in the atmosphere and on ~ow fast it is removed from the atmosphere. We do not have a very good understanding of the removal processes, i.e., when it rains, how much smoke might be washed out by the rain. The most recent results from the Los Alamos National Laboratory, one of the two U.S. weapons laboratories where nuclear weapons are made, show that about a third of the smoke would be heated by the sun and lofted above the region of the atmosphere where the weather occurs. So although about two-thirds of the smoke would be washed out fairly rapidly in a summertime case, about a third ~vould remain in the stratosphere for quite a long time, which would prolong the cold surface temperatures. My model looks at feedbacks between snow and sea ice in the climate system which are kept ~,onstant in the other calculations. When it gets cold more snow and ice are produced which act to make it colder still, by reflecting sunlight from this bright surfaces and insulating the ocean from the atmosphere. This mechanism produces still more snow and ice, and is called a "positive feedback." I found that the initial atmospheric cooling might be prolonged for one or two years. Although most of the model results suggest that agriculture would be virtually impossible after a spring or summertime conflict because of the large climatic effects, my model suggests that even in the next year, agriculture could be quite difficult because it still might be very cold at the earth's surface. Q: For some of the problem areas that have yet to be formulated satisfactorily, what approaches might be taken in the next year or two in order to get a better understanding of these processes ? What new software might have to be developed in order to implement these new ideas? A: There are two main problem areas. The first, which I mentioned, is the source function. If you drop a certain number of weapons on a certain number of cities, how much smoke is generated? You need to know what the number of grams of burnable fuel are per square centimeter in each city is; what fraction of that turns into smoke; and what fraction of the smoke remains in the atmosphere. In order to do this calculation, we need to do detailed smoke-source inventories. Microscale or mesoscale weather models can calculate on the scale of a smoke cloud in three dimensions.They can compute how the smoke is lofted up into the atmosphere, and how raindrops and ice crystals Environmental Software, 1986, Vol. 1, No. 2
133
are formed to remove the smoke. Some detailed calculations have been done in this area, but more remains to be done. In one simulation, Dr. Bill Cotton at the Colorado State University, simulated the burning of Denver. Using the Cray I computer at NCAR, it took two hours to simulate a half hour of burning. We found that a large fraction of the smoke would end up high in the atmosphere and would not be washed out. On the larger climatic scale, there has already been extensive model development. The first three-dimensional models kept the smoke fixed in height and horizontal extent and did not calculate the transport and removal of the smoke. In the last two years, new code has been developed to keep track of the distribution of the smoke as it moves with the wind, its radiative impact, and the processes which remove it from the atmosphere. We have also discovered that because we are working in a climate regime so different from that for which the models were developed, that certain parts of the model probably do not do a very good job of simulating the system. In particular, at the surface of the earth, the model predicts a very cold surface above which the atmosphere is very warm - a regime which does not exist in the real world. Thus, one area in which models are being developed is to do more detailed calculation of the flux of heat and temperature between the surface of the earth and the atmosphere, including fog formation. Another area is the vertical distribution of smoke in the upper part of the atmosphere, in the stratosphere. The most detailed models only consider the stratosphere in a few layers, and we have discovered that the models remove smoke from the atmosphere faster than occurs in reality. We can look at volcanic eruptions or radiactive fallout from atmospheric bomb tests in the 60's and measure residence times which are about 1 1 or 12 months. But the models have enhanced the vertical diffusion process which produces an unrealistically large amount of smoothing between the different layers in the model. This acts to mix the smoke down in the atmosphere and remove it after only one to four months. The solution is to put in more model layers, but this requires additional computer time. This is being done at the Lawrence Livermore and Los Alamos national laboratories and at the National Center for-Atmospheric Research in Boulder, Colorado, which have Cray XMP computers. Q: What has the government's reaction been to the results showing the dire cfimate consequences of nuclear war? A: The first reaction, especially from the Defense Department which has the mandate to control nuclear weapons and to calculate their effects, was embarrassment, as the first studies were carried out by university scientists without any support from the Defense Department. The Defense Department was ordered by Congress to write a report on the policy and science implications of nuclear war. A very short report was published in March 1985. It glossed over many of the details. It basically, said that "our policy is to prevent nuclear war, and if we prevent nuclear war, we'll prevent duclear winter." In June 1 986, two months late, they released this year's report, which was 5 pages long! They say that the results are so uncertain that we can not really make policy decisions because we can not be sure that it would actually happen. This is opposite to their response to many other problems, in which they take a worst-case scenario. Q: Has the government supported research within their own laboratories and within the university community? A: The National Climate Program Office submitted a plan to the President to spend $10 million dollars a year for five years on nuclear winter research two years ago. The recommendation was not approved. The current national research budget for nuclear winter research - is about $51/2 million dollars. All money reprogrammed from that already existing in the various agencies. $21/2 million dollars a year is being spent by the Department of Energy, mainly at Los Alamos and Livermore. $21/2 million is also being spent by-the Defense Department, the Defense Nuclear Agency, with much of the work done at universities. In addition, half a million dollars is supposed to be spent by the National Science Foundation, but it is not clear that all of it will actually be spent on nuclear winter research. All of this money is being spent on the climatic effects, with virtually none at all being spent on biological impacts. Congressman Tim Wirth (D - Colorado), frustrated at the Pentagon's response to Congress, has recently introduced a bill to mandate substantially more funding for nuclear winter research. Q: Could you summarize the implications of nuclear winter for human life and the biosphere in general? A: The climatic effects are that following a large scale nuclear war, there would be a great deal of smoke generated by burning cities. This black city smoke would rise up into the atmosphere and produce cold and dark conditions for weeks or months. Biological systems would not be able to 134
Environmental Software, 1986, Vol. 1, No. 2
~ustain themselves, and agriculture would be virtually impossible for the first year. The main effect )n the people who would not be killed outright by the blast, fire and radioactivity, would be ~tarvation, because food could not be produced. Countries like the Soviet Union and the United ~tates, which would be hit by the weapons, would suffer so much anyway that nuclear winter .~ffects would not have a significant effect. However, for countries away from the conflict, such as ndia or Kenya or Brazil, there might be large climatic consequences. ~: If nuclear war is limited to the Northern Hemisphere, what climate effects would the Southern Hemisphere suffer? ~,: t would suffer smaller effects for two reasons: one is that the Southern Hemisphere has a lot more )cean than the Northern Hemisphere, which acts to buffer the climate change. In addition, most of :he smoke would be generated in the Northern Hemisphere. Some of it would blow into the 3outhern Hemisphere by the changed atmospheric circulation arising from the heating of the ~tmosphere by the absorption of sunlight by the smoke. If a war took place in summer in the ~lorthern Hemisphere, there would be a lot of absorbed sunlight and a large shift in the ]tmospheric circulation. If it took place in the Northern Hemisphere winter, there would be less ~unlight and so the changed circulation might not take place. The Southern Hemisphere effect Nould then be much less. 3: How has the media covered this issue and how has the public responded to what has been in the media? ~,: 3arl Sagan wrote an article in Parade Magazine on nuclear winter which received a great deal of 3ress coverage. The term "nuclear winter" was coined by Rich Turco, the lead author of the first 3aper. It has been a catalyst to get people to think more about all the horrible effects of nuclear war. The uncertainties involved in the theory have not been described that well by the media Oecause it is easier to write about the catastrophic effects, and some scientists have not been sareful enough to point out the uncertainties in their work. In general I think the coverage has been rather fair, although its political implications frequently depended on people's previous political biases. For instance, nuclear winter has been used to argue both for and against Star Wars. Q: Where do you see the research in nuclear winter developing in the next year or two and, in particular, what implication might this have for the development of new software techniques? A:
It has already produced much better climate models that can be used for other problems, e.g. Arctic haze, the transport of volcanic dust, and transport of dust from desert storms. I expect that there will be further developments in large scale climate models, and also in the mesoscale cloud models. These models will be quite useful in the future for many other climate problems. There will also be studies not involving computers, eg. observations of actual fires. There will be a controlled brush burn in Los Angeles during this summer, which will be studied by airplanes and by satellites. Q: Can you say that we might know for sure in several years that the climatic implications will be certain, or will there always be significant uncertainties given the nature of the problem? A:
We will never be able to know what combination of bombs might be used on which targets, at what time of year, or what the weather will be that day. I hope we will never find out. As far as the response of the climate system, these are also uncertainties, but we will narrow them down. Some of the things which we have to know better concern the optical properties of smoke, the amount of sunlight it absorbs, and how much terrestrial radiation is absorbed and emitted. It is the job of scientists to communicate their results to the public so that informed decisions can be made on arms control. I hope that by studying nuclear winter, we will learn enough about the dangers of nuclear war to reduce the changes of it ever happening.
Environmental Software, 1986, Vol. 1, No. 2
135