carl sagan - Academia.edu (original) (raw)
Papers by carl sagan
Icarus, 1979
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Science, 1973
The equatorial sinuous channels on Mars detected by Mariner 9 point to a past epoch of higher pre... more The equatorial sinuous channels on Mars detected by Mariner 9 point to a past epoch of higher pressures and abundant liquid water. Advective instability of the martian atmosphere permits two stable climates-one close to present conditions, the other at a pressure of the order of 1 bar depending on the quantity of buried volatiles. Variations in the obliquity of Mars, the luminosity of the sun, and the albedo of the polar caps each appear capable of driving the instability between a current ice age and more clement conditions. Obliquity driving alone implies that epochs of much higher and of much lower pressure must have characterized martian history. Climatic change on Mars may have important meteorological, geological, and biological implications.
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Icarus, 1977
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Nature, 1981
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Journal of Geophysical Research, 1976
Volcanic explosions introduce silicate dust particles and sulfur gases into the stratosphere. The... more Volcanic explosions introduce silicate dust particles and sulfur gases into the stratosphere. The sulfur gases are slowly converted to sulfuric acid particles. We have performed radiative transfer calculations at visible and infrared wavelengths to determine the effect of these aerosols ...
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Journal of Geophysical Research, 1977
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Science, 1990
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Nature, 1976
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Science, 1976
Drifts of fine-grained sediment are present in the vicinity of the Viking 1 lander. Many drifts o... more Drifts of fine-grained sediment are present in the vicinity of the Viking 1 lander. Many drifts occur in the lees of large boulders. Morphologic analysis indicates that the last dynamic event was one of general deflation for at least some drifts. Particle cohesion implies that there is a distinct small-particle upturn in the threshold velocity-particle size curve; the apparent absence of the most easily moved particles (150 micrometers in diameter) may be due to their preferential transport to other regions or their preferential collisional destruction. A twilight rescan with lander cameras indicates a substantial amount of red dust with mean radius on the order of 1 micrometer in the atmosphere.
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Journal of Geophysical Research, 1973
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Science, 1979
The human species has been altering the environment over large geographic areas since the domesti... more The human species has been altering the environment over large geographic areas since the domestication of fire, plants, and animals. The progression from hunter to farmer to technologist has increased the variety and pace more than the geographic extent of human impact on the environment. A number of regions of the earth have experienced significant climatic changes closely related in time to anthropogenic environmental changes. Plausible physical models suggest a causal connection. The magnitudes of probable anthropogenic global albedo changes over the past millennia (and particularly over the past 25 years) are estimated. The results suggest that humans have made substantial contributions to global climate changes during the past several millennia, and perhaps over the past million years; further such changes are now under way.
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Science, 1983
The potential global atmospheric and climatic consequences of nuclear war are investigated using ... more The potential global atmospheric and climatic consequences of nuclear war are investigated using models previously developed to study the effects of volcanic eruptions. Although the results are necessarily imprecise due to wide range of possible scenaros and uncertainty in physical parameters, the most probable first-order effects are serious. Significant hemispherical attenuation of the solar radiation flux and subfreezing land temperatures may be caused by fine dust raised in high-yield nuclear surface bursts and by smoke from city and forest fires ignited by airbursts of all yields. For many simulated exchanges of several thousand megatons, in which dust and smoke are generated and encircle the earth within 1 to 2 weeks, average light levels can be reduced to a few percent of ambient and land temperatures can reach -15 degrees to -25 degrees C. The yield threshold for major optical and climatic consequences may be very low: only about 100 megatons detonated over major urban centers can create average hemispheric smoke optical depths greater than 2 for weeks and, even in summer, subfreezing land temperatures for months. In a 5000-megaton war, at northern mid-latitude sites remote from targets, radioactive fallout on time scales of days to weeks can lead to chronic mean doses of up to 50 rads from external whole-body gamma-ray exposure, with a likely equal or greater internal dose from biologically active radionuclides. Large horizontal and vertical temperature gradients caused by absorption of sunlight in smoke and dust clouds may greatly accelerate transport of particles and radioactivity from the Northern Hemisphere to the Southern Hemisphere. When combined with the prompt destruction from nuclear blast, fires, and fallout and the later enhancement of solar ultraviolet radiation due to ozone depletion, long-term exposure to cold, dark, and radioactivity could pose a serious threat to human survivors and to other species.
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Journal of Geophysical Research, 1967
Expressions have been obtained in a modified Schuster-Schwarzschild approximation describing the ... more Expressions have been obtained in a modified Schuster-Schwarzschild approximation describing the monochromatic transmissivity, reflectivity, and absorptivity of a cloud layer characterized by an arbitrary single-scattering albedo and anisotropic phase function. These analytic ...
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Icarus, 1972
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Nature, 1969
Bookmarks Related papers MentionsView impact
Icarus, 1979
Bookmarks Related papers MentionsView impact
Science, 1973
The equatorial sinuous channels on Mars detected by Mariner 9 point to a past epoch of higher pre... more The equatorial sinuous channels on Mars detected by Mariner 9 point to a past epoch of higher pressures and abundant liquid water. Advective instability of the martian atmosphere permits two stable climates-one close to present conditions, the other at a pressure of the order of 1 bar depending on the quantity of buried volatiles. Variations in the obliquity of Mars, the luminosity of the sun, and the albedo of the polar caps each appear capable of driving the instability between a current ice age and more clement conditions. Obliquity driving alone implies that epochs of much higher and of much lower pressure must have characterized martian history. Climatic change on Mars may have important meteorological, geological, and biological implications.
Bookmarks Related papers MentionsView impact
Icarus, 1977
Bookmarks Related papers MentionsView impact
Nature, 1981
Bookmarks Related papers MentionsView impact
Journal of Geophysical Research, 1976
Volcanic explosions introduce silicate dust particles and sulfur gases into the stratosphere. The... more Volcanic explosions introduce silicate dust particles and sulfur gases into the stratosphere. The sulfur gases are slowly converted to sulfuric acid particles. We have performed radiative transfer calculations at visible and infrared wavelengths to determine the effect of these aerosols ...
Bookmarks Related papers MentionsView impact
Journal of Geophysical Research, 1977
Bookmarks Related papers MentionsView impact
Science, 1990
Bookmarks Related papers MentionsView impact
Nature, 1976
Bookmarks Related papers MentionsView impact
Science, 1976
Drifts of fine-grained sediment are present in the vicinity of the Viking 1 lander. Many drifts o... more Drifts of fine-grained sediment are present in the vicinity of the Viking 1 lander. Many drifts occur in the lees of large boulders. Morphologic analysis indicates that the last dynamic event was one of general deflation for at least some drifts. Particle cohesion implies that there is a distinct small-particle upturn in the threshold velocity-particle size curve; the apparent absence of the most easily moved particles (150 micrometers in diameter) may be due to their preferential transport to other regions or their preferential collisional destruction. A twilight rescan with lander cameras indicates a substantial amount of red dust with mean radius on the order of 1 micrometer in the atmosphere.
Bookmarks Related papers MentionsView impact
Journal of Geophysical Research, 1973
Bookmarks Related papers MentionsView impact
Science, 1979
The human species has been altering the environment over large geographic areas since the domesti... more The human species has been altering the environment over large geographic areas since the domestication of fire, plants, and animals. The progression from hunter to farmer to technologist has increased the variety and pace more than the geographic extent of human impact on the environment. A number of regions of the earth have experienced significant climatic changes closely related in time to anthropogenic environmental changes. Plausible physical models suggest a causal connection. The magnitudes of probable anthropogenic global albedo changes over the past millennia (and particularly over the past 25 years) are estimated. The results suggest that humans have made substantial contributions to global climate changes during the past several millennia, and perhaps over the past million years; further such changes are now under way.
Bookmarks Related papers MentionsView impact
Science, 1983
The potential global atmospheric and climatic consequences of nuclear war are investigated using ... more The potential global atmospheric and climatic consequences of nuclear war are investigated using models previously developed to study the effects of volcanic eruptions. Although the results are necessarily imprecise due to wide range of possible scenaros and uncertainty in physical parameters, the most probable first-order effects are serious. Significant hemispherical attenuation of the solar radiation flux and subfreezing land temperatures may be caused by fine dust raised in high-yield nuclear surface bursts and by smoke from city and forest fires ignited by airbursts of all yields. For many simulated exchanges of several thousand megatons, in which dust and smoke are generated and encircle the earth within 1 to 2 weeks, average light levels can be reduced to a few percent of ambient and land temperatures can reach -15 degrees to -25 degrees C. The yield threshold for major optical and climatic consequences may be very low: only about 100 megatons detonated over major urban centers can create average hemispheric smoke optical depths greater than 2 for weeks and, even in summer, subfreezing land temperatures for months. In a 5000-megaton war, at northern mid-latitude sites remote from targets, radioactive fallout on time scales of days to weeks can lead to chronic mean doses of up to 50 rads from external whole-body gamma-ray exposure, with a likely equal or greater internal dose from biologically active radionuclides. Large horizontal and vertical temperature gradients caused by absorption of sunlight in smoke and dust clouds may greatly accelerate transport of particles and radioactivity from the Northern Hemisphere to the Southern Hemisphere. When combined with the prompt destruction from nuclear blast, fires, and fallout and the later enhancement of solar ultraviolet radiation due to ozone depletion, long-term exposure to cold, dark, and radioactivity could pose a serious threat to human survivors and to other species.
Bookmarks Related papers MentionsView impact
Journal of Geophysical Research, 1967
Expressions have been obtained in a modified Schuster-Schwarzschild approximation describing the ... more Expressions have been obtained in a modified Schuster-Schwarzschild approximation describing the monochromatic transmissivity, reflectivity, and absorptivity of a cloud layer characterized by an arbitrary single-scattering albedo and anisotropic phase function. These analytic ...
Bookmarks Related papers MentionsView impact
Icarus, 1972
Bookmarks Related papers MentionsView impact
Nature, 1969
Bookmarks Related papers MentionsView impact