An unparalleled, open activity toward a worldwide process of research and education, which goes beyond the traditional understanding of scientific responsibility in terms of specialist's denial, the public action of the scientific elite, and the work in closed circles, was launched after delivery of the AMBIO study by the International Council of Scientific Unions (ICSU). Steered by the project ''Environmental Consequences of Nuclear War'' (ENUWAR) of the Scientific Committee on Problems of the Environment (SCOPE), resulted it by the end of 1985 in the two-volume report SCOPE-28. This study cannot offer an overall view on the complex entity 'eco-sphere' after nuclear war. None of the major physical control parameters (light, temperature, water) are expected to be disturbed that hard or weak at planetary scale so as to justify 'simple' conclusions. A substantial impact on the stratospheric ozone budget, however, maintained by the US National Research Council (NRC; 1985), holds the more, since smoke-induced heating would change all chemical reaction rates.
Long-term problems due to radioactive exposure are borne in the selective vulnerability offorest communities. Nuclear war might change the biogeography ofvast areas, notably where coniferous temperate forests dominate and the 'radiation shock' combines with large-scale fire, climatic change, UV-B effects, etc. SCOPE-28 notes specific sensitivities: ''Temperature effects would be dominant for terrestrial ecosystems in the Northern Hemisphere and in the Tropics and subtropics; light reductions would be most important for oceanic ecosystems; precipitation effects would be more important to grasslands and to many Southern Hemisphere ecosystems.'' Such a 'distributed vulnerability' structure and its more subtle patterns, the other side of the 'biogeography' medal, reflects a range of stabilizing feedbacks against gradual or abrupt transitions in atmospheric or oceanic conditions and related compositional, thermal, meteorological, and hydrological regimes. The 'acute' phase of nuclear winter would bear structural changes in the physical environment of a dimension that might transgress those stability limits, maybe at hemispheric scale. The crucial question is the one posed by the NAS 10 years before: Will new feedbacks take over to stabilize the system in a regime different from present day, or will it return? Latest, the transition to 'chronic' response would be influenced by climate-biosphere feedbacks. The result of acute-phase environmental devastations, like the patchiness ofsurviv-ing communities, may thus attain a structural role in shaping a postwar environment.
The vulnerability of the 'noosphere' - taken as the complex entity of man's society and managed environment - against the direct effects of nuclear war is much higher than that of the (natural) ecosphere. Agricultural systems may only exist due to human maintenance. Worldwide disruption of functioning agriculture and food supply after nuclear war would expose the majority of survivors to the risk of starvation. The OTA study suggests that this would even hold without severe environmental aftereffects. Climatic impacts that hit agriculture at vulnerable spots (length of the growing season, hydrological change, etc.) may bear just that sort of feedback, however, which keeps surviving humans stuck to marginal subsistence for any period relevant to societal restoration. The impact on the Southern Hemisphere of nuclear war in the north is a key issue in view ofa postwar noosphere. Beyond the 'import' of climatic effects due to interhemispheric smoke transport, with their ecological and agricultural consequences, a major disturbance would be caused by interruption of the lifeline of international trade, even if agricultural productivity could be maintained at a level of sufficiency. The risk consists in a large societal setback to which a modern society may not adapt without existential disturbance.
A convincing approach to environmental impacts addresses productivity limits and 'convolves' this knowledge with a realistic range ofstresses derived from climate model output. The resulting 'response surfaces' to stress factors as expected after nuclear war (changes in temperature, light level, precipitation) are not of a simple shape for grassland ecosystems, notably when secondary productivity of herbivores is considered. Regulatory feedbacks act together, that is, stresses are not generally additive or even mutually enhancing ('synergistic'). The 'nonsevere factor space' of functioning ecosystem response may have rather sharp boundaries, however, beyond which the 'message' becomes simple: ecosystem productivity reduces almost abruptly to a level that would not support a human population. An important conclusion is on uncertainty again: a group of survivors who found an ecological niche in a postwar environment may be ''plunged into destruction by seemingly minor drift away from those conditions.'' Ecosystems become unpredictable when driven to marginal existence, in the vicinity of critical transition, by a changing climate.
In two authoritative assessments, the World Meteorological Organization (WMO) confirmed the risk of a severe smoke-induced climatic impact. Among the pertaining uncertainties, a potential modification of the hydrological cycle was emphasized. This concerns the 'Hadley circulation' above all, a double-cell of upward and poleward circulation (in the zonal mean) flanking the meteorological equator, which is driven by the strongest heating there. As the season advances, the southern 'Hadley cell' shifts northward and blows up to form the 'monsoon cell' in boreal summer, with upward legs as far north as the Tibetan and Mexican plateaus. A smoke veil above would attenuate this structure, that is, weaken or disrupt the monsoons, but depending on season, injection heights, and location of the smoke source, the Hadley circulation may also become enhanced. The WMO assessments posed into doubt that climate models may reach the required realism and reliability soon, but confirmed both a potential monsoon disruption in boreal summer and smoke lofting as well as transport into the Southern Hemisphere.
A minimum demand, the realistic simulation of seasonally varying rainfall, is not easily met by global climate models. Even more challenging is the agriculturally important intraseasonal activity, notably the active-break cycles of the major monsoon branches and their dynamic interplay. Key knowledge about monsoon dynamics, and thus about the atmospheric hydrological cycle and its interactions, did just settle when the scientific consensus formed about major climatic effects of nuclear war. This bears potential for surprise, and the consensus may deserve further development just where it directly concerns half the world population. Abrupt onset and retreat of the boreal summer monsoon are known for decades, its oscillatory (interhemispheric) nature since the mid-1970s. These are features typical of a dynamic system that passes a critical transition. Long-term consequences for man and the biosphere of the climatic response to nuclear war may thus be borne in the potential for structural recovery of the present-day 'monsoon climate' on Earth. This includes monsoon interactions with the El Nino-Southern Oscillation (ENSO) system. Both dynamic subsystems mediate climatic and environmental impacts on the Southern Hemisphere, beyond the more direct effects of interhemispheric smoke transport.
SCOPE successor studies to ENUWAR (1982-88) took another turn: the projects RADPATH (1988-93) and RADTEST (1993-99) addressed the pathways of radionuclides across the environment, exemplified by field studies into the consequences of the 1986
Chernobyl nuclear reactor accident and at selected nuclear test sites worldwide. These projects mounted a substantial database, improved the knowledge of processes, and identified gaps in understanding the biogeochemical dispersion of radionuclides. All three projects were led by Sir Frederick Warner. Their documented results, SCOPE report nos. 28, 50, and 59, are reference sources for the state of scientific knowledge toward the turn of the twentieth century about the gravest risk and challenge of its second half - the 'doomsday' of man in an all-out nuclear conflict.
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Remember to prepare for everyone in the home. When you are putting together a plan to prepare in the case of an emergency, it is very important to remember to plan for not only yourself and your children, but also for your family pets and any guests who could potentially be with you at the time of the emergency.