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2007 MacCracken

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Published on April 7, 2008

Author: Moorehead

Source: authorstream.com

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Slide1:  Geoengineering: A Possible Insurance Policy Michael C. MacCracken Climate Institute Washington DC 20-23 August 2007 Erice International Seminars on Nuclear War and Planetary Emergencies Intensifying indications of climate change as an inadvertent consequence of fossil fuel combustion raise the question of whether advertent change may be possible:  Intensifying indications of climate change as an inadvertent consequence of fossil fuel combustion raise the question of whether advertent change may be possible Talk intended to provide background for considering geoengineering as a component of overall response to climate change: Are there ways to counterbalance the warming influence in order to slow or halt the pace of inadvertent climate change? Are there ways to intentionally moderate the adverse consequences of climate change to delay a “dangerous” level of interference with the climate system? Inadvertent and Advertent Change:  Inadvertent and Advertent Change For the purposes of my discussion: “Inadvertent Climate Change” is an unintended consequence of doing something else. “Advertent Climate Change” is a change that is intentionally induced, whether or not to offset an inadvertent change. “Geoengineering” is an attempt to intentionally respond to an inadvertent change (e.g., redirecting the climate to an alternative path) A question that arises is what does one call choosing not to take reasonable and cost-effective actions that would limit inadvertent climate change? Examples of Factors Leading to Inadvertent Climate Change:  Examples of Factors Leading to Inadvertent Climate Change Both Inadvertent and Advertent Changes are the Subject of International Protocols:  Both Inadvertent and Advertent Changes are the Subject of International Protocols Inadvertent change is now governed by the UN Framework Convention on Climate Change (and the Kyoto Protocol covering initial implementation). Advertent (and maybe inadvertent) climate change would seem to be subject to the UN Convention on the Prohibition of Military or any Other Hostile Use of Environmental Modification Techniques agreed to in 1978 (and the US ratification was filed on January 17, 1980). The UN Framework Convention on Climate Change (UNFCCC) sets an objective of atmospheric stabilization:  The UN Framework Convention on Climate Change (UNFCCC) sets an objective of atmospheric stabilization Objective 2 of the UNFCCC calls for: Stabilization of the greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened, and to enable economic development to proceed in a sustainable manner. Earth Summit, Rio de Janeiro, 1992 (adopted widely by the world community and ratified by the US Senate in 1992) Provisions of the 1978 “Convention on the Prohibition of Military or any Other Hostile Use of Environmental Modification Techniques”:  Provisions of the 1978 “Convention on the Prohibition of Military or any Other Hostile Use of Environmental Modification Techniques” Article I.1. Each State Party to this Convention undertakes not to engage in military or any other hostile use of environmental modification techniques having widespread, long-lasting or severe effects as the means of destruction, damage or injury to any other State Party. Article I.2. Each State Party to this Convention undertakes not to assist, encourage or induce any State, group of States or international organization to engage in activities contrary to the provisions of paragraph 1 of this article. Understanding Relating to Article I:  Understanding Relating to Article I It is the understanding of the Committee that, for the purposes of this Convention, the terms, "widespread", "long-lasting" and "severe" shall be interpreted as follows: (a) "widespread": encompassing an area on the scale of several hundred square kilometres; (b) "long-lasting": lasting for a period of months, or approximately a season; (c) "severe": involving serious or significant disruption or harm to human life, natural and economic resources or other assets. It is further understood that the interpretation set forth above is intended exclusively for this Convention and is not intended to prejudice the interpretation of the same or similar terms if used in connexion with any other international agreement. Slide9:  Article II: As used in Article I, the term "environmental modification techniques" refers to any technique for changing -- through the deliberate manipulation of natural processes -- the dynamics, composition or structure of the Earth, including its biota, lithosphere, hydrosphere and atmosphere, or of outer space. Article III.1. The provisions of this Convention shall not hinder the use of environmental modification techniques for peaceful purposes and shall be without prejudice to the generally recognized principles and applicable rules of international law concerning such use. Article III.2. The States Parties to this Convention undertake to facilitate, and have the right to participate in, the fullest possible exchange of scientific and technological information on the use of environmental modification techniques for peaceful purposes. Article IV: Each State Party to this Convention undertakes to take any measures it considers necessary in accordance with its constitutional processes to prohibit and prevent any activity in violation of the provisions of the Convention anywhere under its jurisdiction or control. Understanding Relating to Article II:  Understanding Relating to Article II It is the understanding of the Committee that the following examples are illustrative of phenomena that could be caused by the use of environmental modification techniques as defined in Article II of the Convention: earthquakes, tsunamis; an upset in the ecological balance of a region; changes in weather patterns (clouds, precipitation, cyclones of various types and tornadic storms); changes in climate patterns; changes in ocean currents; changes in the state of the ozone layer; and changes in the state of the ionosphere. It is further understood that all the phenomena listed above, when produced by military or any other hostile use of environmental modification techniques, would result, or could reasonably be expected to result, in widespread, long-lasting or severe destruction, damage or injury. Thus, military or any other hostile use of environmental modification techniques as defined in Article II, so as to cause those phenomena as a means of destruction, damage or injury to another State Party, would be prohibited. It is recognized, moreover, that the list of examples set out above is not exhaustive. Other phenomena which could result from the use of environmental modification techniques as defined in Article II could also be appropriately included. The absence of such phenomena from the list does not in any way imply that the undertaking contained in Article I would not be applicable to those phenomena, provided the criteria set out in that article were met. [Emphasis added] However: Understanding relating to Article III:  However: Understanding relating to Article III It is the understanding of the Committee that this Convention does not deal with the question whether or not a given use of environmental modification techniques for peaceful purposes is in accordance with generally recognized principles and applicable rules of international law. Unresolved Questions (in my view): Would this convention be applicable in the case of advertent changes in the climate if some party considers them to have an adverse (hostile) influence on them? Is intentionally not taking an action to limit inadvertent changes in the climate subject to this convention if it has an adverse (hostile) influence on another party? Assuming the Convention does not apply, several questions merit consideration in evaluating the potential for geoengineering :  Assuming the Convention does not apply, several questions merit consideration in evaluating the potential for geoengineering Is the climate changing significantly in an unprecedented way, and not merely varying? Do we understand the factors that have caused recent and past changes in climate well enough to evaluate geoengineering proposals? Is climate change in the future going to be large and cause significant enough impacts to merit considering geoengineering--and what are these critical impacts? What degree of action is necessary and how costly and effective might actions other than geoengineering be? What geoengineering approaches are available and how costly and effective might they be? What are their short- and long term implications? 1. Is the climate changing significantly in an unprecedented way, and not merely varying?:  1. Is the climate changing significantly in an unprecedented way, and not merely varying? 2. Do we understand the factors that have caused recent & past changes in climate?:  2. Do we understand the factors that have caused recent & past changes in climate? 3. Is climate change in the future going to be large and cause significant impacts-- and what are they? :  3. Is climate change in the future going to be large and cause significant impacts-- and what are they? Probability ranges for projected changes in global average temperature for the early and late 21st century :  Probability ranges for projected changes in global average temperature for the early and late 21st century IPCC, 2007 The projected increase in global average temperature is very likely to result in global temperatures being higher than they have been in tens of millions of years:  The projected increase in global average temperature is very likely to result in global temperatures being higher than they have been in tens of millions of years Prather diagram Source: IPCC TAR, 2001 and M. Prather Projection of future warming compared to last 1000 years Given the sharpness of the change, the risk of crossing a threshold seems significant:  Given the sharpness of the change, the risk of crossing a threshold seems significant Sea level: The Greenland and Antarctic Ice Sheets are starting to lose mass; significant melting could inundate coastal cities and vital estuaries and wetlands Temperature increase: Sea ice reduction, methane and CO2 from melting of permafrost and methane clathrates, and sulfate limitations could amplify warming Water resources: Mountain glaciers and snowpack are disappearing, greatly reducing warm season runoff Tropical cyclones and hurricanes: Oceans are warming and atmosphere holds more water vapor Ecosystem changes are underway; biodiversity will be lost Slide19:  Agriculture Impacts Crop yields and commodity prices Irrigation demands Pests and weed Water Resource Impacts Changes in water supply and timing Water quality Increased competition for water Coastal Area Impacts Erosion of beaches Inundation of coastal wetlands Costs to defend coastal communities Forest Impacts Change in forest composition Shift geographic range of forests Forest health and productivity Ecosystem Impacts Shifts in ecological zones Loss of habitat and species Coral reefs threatened Climate change is likely to lead to a range of important environmental and societal impacts Carbon Dioxide and Climate Changes Sea Level Rise Temperature Precipitation Adapted from EPA Societal Impacts Indigenous peoples and developing nations Exacerbated impacts on the poor Dramatically different situation for future generations Health Impacts Weather-related mortality/heat stress Infectious diseases Air quality-induced respiratory effects CO2 and GHGs Coral reefs are threatened by both ocean warming and the acidification caused by the rising CO2 concentration itself:  Coral reefs are threatened by both ocean warming and the acidification caused by the rising CO2 concentration itself Source: Kleypas, Buddemeier, et al., Science, 1999; and U.S. National Assessment. Slide21:  47 of 49 different model climate simulations project substantial drought for the southwestern U.S. by 2100 Reported by Seager et al., Science, 2007 There will be significant changes in many regions Slide22:  An increase in the intensity of extreme events is likely to worsen many types of disasters The average summertime heat index will increase more than will the temperature, and the absolute humidity will increase exponentially-- estimated increases basically break the scale:  The average summertime heat index will increase more than will the temperature, and the absolute humidity will increase exponentially-- estimated increases basically break the scale Slide24:  Ocean temperatures are rising Projections are for more powerful hurricanes and more drenching rains Source: Webster et al., Science, 2005 Source: Knutson and Tuleya, Science, 2004 Hurricanes appear to be intensifying and releasing more energy, and society has become more vulnerable due to more coastal residents and buildings A higher number and a larger fraction of storms are high intensity Sea level rise: The long term potential is very large :  Sea level rise: The long term potential is very large Glaciers and small ice caps (total amount 0.15 – 0.72 m) Thermal expansion (0.2 – 0.6 m per oC) Greenland Ice Sheet (becomes unsustainable somewhere between 1.9 - 4.8oC) Some to all? West Antarctic Ice Sheet East Antarctica?? Corings indicate the Greenland Ice Sheet was much smaller during the Eemian interglacial:  Contours are from average of three ice sheet models. Circles show drill sites that had ice. Squares show sites that did not have ice. The last time polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 m of sea level rise. Corings indicate the Greenland Ice Sheet was much smaller during the Eemian interglacial Climatic evidence suggests that the equilibrium sensitivity of sea level to global average temperature is ~20 m per degree:  Climatic evidence suggests that the equilibrium sensitivity of sea level to global average temperature is ~20 m per degree That sea level was 4-6 m higher than at present during the relatively brief Eemian (~125 ka) suggests that the response time is centuries-- not millennia [About 125 ka] [About 20 ka] [About 34-56 Ma] [About 1.8-5.3 Ma] Slide28:  Many coastal communities and facilities face increasing exposure to storms; relocation of whole villages is very expensive Shishmaref, Alaska 2005 About 40 m (125 ft) in one storm There are serious and imminent impacts that society is going to demand be addressed:  There are serious and imminent impacts that society is going to demand be addressed Rising CO2 concentration and impact on ocean chemistry and marine life Rising sea level resulting from deterioration of ice sheets and thermal expansion, and consequent coastal erosion and inundation Intensification of tropical cyclones and very sharp increase in potential for drenching rains and floods Increasing frequency of heat waves, greater spread of disease vectors, and other extremes resulting from higher temperature Ecosystem disruption caused by climate-driven shifts in ranges of plant and animal species, temperature increases, moisture stress, pest infestations, melting permafrost, and wild fire Increased stress on water resources and the systems supplying water due to altered storm tracks, greater evaporation, rising snowline causing reduced snowpack, more extreme rains and consequent flooding, and rising demand And more …. 4. What degree of action is necessary and how costly and effective might actions other than geoengineering be?:  4. What degree of action is necessary and how costly and effective might actions other than geoengineering be? Kyoto is clearly not enough!!! Meeting the UNFCCC objective of stabilizing the climate will require very stringent limits on per capita CO2 emissions:  Meeting the UNFCCC objective of stabilizing the climate will require very stringent limits on per capita CO2 emissions Assuming the world population rises from 6 billion to 10 billion, stabilizing CO2 implies the following per capita limits for the 21st century (compared to current level of 1 tC/person/yr): Current CO2 level (380 ppmv)  Near zero Double preindustrial (560 ppmv)  1 tC/person/yr Double 1990s CO2 level(710 ppmv) 2 tC/person/yr Unconstrained (>1000 ppmv)  3 tC/person/yr US/Canada/Australian usage today  >5 tC/person/yr Global average decrement that Kyoto agreement would create is <0.25 tC/person/yr Achieving a high probability of limiting global average temperature to 2ºC (~ 3.5ºF) requires keeping CO2-equiv to under 450 ppm:  Achieving a high probability of limiting global average temperature to 2ºC (~ 3.5ºF) requires keeping CO2-equiv to under 450 ppm Source: D.P. van Vuuren, et al., 2006: Stabilising greenhouse gas concentrations at low levels: An assessment of options and costs, Netherlands Environmental Assessment Agency, MNP Report 500114002/2006, available at: http://www.mnp.nl/en/publications/2006/index.html Each increase of 50 ppm is roughly equivalent to a global warming of 0.5ºC (or 1 º F), and changes in mid to high latitudes over land can be twice as much as global increase. Baseline emissions projection and allowable emissions for stabilization at various levels:  Baseline emissions projection and allowable emissions for stabilization at various levels Source: D.P. van Vuuren, et al., 2006: Stabilising greenhouse gas concentrations at low levels: An assessment of options and costs, Netherlands Environmental Assessment Agency, MNP Report 500114002/2006, available at: http://www.mnp.nl/en/publications/2006/index.html Cutting methane and soot concentrations to below 1990 levels and reducing deforestation and encouraging afforestation would provide some leeway to deal with CO2 5. What types of geoengineering approaches are available and how effective might they be? What are the short- and long term implications?:  5. What types of geoengineering approaches are available and how effective might they be? What are the short- and long term implications? Reducing the concentrations of greenhouse gases in the atmosphere already in the atmosphere Counter-balancing the radiative forcing of greenhouse gases Altering the processes that lead to accelerating climate change and “dangerous” impacts Approaches to limiting or reducing greenhouse gas concentrations:  Approaches to limiting or reducing greenhouse gas concentrations Reducing the extent of the activity (reducing emissions, i.e., mitigation) Expanding and/or enhancing biospheric uptake of GHGs (e.g., reforestation, fertilizing forests, changing agricultural practices) Enhancing oceanic uptake and/or storage of GHGs (e.g., iron fertilization to enhance biospheric pump, genetically engineer phytoplankton or algae, sinking tree trunks, accelerate carbonate dissolution, etc.) Capturing GHGs at the point of emission and sequestering them (e.g., deep underground, in the deep ocean) Scrubbing GHGs from the atmosphere and storing or sequestering them (e.g., underground, in the deep ocean) Altering solar radiation to counterbalance GHG effects depends on an important assumption:  Altering solar radiation to counterbalance GHG effects depends on an important assumption Temperature responses to::  Temperature responses to: Top: Doubling the CO2 concentration Bottom: Doubling the CO2 concentration and reducing solar intensity by 1.8% Caldeira et al., in prep, 2007 Precipitation response:  Precipitation response 2 x CO2 (Significant change over 47 % of Earth’s area) 2 x CO2 and 1.8% reduction in solar intensity (Significant change remains over 4 % of Earth’s surface) Caldeira et al., in prep, 2007 Area where change is significant at 0.05 level based on 30-yr climatology Slide39:  Seasonal and latitudinal temperature change So, it appears that counter-balancing of the effects of greenhouse gases is workable Govindasamy and Caldeira 2000 90N to 20N 20N to 20S 20S to 90S Latitude band Somewhat surprisingly, the cancellation is nearly complete, and closer agreement might be possible There are, however, a few reasons to wonder about the supposed equivalence:  There are, however, a few reasons to wonder about the supposed equivalence Ice age cycling is driven by changes in the Earth’s orbital elements. These changes provide virtually no annual global forcing, yet cause the largest changes in climate the Earth has experienced. How is that situation different? Sulfate aerosol forcing is largely present in the Northern Hemisphere and causes its largest effect there, so does this not mean that regional forcing patterns matter? El Niño induced warming of the eastern tropical Pacific causes very strong regional response patterns--both locally and at distances. Why not for geoengineering? Approaches to counterbalancing the radiative forcing of greenhouse gases:  Approaches to counterbalancing the radiative forcing of greenhouse gases Reduce incoming solar radiation (“veiling the Sun”) by placing 1400-km diameter deflector at first Lagrange Point (1.5M km toward Sun), manufactured and launched from the Moon--proposed by J. Early (1989) Reduce incoming solar radiation by placing 55,000 mirrors in near-Earth orbit, each 100 km2 (or half as many if actively aligned; particles would come out of orbit too fast--described in NAS 1992) Increase the albedo of the stratosphere (create a so-called “human volcano”; older proposal made prominent by Crutzen) Increase the albedo of the troposphere (e.g., adding 50-100 Mt/yr of sulfate aerosols, increasing cloud albedo, enhance cloudiness) Increase the Earth’s albedo by increasing surface reflectivity (e.g., whitening roofs and pavements, lightening trees, increasing desert reflectivity, floating continent-sized reflector on the ocean) For comparison purposes, counterbalancing half the effect of a CO2 doubling is assumed Deflector(s) at the first Lagrange point (L1):  Deflector(s) at the first Lagrange point (L1) Hoffert et al., 2002 Options: A single deflector about 1400 km in diameter, manufactured and launched from the Moon (Early, 1989) A cloud of smaller deflectors lofted from Earth over up to a few decades by 20M electro-magnetic launches, each with 800k reflectors, and carried to position by ion propulsion (Angel, 2006) (or about 1.5M km or 1M mi) Mirrors in Near-Earth Orbit:  Mirrors in Near-Earth Orbit NAS (1992) panel report estimated it would require 55,000 orbiting mirrors, each covering an area of 100 square kilometers: The Sun would be obscured with numerous mini-eclipses It would be difficult to harden the mirrors to deal with space debris The number could be cut in half if the mirrors were actively aligned, but this would likely take significant energy The number would be increased as the size is reduced A number of approaches to augmenting stratospheric reflectivity have been proposed:  A number of approaches to augmenting stratospheric reflectivity have been proposed Increase the loading of sulfate aerosols (e.g., lofting 10 Mt/yr of sulfur by artillery shots to high altitude--NAS, 1992); would tend to turn sky whitish and likely destroy ozone Seed lower stratosphere/upper troposphere on a continuing basis with spectrally-dependent aerosols [made of Welsbach (e.g. aluminum oxide) materials and of diameter 10 to 100 m] that absorb in near IR and emit in visible and far IR (Patent 5,003,186 to Chang and Shih of Hughes Aircraft). Teller, Wood, et al. proposed very small particles optimally sized to reflect UV wavelengths, which would also affect atmospheric chemistry. Loft hydrogen-filled balloons (for 10 m2 cross-section, would require roughly 1012 balloons to be aloft, ignoring bottom reflection--see NAS, 1992). Shaping them like corner reflectors reduces scattering and increases effectiveness; both large and microscopic balloons would be subject to chemical attack by ozone and penetration by micrometeorites. Creating a stratospheric parasol roughly equivalent to Mt. Pinatubo, 15 June 1991:  Creating a stratospheric parasol roughly equivalent to Mt. Pinatubo, 15 June 1991 T Alipalo/UNEP/Topham Engineering options for placing aerosols in stratosphere:  Engineering options for placing aerosols in stratosphere “Hose to the stratosphere” Skinny pipe/hose, ground to ~25 km-high HAA (DoD) Artillery (shooting barrels of particles into stratosphere) “…surprisingly practical” – NAS Study, 1992 High-altitude transport aircraft “Condor/Global Hawk, with a cargo bay” Half-dozen B-747s deploy 106 tonnes/year of engineered aerosol; towed lifting-lines/bodies for height-boosting the sprayer-dispenser an additional 5-10 km above normal cruising ceilings Other options Anthropogenic (mini-) volcanoes (e.g., created by explosions) Tethered (set-of-) lifting-body – a set of high-tech kites Lofting of balloons into the stratosphere (possibly micro-scale and shaped as corner reflectors to reduce problems of light scattering) Modified from original by Lowell Wood Increasing tropospheric or surface reflectivity requires very extensive measures:  Increasing tropospheric or surface reflectivity requires very extensive measures Approaches for increasing tropospheric reflectivity: Increase sulfate aerosol loading, but significant side effects on precipitation and visibility. Might also maintain sulfate loading as reduce CO2 emissions by deregulating SO2 emissions. Increase reflectivity of marine stratus by injecting sea water droplets (Latham and Salter, 2006); would require launching and operating 50 new 200-ton trimarans per year (roughly the size of a three-masted sailing ship) Approaches for increasing surface reflectivity: Brightening urban areas would help in that area, but too small for global influence Covering desert areas with a reflecting material would require large areas and likely modify regional weather Selecting or genetically engineering vegetation to make it brighter Increasing ocean albedo with a floating reflector would require a continental size area, allowing for cloud obscuring effects. Latham and Salter propose controlled enhancement of the albedo and longevity of low-level maritime clouds:  Latham and Salter propose controlled enhancement of the albedo and longevity of low-level maritime clouds The ships are wind-powered (the masts rotate, generating Bernoulli effect to push the ship forward) They loft a spray of very fine sea water that is carried by turbulent mixing up into clouds, brightening their albedo The approach works best in pristine areas Ship locations could shift with the season The basic intent is to reduce uptake of solar energy by the oceans Approaches for altering climatic processes to counterbalance GHG-induced climate impacts:  Approaches for altering climatic processes to counterbalance GHG-induced climate impacts Promoting Arctic sea ice formation by redirecting Russian rivers or damming the Bering Strait (and perhaps directed pumping of ocean waters) Limiting oceanic heating of Europe in winter by damming the Strait of Gibraltar Limiting water vapor feedback by use of an oceanic film Limiting sea level rise by insulating melting glaciers, adding snow to East Antarctica, or melting methane clathrates in ocean sediments Limiting strength or altering track of hurricanes by cloud seeding, oceanic films to limit heat transfer, or solar beams created by orbiting mirrors (conceivably, monsoons might also be altered) Slide50:  Ocean temperatures are rising Hurricanes are becoming more intense Hurricane models project warming will further intensify hurricanes Source: Webster et al., Science, 2005 Source: Knutson and Tuleya, Science, 2004 Would one consider seeding clouds if geoengineeering marine clouds could limit the increasing vulnerability of coastal residents and communities? Global Geoengineering would, however, lead to significant costs and implications:  Global Geoengineering would, however, lead to significant costs and implications Environmental impacts to consider include shifting direct to diffuse radiation (limiting some direct solar electric technologies), modifying sky color, biospheric impacts, altering carbon storage rate, and increasing ozone depletion; Reducing incoming solar radiation would not slow the build-up of CO2 itself, thus would do nothing to alleviate the imminent threat of ocean acidification; As a substitute for mitigation, maintaining the solar shield would require a permanent, increasing commitment for many future generations; very long legacy of our energy choices; System failure or a decision to halt an ongoing geoengineering operation would commit the world to a period of even more rapid warming than is ongoing today; The challenge of coming to international agreement on a governance structure for optimizing the global climate, and paying for system operation, is almost beyond comprehension--unless an abrupt, possibly irreversible, change has already begun. Coral reefs are threatened by both ocean warming and the acidification caused by the rising CO2 concentration itself:  Coral reefs are threatened by both ocean warming and the acidification caused by the rising CO2 concentration itself Source: Kleypas, Buddemeier, et al., Science, 1999; and U.S. National Assessment. The disadvantages might be much less if geoengineering is used to moderate critical GHG-induced climate impacts:  The disadvantages might be much less if geoengineering is used to moderate critical GHG-induced climate impacts Could we limit Arctic warming and the contribution to sea level rise of melting glaciers and ice sheets? Proposals have included: Redirecting Russian rivers, Damming the Bering Strait (and perhaps directed pumping of waters) Insulating glaciers (in some regions) Reducing solar heating by significantly increasing aerosol loading of the Arctic lower stratosphere [Caldeira to discuss] Could we limit the increasing strength, and perhaps the track, of hurricanes and typhoons? Proposals have included: Enhancing cloud albedo to limit warming of the ocean in the regions where they form and/or intensify Oceanic films to limit heat transfer Redirection of solar energy using orbiting mirrors Concluding Thoughts:  Concluding Thoughts The scale of what would need to be done to completely counteract the ongoing build-up of greenhouse gases would be massive and leave a very long-lasting legacy to future generations in that adding an incremental cost to burning fossil fuels as the approaches do not generally provide other benefits. The incidental side effects of many geoengineering approaches are smallest for those approaches that have the greatest up-front costs and would take the most time to implement---and vice-versa. It is much easier to warm the world than it is to cool it (protecting the Earth from advancing glaciers would be comparatively easy)--we need to work hard to stop warming it further.

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