Are Humans Responsible for Global Warming?

Are adult male Responsible for orbiculate perferviding? A REVIEW OF THE FACTS APRIL 2007 AUTHORS James Wang, Ph. D. measurement Chameides, Ph. D. Are Humans Responsible for spherical fonding? The look for attri stilling the upstart spherical estrusing formation to homophile activities rests on the following undisputed scientific facts Carbon dioxide (CO2) is a babys room splosh that readys the cash machine. Since pre-industrial eons, atmospherical CO2 dumbnesss realize multifariousness magnitude from al roughly 280 go bads per one thousand thousand (ppm) to everyplace 380 ppm.Current absorptions of CO2 and otherwisewise babys room gases atomic number 18 unprecedented in at least the pop off 650,000 days, ground on records from gas bubbles confine in polar scratch. freelancer measurements demonstrate that the change magnitude CO2 in the atmosphere comes from tan dodo fuels and forests. The isotopic composition of carbon from these obtains contains a droll fingerprint. Since pre-industrial times, spherical ordinary temperatures defend maturationd by close 0. 7? C, with or so unmatchable-half of the warm occurring everyplace the early(prenominal) hardly a(prenominal) decades. The only decimal and immanently unchanging explanation for the upstart orbicular warm includes the intensified nursery incumbrance caused by the increase in CO2 and other greenhouse gases. The U. S. field honorary society of Sciencesthe independent judicature of the countrys most(prenominal) re instanterned scientists established by sexual intercourse to advise the nation on scientific and technical issueshas concluded The scientific concord of mood variety show is now sufficiently clear to discharge nations taking prompt action. several(prenominal) argue that the recent spherical warming is oer collectible to immanent fluctuations and non to kind-hearted activities. This argument and its fallacies ar discusse d below. crease 1 CO2 is non coming from human activities CO2 has native sources vol empenn hop onoes for example. All animals exhale it. How chamberpot human activities be affecting the concentration of CO2 on a ball-shaped scale? The Facts Natural processes verbalise large quantities of CO2 into the atmosphere, provided they also remove itat n untimely identical rates.This balance keep the concentration of CO2 at a stable level for thousands of age prior to the Industrial Revolution. In the casing of globose warming, the question is What is do the increase in CO2 concentrations? The root turns out to be incontr everywheretible. The isotopic composition of carbon in atmospheric CO2 supports a unique fingerprint that tells scientists that the lions sh be of the additional CO2 accumulating in the atmosphere is from the burning of fossil fuels. public debate 2 No unriva leading really knows why the mode variesThe globose climate has fluctuated considerably oer the military mans history, either for inexplicable reasons or because of internal discrepancy in the climate system. We do non know enough to the highest degree the climate system to attribute the chip in orbicular warming to either specific cause. The Facts It is true that the human races climate has exhibited wide quivers over geologic time ascribable to instinctive processes. However, scientists drop reasonable soft explanations for most of the signifi give the axet variations in 2 limate over geologic time1 they john be more often than non attributed to specific processes, non to mystic internal oscillations. Many of the major(ip) climatic stirs can be traced to changes in the Earths orbit near the sun (Hays et al. Science, 194, 1976, pg. 1121). Others can be linked to specific events ( such as the touch on of a comet or meteorite or the assembly or breakup of supercontinents) that led to large changes in the concentration of atmospheric greenhouse gases.For to a greater extent recent times (the past millennium), scientists nourish been able to denaryly attribute the major temperature fluctuations to changes in solar activity, volcanic eruptions, and human-produced greenhouse gases and particulate pollution. These subjective processes can not explain the menses warming. Argument 3 The Medieval potent arrest dis trys global warming The incumbent warming arch is like to the Medieval Warming gunpoint (MWP). Since the MWP was obviously a vivid event, the circulating(prenominal) warming is also presumable caused by natural processes. The FactsThe Medieval Warm Period (MWP) refers to a comparatively warm period long-lasting from about the 10th to the 14th one C. 2 However, the initial record for the MWP was largely ground on selective information3 ga on that pointd from Europe, and to a greater extent recent analyses indicate that the MWP was not a global phenomenon. A number of reconstructions of millennium-scale global t emperatures have indicated that the maximum globally averaged temperature during the MWP was not as uttermost(prenominal) as present-day temperatures and that the warming was regional kind of than global. Perhaps the most well-known of these is that of Michael Mann and colleagues (Nature, 392, 1998, pg. 779).Their reconstruction produced the so-called frosting hockey pegleg graphic that contributed to this remnant in the 2001 assessment of the Intergovernmental Panel on Climate Change TheMedieval Warm Period appear(s) to have limited utility in describing turns in hemispheric or global mean temperature changes in past centuries. The accuracy of the hockey stick graphic was widely discussed in the tender when the Mann et al. methodology was criticized by McIntyre and McKitrick (Geophys. Res. Lettr, 32, 2005, pg. L03710). less(prenominal) attention was given up to subsequent studies, such as that of Moberg and colleagues (Nature, 433, 2005, pg. 13) and Osborn and Briffa (Scie nce, 311, 2006, pg. 841) that were based on different, independent methodologies but reached conclusions similar to Mann. Observations of break up high altitude glaciers be perhaps even more telling. Andean glaciers that have been intact for more than 5,000 years argon now rapidly melting (Thompson et al. Proc. Nat. Acad. Sci. , 103, 2006, pg. 10536). If the MWP was truly global, these glaciers would not have survived. More generally, it is a logical fallacy to argue that because the climate has changed in the past due to natural causes, the current warming drive must also be due to natural causes.The debate over the magnitude and causes of earlier climate change such as the MWP is of scientific interest, but it does not invalidate the huge direct scientific evidence that human-produced greenhouse gases have been causing the Earth to warm recently. Argument 4 Recent predictions of a new deoxyephedrine age disprove global warming In the 1970s climate scientists were saying an ice age was close at hand(predicate). Now they say the Earth is warming. They put ont know what they are talking about. The FactsThe Earths climate for the past 2 million years has been characterized by ice ages lasting close to 100,000 years, punctuated by comparatively short (10,000- to 30,000-year) warm periods or inter frigids. The throw from glacial to interglacial is caused by changes in the Earths orbit around the sun amplified by natural feedbacks involving greenhouse gases (Hays et al. Science, 194, 1976, pg. 1121). The Earth entered the present interglacial about 10,000 years ago. All things creation equal (i. e. , in the absence of a large human-produced source of CO2) it is exceedingly the likely that the Earth leave alone swing back into a glacial period or ice age.But this will not occur for thousands of years. 3 As early as the nineteenth century, scientists recognized that greenhouse gases warm the planet, and that increases in atmospheric carbon dioxide coul d lead to global warming on time scales of decades to centuriesmuch shorter than the fluctuations related to ice ages and interglacials. Around the same time, global temperatures began to increase and scientists became increasingly concerned that humans were interfering with the climate. In the mid-fifties the upward trend in global temperatures unexpectedly halted and temperatures declined nighwhat.This led some scientists to become concerned about global cooling and, in turn, to headlines in the popular pressure sensation about an imminent ice age. What the skeptics fail to let in is that within the scientific literatureas opposed to the popular pressglobal warming remained a wicked concern. Many scientists of the time argued that whatsoever the cause of the cooling, natural or otherwise, it would be eventually overshadowed by the warming effect of carbon dioxide. In 1979, the National Academy of Sciences warned that a stunt man of carbon dioxide would increase global temper atures by 1. 5 to 4. oC (Carbon Dioxide and Climate A Scientific Assessment, NAS Press, 1979) and shortly thereafter a resumption of the upward trend in temperatures was detected. Over the past draw off century, scientific research on global climate change has intensified, and programs on an international scale have been organized. More and more data are included in computer models that are capable of recreating past trends and more precisely predicting future scenarios. We now know that the mid-20th century pause in global warming was caused by pollution from burning coal, which produced tiny particles or fuel-air bombs that blocked the energy from the sun.As aerosol emissions were controlled but greenhouse gas pollution continued to increase, the cooling effect of the aerosols was overwhelmed by the greenhouse gases, and global warming resumed. Argument 5 Scientists cannot prove current warming is not natural Climate scientists can not prove that the current warming is not due to natural processes and thus can not claim with proof that the warming is due to human interference. The Facts It is of course true that, in a complex system like climate, it is virtually impossible to prove a negative i. e. that natural processes are not causing the current warming. What we can do is eliminate every possible natural explanation that can be posited. Thermodynamics tells us that the warming of the Earths lower atmosphere must arise from one or more processes that supply tautologic combust to the lower atmosphere. anyhow the greenhouse effect, the executable processes are (1) increased output from the sun (2) increased absorption of heat from the sun due to a change in the Earths planetary reflectivity or albedo and (3) an internal variation in the climate system that transfers heat from one part of the Earth to the atmosphere.Direct observations confirm that none of these explains the detect warming over the latter(prenominal) half of the 20th century. For example there has been no appreciable change in solar output over the past both decades (see radiation diagram 1). Figure 1. Change in solar output from 1980 to 2005. Figure 1 shows the relative change in solar output determined from two of satellite measurements over a two-decade period. The data show variability in solar output corresponding to the 11-year yellow spot cycle, but no profane trend. Source later Lean and Froelich, 2006. 4Satellite data reveal that the Earths reflectivity increased (causing cooling kinda of warming) in the 60s, 70s, and early 80s and has step-downd modestly since. 4 The overall warming from the recent decrease in reflectivity is also comminuted compared to the greenhouse warming. In the case of internal variations, the oceanic is the only viable reservoir of internal heat that could have caused the atmosphere to warm on decadal time-scales. However, observations show that the heat capacity of the ocean has increased instead of decreased ove r the past a few(prenominal) decades (See Figure 2).This indicates that the atmosphere has been a source of heat to the ocean sooner than vice versa. Moreover, the amount of heat increase in the ocean is consistent with what is needed to balance the Earths energy budget given the intemperance heating from the enhanced greenhouse effect and the amount of excess heat observed to be stored in the atmosphere (Hansen et al. Science, 308, 2005, pg. 1431). In other words, the amount of heat stored in the ocean over recent years matches the amount of heat that models predict should be trapped on Earth due to the increase in greenhouse gases. Figure 2.Change in heat content of ocean 1955 to 2005 Source After Levitus et al. 2005. FIGURE 2 SHOWS THE intercourse CHANGE IN THE HEAT COTENT OF THE naval FROM 1955 TO 2005 BASED ON A COMPREHENSIVE ANALYSIS OF OCEAN TEMPERATURE MEASUREMENTS. THE entropy SHOW SHORT boundary VARIABILITY BUT A unload UPWARD TREND ON DECADAL TIME-SCALES. Conclusio n The Medieval Warm Period does not represent an relation to the warming of the late 20th century, for which scientists have independent evidence of human causation, and the evidence strongly suggests that the MWP was a regional, rather than a global phenomenon. Our understanding of the climate system is sufficient to provide qualitative models for most global or hemispheric climatic variations over geologic history and quantifiable models for variations over the past millennium. The Earths climate may establish to ice age conditions in thousands of years, but this does not preclude crushing effects from global warming over the next few centuries. 5 All known natural explanations for the current global warming trend have been eliminated by direct observations.The human-intensified greenhouse effect provides the only numeric explanation for the current warming trend. intimately the authors Dr. Wang have his doctorate from Harvard University and plant life as a climate sci entist at environmental Defense. He has publish several peer-reviewed papers on the global methane budget and was the author of The in style(p) Myths and Facts on Global Warming, which was read into the congressional record by Senator backside McCain in 2005. The report is available at http//www. undoit. org/pdfs/mythsvfacts. pdf. Dr. Chameides, chief scientist at Environmental Defense, is a member of the U.S. National Academy of Sciences and has been named a National accord of the National Academies. He is also an American Geophysical Union Fellow, and has received the American Geophysical Unions Macelwane Award. Dr. Chameides has served as editor of the Journal of Geophysical seek and is the author or coauthor of more than 120 scientific publications and quintet books. He received his doctorate from Yale University. The explanations are qualitative instead of quantitative because we do not have quantitative data from these events in the long-distance past to construct thei r exact histories. It has been suggested based on temperature reconstructions and model simulations that the MWP may have been caused by increased solar activity or a dearth of volcanic activity. 3 th Because worldwide temperature measurements do not exist onwards the 19 century, temperature records before th the 19 century are based on reconstructions of the temperature from the variations in temperature-sensitive proxies (e. g. , tree rings, isotopes in ice cores). 4 These variations are possibly due to changes in the concentrations of atmospheric aerosols produced from the burning of fossil fuels and biomass. 1 6Are Humans Responsible for Global Warming?Are Humans Responsible for Global Warming? A REVIEW OF THE FACTS APRIL 2007 AUTHORS James Wang, Ph. D. Bill Chameides, Ph. D. Are Humans Responsible for Global Warming? The case for attributing the recent global warming to human activities rests on the following undisputed scientific facts Carbon dioxide (CO2) is a greenhouse ga s that warms the atmosphere. Since pre-industrial times, atmospheric CO2 concentrations have increased from about 280 parts per million (ppm) to over 380 ppm.Current concentrations of CO2 and other greenhouse gases are unprecedented in at least the last 650,000 years, based on records from gas bubbles trapped in polar ice. Independent measurements demonstrate that the increased CO2 in the atmosphere comes from burning fossil fuels and forests. The isotopic composition of carbon from these sources contains a unique fingerprint. Since pre-industrial times, global average temperatures have increased by about 0. 7? C, with about half of the warming occurring over the past few decades. The only quantitative and internally consistent explanation for the recent global warming includes the intensified greenhouse effect caused by the increase in CO2 and other greenhouse gases. The U. S. National Academy of Sciencesthe independent organization of the countrys most renowned scientists esta blished by Congress to advise the nation on scientific and technical issueshas concluded The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. Some argue that the recent global warming is due to natural fluctuations and not to human activities. This argument and its fallacies are discussed below. Argument 1 CO2 is not coming from human activities CO2 has natural sources volcanoes for example. All animals exhale it. How can human activities be affecting the concentration of CO2 on a global scale? The Facts Natural processes emit large quantities of CO2 into the atmosphere, but they also remove itat well identical rates.This balance maintained the concentration of CO2 at a stable level for thousands of years prior to the Industrial Revolution. In the case of global warming, the question is What is causing the increase in CO2 concentrations? The answer turns out to be incontrovertible. The isotopic composition of carbon in at mospheric CO2 provides a unique fingerprint that tells scientists that the lions apportion of the additional CO2 accumulating in the atmosphere is from the burning of fossil fuels. Argument 2 No one really knows why the climate variesThe global climate has fluctuated considerably over the Earths history, either for unknown reasons or because of internal variability in the climate system. We do not know enough about the climate system to attribute the present global warming to any specific cause. The Facts It is true that the Earths climate has exhibited wide swings over geologic time due to natural processes. However, scientists have reasonable qualitative explanations for most of the significant variations in 2 limate over geologic time1 they can be largely attributed to specific processes, not to unknown internal oscillations. Many of the major climatic changes can be traced to changes in the Earths orbit around the sun (Hays et al. Science, 194, 1976, pg. 1121). Others can be li nked to specific events (such as the impact of a comet or meteorite or the assembly or breakup of supercontinents) that led to large changes in the concentration of atmospheric greenhouse gases.For more recent times (the past millennium), scientists have been able to quantitatively attribute the major temperature fluctuations to changes in solar activity, volcanic eruptions, and human-produced greenhouse gases and particulate pollution. These natural processes can not explain the current warming. Argument 3 The Medieval Warm Period disproves global warming The current warming trend is analogous to the Medieval Warming Period (MWP). Since the MWP was obviously a natural event, the current warming is also likely caused by natural processes. The FactsThe Medieval Warm Period (MWP) refers to a relatively warm period lasting from about the 10th to the 14th century. 2 However, the initial evidence for the MWP was largely based on data3 gathered from Europe, and more recent analyses indica te that the MWP was not a global phenomenon. A number of reconstructions of millennium-scale global temperatures have indicated that the maximum globally averaged temperature during the MWP was not as extreme as present-day temperatures and that the warming was regional rather than global. Perhaps the most well-known of these is that of Michael Mann and colleagues (Nature, 392, 1998, pg. 779).Their reconstruction produced the so-called hockey stick graphic that contributed to this conclusion in the 2001 assessment of the Intergovernmental Panel on Climate Change TheMedieval Warm Period appear(s) to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries. The accuracy of the hockey stick graphic was widely discussed in the press when the Mann et al. methodology was criticized by McIntyre and McKitrick (Geophys. Res. Lettr, 32, 2005, pg. L03710). Less attention was given to subsequent studies, such as that of Moberg and colleagues (Nature, 433, 2005, pg. 13) and Osborn and Briffa (Science, 311, 2006, pg. 841) that were based on different, independent methodologies but reached conclusions similar to Mann. Observations of melting high altitude glaciers are perhaps even more telling. Andean glaciers that have been intact for more than 5,000 years are now rapidly melting (Thompson et al. Proc. Nat. Acad. Sci. , 103, 2006, pg. 10536). If the MWP was truly global, these glaciers would not have survived. More generally, it is a logical fallacy to argue that because the climate has changed in the past due to natural causes, the current warming trend must also be due to natural causes.The debate over the magnitude and causes of earlier climate change such as the MWP is of scientific interest, but it does not invalidate the considerable direct scientific evidence that human-produced greenhouse gases have been causing the Earth to warm recently. Argument 4 Recent predictions of a new ice age disprove global warming In the 1970s climate scientists were saying an ice age was imminent. Now they say the Earth is warming. They dont know what they are talking about. The FactsThe Earths climate for the past 2 million years has been characterized by ice ages lasting close to 100,000 years, punctuated by relatively short (10,000- to 30,000-year) warm periods or interglacials. The swing from glacial to interglacial is caused by changes in the Earths orbit around the sun amplified by natural feedbacks involving greenhouse gases (Hays et al. Science, 194, 1976, pg. 1121). The Earth entered the present interglacial about 10,000 years ago. All things being equal (i. e. , in the absence of a large human-produced source of CO2) it is highly likely that the Earth will swing back into a glacial period or ice age.But this will not occur for thousands of years. 3 As early as the 19th century, scientists recognized that greenhouse gases warm the planet, and that increases in atmospheric carbon dioxide could lead to global warming on time scales of decades to centuriesmuch shorter than the fluctuations related to ice ages and interglacials. Around the same time, global temperatures began to increase and scientists became increasingly concerned that humans were interfering with the climate. In the 1950s the upward trend in global temperatures unexpectedly halted and temperatures declined somewhat.This led some scientists to become concerned about global cooling and, in turn, to headlines in the popular press about an imminent ice age. What the skeptics fail to admit is that within the scientific literatureas opposed to the popular pressglobal warming remained a serious concern. Many scientists of the time argued that whatever the cause of the cooling, natural or otherwise, it would be eventually overshadowed by the warming effect of carbon dioxide. In 1979, the National Academy of Sciences warned that a doubling of carbon dioxide would increase global temperatures by 1. 5 to 4. oC (Carbon Dioxid e and Climate A Scientific Assessment, NAS Press, 1979) and shortly thereafter a resumption of the upward trend in temperatures was detected. Over the past quarter century, scientific research on global climate change has intensified, and programs on an international scale have been organized. More and more data are included in computer models that are capable of recreating past trends and more precisely predicting future scenarios. We now know that the mid-20th century pause in global warming was caused by pollution from burning coal, which produced tiny particles or aerosols that blocked the energy from the sun.As aerosol emissions were controlled but greenhouse gas pollution continued to increase, the cooling effect of the aerosols was overwhelmed by the greenhouse gases, and global warming resumed. Argument 5 Scientists cannot prove current warming is not natural Climate scientists can not prove that the current warming is not due to natural processes and therefore can not claim with certainty that the warming is due to human interference. The Facts It is of course true that, in a complex system like climate, it is virtually impossible to prove a negative i. e. that natural processes are not causing the current warming. What we can do is eliminate every possible natural explanation that can be posited. Thermodynamics tells us that the warming of the Earths lower atmosphere must arise from one or more processes that supply excess heat to the lower atmosphere. Besides the greenhouse effect, the viable processes are (1) increased output from the sun (2) increased absorption of heat from the sun due to a change in the Earths planetary reflectivity or albedo and (3) an internal variation in the climate system that transfers heat from one part of the Earth to the atmosphere.Direct observations confirm that none of these explains the observed warming over the latter half of the 20th century. For example there has been no appreciable change in solar output over th e past two decades (see Figure 1). Figure 1. Change in solar output from 1980 to 2005. Figure 1 shows the relative change in solar output determined from two of satellite measurements over a two-decade period. The data show variability in solar output corresponding to the 11-year sunspot cycle, but no secular trend. Source After Lean and Froelich, 2006. 4Satellite data reveal that the Earths reflectivity increased (causing cooling instead of warming) in the 60s, 70s, and early 80s and has decreased modestly since. 4 The overall warming from the recent decrease in reflectivity is also small compared to the greenhouse warming. In the case of internal variations, the ocean is the only viable reservoir of internal heat that could have caused the atmosphere to warm on decadal time-scales. However, observations show that the heat content of the ocean has increased instead of decreased over the past few decades (See Figure 2).This indicates that the atmosphere has been a source of heat to the ocean rather than vice versa. Moreover, the amount of heat increase in the ocean is consistent with what is needed to balance the Earths energy budget given the excess heating from the enhanced greenhouse effect and the amount of excess heat observed to be stored in the atmosphere (Hansen et al. Science, 308, 2005, pg. 1431). In other words, the amount of heat stored in the ocean over recent years matches the amount of heat that models predict should be trapped on Earth due to the increase in greenhouse gases. Figure 2.Change in heat content of ocean 1955 to 2005 Source After Levitus et al. 2005. FIGURE 2 SHOWS THE RELATIVE CHANGE IN THE HEAT COTENT OF THE OCEAN FROM 1955 TO 2005 BASED ON A COMPREHENSIVE ANALYSIS OF OCEAN TEMPERATURE MEASUREMENTS. THE DATA SHOW SHORT TERM VARIABILITY BUT A CLEAR UPWARD TREND ON DECADAL TIME-SCALES. Conclusion The Medieval Warm Period does not represent an analogy to the warming of the late 20th century, for which scientists have independent evi dence of human causation, and the evidence strongly suggests that the MWP was a regional, rather than a global phenomenon. Our understanding of the climate system is sufficient to provide qualitative models for most global or hemispheric climatic variations over geologic history and quantitative models for variations over the past millennium. The Earths climate may return to ice age conditions in thousands of years, but this does not preclude devastating effects from global warming over the next few centuries. 5 All known natural explanations for the current global warming trend have been eliminated by direct observations.The human-intensified greenhouse effect provides the only quantitative explanation for the current warming trend. About the authors Dr. Wang received his doctorate from Harvard University and works as a climate scientist at Environmental Defense. He has published several peer-reviewed papers on the global methane budget and was the author of The Latest Myths and Facts on Global Warming, which was read into the congressional record by Senator John McCain in 2005. The report is available at http//www. undoit. org/pdfs/mythsvfacts. pdf. Dr. Chameides, chief scientist at Environmental Defense, is a member of the U.S. National Academy of Sciences and has been named a National Associate of the National Academies. He is also an American Geophysical Union Fellow, and has received the American Geophysical Unions Macelwane Award. Dr. Chameides has served as editor of the Journal of Geophysical Research and is the author or coauthor of more than 120 scientific publications and five books. He received his doctorate from Yale University. The explanations are qualitative instead of quantitative because we do not have quantitative data from these events in the distant past to construct their exact histories. It has been suggested based on temperature reconstructions and model simulations that the MWP may have been caused by increased solar activity or a d earth of volcanic activity. 3 th Because worldwide temperature measurements do not exist before the 19 century, temperature records before th the 19 century are based on reconstructions of the temperature from the variations in temperature-sensitive proxies (e. g. , tree rings, isotopes in ice cores). 4 These variations are possibly due to changes in the concentrations of atmospheric aerosols produced from the burning of fossil fuels and biomass. 1 6