Contents:

Executive summary: Al Gore's new book and movie, both titled An Inconvenient Truth, have been hailed by environmentalists--despite being filled with false or misleading claims about the science of global warming and related issues. This page details errors in the book (2006, Rodale Books), which in summary include:

Gore's portrayal of the subject of global warming is scientifically unsupportable; even some scientists who accept the premise of global warming have been willing to call him on some errors. His portrayal of scientific skepticism regarding global warming is shameful; science requires healthy criticism to progress. The effect of attempts by Gore and others to silence dissent is harmful to scientific understanding as well as its application by society. The effort to use such twisted science to further a political agenda is such a harm.

Details--the science:

"The most vulnerable part of the Earth's ecological system is the atmosphere. It's vulnerable because it's so thin." (p. 22) Other parts of our environment are arguably more vulnerable and are clearly thinner: the hydrosphere (oceans and rivers), for example. Whatever is meant by "vulnerable", it probably is poorly described as being a consequence of "thinness".

"In particular, we have vastly increased the amount of carbon dioxide--the most important of the so-called greenhouse gases." (p. 25) While "most important" is a subjective term, the implication that most of the existing greenhouse effect is due to CO 2 is false: water vapor is the source of most of the existing greenhouse effect.

"The Sun's energy enters the atmosphere in the form of light waves and heats up the Earth. Some of that energy warms the Earth and then is re-radiated back into space in the form of infrared waves." (p. 26) Solar energy reaching the Earth is about 42% visible light and 50% shortwave infrared. Some is reflected; only the absorbed portion heats the Earth. "Re-radiate" is a an incorrect and misleading term and should not be used; rather, the Earth and its atmosphere radiate longwave infrared as a function of its temperature, with the balance between this radiation and temperature mediated by the presence of greenhouse gases.

"The greenhouse gases surrounding Mars are almost nonexistent, so the temperature is far too cold." (p. 26) Mars' atmosphere, although much thinner than Earth's, is almost entirely CO 2 . The partial pressure of CO 2 at the surface of Mars is 6.1 millibars, compared to 0.38 millibars at the surface of Earth. The greenhouse warming on Mars due to CO 2 is greater than that due to CO 2 alone on the Earth (but not that due to H 2 O). Mars is colder because it is further from the Sun and receives less than half the sunlight the Earth does.

"The problem we now face is that this thin layer of atmosphere is being thickened by huge quantities of human-caused carbon dioxide and other greenhouse gases." (p. 27) The Earth's atmosphere is not thicker as a result of increased greenhouse gases; rather, the effects of changes in these gases are associated with the different absorptive properties of these minor constituents.

"Professor Revelle was the first scientist to propose measuring CO 2 in the Earth's atmosphere." (p. 30) Scientists had been measuring atmospheric CO 2 since the 1800s, before Revelle was born. Guy Stewart Callendar identified the modern increase in atmospheric CO 2 from such measurements about 20 years before Revelle's project, which itself was motivated in part by Hans Suess's identification of fossil carbon in atmospheric CO 2 . An article by Revelle and two coauthors in 1991 stated "The scientific base for a greenhouse warming is too uncertain to justify drastic action at this time." (Singer et al., 1991). Gore instigated a campaign by J. Lancaster to slander the coauthors in 1992; one coauthor sued for libel and obtained an admission by Lancaster that Revelle had indeed participated in authoring those words (Singer, 2003).

"The pre-industrial concentration of CO 2 was 280 parts per million. In 2005, that level, measured high above Mauna Loa, was 381 parts per million." (p. 37) Average CO 2 concentration in 2005 at Mauna Loa was 379.75 ppm (Tans, 2006).

"It is evident in the world around us that very dramatic changes are taking place... This is Mount Kilimanjaro in 1970 with its fabled snows and glaciers... [Lonnie Thompson] predicts that within 10 years there will be no more 'Snows of Kilimanjaro'." (pp. 42-45) The retreat of Kilimanjaro's glaciers is not attributable to contemporary temperature changes. Kaser et al., 2004, cite a drastic drop in local atmospheric moisture around the late 1800s; Mason, 2003, cites deforestation around Kilimanjaro, resulting in a drop in local precipitation. Young and Hastenrath, 1991, list several potential factors but single out climate changes than occurred in the late 1800s-early 1900s. Cullen et al., 2006, conclude that Kilimanjaro's glaciers have been out of equilibrium with local climate since about 1900, i.e. that their retreat reflects climate change a century ago, not climate change today. Thompson's actual prediction is for loss of the ice fields in 9-14 years, between 2015 and 2020 (Thompson et al., 2002).

"Our own Glacier National Park will soon need to be renamed 'the park formerly known as Glacier'." (p. 46) Glacier retreat has been ongoing in Glacier National Park since 1850 (USGS, 2003a) due to natural climate variations; the USGS suggests that with no additional warming the glaciers will likely be gone by 2100, with one model assuming continued warming predicting their disappearance by 2030 (USGS, 2003b). Even without the current warming blamed by some on humans, the glaciers of Glacier National Park would be disappearing since they have been out of equilibrium with the local environment ever since the end of the Little Ice Age in 1850.

"Almost all of the mountain glaciers in the world are now melting..." (p. 48) All glaciers are losing mass to melting and gaining mass to precipitation. Losses outpace gains for most, but not all. Even at the regional level, some regions show net gains (Dyurgerov and Meier, 2005).

"The Himalayas... provide more than half of the drinking water for 40% of the world's population... Within the next half-century, that 40% of the world's people may well face a very serious drinking water shortage, unless the world acts boldly and quickly to mitigate global warming." (p. 58) Research suggests runoff reductions of only 1-8% under various climate change scenarios (Sharma et al., 2000). Dyurgerov and Meier, 2005, conclude that the mass loss of Himalayan glaciers from 1960 to 1992 was offset by mass gain of Tibetan glaciers (with little net loss or gain by Tibetan glaciers since then). Zhao and Moore, 2006, report that Himalayan snow accumulation has been steadily declining since 1840, predating any current climate change. Even if predictions were correct regarding disappearance of these glaciers, such melting would increase river flows in the period of time described by Gore.

(map, p. 59) The white areas on the map represent high elevations, not glaciers; only a small fraction of this area (less than 10%) is covered by glaciers.

"1000 years of northern hemisphere temperature (° C)" (p. 63)

"But as Dr. Thompson's thermometer shows, the vaunted Medieval Warm Period... was tiny compared to the enormous increases in temperature of the last half-century" (p. 64)

"Those global warming skeptics--a group diminishing almost as rapidly as the mountain glaciers--launched a fierce attack against another measurement of the 1,000-year correlation between CO2 and temperature known as "the hockey stick," a graphic image representing the research of climate scientist Michael Mann and his colleagues. But in fact, scientists have confirmed the same basic conclusions in multiple ways--with Thompson's ice core record as one of the most definitive." (p. 65) The depicted graph is not based on the ice core data of Thompson as claimed, but is the (mostly tree-ring based) proxy reconstruction of Mann et al., 1999, combined with the 1840-2000 surface measurement-based series of Jones et al., 1999. (Specifically, it is a defective reproduction of a figure from a secondary source.) The lack of variance before 1840 is relatively unique to Mann et al.'s methodology for combining proxies, a methodology which has been shown to have flaws (McIntrye and McKitrick, 2003) and appears to suppress temperature variations prior to the 20th century relative to other methods (Dahl-Jensen et al., 1998; von Storch et al., 2004; Moberg et al., 2005). The actual ice core-based reconstruction by Thompson et al., 2003, is based on only 6 tropical glaciers and shows a similar "hockey-stick" shape primarily due to the influence of two cores, while the other four cores show Medieval Warm Period temperatures very similar to modern temperatures.

"Nonetheless, the so-called global-warming skeptics often say that global warming is really an illusion reflecting nature's cyclical fluctuations. To support their view, they frequently refer to the Medieval Warm Period." (p. 65) This is an inaccurate caricature of skeptical views, which really cover a wide range of views. First, a short-term warming that was part of a cyclical variation would be real warming, not illusional; second, "cyclical" does not accurately describe some of the types of natural effects described by the scientific community that could explain modern warming. More to the point, many (not all but many) "skeptics" believe that warming is now occurring, but simply disagree with Gore on the cause of this warming. Many scientists--some who agree with Gore on the magnitude of modern warming and some who don't--also accept the historical evidence for a Medieval Warm Period either locally or globally as warm as temperatures today. By the same token, it should not be necessary for Gore to deny the Medieval Warm Period to assert that warming is occurring today.

"In Antarctica, measurements of CO 2 concentrations and temperature go back 650,000 years... It's a complicated relationship, but the most important part of it is this: When there is more CO 2 in the atmosphere, the temperature increases because more heat from the Sun is trapped inside... There is not a single part of this graph--no fact, date, or number--that is controversial in any way or in dispute by anybody." (pp. 66-67) These measurements are directly of CO 2 and deuterium (or oxygen-18 in other cases) in air bubbles in ice cores; the relationship of deuterium to temperature is indirect and requires assumptions regarding past isotopic abundances. The reconstructed temperature series is local, not global; similar ice core temperature reconstructions from other locations, while correlated with CO 2 abundances, are not as strongly correlated as these series selected by Gore, possibly suggesting local influences. The claim that this correlation shows that more CO 2 leads to higher temperatures is false: higher resolution studies of the ice cores show that the temperature increases came first, followed by CO 2 increases. For the composite series shown in this graph, Siegenthaler et al., 2005, find the best match shows CO 2 concentrations lagging 1,900 years behind the deuterium-derived temperature values. It is believed that the temperature changes led to changes in the balance between greenhouse gases in the atmosphere and greenhouse gases in locations such as the oceans. Apart from this, atmospheric CO 2 does not trap heat (such a statement is linked to misunderstanding of the greenhouse effect); rather, CO 2 and other greenhouse gases selectively absorb outgoing longwave infrared resulting in a radiative balance at a different global temperature than without the gases. The fact that the data within the graph is basically accepted in the scientific community is a separate issue from the fact that Gore is misinterpreting it.

"The top right point... shows current global temperatures. And the bottom right point marks the depth of the last ice age. That short distance--about an inch in the graph--represents the difference, in Chicago, between a nice day and a mile of ice over your head. Imagine what three times that much on the warm side would mean." (p. 67) The implied connection between these temperatures and climate is misleading. The ice core-based temperature series has a poor time resolution and does not reflect much larger temperature variations on timescales of years or decades. Further, the high correlation over this time period used to support Gore's interpretation does not hold in the more distant geologic past (Royer et al., 2004).

"This graph charts the actual measurements of global temperature since the Civil War... And in recent years the rate of increase has been accelerating... The hottest year recorded during this entire period was 2005." (pp. 72-73) Gore does not give a source for this graph, but reportedly it is based on the GISS temperature series from NASA (Hansen et al., 2006), which only goes back to 1880. These and other similar series are composite averages based on ground-based and sea-based measurements, adjusted and averaged in various ways. Such series cannot absolutely specify the "hottest" year because the precise temperature values are highly dependent on the methodology used to average measurements and the selection of stations to be included in the averages. For example, the GISS series gives the three successively hottest years as 2005, 1998, and 2002. The UK Climate Research Unit series (Jones et al., 1999) instead gives 1998, 2005, and 2002, with 1998 0.1° C warmer than 2005 due to the 1998 El Nino event (Jones and Palutikof, 2006). The Global Historical Climate Network series gives 2005, 1998, and 2003 as the hottest years (NOAA, 2006). All of these series, however, show much greater warmings in the last three decades than more uniform sampling from satellite-based observations. This post-1970 warming bias may result from local effects such as the urban heat island effect, or from problems with the selection of stations used in the average and the adjustments applied to this data. With such relative extremes so heavily dependent on the particular methodology used, Gore is incorrect to make such an absolute claim without qualification.

"We have already begun to see the kind of heatwaves that scientists say will become much more common if global warming is not addressed. In the summer of 2003 Europe was hit by a massive heatwave that killed 35,000 people." (p. 75) This death toll is dominated by 14,082 deaths in France and 4,000 in Italy, both calculated by comparing observed deaths in August 2003 to what would "normally be expected" (UNEP, 2004); these deaths, predominantly among the elderly, have not been individually attributed to heat-related causes. The French government in particular offered these precise estimates after initially stating that there was no accurate way of measuring deaths from the heat. These death tolls partly reflect the aging population of Europe, but in the case of France have also been attributed to failed government and health care system response to the heat wave (BBC, 2003). More generally, despite the anomaly of the 2003 European heat wave, more accurate treatment of regional temperatures does not support the claim that regional heat waves are becoming more frequent (Pielke, 2006).

"In the summer of 2005 many cities in the American West broke all-time records for high temperatures... And in the East, a number of cities set daily temperature records..." (pp. 76-77) Individual local highs and lows always occur, due to the chaotic variations in weather; when discussing climate, this is not an appropriate measure. (Note that Gore dismisses local measures of climate on p. 321.) Such highs are likely attributable to the urban heat island effect, not to global warming. According to the GISS-compiled temperature series for the lower 48 states, 2005 tied as the 9th hottest year on record; the hottest years, from hottest to cooler, were 1934, 1998, 1921, 1931, 1999, tie between 1953, 1990, and 2001, and tie between 1987 and 2005; 2005 was a full 0.4° C cooler than 1934 (Sato and Hansen, 2006).

"But scientists who specialize in global warming have been using evermore accurate computer models that long ago predicted a much higher range of ocean temperatures as a result of man-made global warming... The actual ocean temperatures are completely consistent with what has been predicted as a result of man-made global warming. And they're way above the range of natural variability." (pp. 78-79) The global circulation models (GCMs) referred to still fail to replicate observed temperature changes from first principles; several phenomena are not well understood but are incorporated with empirical factors to produce the apparent agreement between models and past observations. But as more such empirical adjustments are applied, the models can be forced to reproduce a particular result without necessarily reproducing the physics correctly. Still, on several points, GCMs continue to fail the basic scientific test of making predictions which are subsequently verified (Pielke, 2006). The predictions from these models tend to be larger than empirical predictions for a given change in atmospheric CO 2 (Lindzen, 1997). Indirect solar effects, which are highly correlated with climate, are ignored by these models. Any claim that observed changes are outside the range of natural variability necessarily assumes that natural influences have been constant, an assumption which has been questioned.

"As the oceans get warmer, storms get stronger... there is now a strong, new emerging consensus that global warming is indeed linked to a significant increase in both the duration and intensity of hurricanes. Brand-new evidence is causing some scientists to assert that global warming is even leading to an increased frequency of hurricanes, overwhelming the variability in frequency long understood to be part of natural deep-current cycles." (pp. 80-81) Gore acknowledges some limitations of the claimed global warming-hurricane link, but still claims a stronger consensus than what actually exists. In fact, the scientific community is divided as to whether recent peaks in hurricane activity are the result of a global warming trend or merely an indicator of natural cycles. The research which Gore apparently refers to (Emanuel, 2005; Webster et al., 2005) has been questioned (Pielke, 2005), and many researchers (including many in the NOAA) tend to attribute recent active storm seasons to natural cycles including the Atlantic oscillation (Elsner et al., 2000; Goldenberg et al., 2001; NOAA, 2005; Chan, 2006). Kloztbach, 2006, found that the recent increase in North Atlantic tropical storm activity was offset by a significant decrease in Northeast Pacific tropical storm activity, leading to minimal global change. Further, theoretical research has produced varying conclusions regarding the effect of any global warming on hurricane activity: some predict more storms, some predict the same number of storms but stronger storms on average, some models predict limited changes. Continuing research may yet identify and attribute a trend, but claims that this has already been settled are premature (Pielke et al., 2005; Michaels et al., 2006).

"The science textbooks had to be rewritten in 2004. They used to say, 'It's impossible to have hurricanes in the South Atlantic'. But that year, for the first time ever, a hurricane hit Brazil." (p. 84) Any textbook making such a claim would not have been credible before 2004. Two other weak tropical storms short of hurricane strength have been reported in this area during the last 40 years (Pezza and Simmonds, 2005). Rather than the "first time ever", the "first recorded instance" would be more accurate.

"Also in 2004, the all-time record for tornadoes in the United States was broken." (p. 86) To imply a significance to this fact is misleading, since increased observations and technological methods permit the tallying of more weak tornadoes than ever before. No F5 tornado damage occurred in 2004 (McCarthy and Schaefer, 2005), and no trends regarding consistently measured tornadoes are observed (McCarthy, 2000). Gore also fails to acknowledge that tornado activity in 2005 was unusually low, with this the first year in which no tornadoes were reported in Oklahoma in the month of May.

"... less than a month before Hurricane Katrina hit the United States, a major study from MIT supported the scientific consensus that global warming is making hurricanes more powerful and more destructive... And then came Katrina... The consequences were horrendous..." (pp. 92-95) Hurricane Katrina cannot be linked individually to any climate trend, human-caused or otherwise. Further, the uniquely disastrous consequences of Katrina are mostly a reflection of the fact that it struck a city below sea level protected by inadequate levees, with consequences worsened by inept government response at the city, state, and federal levels. Finally, there is no scientific consensus either on any trends regarding hurricanes or on the causes for any such trends, as previously discussed.

"Partly as a result, the number of large flood events has increased decade by decade, on every continent." (p. 106) This data cannot be used to support claimed trends in climate. Observed flood events are influenced by increasing population and distribution of people in flood-prone areas, as well as by land use changes which increase runoff during heavy rains. Studies on weather extremes show heavy rain events are more frequent in some locations and less frequent in others, not uniformly more frequent as Gore implies (Easterling et al., 2000).

"In 2005 Europe had a year of unusual catastrophes very similar to the one in the United States... Europe was experiencing a disastrous number of floods." (pp. 106-107) Mudelsee et al., 2003, examined flood records for the Elbe and Oder rivers in central Europe as far back as 1021 and 1269, respectively, and found no modern trend regarding the occurrence of floods.

"There has also been record flooding in China, which, as one of the planet's oldest civilizations, keeps the best flood records of any nation in the world." (p. 112) Jiang et al., 2005, examined Chinese flood records for the Yangtze Delta from 1000 AD to the present and found the frequency of large floods was greatest from about 1500 to 1700; this was identified as the transition from the Medieval Warm Period to the Little Ice Age.

"Paradoxically, however, global warming causes not only more flooding, but also more drought." (p. 112) There is some tendency to claim that global warming will produce opposite extremes, which tends to make it impossible to scientifically test such claims, given that weather extremes such as flood events and droughts are natural aspects of a chaotic climate system. Gore makes the claims here that (1) global warming will causes regional changes in weather extremes and (2) such trends in weather extremes are observed. On point one, the general circulation models have deficiencies previously noted which are even worse with regard to predictions at the regional level. For some regions, various GCMs give contradictory predictions. On point two, individual events cited by Gore do not constitute a trend. Studies on weather extremes show heavy rain events are more frequent in some locations and less frequent in others and show little trends for droughts to date (Easterling et al., 2000).

"The map to the left shows what is projected to happen to soil moisture in the United States with the doubling of CO 2 , which would happen in less than 50 years if we continue business as usual... Moreover, scientists are now telling us that if we do not act quickly to contain global warming pollution, we will soon ... more toward a quadrupling, in which case, scientists tell us, most of the United States would lose up to 60% of its soil moisture." (p. 121) These models are based on some questionable assumptions, including dominance of positive feedbacks in a perturbed climate state. The particular model used, the GFDL model, produces a greater sensitivity to a doubling of CO 2 than either the median IPCC projection (GFDL, 2004) or recent empirical studies (Annan and Hargreaves, 2006). Further, while Gore's only reference to the time needed for these changes is the claim that CO 2 doubling could happen "in less than 50 years", the depicted model results are for a doubling in 70 years followed by a few centuries' climate stabilization, or a quadrupling in 140 years followed by a few centuries' climate stabilization. Results are also seasonally dependent (summer is shown). Recently, greenhouse emission growth rates have slowed, so assumptions of a CO 2 doubling in less than 50 years or a quadrupling do not appear appropriate. Hansen et al., 2000, suggest that non-CO 2 greenhouse gases are the principal causes of recent warming, in which case the assumptions regarding accelerated carbon dioxide emissions are also inappropriate.

"Three years ago [the Ward Hunt shelf] cracked in half, to the astonishment of scientists. This had never happened before." (p. 128) The Ward Hunt Ice Shelf had loss 90% of its area from 1906 to 1982, and only covered 443 sq. km at the time of the breakup, which occurred over the period 2000 to 2002 (Mueller et al., 2003). The breakup of this shelf was not particularly astonishing, given observed calving of icebergs over the preceding decades; the remarkable aspect was the emptying of low-salinity surface water from Disraeli Fiord, previously trapped by the shelf and overlying high-salinity water.

"Since the 1970s, the extent and thickness of the Arctic ice cap has diminished precipitously. There are now studies showing that if we continue with business as usual, the Arctic ice cap will completely disappear each year during the summertime. At present, it plays a crucial role in cooling the Earth. Preventing its disappearance must be one of our highest priorities." (p. 143) Studies of actual observations of Arctic sea ice show significant year-to-year variability (Laxon et al., 2003), which is not reproduced in the model studies Gore cites, indicating that they do not correctly simulate sea ice dynamics. The role of Arctic sea ice in affecting global climate by reflecting sunlight back to space is not uniquely crucial, since cloud cover over the same region has a similar effect, and clouds are not well simulated in the GCMs in question (Potter and Cess, 2004).

"The reason this Arctic ice cap has been melting so quickly is first because it is much thinner than the Antarctic ice cap, since it floats on top of the Arctic Ocean. Second, as soon as a portion of the ice melts, there is a dramatic difference in the amount of heat absorbed from the sun." (p. 144) Antarctica has a much colder climate than the Arctic because the thick icecap is built up to an altitude much higher than sea level. Many studies attribute the recent thinning of the Arctic ice cap not directly to more melting at a given location as Gore implies, but to changes in the winds and ocean currents that move the sea ice from one location to another (Hilmer and Jung, 2000; Laxon et al., 2003).

"A new scientific study shows that, for the first time, polar bears have been drowning in significant numbers." (p. 147) The "significant numbers" are four drowned polar bears observed in 2004 (Monnett et al., 2005). Of thirteen polar bear populations in Canada, only two show recent decreases while eleven show increases or no population change (Taylor, 2006); in Alaska, the two populations are relatively stable (NFS, 2002a; NFS, 2002b).

"A study from the Netherlands, depicted below... As a result [of warming], the chicks are in trouble." (p. 153) The depicted graph does not accurately represent the sensitivity of the great tit (which was the subject of the study, not the black tern depicted in the photo on p. 153) to the relative time of peak caterpillars/bird-hatching. The graph is reproduced from National Geographic, 2004, which appears to have arbitrarily chosen the widths of these curves, since their cited source (Both and Visser, 2001) does not report such data on the distributions of this data. Consequently, the graph exaggerates the sensitivity of the great tit to the change in peak caterpillar population. Some factors are not represented such as the birds adapting by finding other sources of food. The Scientific American article in question states "The gap between the schedules of the caterpillars and the birds has had no demonstrable effect so far on tit numbers" (Grossman, 2004).

"Swiss frost days...invasive species..." (p. 154) The graph is reproduced from National Geographic, 2004, which in turn reproduced it from Walther et al., 2002: both of these use the more accurate label "exotic species", while Gore uses "invasive species". Gore does not identify these species or the nature of this measurement: this represents broad-leafed plant species imported by humans to gardens and parks in southern Switzerland, which have subsequently spread from these locations. The actual methodology used to produce this data is discussed elsewhere (Walther, 2000; Walther, 2002) and may not be a linear indicator of the spread of such plant life. While such spread is influenced by milder local climate, it is also influenced by the selection and frequency of plants imported.

"...14 million acres of spruce trees in Alaska and British Columbia that have been killed by bark beetles, whose rapid spread was once slowed by colder and longer winters." (p. 156) The bark beetle outbreaks in the late 1990s reflected a combination of several warm winters and poor forest management practices, such as fire suppression practices (ADNR, 2004).

"In fact, we are facing what biologists are beginning to describe as a mass extinction crisis, with a rate of extinction now 1,000 times higher than the normal background rate." (p. 163) Known species extinctions in the last several centuries total about 1,000, with very few attributed to climate change. The estimates Gore refers to here are unconfirmed estimates which either assume that GCM predictions of future warming are reliable or consider the effects of phenomena apart from global warming.

"Corals--along with many other ocean life forms--are threatened by the unprecedented growth of carbon dioxide emissions worldwide..." (p. 168) Gore does not acknowledge significant variations in coral reef response to perturbations such as temperature or dissolved carbon dioxide. A recent review (Hughes et al., 2003) states "reefs will change rather than disappear entirely, with some species already showing far greater tolerance to climate change and coral bleaching than others."

"In general, the relationship between the human species and viruses is less threatening when there are colder winters, colder nights, more stability in climate patterns, and fewer disruptions... Global warming pushes all of these boundaries in the wrong direction, thereby increasing human vulnerability to new and unfamiliar diseases, as well as new strains of diseases once under control... mosquitoes are profoundly affected by global warming... Some 30 so-called new diseases have emerged over the last 25 to 30 years. And some old diseases that had been under control are now surging again. One example is the West Nile virus..." (pp. 172-175) Most of the "new diseases" in this sensationalist listing are irrelevant to climate change discussions, as the disease-spread mechanisms are poorly linked to climate or not linked to climate at all. Most of the new diseases listed on p. 174 are associated with human interaction/infrastructure changes, i.e. spread by global transportation, spread in closed artificial environments, spread mainly by direct contact with body fluids, etc. Claims regarding climate change-disease links must be limited to those diseases which have some relation to climate, such as mosquito-borne malaria. However, health experts point out that even for these diseases such claims exaggerate the dependence of disease spread on climate to the exclusion of other factors. Malaria, for example, is affected more by health care practices, degree of development, and degree of past control exercised. In particular, control of malaria has suffered from the opposition to the use of DDT for mosquito control (Roberts et al., 1997). Further, research indicates that estimates of climate-related malaria impact are exaggerated (Rogers and Randolph, 2001) and tend to disregard the body of knowledge about the disease (Reiter et al., 2004).

"Once the sea-based ice shelf was gone, the land-based ice... began to shift and fall into the sea... This is one of the reasons sea levels have been rising worldwide..." (p. 184) Current sea level rise, estimated at 2.8 centimeters per decade, is mostly attributed to thermal expansion of the oceans (Cazenave and Nerem, 2004), with additional contributions from net mass loss from mountain glaciers (IPCC, 2001). Glacial outflow as described is a minor contributor to current sea level change, given that ice accumulation on inland ice caps mostly offsets this.

"Many residents of low-lying Pacific Island nations have already had to evacuate their homes because of rising seas." (p. 187) The evacuations referred to cannot be linked to global sea level rise. Measurements of sea level change at Pacific Islands vary from island to island, with some showing rises and some showing drops. These changes are primarily the result of local geologic subsistence or uplift. The primary issue here is the increase of population living in the lowest locations on these islands, and the increase in more permanent habitations at such locations. The situation is somewhat analogous to the increase in flood-related damage in the United States, which results not from more floods but from more construction in areas known to be vulnerable to floods.

"The Thames River... In recent decades, higher sea levels began to cause more damage... The graph below shows how frequently London has had to use these barriers... The resulting pattern is similar to many others that measure the increasing impact of global warming worldwide." (pp. 188-189) Recent increases in Thames barrier closures reflect changes in the rules for such closures along with increasing closures to keep river water in, i.e. a response to relatively low sea level, not high sea level. The British government has stated that Thames barrier closures should not be considered an indicator for climate change (DEFRA, 2004).

"The East Antarctic ice shelf...had been thought to be still increasing in size... However, two new studies in 2006 showed first that the overall volumes of ice in East Antarctica now appear to be declining..." (p. 190) The one study related to East Antarctic ice volume is based on only three years' observations from the GRACE satellite and actually show no net change over the study period (Velicogna and Wahr, 2006). These results are somewhat model dependent, and other researchers using the same dataset have concluded that East Antarctic ice volume increased (Chen et al., 2006; Ramillien et al., 2006). The broader body of scientific research on this topic, using both measurements and models, shows East Antarctic ice volume has increased in the past few decades (IPCC, 2001; van de Berg et al., 2006).

"In recent years, the melting [in Greenland] has accelerated dangerously." (p. 194) While some recent research has described mechanisms for acceleration of glacier outflow in Greenland (Zwally et al., 2002), measurements of the cumulative mass balance for Greenland show that its contribution to sea level is about 0.1-0.4 millimeters per year, such that "dangerous" is not a useful term. Further, the current conditions in Greenland are not unprecedented; measurements show that temperatures in Greenland in the 1930s were about the same as temperatures today (Chylek et al., 2006; Vinther et al., 2006). In general, observed Arctic warmings are significantly less than predicted, also refuting the GCMs.

"If Greenland melted or broke up and slipped into the sea--or if half of Greenland and half of Antarctica melted or broke up and slipped into the sea, sea levels worldwide would increase by between 18 and 20 feet." (p. 196) The Greenland ice sheet cannot slip into the sea, since it is resting in a bowl-shaped depression produced by its own weight, surrounded by mountains which permit only limited glacier outflow to the sea. Gore's reference to "half of Antarctica" should be to "half of the West Antarctic ice sheet", which is the portion of Antarctica's ice comparable to Greenland in volume and the portion showing any sensitivity to climate change. Only with regard to the West Antarctic ice sheet have any scientists proposed any potential for accelerated outflow into the sea, but even under the most pessimistic scenarios described in the scientific literature this would take hundreds of years. The consensus of the scientific community is for estimates of thousands of years for both Greenland (Greve, 2000; Alley et al., 2005; Lowe et al., 2006) and West Antarctica (Oppenheimer, 1998; Vaughan and Spouge, 2002; Oppenheimer and Alley, 2004).

"This is what would happen to Florida... San Francisco Bay... the Netherlands... Beijing... More than 20 million people would have to be evacuated... In Shanghai and the surrounding area, more than 40 million people would be forced to move... In Calcutta and Bangladesh, 60 million people would be displaced... The site of the World Trade Center would be underwater." (pp. 198-209) The United Nations IPCC predictions for sea level rise over the next 100 years, even though they are based on models and assumptions which exaggerate warming over that period, are only 0.1 to 0.8 meters (median estimate 0.48 meters) (IPCC, 2001). As mentioned above, the consensus of the scientific community is that sea level rise of 6 meters/20 feet as described by Gore, even if it does happen, would take thousands of years. A minority view in the scientific community suggests scenarios in which this could occur in 250-400 years. Such timescales, which are longer than the history of the country that built the World Trade Center, would certainly not require any "evacuations". The depicted images also use a subtle technique to exaggerate the appearance of sea level rise: the post-rise images are from a more distant perspective, causing the remaining land to be even smaller in appearance.

"The graph below shows the steady increase in major wildfires in North and South America..." (p. 229) Such wildfires are less a reflection of any climate change and more a reflection of increases in population, poor historical management practices by the U.S. government of woodlands and grasslands, and increased use of fires for clearing forest in Latin America.

"Moreover, since science thrives on uncertainty and politics is paralyzed by it, scientists have a difficult time sounding the alarm bells for politicians, because even when their findings make it clear that we're in grave danger, their first impulse is to replicate the experiment to see if they get the same result." (p. 260) This statement mischaracterizes science. Many scientists are quite willing to "sound alarm bells", some whether or not the evidence justifies such concern. More generally, scientists are engaged in evidence-based testing of descriptions of the world we live in, and are disinclined to involve themselves in political applications of their work. Nonetheless, scientists are human beings and tend to be quite ready to call attention to hazards they discover, as is evident from a cursory inspection of the history of science in the public arena. It is unfair to suggest that scientists will tend not to call for attention to clear evidence of danger.

"For example, the so-called global warming skeptics cite one article more than any other in arguing that global warming is just a myth: a statement of concern during the 1970s that the world might be in danger of entering a new ice age..." (pp. 260-261) Gore is incorrect to claim that such references to past concerns about global cooling stem from a single article, or only from non-peer reviewed sources. Kukla et al., 1972, discussed the possibility of an ice age, and similarly the review by Kukla and Matthews, 1972, of a scientific conference titled "The Present Interglacial, How and When Will it End?" stated "several investigators showed ... if nature were allowed to run its course unaltered by man, events similar to those which ended the last interglacial should be expected to occur perhaps as soon as the next few centuries." To be clear, the scientific community was only beginning to evaluate long-term climate change, whether from natural or man-made causes, but such views were more widely disseminated (out of context) by the press and by environmentalists as well. The Newsweek article cited by Gore (Gwynne, 1975) is only one such example (it was cited by Rush Limbaugh in 2002, perhaps Gore's source of information); other such reports included an article in National Geographic (Mathews, 1976) and a vague statement by prominent environmentalist (Ehrlich, 1968). The point raised by "skeptics" here is not so much a reference to the vetted claims of the scientific community, but to the tendency of the popular media in general and some environmentalists in particular to take scientific claims out of context, to single out the worst case scenario from a range of possibilities, and to present this scenario as fact, as Gore does.

"There is a misconception that the scientific community is in a state of disagreement about whether global warming is real, whether human beings are the principal cause, and whether its consequences are so dangerous as to warrant immediate action. In fact, there is virtually no serious disagreement remaining on any of these central points..." (p. 261) This statement is false. A significant number of scientists reject the first two points, or would qualify any agreement. The third claim, that "consequences are so dangerous as to warrant immediate action," is likely rejected by a majority of the scientific community, particularly if the context is Gore's specific claims. To declare the debate over, as Gore does, is a rejection of scientific methodology. The survey by Bray described below (Bray, 2005) demonstrates a very mixed set of opinions in the scientific community.

"Dr. Naomi Oreskes, published in Science magazine a massive study of every peer-reviewed science journal article on global warming from the previous 10 years... Percentage of articles in doubt as to the cause of global warming: 0%" (p. 262) The cited "study" by Oreskes, a historian, comprised a review of only 928 abstracts identified by a search engine using the keywords "global climate change" (not "climate change" as her article originally claimed, as this yields 12,000 abstracts). Her results were presented in an opinion editorial in Science (Oreskes, 2004), days before the 10th Conference on Parties of the United Nations Framework Convention on Climate Change. The scientific method for validating research is to replicate results, and Oreskes' work fails this test. Review of the Oreskes' set shows at least two that explicitly reject the 'consensus position' within the abstract, even apart from the remainder of the paper. Peiser conducted a similar study of abstracts identified in a search for "global climate change": of 1,117 abstracts, he found that only 1% "explicitly endorse the 'consensus view'," 29% "implicitly accept the 'consensus view'," 3% "reject or doubt the view that human activities are the main drivers of 'the observed warming over the last 50 years'," and most take no position or are unrelated to the global warming hypothesis (Peiser, 2005). A 2003 survey by Bray (Bray, 2005) of 530 climate scientists asking "To what extent do you agree or disagree that climate change is mostly the result of anthropogenic causes?" yielded very mixed results: on a scale of one to seven, 56% agreed strongly to slightly (including 9% strongly) and 29% disagreed strongly to slightly (including 10% strongly). Letters on both of these studies, incidentally, were rejected by Science. Such superficial studies as that by Oreskes are biased by the obligatory acknowledgement of "climate change" that researchers must make in order to get research published, particularly in view of editorial bias such as that exhibited by Science.

"The misconception that there is serious disagreement among scientists about global warming is actually an illusion that has been deliberately fostered by a relatively small but extremely well-funded cadre of special interests, including Exxon Mobil and a few other oil, coal, and utilities companies." (p. 263) This is a slanderous misrepresentation of the nature of scientific debate on the issue of climate change. Many scientists, based on conclusions drawn from their examination of the evidence, hold sincere disagreements with some or all aspects of the global warming hypothesis as described by Gore. Some are falsely accused of financial ties to the energy industry, despite the fact that they may have difficulty obtaining funding from traditional sources with a pro-global warming bias. Whatever expenditures undertaken by the energy industry on public relations related to global warming, similar large expenditures have been undertaken by the environmentalist lobby. (And only one of these two lobbies has produced a major motion picture.)

"In 1984 a dramatic hole in the ozone layer was discovered above Antarctica, just as the scientists forecasted." (p. 295) The discovery of the ozone "hole", a seasonal partial depletion of ozone over Antarctica, was not consistent with the forecasts. The "hole" represented depletion phenomena specific to the the climate conditions and presence of cloud particles over Antarctica, a phenomena not anticipated.

"Misconception 1 'Scientists disagree...'

"In fact... scientists overwhelmingly agree..." (p. 308) The issue is not whether humans perturb the climate system at all, but whether they are the dominant driver for dangerous global temperature increases as Gore claims. As previously discussed, Gore is incorrect to claim of a strong scientific consensus on this point.

"Misconception 2 'Lots of things can impact climate--so there's no reason we should single out CO 2 to worry about.'

"We have become more powerful than any force of nature." (p. 309) The real issue is whether the specific actions advocated by Gore--the Kyoto protocol, for one--will have a meaningful impact when considered against natural influences, known and unknown.

"Misconception 3 'Climate naturally varies over time, so any change we're seeing now is just part of a natural cycle.'

"But these changes all took place with natural variations in carbon dioxide levels that were smaller than the ones we are now causing... we are outside the realm of natural climate variation. More CO 2 in the atmosphere means warming temperatures" (p. 312) Derived CO 2 data predating the ice core data cited by Gore show CO 2 concentrations several times greater than modern concentrations.

"Misconception 4 'The hole in the ozone layer causes global warming'

(p. 313) The ozone layer has ozone concentrations of about 6 parts per million--ten times higher than at the Earth's surface, but still a very minor constituent. Ozone absorbs only a narrow energy range of solar radiation; higher energy radiation is absorbed by the thin atmosphere at much higher altitudes, for example, and most radiation is visible or infrared radiation which can reach the surface. The ozone "hole" is a seasonal region where concentrations are noticeably lower, say 2-4 parts per million, limited to the polar regions. While more ultraviolet radiation reaches the surface in the polar areas when the hole is present than when it is not, the amount of radiation is still significantly lower than that reaching the surface near the equator. Despite the modeled effect of stratospheric cooling on ozone depletion, the ozone layer is currently recovering faster than some predictions.

"Misconception 5 'There is nothing we can do about climate change. It's already too late.'

(p. 315) Gore urges various specific actions, including regulatory actions, but does not discuss the negative consequences of these actions or the magnitude of their impact on the supposed problem.

"Misconception 7 'Global warming is a good thing...'

"Melting ice sheets are causing sea levels to rise, and if big ice sheets melt...millions of people will become refugees...Other predicted impacts...drought...flooding...new diseases." (p. 317) Gore's predicted consequences are exaggerated, as previously discussed, beyond even the predictions based on models which arguably overestimate future climate change. Positive effects of climate change are generally ignored. Both globally and in the U.S., mortality from extreme weather events continues to steadily decline and is a minor contributor to overall mortality (Goklany, 2006).

"Misconception 8 'The warming scientists are recording is just the effect of cities trapping heat...'

"People who want to deny global warming because it's easier than dealing with it try to argue that what scientists are really observing is just the 'urban heat island' effect... This is simply wrong. Temperature measurements are generally taken in parks, which are actually cool areas within the urban heat islands... Most scientific research shows that 'urban heat islands' have a negligible effect..." (p. 318) Scientists who point out measurement bias due to the urban heat island effect are doing so because the evidence demands it, not from denial. Temperature measurements in urban "parks" are still subject to bias from the effect, since air throughout the urban area is heated by the effect. Scientific research has produced varying estimates of the amount of bias. Insufficient work has been done to examine bias in the principal surface-based temperature series cited in support of global warming.

"Misconception 9 'Global warming is the result of a meteor that crashed in Siberia in the early 20th century'

(p. 320) This spurious claim by Shaidurov, 2005, is not particularly relevant to the debate. Gore cites the effect of water vapor, the effect discussed by Shaidurov, but the larger body of scientific research on such asteroid/comet impacts cites the effects of dust, sulfur dioxide, and nitric oxides as more important to climate. These effects could be long-term for impacts larger than the 1908 Tunguska impact.