Here is a summary of what the science says on each skeptic argument. You can also view the arguments sorted by taxonomy.
Skeptic Argument vs What the Science Says
1 "It's the sun" In the last 35 years of global warming, the sun has shown a slight cooling trend. Sun and climate have been going in opposite directions.
2 "Climate's changed before" Natural climate change in the past proves that climate is sensitive to an energy imbalance. If the planet accumulates heat, global temperatures will go up. Currently, CO2 is imposing an energy imbalance due to the enhanced greenhouse effect. Past climate change actually provides evidence for our climate's sensitivity to CO2.
3 "There is no consensus" That humans are causing global warming is the position of the Academies of Science from 19 countries plus many scientific organisations that study climate science. More specifically, 97% of climate scientists actively publishing climate papers endorse the consensus position.
4 "It's cooling" Empirical measurements of the Earth's heat content show the planet is still accumulating heat and global warming is still happening. Surface temperatures can show short term cooling when heat is exchanged between the atmosphere and the ocean, which has a much greater heat capacity than the air.
5 "Models are unreliable" While there are uncertainties with climate models, they successfully reproduce the past and have made predictions that have been subsequently confirmed by observations.
6 "Temp record is unreliable" Numerous studies into the effect of urban heat island effect and microsite influences find they have negligible effect on long term trends, particularly when averaged over large regions.
7 "It hasn't warmed since 1998" The planet has continued to accumulate heat since 1998 - global warming is still happening. Nevertheless, surface temperatures show much internal variability due to heat exchange between the ocean and atmosphere. 1998 was an unusually hot year due to a strong El Nino.
8 "Ice age predicted in the 70s" 1970s ice age predictions were predominantly media based. The majority of peer reviewed research at the time predicted warming due to increasing CO2.
9 "We're heading into an ice age" The warming effect from CO2 increases greatly outstrips the influence from orbital changes or variations in solar activity even if solar levels were to drop to Maunder Minimum levels.
10 "Antarctica is gaining ice" While the interior of East Antarctica is gaining land ice, overall Antarctica is losing land ice at an accelerating rate. Antarctic sea ice is growing despite a strongly warming Southern Ocean.
11 "CO2 lags temperature" When the Earth comes out of an ice age, the warming is not initiated by CO2 but by changes in the Earth's orbit. The warming causes the oceans to give up CO2. The CO2 amplifies the warming and mixes through the atmosphere, spreading warming throughout the planet. So CO2 causes warming AND rising temperature causes CO2 rise.
12 "Global warming is good" The negative impacts of global warming on agriculture, health, economy and environment far outweigh any positives.
13 "Al Gore got it wrong" While there are minor errors in An Inconvenient Truth, the main truths presented - evidence to show mankind is causing global warming and its various impacts is consistent with peer reviewed science.
14 "It's freaking cold!" Since the mid 1970s, global temperatures have been warming at around 0.2 degrees Celsius per decade. However, weather imposes its own dramatic ups and downs over the long term trend. We expect to see record cold temperatures even during global warming. Nevertheless over the last decade, daily record high temperatures occurred twice as often as record lows. This tendency towards hotter days is expected to increase as global warming continues into the 21st Century.
15 "Hurricanes aren't linked to global warming" It is unclear whether global warming is increasing hurricane frequency but there is increasing evidence that warming increases hurricane intensity.
16 "Mars is warming" Martian climate is primarily driven by dust and albedo and there is little empirical evidence that Mars is showing long term warming.
17 "It's cosmic rays" While the link between cosmic rays and cloud cover is yet to be confirmed, more importantly, there has been no correlation between cosmic rays and global temperatures over the last 30 years of global warming.
18 "1934 - hottest year on record" 1934 is the hottest year on record in the USA which only comprises 2% of the globe. According to NASA temperature records, the hottest year on record globally is 2005.
19 "It's just a natural cycle" The 1500 year cycles, known as Dansgaard-Oeschger events, are localized to the northern hemisphere and accompanied with cooling in the southern hemisphere. In contrast, current global warming is occuring in both hemispheres and particularly throughout the world's oceans, indicating a significant energy imbalance.
20 "Sea levels aren't rising (much)" Sea levels are measured by a variety of methods that show close agreement - sediment cores, tidal gauges, satellite measurements. What they find is sea level rise has been steadily accelerating over the past century.
21 "It's Urban Heat Island effect" While urban areas are undoubtedly warmer than surrounding rural areas, this has had little to no impact on warming trends.
22 "Hockey stick is broken" Since the hockey stick paper in 1998, there have been a number of proxy studies analysing a variety of different sources including corals, stalagmites, tree rings, boreholes and ice cores. They all confirm the original hockey stick conclusion: the 20th century is the warmest in the last 1000 years and that warming was most dramatic after 1920.
23 "Arctic icemelt is a natural cycle" Arctic sea ice has been retreating over the past 30 years. The rate of retreat is accelerating and in fact is exceeding most models' forecasts.
24 "Other planets are warming" There are three fundamental flaws in the 'other planets are warming' argument. Not all planets in the solar system are warming. The sun has shown no long term trend since 1950 and in fact has shown a slight cooling trend in recent decades. There are explanations for why other planets are warming.
25 "Water vapor is the most powerful greenhouse gas" Water vapour is the most dominant greenhouse gas. Water vapour is also the dominant positive feedback in our climate system and amplifies any warming caused by changes in atmospheric CO2. This positive feedback is why climate is so sensitive to CO2 warming.
26 "Greenland was green" The Greenland ice sheet has existed for at least 400,000 years. There may have been regions of Greenland that were 'greener' than today but this was not a global phenomenon.
27 "Human CO2 is a tiny % of CO2 emissions" The CO2 that nature emits (from the ocean and vegetation) is balanced by natural absorptions (again by the ocean and vegetation). Therefore human emissions upset the natural balance, rising CO2 to levels not seen in at least 800,000 years. In fact, human emit 26 gigatonnes of CO2 per year while CO2 in the atmosphere is rising by only 15 gigatonnes per year - much of human CO2 emissions is being absorbed by natural sinks.
28 "We're coming out of an ice age" The main driver of the warming from the Little Ice Age to 1940 was the warming sun with a small contribution from volcanic activity. However, solar activity leveled off after 1940 and the net influence from sun and volcano since 1940 has been slight cooling. Greenhouse gases have been the main contributor of warming since 1970.
29 "Oceans are cooling" Early estimates of ocean heat from the Argo showed a cooling bias due to pressure sensor issues. Recent estimates of ocean heat that take this bias into account show continued warming of the upper ocean. This is confirmed by independent estimates of ocean heat as well as more comprehensive measurements of ocean heat down to 2000 metres deep.
30 "It cooled mid-century" There are a number of forcings which affect climate (eg - stratospheric aerosols, solar variations). When all forcings are combined, they show good correlation to global temperature throughout the 20th century including the mid-century cooling period. However, for the last 35 years, the dominant forcing has been CO2.
31 "It warmed before 1940 when CO2 was low" Early 20th century warming was in large part due to rising solar activity and relatively quiet volcanic activity. However, both factors have played little to no part in the warming since 1975. Solar activity has been steady since the 50's. Volcanoes have been relatively frequent and if anything, have exerted a cooling effect.
32 "Mt. Kilimanjaro's ice loss is due to land use" Mount Kilimanjaro's shrinking glacier is complicated and not due to just global warming. However, this does not mean the Earth is not warming. There is ample evidence that Earth's average temperature has increased in the past 100 years and the decline of mid- and high-latitude glaciers is a major piece of evidence.
33 "Climate sensitivity is low" Climate sensitivity can be calculated empirically by comparing past temperature change to natural forcings at the time. Various periods of Earth's past have been examined in this manner and find broad agreement of a climate sensitivity of around 3°C.
34 "There's no empirical evidence" Direct observations find that CO2 is rising sharply due to human activity. Satellite and surface measurements find less energy is escaping to space at CO2 absorption wavelengths. Ocean and surface temperature measurements find the planet continues to accumulate heat. This gives a line of empirical evidence that human CO2 emissions are causing global warming.
35 "Polar bear numbers are increasing" While there is some uncertainty on current polar bear population trends, one thing is certain. No sea ice means no seals which means no polar bears. With Arctic sea ice retreating at an accelerating rate, the polar bear is at grave risk of extinction
36 "Glaciers are growing" While there are isolated cases of growing glaciers, the overwhelming trend in glaciers worldwide is retreat. In fact, the global melt rate has been accelerating since the mid-1970s.
37 "Extreme weather isn't caused by global warming" There is growing empirical evidence that warming temperatures cause more intense hurricanes, heavier rainfalls and flooding, increased conditions for wildfires and dangerous heat waves.
38 "Satellites show no warming in the troposphere" Satellite measurements match model results apart from in the tropics. There is uncertainty with the tropic data due to how various teams correct for satellite drift. The U.S. Climate Change Science Program conclude the discrepancy is most likely due to data errors.
39 "IPCC does not represent a scientific consensus" The IPCC lead authors are experts in their field, instructed to fairly represent the full range of the up-to-date, peer-reviewed literature. Consequently, the IPCC reports tend to be cautious in their conclusions. Comparisons to the most recent data consistently finds that climate change is occurring more rapidly and intensely than indicated by IPCC predictions.
40 "CO2 effect is weak" An enhanced greenhouse effect from CO2 has been confirmed by multiple lines of empirical evidence. Satellite measurements of infrared spectra over the past 40 years observe less energy escaping to space at the wavelengths associated with CO2. Surface measurements find more downward infrared radiation warming the planet's surface. This provides a direct, empirical causal link between CO2 and global warming.
41 "CO2 is not a pollutant" While there are direct ways in which CO2 is a pollutant (acidification of the ocean), it's primary impact is its greenhouse warming effect. While the greenhouse effect is a natural occurance, too much warming has severe negative impacts on agriculture, health and environment.
42 "There's no correlation between CO2 and temperature" Even during a period of long term warming, there are short periods of cooling due to climate variability. Short term cooling over the last few years is largely due to a strong La Nina phase in the Pacific Ocean and a prolonged solar minimum.
43 "CO2 has been higher in the past" When CO2 levels were higher in the past, solar levels were also lower. The combined effect of sun and CO2 matches well with climate.
44 "Scientists can't even predict weather" Weather is chaotic, making prediction difficult. However, climate takes a long term view, averaging weather out over time. This removes the chaotic element, enabling climate models to successfully predict future climate change.
45 "Greenland is gaining ice" While the Greenland interior is in mass balance, the coastlines are losing ice. Overall Greenland is losing ice mass at an accelerating rate. From 2002 to 2009, the rate of ice mass loss doubled.
46 "Neptune is warming" Neptune's orbit is 164 years so observations (1950 to present day) span less than a third of a Neptunian year. Climate modelling of Neptune suggests its brightening is a seasonal response. Eg - Neptune's southern hemisphere is heading into summer.
47 "Jupiter is warming" Jupiter's climate change is due to shifts in internal turbulence fueled from an internal heat source - the planet radiates twice as much energy as it receives from the sun.
48 "CRU emails suggest climate conspiracy" While some of the private correspondance is not commendable, an informed examination of their "suggestive" emails reveal technical discussions using techniques well known in the peer reviewed literature. Focusing on a few suggestive emails merely serves to distract from the wealth of empirical evidence for man-made global warming.
49 "There's no tropospheric hot spot" Satellite measurements match model results apart from in the tropics. There is uncertainty with the tropic data due to how various teams correct for satellite drift. The U.S. Climate Change Science Program conclude the discrepancy is most likely due to data errors.
50 "Pluto is warming" Pluto's climate change over the last 14 years is likely a seasonal event. Pluto experiences drastic season changes due to an elliptical orbit (that takes 250 Earth years). Any Plutonian warming cannot be caused by solar variations as the sun has showed little to no long term trend over the past 50 years and sunlight at Pluto is 900 times weaker than it is at the Earth.
51 "It's Pacific Decadal Oscillation" PDO as an oscillation between positive and negative values shows no long term trend, while temperature shows a long term warming trend. When the PDO last switched to a cool phase, global temperatures were about 0.4C cooler than currently. The long term warming trend indicates the total energy in the Earth's climate system is increasing due to an energy imbalance.
52 "Greenland ice sheet is stable" Satellite gravity measurements show Greenland is losing ice mass at an accelerated rate, increasing its contribution to rising sea levels.
53 "It's the ocean" Oceans are warming across the globe. In fact, globally oceans are accumulating energy at a rate of 4 x 1021 Joules per year - equivalent to 127,000 nuclear plants (which have an average output of 1 gigawatt) pouring their energy directly into the world's oceans. This tells us the planet is in energy imbalance - more energy is coming in than radiating back out to space.
54 "The CO2 effect is saturated" If the CO2 effect was saturated, adding more CO2 should add no additional greenhouse effect. However, satellite and surface measurements observe an enhanced greenhouse effect at the wavelengths that CO2 absorb energy. This is empirical proof that the CO2 effect is not saturated.
55 "Animals and plants can adapt to global warming" A large number of ancient mass extinction events have been strongly linked to global climate change. Because current climate change is so rapid, the way species typically adapt (eg - migration) is, in most cases, simply not be possible. Global change is simply too pervasive and occurring too rapidly.
56 "Volcanoes emit more CO2 than humans" Volcanoes emit around 0.3 billion tonnes of CO2 per year. This is about 1% of human CO2 emissions which is around 29 billion tonnes per year.
57 "Less than half of published scientists endorse global warming" Schulte's paper makes much of the fact that 48% of the papers they surveyed are neutral papers, refusing to either accept or reject anthropogenic global warming. The fact that so many studies on climate change don't bother to endorse the consensus position is significant because scientists have largely moved from what's causing global warming onto discussing details of the problem (eg - how fast, how soon, impacts, etc).
58 "CO2 measurements are suspect" CO2 levels are measured by hundreds of stations scattered across 66 countries which all report the same rising trend.
59 "It's aerosols" The global dimming trend reversed around 1990 - 15 years after the global warming trend began in the mid 1970's.
60 "It's El Niño" The El Nino Southern Oscillation shows close correlation to global temperatures over the short term. However, it is unable to explain the long term warming trend over the past few decades.
61 "It's a climate regime shift" A full reading of Tsonis and Swanson's research shows that internal variability from climate shifts merely cause temporary slow downs or speeding up of the long-term warming trend. When the internal variability is removed from the temperature record, what we find is nearly monotonic, accelerating warming throughout the 20th Century.
62 "Humans are too insignificant to affect global climate" Atmospheric CO2 levels are rising by 15 gigatonnes per year. Humans are emitting 26 gigatonnes of CO2 into the atmosphere. Humans are dramatically altering the composition of our climate.
63 "It's land use" Correlations between warming and economic activity are most likely spurious. They don't take into account local forcing agents such as tropospheric ozone or black carbon. Correlations are likely over-estimated since grid boxes in both economic and climate data are not independent. Lastly, there is significant independent evidence for warming in the oceans, snow cover and sea ice extent changes.
64 "It's microsite influences" Data analysis comparing the temperature trends from poorly sited weather stations to well sited stations find the poor sites actually show a cooling bias compared to good sites. The cooling bias is caused by a change to the Maximum/Minimum Temperature Systems which is found more often at poor sites. When the change of instrument biases are taken into account, there is very little difference between the trends from poor and well sited weather stations.
65 "It's methane" While methane is a more potent greenhouse gas than CO2, there is over 200 times more CO2 in the atmosphere. Hence the amount of warming methane contributes is 28% of the warming CO2 contributes.
66 "Medieval Warm Period was warmer" While the Medieval Warm Period saw unusually warm temperatures in some regions, globally the planet was cooler than current conditions.
67 "Solar Cycle Length proves its the sun" The claim that solar cycle length proves the sun is driving global warming is based on a single study published in 1991. Subsequent research, including a paper by a co-author of the original 1991 paper, finds the opposite conclusion. Solar cycle length as a proxy for solar activity tells us the sun has had very little contribution to global warming since 1975.
68 "Naomi Oreskes' study on consensus was flawed" An examination of the papers that critics claim refute the consensus are found to actually endorse the consensus or are review papers (eg - they don't offer any new research but merely review other papers). This led the original critic Benny Peisner to retract his criticism of Oreskes' study.
69 "Water levels correlate with sunspots" There seems to be evidence for a link between solar activity and water levels. However, more direct comparisons between solar activity and global temperature finds that as the sun grew hotter or cooler, Earth's climate followed it with a 10 year lag - presumably due to the dampening effect of the ocean. Also found was that the correlation between solar activity and global temperatures ended around 1975, hence recent warming must have some other cause than solar variations.
70 "Solar cycles cause global warming" A full reading of Tung 2008 finds a distinct 11 year solar signal in the global temperature record. However, this 11 year cycle is superimposed over the long term global warming trend. In fact, the authors go on to estimate climate sensitivity from their findings, calculate a value between 2.3 to 4.1°C. This confirms the IPCC estimate of climate sensitivity.
71 "The sun is getting hotter" Various independent measurements of solar activity all confirm the sun has shown a slight cooling trend since 1978.
72 "IPCC were wrong about Himalayan glaciers" The IPCC error on the 2035 prediction was unfortunate and it's important that such mistakes are avoided in future publications through more rigorous review. But the central message of the IPCC AR4, is confirmed by the peer reviewed literature. The Himalayan glaciers are of vital importance, providing drinking water to half a billion people. Satellites and on-site measurements are observing that Himalayan glaciers are disappearing at an accelerating rate.
73 "It's albedo" The long term trend from albedo is that of cooling. In recent years, satellite measurements of albedo show little to no trend.
74 "Water vapor in the stratosphere stopped global warming" The effect from stratospheric water vapor contributes a fraction of the temperature change imposed from man-made greenhouse gases. Also, it's not yet clear whether changes in stratospheric water vapor are caused by a climate feedback or internal variability (eg - linked to El Nino Southern Oscillation). However, the long term warming trend seems to speak against the possibility of a negative feedback.
75 "Phil Jones says no global warming since 1995" When you read Phil Jones' actual words, you see he's saying there is a warming trend but it's not statistically significant. He's not talking about whether warming is actually happening. He's discussing our ability to detect that warming trend in a noisy signal over a short period.
76 "CO2 is not the only driver of climate" While there are many drivers of climate, CO2 is the most dominant radiative forcing and is increasing faster than any other forcing.
77 "Sea level rise predictions are exaggerated" Observed sea levels are actually tracking at the upper range of the IPCC projections. When accelerating ice loss from Greenland and Antarctica are factored into sea level projections, the estimated sea level rise by 2100 is between 75cm to 2 metres.
78 "December 2009 saw record cold spells" The cold snap is due to a strong phase of the Arctic Oscillation. This is causing cool temperatures at mid-latitudes (eg - Eurasia and North America) and warming in polar regions (Greenland and Arctic Ocean). The warm and cool regions roughly balance each other out with little impact on global temperature.
79 "It's not happening" There are many lines of independent empirical evidence for global warming, from accelerated ice loss from the Arctic to Antarctica to the inexorable poleward migration of plant and animal species across the globe.
80 "Trenberth can't account for the lack of warming" Trenberth's views are clarified in the paper "An imperative for climate change planning: tracking Earth's global energy". We know the planet is continually heating due to increasing carbon dioxide but that surface temperature sometimes have short term cooling periods. This is due to internal variability and Trenberth was lamenting that our observation systems can't comprehensively track all the energy flow through the climate system.
81 "It's CFCs" Models and direct observations find that CFCs only contribute a fraction of the warming supplied by other greenhouse gases.
82 "CO2 is not increasing" Currently, humans are emitting around 29 billion tonnes of carbon dioxide into the atmosphere per year. Around 43% remains in the atmosphere - this is called the 'airborne fraction'. The rest is absorbed by vegetation and the oceans. While there are questions over how much the airborne fraction is increasing, it is clear that the total amount of CO2 in the atmosphere is increasing dramatically. Current CO2 levels are the highest in 15 million years.
83 "Climate is chaotic and cannot be predicted" Weather is chaotic because air is light, it has low friction and viscosity, it expands strongly when in contact with hot surfaces and it conducts heat poorly. Therefore weather is never in equilibrium and the wind always blows. The climate is mostly explained by equilibrium radiation physics, which puts the brakes on variations in global temperatures. Effects from weather, the Sun, volcanoes etc. currently only causes a small amount of chaotic behavior compared to the deterministic, predictable greenhouse gas forcing for the next 100 years"
84 "It's ozone" Multiple satellite measurements and ground-based observations have determined the ozone layer has stopped declining since 1995 while temperature trends continue upwards.
85 "It's satellite microwave transmissions" A generous estimate of the energy generated by satellites is around 1 million times too small to cause global warming.
86 "Global temperatures dropped sharply in 2007" 2007's dramatic cooling is driven by strong La Nina conditions which historically has caused similar drops in global temperature. It is also exacerbated by unusually low solar activity.
87 "Ice isn't melting" Ice mass loss is occuring at an accelerated rate in Greenland, Antarctica and globally from inland glaciers. Arctic sea ice is also falling at an accelerated rate. The exception to this ice loss is Antarctic sea ice which has been growing despite the warming Southern Ocean. This is due to local factors unique to the area.
88 "Tree-rings diverge from temperature after 1960" The divergence problem is a physical phenomenon - tree growth has slowed or declined in the last few decades, mostly in high northern latitudes. The divergence problem is unprecedented, unique to the last few decades, indicating its cause may be anthropogenic. The cause is likely to be a combination of local and global factors such as warming-induced drought and global dimming. Tree-ring proxy reconstructions are reliable before 1960, tracking closely with the instrumental record and other independent proxies.
89 "A drop in volcanic activity caused warming" A drop of volcanic activity in the early 20th century may have had a warming effect. However, volcanoes have had no warming effect in the last 40 years of global warming. If anything, they've imposed a slight cooling effect.
90 "IPCC were wrong about Amazon rainforests" The IPCC statement on Amazon rain forests is correct. The error was incorrect citation, failing to mention the peer-reviewed papers where the data came from. The peer-reviewed science prior to the 2007 IPCC report found that up to 40% of the Brazilian forest is vulnerable to drought. Subsequent field research has confirmed this assessment.
91 "We didn't have global warming during the Industrial Revolution" Global CO2 emissions during the Industrial Revolution were a fraction of the CO2 we are currently emitting now.
© Copyright 2010 John Cook
"The era of procrastination, of half-measures, of soothing and baffling expedients, of delays, is coming to a close. In its place, we are entering a period of consequences." - Winston Churchill, The Gathering Storm