Myth: Global temperature data is inaccurate and/or too sparse to be able to establish a meaningful average temperature over the entire planet. Therefore, any claims of global warming are unfounded.

Fact: NASA has collected and acquired massive amounts of temperature data from various sources, including land-based, meteorological stations, sea surface temperature measurements from ships, and measurements taken from satellites. This data encompasses the entire planet, and is run through a method that is explained on NASA’s website, which results in a statistically significant global average temperature.

The first thing to note here is that there are not many who still make this argument, at least not among climate scientists. The IPCC, in its latest report, actually states that global warming is "unequivocal". Even skeptical scientists, such as Richard Lindzen and John Christy, will admit that we are indeed warming. Their only argument is against the cause of the warming, which is where most skeptics’ arguments have shifted. This should be a clue that there is no argument against warming, however some continue to insist that the planet is not warming.

It seems that the major impetus for the recent resurgence of this argument is a website, www.surfacestations.org, which attempts to question data collection equipment. This is actually a very nifty little trick. This site, launched in June of this year, has established a fairly large following. These devoted followers are commissioned to go out and take pictures of the US meteorological stations. Armed with these pictures, surfacestations.org scrutinizes them, looking for indications that they might be susceptible to a warm bias. This has filled many contrarians’ minds with the idea that the entire temperature data set is flawed, which is ultimately the point. Not surprisingly, there is no mention on the site of existing methods for removing biases from temperature measurements. First, the thermometers are now protected by Stevenson screens (emphasis added):

A Stevenson screen or Instrument shelter is a meterological screen to shield instruments against precipitation and direct heat radiation from outside sources, while still allowing air to circulate freely around them. It forms part of a standard weather station. The screen creates, as near possible, a uniform environment in relation to the air outside. - Wikipedia

Second, NASA’s GISTEMP compares urban stations to rural stations, in an attempt to further remove any potential biases:

We modify the GHCN/USHCN/SCAR data in two stages to get to the station data on which all our tables, graphs, and maps are based: in stage 1 we try to combine at each location the time records of the various sources; in stage 2 we adjust the non-rural stations in such a way that their longterm trend of annual means is as close as possible to that of the mean of the neighboring rural stations. Non-rural stations that cannot be adjusted are dropped. - NASA GISS

Another common argument is that we simply don’t have enough temperature data to be able to compute a global average temperature. This argument usually comes with a map of the world, showing the locations of existing surface meteorological stations. Obviously, on such a map, there are very large areas that are not covered (oceans, deserts, mountain ranges, etc.). However, NASA states that they have sufficient data, dating as far back as 1880:

The NASA GISS Surface Temperature Analysis (GISTEMP) provides a measure of the changing global surface temperature with monthly resolution for the period since 1880, when a reasonably global distribution of meteorological stations was established…We limit our analysis to the period since 1880 because of the poor spatial coverage of stations prior to that time and the reduced possibility of checking records against those of nearby neighbors. - NASA GISS

A major problem for both of these arguments is that they only focus on land-based temperature readings. This is because there is a preponderance of evidence in favor of global warming outside of those temperature measurements, which are completely ignored by these objections. In order to truly call global warming into question, one would also have to prove satellite data, borehole analysis, glacial melt, sea ice melt, sea level rise, proxy data, and rising ocean temperature to be flawed.

UPDATE: A new instance of this questioning of temperature data occurred when NASA made some small corrections to data at the turn of the millenium, thanks to a tip from Stephen McIntyre from Climate Audit. This was a good tip, and NASA’s data is now more accurate for it, but some skeptics have tried to misrepresent it as proof that NASA’s temperature data is faulty. Recently, Fox News provided an excellent example of this misrepresentation:

On Special Report, Jim Angle reported that NASA was forced "to admit it was wrong when it said that 1998 was the hottest year on record" and that NASA "now says 1934 was the hottest year, followed by 1998, then 1921." But Angle did not inform viewers that NASA’s revision affected annual temperature rankings for the United States only; it had no effect on the annual global temperature rankings. - Media Matters

As the fine folks at Media Matters pointed out, while the change did result in 1934 topping 1998 as the hottest year in the US, it had literally no effect on global temperature trends, and actually even a very miniscule effect on US trends. Looking at the global temperature graph below, one can see that the global warming trend is still very much intact:

Myth: According to Occam’s razor, the theory that our current climate change is part of a natural cycle is correct.

Fact: Occam’s razor does not apply for two reasons: the theory of natural variation is no simpler than that of anthropogenic global warming, and most importantly, natural variation is not a valid theory, which is a prerequisite for the use of Occam’s razor.

Many times, when engaged in a debate with a global warming skeptic, I will encounter an invocation of Occam’s Razor. According to this maxim, all other things being equal, the simpler of two competing theories is most likely the correct one:

Occam’s razor (sometimes spelled Ockham’s razor) is a principle attributed to the 14th-century English logician and Franciscan friar William of Ockham. The principle states that the explanation of any phenomenon should make as few assumptions as possible, eliminating those that make no difference in the observable predictions of the explanatory hypothesis or theory…This is often paraphrased as "All things being equal, the simplest solution tends to be the best one." In other words, when multiple competing theories are equal in other respects, the principle recommends selecting the theory that introduces the fewest assumptions and postulates the fewest hypothetical entities. - Wikipedia

When global warming skeptics invoke Occam’s Razor, they generally mean that the idea that climate change is caused primarily, if not solely, by natural factors is much simpler than the idea that human activity has caused such changes. Therefore, according to Occam’s Razor, the natural variations idea is the correct theory. As I stated above, this is an incorrect use of the maxim.

First, the natural variation theory is actually no simpler than anthropogenic global warming. The idea that current climate change is a natural phenomenon seems to be simpler to many skeptics because they generally don’t exercise the same amount of skepticism towards theories that agree with their ideologies, which results in a lack of any true examination of this idea. The argument I hear most often in favor of this idea is that our climate has always changed in the past, and humans weren’t around back then to influence it, so it must follow that our current climate is also due to natural factors. However, that is not a valid argument. Just because something caused changes in the past, it doesn’t mean that when a new variable is added, the new variability is not caused primarily by the new variable. So, in order to prove that climate change is indeed caused by natural factors, one must actually specify which natural factors are causing the change, and provide a statistically valid, quantified comparison of both natural and man-made causes, which shows that the natural factors outweigh human greenhouse gas emissions. Therefore, if one put the necessary effort into proving the natural variation theory, it would no longer be considered any simpler than anthropogenic global warming.

Second, Occam’s razor requires that "all things [be] equal". In other words, the prerequisite for the maxim is that both competing theories be equally verifiable. This is a major problem for skeptics who would like to use it because there is no valid theory which explains our current warming as being due to natural causes. Many of the largest changes in our planet’s temperature in the past were due to changes in the earth’s orbit and tilt, called Milankovitch cycles. This is does not explain our current warming because we are already in an interglacial period (between ice ages). Some believe the Sun is causing our warming, but the Sun’s energy output stays relatively constant. In fact, recent research has suggested that the Sun’s activity has declined in recent decades. Others blame cloud formation, or the lack thereof, due to cosmic ray flux, but this theory also remains unproven with many problems of its own. Namely, cosmic ray intensity has remained stagnant in the recent past. Conversely, anthropogenic global warming is verifiable. Nearly all research points to a warming due to anthropogenic greenhouse gases, which is what has given the IPCC the confidence to claim that it is "very likely" that global warming is due to human activity.

Simply put, this argument is yet another attempt to obfuscate the issue, rather than an honest attempt at finding the truth.

Myth: Our current global warming is due primarily to a decrease in cosmic ray intensity.

Fact: The fact is that this theory is extremely new, and has only recently been considered possible. There are still many questions left to be answered and more work to be done on quantifying its effect before such a statement could have any validity. Before we get into the details of why this is, I’d like to explain the theory itself a little better.

Basically, this theory, researched by a scientist named Henrick Svensmark, claims that the Sun indirectly affects our climate. The first thing to understand is that clouds generally have a cooling effect on the planet, through an effect called albedo: they reflect sunlight back into space. Next, we have cosmic rays, which are "energetic particles originating from space that impinge on Earth’s atmosphere". Cosmic rays primarily consist of protons, and they originate from outside our solar system. The Sun also emits rays, called solar cosmic rays, which have much lower energy than cosmic rays. When there is an increase in solar activity, the increased solar cosmic ray intensity causes a decrease in the other cosmic rays, called the Forbush decrease.

According to the cosmic ray flux theory, cosmic rays, upon entering our atmosphere, produce small particles called aerosols, which aid in cloud formation. So, more cosmic rays means more clouds and a greater cooling effect. However, this theory’s proponents claim that we are currently in a period of increased solar activity, which is causing less cosmic rays to enter our atmosphere. This means less clouds and therefore, a warming effect.

From the outset, Svensmark’s research has been met with criticism. His problems started when he claimed a correlation between cosmic ray intensity and global cloud cover based on limited data:

One of the biggest criticisms levied against Svensmark was that he had used data from a satellite that did not measure total global cloud cover. When other researchers plugged in a more comprehensive data set, the correlations Svensmark found between cosmic radiation and the Earth’s global cloud cover broke down.

So Svensmark tweaked his theory: Though clouds at middle and high levels are unaffected by cosmic rays, he said, low-level cloud formation was still highly correlated.

Criticism lingered.

Criticism has lingered because, while he’s found a correlation with low-level clouds, his experiments do not reflect real-world conditions. In his experiments, he has taken a mixture of water, sulphur dioxide, ozone, and air, and bombarded it with high energy UV light. According to Eli Rabett, this experiment contained about "5000 times more SO2 than in places where clouds actually form" and "more ozone than in the ozone layer". There is also concern over the use of high energy UV, which according to Gavin Schmidt at RealClimate, "never penetrates the lower troposphere." This is quite a problem, considering Svensmark’s supposed correlation is with low-level cloud formation. Schmidt also listed several additional questions that still need to be answered:

First, the particles observed in these experiments are orders of magnitude too small to be Cloud Condensation Nuclei (CCN). In the press release, this is why they talk about the ‘building blocks’ of CCN, however, aggrandisation of these small particles is in no sense guaranteed (Missing step #1). Secondly, the focus is on low clouds over the ocean. However, over the ocean, there are huge numbers of condensation nuclei related to sea salt particles. Thus to show that the cosmic ray mechanism is important, you need to show that it increases CCN even in the presence of lots of other CCN (Missing step #2). Next, even if more CCN were made, you would need to show that this actually changed cloud cover (or optical thickness etc.) (Missing step #3). And given that change in cloud properties, you would need to show that it had a significant effect on radiative forcing - which despite their hand waving, is not at all well quantified (even the sign!) (Missing step #4). Finally, to show that cosmic rays were actually responsible for some part of the recent warming you would need to show that there was actually a decreasing trend in cosmic rays over recent decades - which is tricky, because there hasn’t been (see the figure) (Missing step #5).

I’d like to clarify here that the purpose of this article is not to discredit Svensmark’s research. The study is peer-reviewed, and is for that reason, at least feasible. For all we know these questions could be answered in the future, with additional research. The point I want to make is that this is a very new theory. Many skeptics have latched onto this theory, claiming that it explains 20th century warming, and therefore debunks anthropogenic global warming. On the contrary, Svensmark’s work has created more questions than it has answered, and is therefore nowhere near solid enough to warrant such bold claims.

Myth: These same climate scientists predicted a coming ice age in the 70’s. They were wrong then, so why should we trust them now?

Fact: No, they didn’t. The situation in the 70’s was very different from our current situation. There was no scientific consensus on climate change. There was no international body of scientists looking into the matter, no global effort to deal with climate change, and no daily news articles on the subject. There were maybe a couple of magazine articles, a book, and some sporadic newspaper articles.

Today, by contrast, we have the IPCC, an organization of the world’s top climate scientists and its four reports, the latest of which claims with 90% certainty that anthropogenic greenhouse gas emissions are primarily responsible for our current warming. We also have other scientific bodies that agree with this assessment, such as the National Academy of Sciences and the American Association for the Advancement of Science. Should one ask for a scientific paper from that time period that makes such a claim, one would certainly be left empty-handed. The most common example used is an article that was published in Newsweek in 1975, titled "The Cooling World", which provides an excellent example of the sensationalist reporting that existed within some media reports.

The situation was also different because the state of climate science was such that there was not enough research to be able to make these supposed predictions with any certainty. A 1975 National Academy of Sciences report stated as much, saying "…we do not have a good quantitative understanding of our climate machine and what determines its course. Without the fundamental understanding, it does not seem possible to predict climate…". Climate science was in its infancy. There wasn’t yet enough data or research available on which to base such a prediction, and scientists were well aware of that fact. Scientists’ current statements on the future of our climate are based on decades of research and massive amounts of data that has been collected over that time.

Also, as the climate scientists at RealClimate have pointed out, we know that climate scientists could not have made such predictions based on the scientific information that was available at the time:

Firstly, there was a trend of cooling from the 40’s to the 70’s (although that needs to be qualified, as hemispheric or global temperature datasets were only just beginning to be assembled then). But people were well aware that extrapolating such a short trend was a mistake (Mason, 1976) . Secondly, it was becoming clear that ice ages followed a regular pattern and that interglacials (such as we are now in) were much shorter that the full glacial periods in between. Somehow this seems to have morphed (perhaps more in the popular mind than elsewhere) into the idea that the next ice age was predicatable and imminent. Thirdly, there were concerns about the relative magnitudes of aerosol forcing (cooling) and CO2 forcing (warming), although this latter strand seems to have been short lived. - RealClimate

This argument, like many other skeptical arguments, is simply an ad hominem attack. Rather than addressing the merits of the science behind anthropogenic global warming, it attempts to discredit climate scientists in general based on arguments and statements they never made. Such arguments hold about as much merit as recent attacks against Al Gore and claims that previous high levels of carbon dioxide in our atmosphere were caused by dinosaur farts. If there were any valid points to be made by skeptics, this would not be one of them.

Carbon Dioxide Molecule

Myth: Compared to natural carbon dioxide emissions, manmade emissions are insignificant.

Fact: The argument is occasionally made by global warming skeptics that manmade carbon dioxide emissions are much smaller than natural emissions. Some skeptics will even quote figures in decimal or percent form, which makes it look even more true. If this is the case, according to their logic, our attempts to stop global warming are futile because we can't make a difference. This argument is blatantly false and is based on a complete lack of understanding of our environment.

On our planet, there is an ongoing process called the carbon cycle, in which carbon dioxide is both emitted and absorbed naturally. The absorption part of the cycle is what is missing from this myth. It is true that very large amounts of CO2 are emitted naturally, but there is also a carbon dioxide sink, which is the name for the absorption process. The sink removes slightly more carbon dioxide from the air than is emitted naturally. Therefore, any natural CO2 emissions are a wash.

Carbon Cycle

Actually, the natural sink is also absorbing much of the emissions resulting from human activity. In fact, the only reason any of our emissions end up in the atmosphere is because we're emitting CO2 faster than the planet can absorb it:

The roughly 500 billion metric tons of carbon we have produced is enough to have raised the atmospheric concentration of CO2 to nearly 500 ppm. The concentrations have not reached that level because the ocean and the terrestrial biosphere have the capacity to absorb some of the CO2 we produce. However, it is the fact that we produce CO2 faster than the ocean and biosphere can absorb it that explains the observed increase. - RealClimate

This has resulted in an increase in CO2 concentrations over the last century and a half of about 100 parts per million, from 280 ppm to 380 ppm. Nearly all of this increase has been due to human activity. Another way we know this, besides a simple look at the increase in human activity over the past two centuries, is by measurements of different isotopes of the carbon atom:

Isotopes are simply different atoms with the same chemical behavior (isotope means “same type”) but with different masses. Carbon is composed of three different isotopes, 14C, 13C and 12C. 12C is the most common. 13C is about 1% of the total. 14C accounts for only about 1 in 1 trillion carbon atoms. CO2 produced from burning fossil fuels or burning forests has quite a different isotopic composition from CO2 in the atmosphere. This is because plants have a preference for the lighter isotopes (12C vs. 13C); thus they have lower 13C/12C ratios. Since fossil fuels are ultimately derived from ancient plants, plants and fossil fuels all have roughly the same 13C/12C ratio – about 2% lower than that of the atmosphere. As CO2 from these materials is released into, and mixes with, the atmosphere, the average 13C/12C ratio of the atmosphere decreases. - RealClimate

So, not only are manmade CO2 emissions significant, they actually make up an overwhelming majority of the recent increase in CO2 concentrations in the atmosphere. Looking into the future, manmade CO2 emissions are predicted to continue increasing, which will no doubt result in higher concentrations of the gas in the atmosphere. Therefore, our efforts to cut back on emissions will indeed make a difference for the future of our planet.

Editor's note: We're pleased to welcome Jason Leggett to the Green Options writing team. A civil engineer based in Huntsville, Alabama, Jason started blogging about climate science, and the myths surrounding it, last December at his blog Reasic. He now also writes for Celsias. We're very happy to have him on board, and to bring back our "Green Myth-Busting" series.

Myth: Mars is warming primarily due to the Sun and therefore, Earth's recent changes in climate are also due to solar activity.

Fact: This theory is based on satellite images that show that the ice caps at the Martian south pole are retreating. According to the theory, Mars has very little atmosphere, so a greenhouse effect can be ruled out. Therefore, the Sun must be causing warming on Mars. If that's true, then it must also be causing warming on Earth:

In 2005 data from NASA's Mars Global Surveyor and Odyssey missions revealed that the carbon dioxide "ice caps" near Mars's south pole had been diminishing for three summers in a row. Habibullo Abdussamatov, head of space research at St. Petersburg's Pulkovo Astronomical Observatory in Russia, says the Mars data is evidence that the current global warming on Earth is being caused by changes in the sun. "The long-term increase in solar irradiance is heating both Earth and Mars," he said. Abdussamatov believes that changes in the sun's heat output can account for almost all the climate changes we see on both planets. Mars and Earth, for instance, have experienced periodic ice ages throughout their histories. "Man-made greenhouse warming has made a small contribution to the warming seen on Earth in recent years, but it cannot compete with the increase in solar irradiance," Abdussamatov said.

There are several problems with Abdussamatov's theory, but I'll just point out the two biggest holes I've found. The first problem is that it is controversial. The mainstream theory is that Mars' warming can be explained by changes in its orbit and tilt, much like Earth's Milankovitch Cycles:

The conventional theory is that climate changes on Mars can be explained primarily by small alterations in the planet's orbit and tilt, not by changes in the sun. "Wobbles in the orbit of Mars are the main cause of its climate change in the current era," Oxford's Wilson explained. All planets experience a few wobbles as they make their journey around the sun. Earth's wobbles are known as Milankovitch cycles and occur on time scales of between 20,000 and 100,000 years. These fluctuations change the tilt of Earth's axis and its distance from the sun and are thought to be responsible for the waxing and waning of ice ages on Earth. Mars and Earth wobble in different ways, and most scientists think it is pure coincidence that both planets are between ice ages right now. "Mars has no [large] moon, which makes its wobbles much larger, and hence the swings in climate are greater too," Wilson said.

The second problem with this theory is that there is an overwhelming amount of scientific research that supports the mainstream theory that increased greenhouse gas concentrations are the primary drivers of our climate. On page 4 of SPM1 for the IPCC's latest report, there is a chart that lists each of the components that affect our climate, including their corresponding values, which quantify their contributions. The components are called radiative forcings, and each forcing's effect is measured in watts per meter squared (W/m^2). According to the chart, carbon dioxide is the dominant forcing at 1.66 W/m^2, while the Sun's effect, called solar irradiance, is much smaller at only 0.12 W/m^2. The latter can also be verified by a simple calculation.

The funny thing about this myth is that it is hypocritical. Many skeptics do not trust or appreciate the massive amounts of data that we have collected here on our planet via land, sea, weather balloon, satellite, and proxy measurements, and yet three photos of one secton of Mars convince them that the Sun is warming not only Mars but also Earth.