Tawonga Gap fire, December 2006

Climate Change is Real, and Important

Miriam O'Brien
32 min readOct 29, 2015


By Josh Halpern, Greg Laden, Collin Maessen, Miriam O’Brien, Ken Rice and Michael Tobis (*see below)

Human caused climate change is real, and it is important. It has such monumental implications that governments around the world have been coming together since the 1980s to work out how best to address it. Yet the scientific consensus that we are changing the climate is constantly being challenged by those who have financial or other interests in the continued use of fossil fuels. This has resulted in a “consensus gap” whereby a measurable, though shrinking, proportion of the general public is not sure that anthropogenic climate change is real or important. Unfortunately, this consensus gap allows for those who do not respect the science to parachute in now and then to help maintain a beachhead of denial.

David Siegel recently penned an article at Medium.com in which he tells us he has spent several hours studying the climate change problem, and he has determined that there really isn’t one. The most cursory inspection of his thesis suggests that Siegel has spent most of those hours studying and re-phrasing the anti-science “denialist” rhetoric, readily available on line. Not one of his points, and he has, conveniently, ten of them, is novel, insightful, or in any way different from what we have seen developed by the other fossil-fuel defending organizations and individuals.

There is a strong argument that David Siegel’s article should be ignored as yet another science denier’s screed, and that may be true. Nevertheless a group of us, including scientists in climate and cognate areas, science communicators, and others, have decided to take a few moments to examine David Siegel’s article and respond do it. Siegel’s article is in the main wrong, but it is well organized and includes quite a few science denier talking points. So we have taken this opportunity to explain the science and how climate change affects us, address some of his misleading claims, and consider what drives some people to take a position contrary to science and experts in the field.

Rejecting Climate Science: Red flags vs smoking guns

Denial of science is a sufficiently well developed industry that there are now people who study it. In the area of climate change denial, more than 170 specific myths about the science have been identified. David Siegel claims to have identified a number of “smoking guns” in his arguments that climate change is not real. Since all of these assertions are drawn from this list of falsehoods and myths, his smoking guns turn into red flags. For example, he claims the Hockey Stick temperature chart is wrong. He claims that it was warmer in medieval times, 1,000 years ago, than it is today. He commits a logical fallacy when he writes that in the past the change in CO2 lagged the change in temperature, implying that it therefore cannot cause the rise in temperature we see today. We deal with some of these issues in this article. The impatient can follow the links to the detailed arguments at Skeptical Science.

In his article, David Siegel makes false accusations that scientists are fudging and cherry picking data. This is a red flag warning that he knows little about climate science. It’s a clue that he has fallen for climate conspiracy theories. Even bigger red flags pop up when you read that David Siegel doesn’t “trust” the most prestigious general science journals, Nature and Science. You start to wonder what sources he does use for science. When he says that some of the most highly regarded scientific institutions, NASA, NOAA and the Intergovernmental Panel on Climate Change (IPCC) are not to be trusted, then you begin to realise that he must not understand what he is reading about science. When he rejects mainstream science outright you have to wonder what he replaces it with.

In effect David Siegel said he doesn’t trust any experts in climate science. His trusted sources for climate science include Michael Crichton, a novelist who died in 2008 and who is not a climate scientist. Instead of published research, Siegel places his trust in blogs maintained by people having no expertise in climate science or any science, blogs that promote climate conspiracy theories. Instead of scientific research organisations, David Siegel places his “trust” in political organisations, such as the Heartland Institute, which promote disinformation about climate science.

Why do people reject science?

It is not possible, just based on a blog article, to determine why an individual rejects mainstream science. However, we asked cognitive scientist Professor Stephan Lewandowsky of Bristol University, what prompts people in general to reject mainstream climate science, and to express distrust of scientific experts and the world’s leading research institutions. He replied:

“The most important factor driving many people’s attitudes to science is not evidence or data but their ‘worldviews’; that is their basic beliefs about how the world should be organized. If scientific facts challenge those worldviews, then this may set in motion an effort to deny those inconvenient facts. In the case of climate change, people perceive a threat to free markets that may arise out of mitigation measures, and so if free markets are really important to them, then they will seek to deny that our economic activities change our climate.”

In his article, David Siegel made a big point about voting Democrat and claims he used to accept climate science. (This tactic is not unheard of from people who reject science.) It is likely he is aware of the cognitive research about climate science denial and the fact that it is more prevalent among conservative voters. Stephan Lewandowsky added that dismissing experts as David Siegel did is one way of managing the dilemma of trying to maintain intellectual respectability. He told us:

“Given that climate change is one of the most thoroughly established scientific findings of recent decades, and given that contrarian positions do not have any remaining intellectual or scientific respectability, this presents a serious dilemma for people who must deny that climate change is occurring for personal or ideological reasons. One solution is to dismiss all the world’s scientists and all reputable scientific institutions by accusing them of being untrustworthy for one reason or another. Another solution is to imagine a giant conspiracy between scientists and governments that invented climate change to raise taxes or create a World Government or whatever. So wherever you look, once you scratch the surface of denial, beneath the veneer of respectability there always is paranoia, an imagined conspiracy, or a political operative.”

Telltale techniques of climate change denial

Researchers have identified telltale techniques of climate science denial, as illustrated in a graphic from the climate website, Skeptical Science, below.

Source: SkepticalScience.com

These were discussed in an article at CBC by John Cook, who does research on the topic of climate science denial at the University of Queensland, and created the website SkepticalScience.com. The most common techniques are:

  1. Fake experts. One technique commonly used is that of calling on fake experts. David Siegel’s article is replete with links to articles on websites dedicated to rejecting climate science, and which contain wrong information mostly written by people with no expertise in climate science.
  2. Logical fallacies. Articles which dispute climate science are often full of logical fallacies, and David Siegel’s article is no exception.
  3. Impossible expectations. When people are arguing against mainstream climate science, in addition to building straw men (a type of logical fallacy), they will often set unrealistic expectations and argue that they haven’t been met.
  4. Cherry-picking. This is a technique that is also commonly used by people who argue that climate experts are wrong. David Siegel wrongly claims that scientists have cherry picked data. In fact, it is he who has done so.
  5. Conspiracy theories. As a fallback position, people who reject climate science will claim that scientists around the world are engaged in some sort of giant global hoax. This may include allegations, such as the ones made by David Siegel, that scientists have fudged data, to make it appear that the world is getting hotter. Such a conspiracy would mean that all scientists were “in” on it. Not only scientists, but staff of scientific journals, governments of all types around the world, and mainstream media. Science from all relevant disciplines from research teams all around the world, over many decades, all point to the fact that global warming is real and happening now, and that our actions are causing it.

Before addressing the other points in David Siegel’s article, let’s consider what climate change means.

Signs of climate change

The signs of climate change are all around us. Warming is proceeding very quickly compared to previous changes in Earth’s history. It is not merely that humans will be living in a warmer world than any human has experienced, warmer than any period since before humans evolved. It is the pace of change. This means that many species will have no time to adapt. Scientists at Stanford have warned that we are on track to warm ten times faster than at any time in the past 65 million years.

  • It’s getting hotter. The mean global surface temperature is increasing, very quickly. This can be seen by monitoring temperatures changes on land and sea. Gardeners, farmers and wine producers know that planting zones are shifting to the poles; northwards in the northern hemisphere, and southwards below the equator. Spring snow has shown a marked decline in the northern hemisphere.
  • Sea level is rising. This is because the oceans are getting warmer (expansion of water) and ice sheets and glaciers are melting.
  • Heat waves are worse than they used to be. The heat wave in India earlier this year was among the most deadly ever recorded anywhere. There have been disastrous heat waves in Europe this century as well, which were most likely exacerbated by global warming (see this article in Nature, also).
  • Worsening drought. Heat waves and warming generally exacerbates drought, like the current drought in California.
  • Wildfires are burning more fiercely. Worsening heat and drought also means that fires can burn more fiercely — like the firestorms in Australia (Canberra, Kinglake and Tasmania and elsewhere), in North America (Canada, Alaska, California, Washington, Arizona and elsewhere), and in Europe (Greece and across the Mediterranean), and Asia (Siberia, Indonesia), and Africa (Cape Town)
  • Flash floods are getting worse. Heavy rains are more frequent and are contributing to flash floods. Events such as the 2013 Colorado floods, this year’s Riviera flash flood, and Australia’s Big Wet are likely to become more frequent. The “worst floods in 50 years” is becoming a more common headline (eg for Malawi, India and Pakistan, and Japan).
  • Tropical cyclones (hurricanes and typhoons) are expected to become stronger. Some scientists feel this is already happening. Because there are only a few tropical cyclones each year, it will take some time to determine trends as the world warms. Haiyan was the fiercest storm ever recorded at landfall, and like Katrina, was strengthened by warm sea water at depth, not just on the surface, which is almost certainly due to global warming. Hurricane Patricia was the most intense ever measured in the Western Hemisphere. The total amount of energy that shows up in tropical cyclones, globally, has been increasing in recent decades.

Global surface temperature changes and human history

Scientific research has revealed that, before the industrial revolution, averaged over the world, global mean surface temperature had been fairly stable over most of the Holocene. Data provides evidence of a slow cooling trend since a maximum about 8,000 years ago. With the advent of the industrial revolution, we started adding greenhouse gases to the atmosphere through the burning of fossil fuels. Atmospheric CO2 has increased from the pre-industrial level of around 280 parts per million (ppm), to around 400 ppm today; an increase of more than 40%. Temperatures have been rising more rapidly since the middle of last century. Professor Michael Mann says:

“The authoritative scientific assessment to date (the 5th report of the Intergovernmental Panel on Climate Change) concludes that human activity has been the “DOMINANT cause” of the warming of the past half century. And in fact, if you read the technical chapters of the report, what you find is that human activity is most likely responsible for MORE than 100% of the warming (because it overcame natural factors which were actually acting to slightly cool the climate over that timeframe).”

To determine changes in surface temperature before the widespread use of weather stations, scientists use indicators or proxies, from as many locations around the world as practicable. This research indicates that global mean surface temperature is higher now than at any time in at least the last 1,000 years. Our planet will continue to get warmer until we take sufficient action on carbon emissions.

Proxy records have been accumulating over time as researchers collect them from different (often dangerous) locations. Proxies can include, for example:

  • ice cores, particularly the long records from sheet ice on Greenland and in Antarctica
  • sediment deposited in lakes and on the ocean floor
  • fossils of plants and animals, including pollen (pollen can be quite resistant to decay, and when deposited in sediments can indicate the plants of the period, which can be used to indicate climate)
  • tree rings (analysis of rings in the tree trunk)
  • coral (analysis of bands in the coral)
  • speleothems (mineral deposits formed from groundwater inside caves, such as stalagmites and stalactites).

Scientists can extend climate data back about 800,000 years using ice cores. Even if there were brief very warm periods over this time, they would not rival the surface temperatures we expect over coming decades. Going back even further in time, over millions of years, the estimate of surface temperatures is less certain. However the best available evidence suggests that surface temperature anticipated in the next few decades was likely not exceeded for any significant period at least since the early Pleistocene, over 2.5 million years ago. From about 4 million years ago back to about 12 million years, during the last half of the Miocene, there were periods of time when the earth was as warm or warmer than today. The earth was often as warm as it is today or warmer, sometimes much warmer, before 12 million years ago.

In short, it is reasonable to say that for the last 4 million years, the earth has been relatively cool compared to earlier periods such as the Jurassic and Cretaceous. The current increase in surface temperatures are approaching those not occurring since millions of years before humans first appeared.

To put this into perspective, agriculture originated around 10,000 years ago. However widespread agriculture, producing most of the world’s food supply, only occurred over the last five thousand years or so. Modern humans evolved around 200,000 years ago. Our ancestors in the genus Homo only emerged about 2.5 million years ago. Most species today, including us, have evolved to adapt to the current climate, not the warmer world we are making.

Life today, plants, animals and microbes, are now facing a rapid change in climate, caused by human greenhouse gas pollution. Some will find themselves in conditions not seen since before grasses (including our edible grains) existed, before our ancestors had left the moist forests of Africa, before North and South America were connected by a land-bridge. The surface temperatures we expect to experience over the next few decades, and are beginning to experience now, were last seen at a time when the world would be unrecognizable to us, were we to travel back in a time machine. Yet it’s not just the change in climate, it’s the pace of change which will make adaptation very difficult, even impossible for many species.

The hockey stick and medieval warming

In his article, David Siegel wrote about what he regarded as “smoking guns”. He wrote about two common myths that are among the more popular listings at SkepticalScience.com. The hockey stick shape of surface temperature reconstructions and the medieval climate anomaly.

Siegel claimed that the temperature rise, as shown by the “hockey stick” shape of the global surface temperature chart, is wrong. Siegel’s “evidence” that it was wrong was a report prepared by the Heartland Institute, an organisation in the USA that lobbies against mitigation of climate change, among other things.

When talking about the hockey stick, David Siegel is referring to global mean surface temperature reconstructions going back 1,000 years or so. An early reconstruction by Professors Mann, Bradley and Hughes in 1998 became known as the hockey stick, because of its shape. Their 1998 paper and its follow up published in 1999, have each been cited by more than a thousand papers published subsequently. That is probably why, ever since it was first published, there have been people trying to discredit it. However, each new reconstruction, using different data, is remarkable similar to the ones that went before.

David Siegel also posted some charts from a popular climate conspiracy blog and tried to argue that it was warmer in medieval times than it is this decade. This is now known to not be the case globally. Current evidence indicates that any warming that may have occurred was regional, not global.

The chart below illustrates recent findings from research conducted by teams of scientists from around the world, as the PAGES 2k project, together with the results from the original “hockey stick” temperature reconstruction. The PAGES 2k reconstruction is based on a lot more evidence than was available in 1999, yet shows how estimates have changed very little over time.

Green dots show the 30-year average (area-weighted mean over the continents) of the new PAGES 2k reconstruction, as shown in Figure 3b. The red curve shows the global mean temperature, according HadCRUT4 data from 1850 onwards (also in Figure 3b, smoothed with a 30-year window). In blue is the original hockey stick of Mann, Bradley and Hughes (1999 ) with its uncertainty range (light blue). Graph by Klaus Bitterman, with permission. Source: Stefan Rahmstorf at Climate Progress.

The chart above is surface temperature over land. As you can see, land surface temperature slowly declined from relative warmth in medieval times (around 1000 CE) to the middle of the 19th century. The surface temperature in the instrumental era, from around 1850 onwards, is shown by the red line in the chart above. It is now much higher than it has been in the past 1,000 years at least, even allowing for the upper bound of uncertainty (the blue shading).

In August, there was a Letter published in Nature Geoscience, which showed the results of a compilation of global sea surface temperature over the past 2,000 years to an average for the twentieth century. This was compiled as part of the Oceans 2K project (a section of PAGES 2k). The researchers found that the oceans had been slowly cooling until the twentieth century. This has now changed, with global warming.

The chart below shows how sea surface temperatures have risen in recent decades, since the instrumental era when thermometers have been used. It is an average for each decade from the middle of the 19th century, from data compiled by the UK Met Office Hadley Centre, and shows how sea surface temperatures have risen since the beginning of the twentieth century:

Data source: UK Met Office, Hadley Centre

When people misrepresent science to argue against more robust scientific findings, they rarely admit that they are basing their disinformation on a misrepresentation of real scientific research, the same scientific research that they are arguing against. David Siegel is no exception.

In this next section, we will discuss each of the ten points made by David Siegel. We will point out the flaws in his claims, and explain what the science shows.

David Siegel’s ten claims about climate


1. Global warming and extreme weather

There are numerous studies that have identified links between extreme weather events and global warming. According to these studies higher temperatures cause more intense hurricanes, heavier rainfalls and flooding, increased conditions for wildfires and dangerous heat waves. Global warming loads the weather dice to make these extreme events more likely. Counter to this evidence Siegel wrote the following statement:

“Weather is not climate. There are no studies showing a conclusive link between global warming and increased frequency or intensity of storms, droughts, floods, cold or heat waves.” (Claim by David Siegel.)

To support this point Siegel linked to an article about hurricanes and tropical cyclones, on the NOAA website. (If you read further down in Siegel’s article, you may have noticed a contradiction. David says that NOAA is one of the sources he doesn’t trust. That the NOAA is not to be listened to. This sort of tactic, cherry picking pieces and rejecting the whole, is a red flag of the type mentioned earlier.)

The article Siegel linked to does not dispute the fact that global warming affects tropical cyclones. All weather is affected by global warming. The first conclusion it lists is that it is not yet possible to determine a detectable impact of climate change. This conclusions are that:

  • It is not yet possible to determine a detectable impact of global warming on Atlantic hurricane or global tropical cyclone activity.
  • It is likely that by the end of this century, human-caused warming will result in more intense tropical cyclones, and an increase in frequency in some ocean basins.
  • Associated rainfall is likely to increase by 10 to 15% over this century.

Just how much global warming will change tropical cyclone frequency and strength over time is an area of active research. However, there is evidence that the increase in strength has already started to happen, associated with increasing ocean temperatures. There is general agreement among experts that there are likely to be more high category (Category 4 and 5) storms as the world continues to warm, and hurricanes will produce much heavier rainfall than in the past. Professor Kerry Emanuel from MIT advised us there is already evidence indicating that in the western North Pacific and in the North Atlantic, hurricanes will reach peak intensity further north. He added that there is less consensus about the frequency of weak hurricanes, which cause much less damage. Kerry Emmanuel said:

“Because the frequency of high intensity (Cat 4 and 5) storms is expected to increase, and because these dominate the total damage done by hurricanes even though they are relatively rare, we expect surge and wind damage from hurricanes to increase in many places. We also expect increased incidence of freshwater flooding from torrential hurricane rains.”

Cyclones are fueled by warm water, provided the wind shear is low. As the seas get warmer, the intensity of tropical cyclones will continue to increase. Events like Hurricane Patricia are a warning sign of what is to come. And the combined effect of stronger storms and rising seas means double trouble, as explained by scientist Peter Jacobs in a video:

Siegel talks about studies showing a “conclusive link” between global warming and storms, droughts, floods, cold or heat waves. Because extreme events are, almost by definition, rare events, it is difficult to assess the relative contribution of global warming. As scientists wrote in a Letter in Nature, following the extreme heat wave in Europe in 2003:

“It is an ill-posed question whether the 2003 heatwave was caused, in a simple deterministic sense, by a modification of the external influences on climate — for example, increasing concentrations of greenhouse gases in the atmosphere — because almost any such weather event might have occurred by chance in an unmodified climate.”

What scientific research can and does show, is the likelihood of extreme events being exacerbated by human-caused warming. This can be done by, for example, assessing the likelihood of such events occurring with and without global warming. In a supplement to the Bulletin of the American Meteorological Society (BAMS), scientists reported that human-caused global warming very likely played a role in the following extreme events in 2012 and 2013:

  • The Californian drought
  • The Australian record heat
  • Extreme rainfall in north eastern Colorado
  • The New Zealand drought
  • The heat waves in Korea and Japan
  • The hot summer in central eastern China
  • Severe precipitation in northern India
  • The hot, dry summer in western Europe.

To understand how extreme events might have changed, one can also refer to IPCC reports, which identify an increase in heatwaves and heavy precipitation. From Chapter 10 of the AR5 WGI document:

“It is likely that human influence has substantially increased the probability of occurrence of heatwaves in some locations.”


“there is medium confidence that anthropogenic forcing has contributed to a global-scale intensification of heavy precipitation over the second half of the 20th century”

2. How much warming?

Scientists have found multiple fingerprints that point to human activity as the cause of the current increase in temperatures. Changes in the types of carbon in the air, the small, but measured parts per million drop in oxygen concentrations, no natural explanations for the change in temperature, the enhanced greenhouse effect seen from satellites, the list goes on. These many lines of empirical evidence are what make scientists so confident in their conclusion that we are causing global warming. Yet Siegel wrote:

“Natural variation in weather and climate is tremendous. Most of what people call “global warming” is natural. The earth is warming, but not quickly, not much, and not lately.” (Claim by David Siegel.)

Natural variation in weather is largely defined by the climate of a region. Some parts of the world have a lot of variability in weather. Other places not so much. Siegel’s claim that global warming is natural is simply not supported by the evidence. The dominant cause is the very large increase in atmospheric carbon dioxide, a greenhouse gas. Global mean surface temperature is already around 1 °C higher than it was in the 1850s, as shown in the chart below. The chart is based on data from the Hadley Centre, UK Met Office and shows the change in temperature from 1850 to the present, from the average over the 30 years 1851 to 1880.

Data source: UK Met Office Hadley Centre

3. Understanding climate, using models

For the third of his ten points, David Siegel, wrote as if he was putting himself forward as some sort of expert in climate models. On the contrary, his article indicates that he does not understand climate models (or the concept of scientific uncertainty). He wrote:

“There is tremendous uncertainty as to how the climate really works. Climate models are not yet skillful; predictions are unresolved.” (Claim by David Siegel.)

You might ask, why trust climate models? The answer is that they provide insight into climate, and what we can expect as the world warms. The claim that models are not yet skillful is certainly incorrect. A model being skillful does not mean that the model is 100% “right”, it means that a model can tell us something about a system that we wouldn’t otherwise know, or be able to understand. There are plenty of examples of climate models being skillful. As early as the 1960s, models predicted that the stratosphere would cool in response to increasing atmospheric greenhouse gases (Manabe & Wetherald 1967). This has indeed been observed (Thomson & Solomon 2005). Predictions, in the late 1980s, of future warming in response to increasing anthropogenic emissions have also been shown to have been skillful (Hargreaves 2010). Predictions in the 1990s of the response to the Pinatubo eruption were, again, skillful (Hansen et al 1992). The response to the solar cycle shows skill.

The Director of the Goddard Institute of Space Science, Dr Gavin Schmidt, explains in a Ted Talk video why climate models are skillful.

4. It’s not the sun

David Siegel’s fourth wrong claim was that global temperature is more highly correlated with solar radiation. That is incorrect. It is currently the second most popular myth listed at SkepticalScience.com. Siegel wrote:

“New research shows fluctuations in energy from the sun correlate very strongly with changes in earth’s temperature, better than CO2 levels.” (Claim by David Siegel.)

Not only does this suffer from the correlation doesn’t imply causation problem, it’s not correct. In the last 50 years there has been a slight reduction in solar insolation while temperatures have continued to rise. Furthermore, changes in solar forcing over the 20th century are small compared to changes in anthropogenic forcings. To argue that the sun has been the dominant driver of 20th century warming suggests that our climate is very sensitive to changes in solar forcing, while being very insensitive to changes in anthropogenic forcings. This is not a logically consistent position.

In his section on “smoking guns”, Siegel refers to papers authored by Willie Soon, whose work claiming “it’s the sun” is seriously flawed. The latest scientific report from the IPCC states there is high confidence that recent warming is not from the sun:

There is high confidence that changes in total solar irradiance have not contributed to the increase in global mean surface temperature over the period 1986 to 2008, based on direct satellite measurements of total solar irradiance. There is medium confidence that the 11-year cycle of solar variability influences decadal climate fluctuations in some regions. No robust association between changes in cosmic rays and cloudiness has been identified.

Credit: Jenna Beekhuis

The science shows that, contrary to what David Siegel wrote, solar forcing had a small negative influence on climate between 1980 and 2011. The chart below is from Chapter 8 of the IPCC AR5 WG1 report. It lists the forcings that have acted on climate between 1980 and 2011. The forcings from human activity, anthropogenic forcings, are shown at the top, and the main natural forcing, solar irradiance, is shown at the bottom. Almost all the forcing is positive (as can be seen from the axis at the bottom of the chart). Changes in solar irradiance over this period were a negative forcing, counteracting the human-caused forcings to a small extent. That’s because the amount of energy coming from the sun over this period was slightly less than in previous periods, so the sun didn’t warm the planet as much as it had been in earlier decades.

Linear trend in anthropogenic, natural and total forcing for the indicated time periods. The uncertainty ranges (5–95% confidence range) are combined from uncertainties in the forcing values (from Table 8.6) and the uncertainties in selection of time period. Monte Carlo simulations were performed to derive uncertainties in the forcing based on ranges given in Table 8.6 and linear trends in forcing. The sensitivity to time periods has been derived from changing the time periods by ±2 years. Source: Figure 8.19 from the IPCC AR5 WG1 report

5. Carbon dioxide as the climate control knob

Atmospheric carbon dioxide is the biggest control knob of climate. More of it and the world heats up. When it drops, the world cools. It is well-mixed in the atmosphere and lasts a very long time before being removed through the carbon cycle.

As his fifth objection to mainstream science, David Siegel wrongly claimed that carbon dioxide has little impact on climate:

“CO2 has very little to do with it. All the decarbonization we can do isn’t going to change the climate much.” (Claim by David Siegel.)

It’s hard not to describe this simply as climate science denial. The influence of CO2 as a greenhouse gas is well understood and goes back to Svante Arrhenius in 1896. Although Arrhenius’ original work suggested that our climate is more sensitive than we currently think, our current understanding is still remarkably similar to what he presented. Based on paleoclimate studies, equilibrium climate sensitivity (how much the planet will eventually warm after doubling atmospheric CO2) is likely to be between 2.2 °C and 4.8 °C. In the short to medium term, the IPCC AR5 report estimates that the planet will warm by between 1.5 and 4 °C with a doubling of CO2. And it will continue to warm more if atmospheric CO2 continues to increase. At a meeting in Ringberg in March this year, many of the talks from experts suggested that, in fact, temperatures will probably increase by more than 2 °C, with a doubling of CO2. The higher range of sensitivity estimates (4.0 °C and higher) are not any less likely than the lower estimates (around 2 °C), but would have much worse impacts.

Given that we’re on track to double atmospheric CO2 by the middle of this century, suggesting that decarbonization would not have much effect is wrong. Stopping CO2 emissions won’t cool the planet in the short to medium term, but it will limit the amount of global warming we will suffer, and reduce the pace of warming.

In 2009, renowned glaciologist and climate researcher, Professor Richard Alley gave the Bjerknes Lecture at the AGU Fall Meeting. He described in some detail how scientists know, based on evidence of climates in the distant past as well as the present, that CO2 is the climate control knob:

6. CO2 as pollution

This sixth objection of David Siegel is commonly raised by people who, for mostly ideological reasons, do not want to take action to mitigate climate change. He objected to the word “pollution”:

“There is no such thing as “carbon pollution.” Carbon dioxide is coming out of your nose right now; it is not a poisonous gas. CO2 concentrations in previous eras have been many times higher than they are today.” (Claim by David Siegel.)

It is indeed true that CO2 concentrations in previous eras have been much higher than today, but not at a time when humans, and most other currently present species, were also on the Earth. It’s also true that CO2 plays an important role in both keeping the surface warmer that it would be in the absence of an atmosphere (the Greenhouse effect) and in the planetary life cycle (photosynthesis requires CO2). Pollution, however, is simply the introduction of substances (foreign, or naturally occurring) into the natural environment that could cause adverse changes. Elevated levels of carbon dioxide, such as commonly encountered indoors or in heavy traffic, have been shown to adversely affect human cognition and decision-making. Claiming that there is no such thing as “carbon pollution” ignores the harm caused by rapid changes to climate from increasing carbon dioxide in the air.

7. What causes the sea to rise?

David Siegel predicts that seas will continue to rise, but he wrongly claims that it’s not from greenhouse warming. He doesn’t indicate what he thinks will cause the sea level to go up. He doesn’t say what he thinks will cause ice sheets to melt and water to expand. He wrote:

“Sea level will probably continue to rise, naturally and slowly. Researchers have found no link between CO2 and sea level.” (Claim by David Siegel.)

Credit: Simon Schmitt

Whether warming or sea level rise at any time is from natural forces or human activity, there is always a cause. Saying “natural” means little unless you can say what natural (or other) force is causing the change.

Sea level rise is associated with thermal expansion as the oceans warm, and the addition of extra water through the melting of land ice. This is one of the more concerning outcomes of climate change. Between 140 and 220 million people live on land that may be below sea level by the end of the century if CO2 emissions continue on their current trend, and three times that number may be affected. An interactive tool was published in the New York Times last year, which shows the countries most at risk from rising sea levels. This is a grave concern not just because of the need to relocate millions of people, it has serious ramifications for trade, commerce, and security.

Jonathan Gregory is the lead author of the study David Siegel used as evidence for his claim that there is no link between CO2 and sea level. Professor Gregory told us that Siegel misrepresents their work, and said:

“According to our estimates, the contribution from thermal expansion of the ocean *did* increase in rate, because of the increasing anthropogenic warming (mostly due to CO2), but this was partly offset by the cooling due to a large number of volcanic eruptions in recent decades.”

Jonathan Gregory added that sea levels would not have risen as quickly, if not for human-caused warming:

“the implication is that, without CO2 forcing, the rate of sea level rise would have decreased during the 20th century, rather than weakly increasing.”

The seas are rising at an increasing rate. In 2011, John Church and Neil White (who were co-authors of the Gregory study cited by David Siegel) analysed the sea level rise from the late 19th to the early 21st century. They found that the linear trend from 1900 to 2009 was 1.7 ± 0.2 mm a year. For the period 1993 to 2009 they estimated the rise to be 3.2 ± 0.4 mm a year. The CU Sea Level Research Group at the University of Colorado report the latest trend from 1993 to 2015 as being 3.3 ± 0.4 mm a year.

This is not a huge rate of increase. However, seas are expected to rise a lot faster and higher as the ice sheets in Antarctica and Greenland melt more rapidly. The rise is unlikely to be gradual. There will be decades when sea level will rise very quickly, and others when it will not rise as fast. Many sea level experts regard as conservative the IPCC projections of 0.5 to 1 metre by 2100 under the highest emission scenario (Chapter 13 in the IPCC AR5 WG1 report). A paper published in 2014, reported an assessment by 90 experts from 18 countries. The range of estimates from these experts were that sea level will rise from between 0.7 meters and 1.2 metres by the end of this century with unmitigated warming (RCP8.5), and two to three metres within two hundred years. The amount will depend on how quickly we add CO2 to the air, and how quickly the ice sheets melt. A paper recently published in Nature by Golledge et al, found that if we don’t constrain greenhouse gas emissions, sea level could rise by up to three metres (almost ten feet) in just two hundred years. From the abstract:

“…substantial Antarctic ice loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to ice loss from Antarctic that will raise sea level by 0.6–3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the Antarctic ice sheet to global sea level.”

RCP’s are the representative concentration pathways used in modeling studies for climate. We have gone beyond being able to achieve the lowest emissions pathway, RCP 2.6, by curbing CO2 emissions. To achieve RCP 2.6, we would most likely have to somehow remove CO2 from the air, using geo-engineering.

8. The Arctic is warming, ice is melting, threatening wildlife

In his eighth objection to science, Siegel refers to the situation in the Arctic, and polar bear numbers:

“The Arctic experiences natural variation as well, with some years warmer earlier than others. Polar bear numbers are up, not down. They have more to do with hunting permits than CO2*.” (Claim by David Siegel.)

Yes, there is natural variation of weather and climate in the Arctic. The bigger impact over time will be from human-caused global warming. (Siegel’s first link is not to a science website, but to a blog that rejects mainstream science. The article discussed is a 2010 paper about the onset of ice breakup in Hudson Bay.)

The Arctic is warming faster than most of the rest of the world. This is as expected by climate science, and is known as polar amplification. Andy Lee Robinson has been illustrating the melting of summer sea ice over recent decades. His latest is shown below.

David Siegel links to an article in Canadian Geographic about polar bears. The article is nuanced, and doesn’t support what he implies, that global warming won’t impact wildlife in the Arctic. From the article, about how some polar bear populations have not declined in recent years:

News like this leaves climate-change deniers crowing from the rooftops. But a closer look reveals that everything may not be quite so sunny. “Some populations appear to be doing OK now, but what’s frightening is what might happen in the very near future,” says wildlife biologist Lily Peacock, who has worked with polar bears for the Government of Nunavut and the U.S. Geological Survey. “All indications are that the future does not look bright.” While population trends might appear stable, she says, “we’re picking up declines in body condition that are really frightening.” Scientists have shown a direct correlation between warm years and skinny bears. Even more distressing, one study predicted that 40 to 73 percent of pregnant females could fail to deliver healthy cubs if ice breakup happens one month earlier than in the 1990s. Polar bears are long-lived animals that reproduce slowly; counting the number of animals that are alive today might not paint an accurate picture.

Global warming won’t just have an impact on polar bears. It will affect one of our major food sources, wild fisheries. Scientists have been examining just how global warming will affect fisheries in the Arctic, pooling their expertise and knowledge. For example, through the FIMAGLOW project involving Norway, Iceland, Denmark and Sweden. (You can download the 2014 report here.)

9. Changes in the world’s oceans: warming and acidification

This penultimate of the ten objections by David Siegel makes a claim that is contrary to scientific evidence about the world’s oceans and marine life:

“No one has shown any damage to reef or marine systems. Additional man-made CO2 will not likely harm oceans, reef systems, or marine life. Fish are mostly threatened by people, who eat them.” (Claim by David Siegel)

In this claim, David Siegel ignores the impact of warming oceans. This year there is yet another major coral bleaching event underway. Bleaching events will happen more frequently as global warming increases. Corals can recover from mild bleaching events. However when they are severe, they can cause permanent damage to reefs. The latest chart from NOAA’s coral reef watch shows large areas of oceans that are on the highest alert.

Source: NOAA Coral Reef Watch

It’s not just events like coral bleaching as seas warm, Siegel ignores another threat caused by CO2 emissions: ocean acidification. Under normal circumstances, when the oceans warm they release CO2. Carbon dioxide dissolves in water more easily as the water cools. However, because atmospheric CO2 is increasing so quickly, the effect of the partial pressure outweighs that of temperature, and the oceans have absorbed about ⅓ of the extra CO2 we have put in the air since industrialisation. If not for that, the world would be warming even more quickly than it is.

This absorption of CO2 causes the pH of the oceans to drop. Some marine species are sensitive to pH. This includes many corals and shellfish. Professor of Marine Science at the University of Queensland, Ove Hoegh-Guldberg tells us:

“Consequently, this is pretty much an open and shut case. We are also continuing to create a situation in the world’s oceans that is unprecedented (in hundreds of millions of years of time), and which is already rapidly overwhelming physiological and genetic responses of marine organisms and processes. Evolution needs time to act — which is not happening faster in the case of ocean warming and acidification. Given the fundamental importance of ocean chemistry to life on earth, rapid changes of this scale are of great concern to anyone who understands this issue.”

10. The IPCC, United Nations and the Grand-Daddy of all Conspiracy Theories

In the final of his ten main objections, Siegel resorts to the “climate conspiracy” theory — that climate science is politics not science. He wrote:

The Intergovernmental Panel on Climate Change and others are pursuing a political agenda and a PR campaign, not scientific inquiry. There’s a tremendous amount of trickery going on under the surface*. (Claim by David Siegel.)

Siegel doesn’t link to any scientific report about this supposed “trickery”. Instead he links to a YouTube video by Richard Lindzen. Richard Lindzen used to be a climate scientist at MIT. These days, rather than publish research, he speaks at events run by organisations that oppose efforts to reduce global warming.

The claim that the IPCC is political is one of the misleading tenets of the “climate conspiracy” theories that circulate around the Internet. In the United States and Australia, climate change has been politicised in a manner different to that in most other countries.

The Intergovernmental Panel on Climate Change (IPCC) is a scientific body, under the auspices of the United Nations. It was established by the United Nations and the World Meteorological Agency in 1988, after governments became very concerned about how humans are changing the world’s climates. The IPCC has a very small staff complement and itself does not conduct any research. It relies on hundreds of scientists from around the world volunteering their time to prepare it’s reports. The IPCC reports are based on a compilation of scientific, technical and socio-economic information, which is relevant to climate change.

IPCC scientific and technical reports are written by people who are active researchers in the relevant subject matter. The report on the Physical Science Basis of Climate Change is prepared by Working Group I (WGI). A typical chapter will have two or three co-ordinating lead authors, 10 lead authors or more, and more than 20 contributing authors from around the world. Each chapter describes and references the findings from hundreds of published scientific papers. Before the final report is released, it is carefully reviewed by scientific experts as well as by external reviewers. The most recent WG1 report has 14 chapters, and the preparation involved:

  • 209 Lead Authors
  • 50 Review Editors from 39 countries
  • More than 600 Contributing Authors from 32 countries
  • Examining and citing more than 9,200 scientific publications
  • Analysing more than 2 million gigabytes of numerical data from climate model simulations, and
  • Considering 31,422 comments from 800 Expert Reviewers from 46 countries and 26 Governments, which were in turn reviewed by experts in the relevant fields.

The scientific report has been scrutinised by scientists, world leaders, government agencies, science journalists, and probably tens of thousands of people around the world. To imagine that all these people have collaborated in some sort of “climate coverup” without anyone noticing, is inconceivable.

It will be obvious to readers that, because the scientific report has been accepted by the 193 member countries, it can hardly be described as “political”. The member nations of the UN span the political spectrum and include government structures ranging from western-style democracies to totalitarian regimes. Climate change is something that politicians the world over would much rather not to have to deal with. Actions to mitigate climate change aren’t automatic vote-winners, except among people who understand the critical importance of climate policies.

The Summary for Policy Makers (SPM) needs to be accepted by representatives of the various governments, but this is not the case for the main scientific report. The process by which the SPM is finalised involves sessions whereby government representatives from around the world meet with scientists, to discuss the content and agree on final edits. To a great extent, the meeting where governments review the Summary for Policy-Makers is a word-smithing exercise, as can be seen by the list of edits and comparisons between the penultimate and final documents.

Either a conspiracy involving thousands of people has been foiled by a lone web design author, or David Siegel has made a foolish claim with no basis in reality.

Science, heresy and critical thinking

At the beginning of his article, David Siegel asks:

What is your position on the climate-change debate? What would it take to change your mind?

In our experience, most people who are motivated to reject climate science are not likely to change their mind. Rather than be swayed by scientific evidence, they decide that the data must be fudged, and that none of the thousands of scientific experts in disciplines related to climate can be “trusted”. They attempt to rationalise the irrational, arguing it must be a decades-long conspiracy of gigantic world-wide proportions.

After summarising his ten objections to mainstream climate science, David Siegel asked:

Could this possibly be right? Is it heresy, or critical thinking — or both?

We have demonstrated that no, David Siegel couldn’t possibly be right. His article is not heresy. The subject is science, not religion. There is no “immutable truth” in science. Knowledge is developed by evidence and rational explanation, which as evidence accumulates over time becomes accepted scientific theory.

Nor was David Siegel’s article an example of critical thinking. Instead, you can regard it as a fairly typical example of climate science denial, involving logical fallacies, cherry-picked data, fake experts and other telltale techniques, the same techniques and climate myths that are replicated on other “climate conspiracy” blogs on the Internet.

*About the authors