Talking To Climate Skeptics

What I learned, and why you should drop your objections about global warming

Like millions of other people, about ten years ago I saw a remarkably convincing polemic (attack) on climate change science called “The Great Global Warming Swindle”. Made in the style of a scientific documentary, it had a narrator that sounded neutral and trustworthy, presenting a withering barrage of critical comments from a series of scientists to explain why global warming is all bullshit. It featured several real scientists, including the contrarian climatologists Roy Spencer and John Christy, and Tim Ball of the “department of Climatology, University of Winnipeg” (though in fact, the University of Winnipeg has never had a climatology department. Tim Ball was a professor of geography, and he has been retired since 1996.) It did not allow the other side of the debate to be heard. The few mainstream scientists in the film said they had been misrepresented.

Until then I had just assumed global warming was a real thing, but that parade of scientists and graphs in the film made me doubt it for the next couple of years.

The narrator said that global warming is simply caused by the sun:

You can see the source of this graph here. The axis marked “Solar” is relabeled and is a peculiar metric: a filtered average of the “solar cycle length in years”. Climate scientists have many reasons to disagree with this sun idea. The simplest reasons? Its final upward bend is caused by an arithmetic error, and the relationship has completely fallen apart. No wonder the graph stops after 1980! Even Friis-Christensen (whose sun graphs the film uses) wrote a statement on the film’s fishy behavior.

As I read more on the topic, I learned that the vast majority of climatologists agree: greenhouse gases are the main cause of global warming, not changes in the sun. It’s scary that I could be misled simply by seeing a documentary that mimicked science — and more scary how many others use similar tactics.

Reason #1: They lied to you. Are you fine with that?
Solar output peaked in 1960. This is ranked as the #2 myth on SkepticalScience

Remember the famous anti-AGW “petition project” signed by over 31,000 “scientists”? The one that says “there is no convincing scientific evidence that human release of […] greenhouse gases is causing or will, in the foreseeable future, cause catastrophic heating of the Earth’s atmosphere and disruption of Earth’s climate”?

It was signed by almost no climate scientists (39 or 0.1%), and it was signed by just 0.3% of the roughly 10 million Americans that are allowed to sign it under the petition’s rules. Over half of signers did not identify themselves as scientists at all, but rather engineers, medical professionals, computer scientists, and mathematicians. As an American with a BSc in Computer Engineering, I am not a scientist, but I’m eligible to sign it.

A month ago, I saw an ad on Facebook by a group called “Friends of Science”, claiming that the sun is the cause of global warming, “not you, not CO2”. And after leaving a one-star review on its Facebook group, comments on that review let me to talk to a few climate change skeptics.

None of the ones I talked to are scientists, and yet for the most part they show a tremendous certainty that they are right. “Friends of Science” fans even pay dozens of dollars to watch slideshows about how “today’s society lives in the grip of a madness — the belief that humans are causing dangerous climate change.”

Note: sorry for all the links. It’s important to back claims with evidence, though I realize links can be a distraction.

The Consensus

Originally I stuck with a simple argument: several studies have been done on the consensus, and depending on which study you look at, 91% to 98% of publishing climate scientists agree that at least half of global warming since 1950 is caused by humans. (I later learned that this range is on the high side — more on that later.)

Since we are not climate scientists, I argued, we don’t have the expert knowledge necessary to evaluate which side of the debate is right. Therefore, we should defer to the majority for the purpose of choosing public policy.

This argument didn’t seem to change any minds. One man even argued it was completely irrelevant. “Science isn’t a democracy!” he said. Well, he’s right! It’s not a democracy at all! That’s why your opinion on the cause of global warming doesn’t matter. I’m not saying that contrarian climatologists are wrong because they are in the minority — I’m saying you need staggering arrogance to insist that over 90% of climatologists are wrong when you aren’t even a scientist, let alone a climatologist.

Reason #2: Humility is a virtue. Beware the Dunning-Kruger effect, or as Shakespeare said: “The fool doth think he is wise, but the wise man knows himself to be a fool.”

In this piece I use two words: “contrarian” meaning “a small minority of legitimate climatologists who believe less than half of global warming since 1950 is caused by humans” — and “denier”, meaning “non-climatologists with an unshakable belief that AGW (Anthropomorphic Global Warming) is BS (Bullshit).” (Edit: By the way, the ideal audience for this article is a third category that I call the “doubter”, who doubts AGW but isn’t impervious to evidence.)

The resistance of the deniers is understandable. I’ve learned that there is a massive web of denial out there, with numerous blogs and hubs like Steven Goddard’s blog and WattsUpWithThat dedicated to “educating” people that AGW is BS.

Readers of WattsUpWithThat agree to disagree with most climatologists

Deniers get good rankings on Google, and they have a voice in Forbes online. Even the New York Times hired one, defending its decision by pointing out there are “millions of people who agree with him” (do they think science is a democracy?)

Experienced deniers have moved beyond simplistic claims that global warming isn’t happening, or that “it’s the sun”; they now argue that global warming is real, and even that CO2 really can cause warming — just not enough to ever worry about. The new trick is to say “I am part of the 97%, because I believe CO2 can have some effect!” Perhaps most famously, contrarian climatologist Roy Spencer (who was featured heavily in the Swindle movie) claimed in Senate testimony that he was part of the 97%.

It wasn’t true. Spencer was talking about John Cook’s 2013 study, which included Spencer’s papers. Its public database shows that he is among less than 2% of scientists in that study whose published research “minimizes or rejects” AGW.

“I am in the 97%” is a lie.

Scrutinizing the consensus numbers

Why study the consensus? Because in a world full of people trying to manipulate your beliefs, it’s the only way to tell what scientists really think. Deniers listen to scientists that refute global warming, and ignore all those that don’t. That’s not science, that’s confirmation bias.

Climate science is hard, and it won’t be fully settled for many years, but we have to decide now what to do about CO2, because it lingers in the atmosphere for centuries (see lifetime statistics here), and our emissions are rising exponentially.

You may have seen smaller numbers than 97% or even 91%. That’s because there are so many to numbers to choose from:


Yes, Obama was wrong that “97% percent of scientists agree”.

There is no consensus among “scientists”. There is only a consensus among scientists that study Earth’s climate. With all the political messages flying around, you can’t really expect scientists with no knowledge of climate science to buy into AGW. Novice climatologists often don’t buy it, either.

There’s a metastudy reviewing the various studies of consensus. The consensus numbers steadily increase among those with more experience in climate science, reaching 91% to 97% among experienced climatologists, depending on which study you choose to believe.

Source: PBL Netherlands Environmental Assessment Agency. This is based on Verheggen’s 2014 study, which showed the weakest consensus among all the studies I looked at.

To understand these studies, be aware that working scientists typically write (or co-write) one or more papers per year, so if an author has 10 “publications”, they have probably have less than 10 years of experience. Every study asked for number of publications, not years of experience.

I reviewed several individual studies personally. Before I discuss their findings, please note that there is no question that global warming is happening: virtually no one actively working in climate science denies that.

  • 97% of “climate researchers” agreed with the IPCC in 2010 that “Anthropogenic greenhouse gases (GHGs) have been responsible for ‘most’ of the ‘unequivocal’ warming of the Earth’s average global temperature over the second half of the 20th century” (Anderegg 2010). This study examined the public opinions of only 908 experienced climatologists who have their names on at least 20 papers. It drew names from several sources including “12 of the most prominent statements criticizing the IPCC conclusions”. (2018 Edit: I eventually learned that I had misread the study — 97% applies only to the top 100-200 scientists; it’s more like 90% for all 908.)
  • 88% of 124 AMS climate scientists who mainly publish in climate science agreed in 2014 that roughly half or more of warming over the past 150 years was caused by human activities, including 78% who agreed that the cause of global warming over the past 150 years was “mostly human” (Stenhouse 2014). The other 12% had a variety of opinions, the most common being that humans have had some effect, but we need more evidence to determine how much. Agreement was lower for for climate scientists publishing mainly in ‘other areas’ (81%). In this study, notice that the question says “150 years”. Most climatologists agree that warming after 1950 was mostly caused by humans, but they also agree that less than half of warming before 1950 was caused by humans. In fact, the study says, “six respondents sent e-mails to notify us that their answers would have been different if we had asked about the most recent 50-yr time frame”.
  • Excluding indeterminate answers (‘I don’t know’, ‘Unknown’, ‘Other’), 84% of survey respondents in Verheggen 2014 said that more than half of “global warming since the mid-20th century can be attributed to human-induced increases in atmospheric GHG concentrations”. This rose to 91% among the 25% with the most “self-declared publications”. This survey was among the largest, with dozens of questions and 1868 respondents. 218 scientists from “signatories to public statements disapproving of mainstream climate science” were contacted and about 4% of all respondents were in this group. The study notes that “by also soliciting responses from signatories of public statements who are not necessarily publishing scientists, it is likely that viewpoints that run counter to the prevailing consensus are somewhat magnified in our results.” Thus, 84% and 91% are probably underestimates of the consensus. Individual survey results were kept anonymous. In my opinion, there’s a flaw in the survey’s design, due to which the indeterminate answers are difficult to interpret.
  • 93% of “working PhD Earth scientists” surveyed in the American Association for the Advancement of Science (AAAS) in 2015 agree that “Earth is warming due mostly to human activity.” This 2015 Pew survey also asked scientists about other controversial issues like GMOs and nuclear energy, so you may find the results interesting for other reasons.
  • Of 11,944 climatology papers published between 1991 and 2011, 4014 expressed or implied an opinion about AGW. Of those, 97.1% of those papers explicitly or implicitly endorsed AGW, 1% expressed uncertainty about human causation, and 1.9% rejected or “minimized” AGW (Cook 2013). Also, endorsement of AGW has increased over time. After criticism by Richard Tol, some abstracts were re-reviewed — producing a new count of 97.2%. When counting the authors of the papers instead of the papers themselves, the agreement was 98.4%.

The last number, 98.4%, is a weak signal, because any acknowledgement that humans cause warming was counted as an endorsement of AGW, unless the paper uses language that “minimizes” that endorsement or offers an alternate explanation. Thus, the most famous contrarians like Spencer and Christy were counted in the 1.6%, while contrarians taking softer positions, such as Judith Curry, were in the 98.4%.

So the real consensus for humans causing “half or more” of the warming since 1950, is between 84% and around 90% for all climatologists, and between 91% and 97% for experienced climatologists. It may be stronger than that: remember that the numbers 91% and 84% were associated with “more than half” and are likely underestimates, so the consensus should be even higher than that if our standard is “roughly half or more”.

Reason #3: The consensus that humans are the main cause is real. It’s above 80% by any reasonable interpretation. Plus, novice contrarians often change their views as they gain experience.

One more thing: Some respondents to Verheggen 2014 say human greenhouse gas emissions are responsible for more than 100% of warming. “more than 100%” means that if it weren’t for our GHG emissions, the Earth would have been in an overall cooling trend since the mid-20th century. In fact, this minority was bigger than the one saying “under 51%”. Plus, the “under 51%” crowd tended to be less certain:

Source: PBL NEAA. Interestingly, contrarians are bimodal: there’s an extra hump (top right), a small group (2% of the total) who are “virtually certain” GHGs don’t affect the climate much, unlike typical contrarians who are less certain. Perhaps these “true believers” form the backbone of the denier community.

I’m not saying the “over 100%” crowd is right. But if you’re going to ignore their warnings, doesn’t it make even more sense to ignore contrarians?

Still not convinced?

When faced with the consensus, vocal deniers ignore it and keep arguing their case. I couldn’t stand to let that go unchallenged, so I spent an unreasonable amount of time learning about climate science to see if I could persuade them on a scientific basis, or at least refute them until they stop talking.

I read SkepticalScience, I looked at some denier and contrarian blogs, and finally I read dozens of pages from IPCC AR5 and did hundreds of Google searches.

From what I’ve seen so far, it’s clear that climate science is quite complex and subtle. Some fine details can make a big difference, but many other details don’t matter very much. It is these minor details that deniers usually focus on.

Climate science is tricky

Major climate system components and interactions (IPCC FAR, 1990)

The basics are simple enough.

The sun is by far our greatest heat source. It blasts Earth’s surface with up to 1000W/m², totalling about 120,000 terawatts of electromagnetic radiation, 24 hours a day — thousands of times greater than the 17 terawatts our civilization uses.

Greenhouse gasses act as a blanket that keeps temperatures in the range that life on earth is tuned for. CO2 is a “minor” greenhouse gas — the dominant one is water vapor (from oceans and so on), and that’s the one that keeps the planet livable. Increasing CO2 a lot — even doubling it—wouldn’t directly raise temperatures by much more than 1°C.

The biggest disagreements and uncertainties lie in the much more complex topic of feedbacks. Most climatologists believe that the direct temperature change caused by CO2 is amplified by these feedbacks. The most obvious example is melting polar ice caps: a little more heat causes some ice to melt. Ice is white, so it reflects solar radiation back into space, whereas seas absorb solar radiation, causing more heating. That heating, in turn, slowly causes more melting, until a new “equilibrium” is reached. This is just the reverse of what happens during a glacial period, when solar energy absorbed by the Earth decreases moderately, causing a magnified temperature drop as more water freezes and reflects more light back.

However, there are other important feedbacks, and it can be difficult for nonscientists to learn about all of them, and their overall effect, from an unbiased source. Climatologists are the only people dedicating hundreds or thousands of hours familiarizing themselves with the small technical details that complete the picture. The rest of us see summaries produced by journalists, bloggers, scientists and politicians — many of whom want to convince you that AGW is either a big lie, or a catastrophic problem.

Major climate feedbacks (IPCC AR5 Synthesis Report)

So that’s the theory. Then there’s the day-to-day practice of measurements.

Satellites do not measure temperature directly, and there are many potential sources of error in their measurements. Land stations do measure temperature directly, but coverage is not as good and there are still various possible sources of error. Even weather balloons have challenges. Small but systematic errors can be important when our goal is to measure differences smaller than 0.1°C over 50+ years. Temperature measurements in U.S. ground stations have historically been done by volunteers taking measurements to record the weather (not the climate). These stations have often moved over decades past and the technologies used have changed too. Climatologists must therefore notice any systematic errors that might have to be corrected.

Having gathered all the temperature readings, climatologists also have to decide how to interpolate readings across the globe and compute a global average in the most reasonable and unbiased way. (Also, if satellite readings aren’t quite matching ground stations, ocean stations, or weather balloons, somebody has to figure out what went wrong and coordinate with other organizations to correct the data—in the U.S. this analysis is reportedly handled by USGCRP.)

Climatologists had legitimate reasons to correct the data from U.S. ground stations, but those corrections increased average temperatures, so deniers cry fraud — forgetting, apparently, that the U.S. makes up only 2% of the area of planet Earth.

Globally, the NOAA adjustments make a difference of less than 0.1°C over 70 years after 1945. Source

Everybody’s globally-averaged temperature charts were produced with help from government-funded climatologists. Even the most hardcore deniers have to trust climatologists’ information at some point. So, who are you going to trust?

One thing I want to highlight is that deniers often talk about “the” temperature record as if there is only one, and they talk about climate science as if it were a single unified group of people. This makes it easier to believe that “they” are under the control of the U.S. or the U.N., that “they” are engaged in groupthink, or that “they” are involved in a giant conspiracy.

Some argue it’s unfair to use red for cold places. A better argument is that one month of data shows weather, not climate.

In fact, there are many independent countries with many independent groups researching every little aspect of climatology, and there are many independent teams doing their own measurements and analyses.

For example, there are seven teams measuring the ocean.

And there are at least four global temperature data sets produced by the U.S., the U.K. and Japan, using data from satellites, ground stations, ocean buoys and weather balloons. Remember this when a denier tries to casts doubt on data from one particular source.


The truth can hinge on facts that are hard for non-scientists to follow. There are plenty of ways to twist the facts around, or use factual graphs to make non-experts believe it’s a fraud, or that the whole thing has been blown out of proportion by “liberals”, or even that most or all of the roughly 10,000 climate scientists in the world are incompetent.

The intricacy of the science also helps explain why roughly 3–9% of experienced climatologists aren’t convinced: there are still little nooks and crannies in the science where one can legitimately question the majority opinion. But legitimate contrarians produce subtle technical arguments, not the smoking guns that deniers want.

The Denier’s New Groove

This idea that CO2 can cause warming, just not very much, is roughly consistent with what the 3% to 9% say, which allows deniers to believe they are being scientific. The idea is incomplete, though, since they have to explain what causes most of the warming, too. Here’s how they complete the picture:

  1. Claim a large naturally-occurring warming (e.g. “the sun”, “recovery from little ice age”, “volcanoes”, “Pacific Decadal Oscillation”/PDO/AMO, or “internal variability”)
  2. Claim that climate scientists are frauds who manipulated the raw data to make the warming look much larger than it actually was, or are so enormously incompetent that they “accidentally” did so.
  3. Both of the above

But if you want to prove any of this, I have a lot of questions for you.

Do you say “naturally occuring”? Then why is warming is faster than was ever seen in proxy records from the last 1200 years? Is your theory consistent with the hottest years on record (2014, 2015, and 2016)? Contrarians don’t actually agree with each other, so which specific contrarians do you think are right?

More than one answer was allowed. On average, those disagreeing with the IPCC gave 2.45 reasons why, yet not one of these answers broke the 50% mark, i.e. there is no consensus among contrarians. And while “natural variability” was the most common answer, it is also pretty vague; many factors go into “natural variability”. Climatologists will tell you that “natural variability” goes up and down — not just up. Source: PBL NEAA. Question 3c (Figure 6) in the original Verheggen study also suggests that contrarians do not agree on what, if not CO2, causes global warming.

I think the lack of agreement among skeptics — a buffet of alternative hypotheses — is an important part of denial that doesn’t get enough attention. Quantifying which alternative hypotheses have merit and which are bogus is not so important; to the denier they all have merit simply because they don’t blame humans.

Do you say “fraud”? Then what is your evidence for massive fraudulent manipulations? Who committed this crime? How many scientists are involved in the conspiracy? What was the motive, back before 1980, before politicians cared about the issue, for these unspecified actors to perpetrate a fraud? How can fraud significantly change not only U.S. weather stations, but the entire global average? Why are fraud theories more likely than oil companies or political operatives seeding misinformation and doubt among the public? Why is fraud more likely than humans spreading baseless conspiracy theories, as they always do? Did the fraud also extend to the nine investigations of ClimateGate that found no fraud? How is that possible?

Tony Heller, BSc Geology, has been the leading proponent of fraud claims

Also, if scientists are easily corrupted, why would the corruption only happen in one direction? For example, if you think pro-AGW scientists were bribed by unidentified liberals, why would there be no bribes for anti-AGW scientists by unidentified conservatives, or by the $5 trillion oil industry? If you think climatologists are unduly influenced by their peers, why would they not be influenced by the media or by movies like “the Great Global Warming Swindle” and “Climate Hustle”?

Do you say “incompetence”? Then who specifically are the incompetent people, and how could any imaginable amount of incompetence cause a large, systemic, worldwide, false warming signal? You do know that there are at least four kinds of data and many independent networks of thermometers around the world, right? Did you know there are four agencies from different countries each computing their own, slightly different, global temperature averages? Did you know that the U.S. is 6% of Earth’s land area and 2% of the total, limiting the global impact of changes to U.S. data? Also, how do you decide who is competent and who is not? Is it based on whether their scientific findings match your political beliefs?

“These days, to get attacked, all we have to do is step foot off campus and tell anybody — even a local Qantus club, or a local church, or even a group of elementary school kids, that climate change is real”

Deniers also complain that funding for climate science has increased — which makes sense given the need to understand how much-or-little we affect the climate. But deniers argue that “they” push the global warming angle just to increase funding for climate science.

But why would a climatologist care that more funding is added for climatology, if they themselves aren’t getting paid any more than they were before? Deniers seem to assume that climatology is a cash cow, but don’t identify any researchers who are now paid more because they supported AGW. If the government spends more on climatology, the natural thing to expect is that more researchers are being hired to do more research. It does not mean that any scientist who originally proposed AGW is given fatter and fatter paychecks.

Deniers seem to want it both ways, arguing there is no consensus and the science isn’t settled, but also that scientists “have to” believe in global warming in order to get funding. If that’s so, why do most climatology papers appear neutral about the causes of global warming (62.5% of nearly 12,000 abstracts)? Isn’t funding granted for research in advance? If dissent is not allowed, how are the 3%-to-16% still receiving funding? And why do they disagree about just how large the CO2 warming effect is?

1,620 climatologists opined about greenhouse gasses in Verheggen 2014

Denier strategies

So, next time you hear “evidence” that global warming isn’t real or isn’t caused by greenhouse gasses, watch for their tricks:

  • Distracting you with arguments that mitigating global warming is too expensive (it is not), that “alarmists” have “extreme views”, that liberal politicians have said false things (so what?), or arguing that the common man is being tricked (I say that too!)
  • Giving plausible reasons why past warming was fake, why GHGs can’t cause much warming, or why Earth will stop warming in the future. They expect your “common sense” to agree, simply because your (and their) lack of expertise makes you unaware that the argument is wrong.
  • Cherry-picking on certain parts of the earth while ignoring the bigger picture. For example, the denier says correctly that the antarctic is gaining sea ice, that one study (controversially) says it’s gaining land ice, and that specific parts of Greenland are gaining ice. What they don’t tell you is that the water around Antarctica has undeniably warmed up, that some scientists believe it’s losing land ice, that the arctic is losing ice faster than the antarctic is gaining ice, and that Greenland as a whole has been losing ice at an accelerating pace for about 13 years.
  • Giving arguments from a small number of contrarian scientists while ignoring most scientists. Notice in this article how little I rely on claims of any one scientist. There are about ten thousand climatologists in the world and many millions of other scientists; some of them will always be wrong.
  • Using extreme underestimates of climate change, e.g. “0.4°C of warming since 1945” or “almost no warming in the last 20 years”. To enhance this trick, combine it with worst-case estimates to make climate science sound suspicious: “and yet they claim there will be 5°C of warming in the future!”
  • Confusing weather and climate, or showing that one location was unusually warm in the past at a time when the global average temperature is recorded as colder, or focusing on U.S. data while ignoring global data, or telling anecdotes about one place or another. In fact, changes in weather patterns are expected to make certain locations colder: global warming is uneven. Colder weather in one place is balanced by hotter weather in another.
  • Arguing ad-hominim, or ignoring an argument based on who made it.
  • Insisting without much explanation that models can’t predict anything. They are partly right: contrarian models did fail to predict the increases over the last 20 years.
  • Using a flurry of different arguments (a “Gish Gallop”) to give off an impression of overwhelming evidence. Here you can see almost 200 common denier claims along with the corresponding facts and majority opinions.
  • Using fake information or graphs like this one:
The views of ‘Cliff Harris’ are a bit unique. There seem to be no climatology papers by him (if you see C Harris, that’s Charles Harris) and this “graph” has multiple errors. Allegedly Cliff Harris actually studied insurance law. Source

Here’s the real data. There is not one historical record, there are many:

Northern hemisphere temperature reconstruction from proxies and simulations (Source: Australian Government)
Scientific temperature reconstruction from various proxy data plus thermometer record (red).
Long-term proxies seem to diverge more, so there is more uncertainty about them. Deniers can convince you that temperatures used to be higher by cherry-picking proxies with higher maximums, but the average of all proxies shows a different story. More information

The Modern Contrarian

The best contrarian arguments focus on genuine uncertainties in the science — the kinds of issues that top contrarian climatologists are studying. For example, climatologists have had difficulty modeling cloud behavior, and the tropospheric not-so-hot spot. The sheer quantity of warming proves that humans have had some effect, but contrarians argue that because of uncertainties about cloud and troposphere behavior, we can’t be sure that warming will accelerate or even continue in the future.

I must admit that this is possible, simply because non-climatologists like me don’t have the expertise to judge such questions. If the questions being raised were easy to answer definitively, the consensus would be very nearly 100%.

Most of the IPCC’s key estimates admit a ten percent chance that they are wrong: five percent that their estimate is too high — and another five percent that it is too low. While contrarians argue IPCC projections are overstated, there are other climatologists on the other side arguing that the IPCC is too conservative.

IPCC AR5 Synthesis Report, page 6: Assessed likely ranges (whiskers) and their mid-points (bars) for warming trends over the 1951–2010 period from well-mixed greenhouse gases, other anthropogenic forcings (including the cooling effect of aerosols and the effect of land use change), combined anthropogenic forcings, natural forcings and natural internal climate variability (which is the element of climate variability that arises spontaneously within the climate system even in the absence of forcings). The observed surface temperature change is shown in black, with the 5 to 95% uncertainty range due to observational uncertainty. The attributed warming ranges (colours) are based on observations combined with climate model simulations, in order to estimate the contribution of an individual external forcing to the observed warming. The contribution from the combined anthropogenic forcings can be estimated with less uncertainty than the contributions from greenhouse gases and from other anthropogenic forcings separately. This is because these two contributions partially compensate, resulting in a combined signal that is better constrained by observations.
Reason #4: If you think 3–9% of experts could be right that our warming effect is small, couldn’t the experts on the other side be right that the overall warming effect is underestimated?

Even if contrarians are right, ocean acidification will still continue unchecked.

Reason #5: CO2 causes ocean acidification even if no additional warming occurs.

The Modern Denier

Denier arguments, on the other hand, misrepresent contrarian science, or focus on issues that are not explained in enough depth on the biggest anti-denial site, SkepticalScience.

For example, deniers take issue with the IPCC first assessment report from 1990, which says

Under the IPCC Business-as-Usual (Scenario A) emissions of greenhouse gases, the average rate of increase of global mean temperature during the next century is estimated to be about 0.3°C per decade (with an uncertainty range of 0.2°C to 0.5°C) This will result in a likely increase in global mean temperature of about 1°C above the present value by 2025. (page xi)
Source: NASA GISS. Based on tabular data

SkepticalScience glosses over this issue, so let’s look more closely. Now, the business-as usual case assumed CO2 emissions would stay roughly the same (page xxxiv). The reality was worse — CO2 emissions increased — but the ocean absorbed the CO2 faster than expected, so that overall CO2 levels match the original scenario.

At the end of 2011, deniers rejoiced as they learned that 2011 was officially a cool year: only 0.14°C above 1990. But then, global temperatures rose five years in a row, and 2014, 2015 and 2016 became the three hottest years on record, for an overall warming of 0.54°C since 1990 or 0.21°C per decade — within the IPCC’s first estimate.

But even back in 2011, deniers were premature in declaring the IPCC wrong. Here’s why:

  • The first report had predicted larger increases later in time, and hey, wouldn’t you know it, 2025 is later in time!
  • Even if FAR had been outright wrong, the first report had said, in bold, “There are many uncertainties in our predictions particularly with regard to the timing, magnitude and regional patterns of climate change, due to our incomplete understanding” (page xii). Their investigation was not over, and in any case they were predicting the climate trend, not temperatures in specific years.
  • Most importantly, the second IPCC report in 1995 (SAR) greatly scaled back global warming projections. How can deniers highlight FAR but ignore SAR, which had more science backing it up? 2016 was much hotter than SAR projected! The answer seems obvious: SAR contradicts the “IPCC is alarmist” narrative, so deniers ignore it. And the rest of the world ignores both FAR and SAR because they are outdated. Have a look:
Greatly reduced projections in IPCC SAR, page 39 (1995). 2016 was 0.54°C above 1990.

But that’s not all. In fact, 1990 was a record-setting hot year, 0.18°C hotter than the average of 1985–1989. The IPCC could not have used 1990 as a baseline, since its report was published in July 1990. If we compare 1989 to 2016 instead, the change was 0.70°C or 0.26°C per decade. And if we (wrongly!) cherry-pick 1992, there has been 0.76°C of warming or 0.32°C per decade, higher than the FAR’s best estimate.

The point is, people can play with these numbers to make FAR look either totally wrong — or downright prophetic. The truth lies in the middle: FAR’s projections were on the high side, but SAR’s projections were on the low side. The newest projections lie in between.

Whatever. The dedicated denier can keep arguing forever.

If you learn enough about climate science, you’ll be able to counter misleading arguments with equally plausible arguments of your own — and perhaps equally wrong, because studying a topic for a few weeks doesn’t make you an expert no matter which side of the debate you are on. Two non-scientists debating the finer points of climate science is stupid. Feel free to do it if you want. I did! But it’s stupid.

What the science says

To better understand the case for global warming, I would refer you to Seth Miller’s article on this. It doesn’t cover every issue — it can’t. But it considers a important issue: evidence that CO2 isn’t just correlated with warming, but can also cause it.

Deniers are correct: this photo is not evidence of climate change.

Other issues

According to various mainstream climate models (negative numbers indicate cooling)

There are many other issues that we could argue about:

  • How much the sea level will rise
  • Why the “haitus” happened
  • Whether there will be more extreme weather
  • Whether global warming has benefits
  • Whether models can predict climate
  • Whether getting off fossil fuels is expensive

But one thing is certain: if the deniers lied to you about past warming, you can’t expect them to be honest about future projections, the impact of climate change, or the cost of getting off fossil fuels. Listen to real climatologists, and if you listen to contrarians, listen to alarmists too — it’s only fair.

Also, listen to risk experts like Nassim Nicolas Taleb of Black Swan fame, who wrote this statement on AGW. Heat waves, rising sea levels, and extra hurricanes are not “catastrophic” by themselves, but they can cause tension between the nations that caused it and the nations that suffer from it. Climate change adds straw to the camel’s back. It’s foolish to think the world is so stable that a World War III could never happen.

Reason #6: Inflaming global tensions is not without risk, and increasing sea levels is not without cost.

What the future holds

Denial follows a progression: first they say “it’s not happening”. Then they say “it’s happening, but humans didn’t do it”. Nowadays “it’s happening, but humans only cause a little bit of it”. Finally they’ll say “it’s happening, and maybe we did it, but global warming isn’t bad, it’s good!”

There is another consensus, less discussed: climate scientists also agree that the net effect of global warming is bad. In the Pew study, 77% of “domain experts who are Earth scientists” say it is “a very serious problem” and another 17% say it is “somewhat serious”. Another study found that “41% of scientists believe global climate change will pose a very great danger to the earth in the next 50 to 100 years, compared to 13% who see relatively little danger. Another 44% rate climate change as moderately dangerous.”

Source: PBL NEAA survey of climate scientists

It may be good for Canadian weather and maybe farms. It is not so good for coastlines, the oceans, weather stability, and so on.

But there is good news!

While deniers were denying, innovators were innovating.

Certainly, publicly-funded clean energy programs, eliminating subsidies for the fossil fuel industry, and a carbon tax would help us innovate and reduce emissions faster.

However, cheap and clean energy is already coming online at an accelerating rate. Rapid price drops in solar, especially, have taken even environmentalists by surprise. Even with no subsidies, it’s only a matter of time before clean technology will win on price alone.

Reason #7: Global warming is solvable. It’s not hard if we all chip in a little: many hands make light work.

But as an American, I find it sad that the U.S. — denier central — is behind other countries, such as China, in developing these technologies.

Reason #8: If we don’t lead the world in green technology, we get left behind.

If you bookmark this, you can read about these clean technologies later:

Battery research didn’t get enough investment in the past, but the growth of solar power and electric cars will probably change that:

There are actually tons of other ways to tackle global warning. Which ways are the best? That’s been researched, too:

Fusion will be developed too slowly to solve global warming, but it’s cool!

P.S. The Psychology of Denial

What’s going on here? Why is it so damn important for some people to believe that our actions can’t affect the climate? I looked into that, too:

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