When it comes to global warming, falsifiable theories are in short supply

Paul MacRae, May 21, 2008

The gold standard for what is and isn’t “science” was set by philosopher of science Karl Popper in his 1959 book The Logic of Scientific Discovery.

For Popper, science begins not with observation of data, as the non-scientist would expect, but with an hypothesis, a way of approaching the data. The hypothesis is then tested by the researcher, the results published if warranted, and then retested and/or peer reviewed by other scientists.

However, these reviewers are not trying to determine if the hypothesis is true, as the non-scientist would expect, but to see if it isn’t true. In other words, the wording of an hypothesis is put into a form that will allow other researchers to test and, potentially, disprove it. This, for Popper, is the test of a scientific hypothesis: does it offer the opportunity to be tested, and does it offer the opportunity to be falsified.

If other researchers can disprove it, then the hypothesis fails or needs to be revised. If they can’t disprove it, this doesn’t mean the hypothesis is True, but it moves closer to the status of a theory that many are willing to accept, provisionally, as true.

Popper’s example is Albert Einstein’s Theory of Relativity. Einstein offered a falsifiable hypothesis for his theory: If light waves weren’t bent by the gravity of the sun, then his theory was false. As it turned out, light waves did curve due to gravity, and Einstein’s hypothesis passed the test (that test, anyway), and has taken the status of a theory. Note: it is still a “theory”: it is not accepted as absolute truth because it is conceivable that a further test could falsify all or part of it.

When it comes to climate science, falsifiable theories are in low supply. The basic hypothesis of those who believe that humans are causing global warming is the following, taken from Al Gore’s book An Inconvenient Truth: for Gore, the unanimous “consensus” is that global warming is “real,” that “human beings are the principal cause,” and that “its consequences are so dangerous as to warrant immediate action.”1

Is Gore’s hypothesis falsifiable?

Is there a falsifiable hypothesis here? For the first part of Gore’s hypothesis, that global warming is “real,” we have considerable evidence–the planet has clearly warmed over the past 15,000 years or so because the northern quarter of the planet isn’t buried in glaciers. A falsifiable hypothesis might be: If the global temperature goes down for a considerable number of years (climatologists usually accept 30 years as a benchmark for a change in climate), then global warming cannot be “real,” at least for that time.

The second part of Gore’s hypothesis is based on the correlation between global warming and increasing levels of carbon dioxide in the atmosphere. As carbon dioxide levels increase due to human activity (and they are increasing; see Figure 1), says Gore’s hypothesis, then global warming should increase since human carbon emissions are the “principal” cause of warming.

CO2 levels increasing
Figure 1. Rising CO2 levels

Putting this into scientific, falsifiable hypothesis language: If carbon dioxide levels increase while global temperatures either remain level or fall, then carbon dioxide cannot be the “principal” cause of global warming.

Here the hypothesis fails. The planet hasn’t warmed since either 1998 or 2001 (see “Is the planet still warming?“) depending on how you crunch the numbers (see blue line in Figure 2, below), yet carbon dioxide levels (the green line) continue to increase. As you can see, there’s very little correlation between carbon dioxide levels and temperature over the past 20 years. (In fact, there’s very little correlation between CO2 and temperature levels over the past hundred million years, either (see Figure 1 in We’re a long way from climate ‘oblivion’.”)

CO2 and temperature compared
Figure 2. Carbon dioxide and temperature levels compared 1979-2008

The planet started to warm in the mid-1850’s, following a five-century-long cold spell called the Little Ice Age (1350-1850), before carbon emissions were a serious factor. The planet cooled between the 1940’s and the 1970’s, while increasing carbon emissions were a factor.

It makes little sense to say, as the official climate “consensus” does, that, although temperatures went up and down naturally before the 20th and 21st centuries, in the last 100 years warming and cooling have primarily been caused by human activity.

Correlation of CO2 and temperature doesn’t prove causation

It’s worth noting, as well, that the hypothesis that humans are the “principal” cause of warming isn’t proved simply because global warming and carbon dioxide levels are both increasing. Correlation doesn’t prove causation and there could be many other factors determining a warming climate apart from carbon dioxide increases: changes in solar intensity, changes in ocean currents, changes in ice cover, changes in cosmic ray intensity, volcanoes — the possible natural causes of climate and climate change are legion and almost all are far more powerful than anything human beings can do to the planet short of a nuclear war.

Of course, the anthropogenic (human-caused) global warming supporters, faced with the evidence that the planet has stopped warming and therefore the death or major revision of their hypothesis, are backpedalling furiously, as they must since rising carbon dioxide but a flat-line or falling temperature is exactly the opposite of what their hypothesis predicts.

Defending the ‘consenus’ hypothesis

Here’s an explanation by Mark Lynas, author of Six Degrees: Our Future on a Hotter Planet, a book that predicts doom and gloom if the planet’s temperature goes up by that amount:

“Although CO2 levels in the atmosphere are increasing each year, no one ever argued that temperatures would do likewise. Why? Because the planet’s atmosphere is a chaotic system, which expresses a great deal of inter-annual variability due to the interplay of many complex and interconnected variables. Some years are warmer and cooler than others.”

Wrong. What Gore, the Intergovernmental Panel on Climate Change and the “consensus” have been arguing is that higher temperatures and CO2 levels are in lock-step. All of the IPCC’s temperature projections for the next century show increasing warming. Also, 10 years of no warming isn’t just normal “inter-annual variation” as Lynas is suggesting — it’s more like a climatic trend. Gore has refused to comment on the latest climate data showing cooling, which also tells us something. Indeed, he refuses to debate the issue with skeptics at all, which also tells us something.

What Lynas is reluctantly admitting is that human carbon emissions aren’t the principal source of global warming or cooling — our CO2 can be trumped by natural factors. In other words, the anthropogenic hypothesis is wrong or at least flawed. Which is what the global warming “deniers” have been saying all along: yes, human beings are contributing to global warming, but we are not the principal or even a major contributor. Lynas is now defending an hypothesis that has been at least partly falsified.

‘Catastrophic’ hypothesis is untestable, and therefore unfalsifiable

As for the third part of Gore’s hypothesis, that global warming must be catastrophic — this is untestable, and therefore unfalsifiable, and therefore not a true scientific hypothesis, because we have no scientific data from the future. It is at best an informed guess, at worst religious-style apocalyptic prophecy. However, from what we do know about past warming, both in the last few thousand years and millions of years ago, global warming will likely be more beneficial than harmful, although of course there will be adjustments needed.

Why are warm times better? Because warm times bring more rain to most areas of the planet and allow longer growing seasons, which means better crop yields. We are currently feeding 6.5 billion people because the planet has been growing warmer over the past three decades. More carbon dioxide in the atmosphere also means most plants grow better — at the moment our planet is at a 250-million-year low in carbon dioxide.

The alternative, since climate isn’t stable and is always changing, is moving toward a colder planet. Past experience shows cold times are tough for human beings, although ice ages may have been a factor in the evolution of homo sapiens. We evolved from tree-dwelling primates to ground-dwellers to cope with colder, less favorable conditions brought on by the current ice age that began about three million years ago. It’s also likely that the Little Ice Age (1350-1850) encouraged technological experimentation, leading to the modern industrial world.

Gore vs. the IPCC

Because the anthopogenic hypothesis either can’t be put into a falsifiable hypothesis or, when it is put in that form, it fails the scientific test, Gore and many climate scientists fall back on the “consensus” that most climate scientists agree with this hypothesis. However, scientific truth isn’t a matter of consensus. Fifty years ago the consensus was that continents couldn’t move; today, we know they do. If the Gore hypothesis supporters had better evidence, they wouldn’t need to rely on the unscientific claim of “consensus.” They’d show us the evidence and we’d be convinced; they wouldn’t need the exaggerations and misinformation that Gore serves up.

Why have I focused so much on Gore’s hypothesis in An Inconvenient Truth? Several reasons. For one, Gore is the best-known spokesman for the anthropogenic hypothesis, even though most of what he preaches is misleading, exaggerated, and often plain wrong. Much of it doesn’t even agree with what the IPCC preaches (see “Al Gore: The speech he needs to give“).

A second reason is that few of the “consensus” climate scientists have come out against Gore’s ideas, although these scientists are very willing to attack those skeptical of the human-caused warming theory. In general, orthodox climate science would rather support Gore than criticize his errors — errors so glaring that even a British judge could easily point them out — lest the anthropogenic hypothesis lose public support.

And, most tellingly, the IPCC’s “consensus” scientists were willing to accept a Nobel Peace Prize with Gore, even though most climate scientists, if not all of them, must be aware that much of what Gore says in his film and books is misleading, exaggerated, and often plain wrong. Clearly, they accept Gore’s hypothesis even though recent climate research, and particularly findings that the planet isn’t currently warming, have falsified most of the anthropogenic hypothesis and the rest — Gore’s predictions of doom — can’t be tested and therefore can’t be falsified and therefore don’t qualify as true scientific hypotheses.

In other words, much of what passes for climate “science” these days isn’t science because it either fails to provide a proper falsifiable hypothesis or, when it does, the hypothesis is falsified but not abandoned or revised. Climate researchers with the true scientific spirit would, at this point, leave the anthropogenic carbon dioxide hypothesis behind and move on to learning more about what are more likely the real causes of climate change: natural cycles.


What would qualify as good hypotheses on global warming? JunkScience.com has issued the Ultimate Global Warming Challenge: $500,000 “to the first person to prove, in a scientific manner, that humans are causing harmful global warming.” The winner only has to disprove (falsify) the following two non-anthropogenic hypotheses, thereby increasing support for the anthropogenic hypothesis:

Global Warming Challenge Hypothesis 1

Manmade emissions of greenhouse gases do not discernibly, significantly and predictably cause increases in global surface and tropospheric temperatures along with associated stratospheric cooling. [In non-hypothesis language: Prove human emissions are causing warming.]

Global Warming Challenge Hypothesis 2

The benefits equal or exceed the costs of any increases in global temperature caused by manmade greenhouse gas emissions between the present time and the year 2100, when all global social, economic and environmental effects are considered. [In non-hypothesis language: Prove that the benefits of fighting warming will be greater than the costs.]

So far, nobody on the anthropogenic side has stepped forward to collect what should be easy money.

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  1. Al Gore, An Inconvenient Truth, Emmaus, PA: Rodale Press, 2006, p. 268.