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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Human fingerprints on climate change rule out natural cycles

What the science says...

Natural cycles cannot be the cause of observed global warming because they don't fit the observed fingerprints of global warming. Only increasing greenhouse gas concentrations due to human activities fit the observed fingerprints and explain the observed energy imbalance. 

Climate Myth...

It's a natural cycle

"Global warming (i.e, the warming since 1977) is over. The minute increase of anthropogenic CO2 in the atmosphere (0.008%) was not the cause of the warming—it was a continuation of natural cycles that occurred over the past 500 years." (Don Easterbrook)

Global warming refers to the long-term warming of global temperature since the 1850s. The cause of global warming has been investigated by many scientists, who have summarized their finding in multiple assessment reports by the Intergovernmental Panel on Climate Change (IPCC). The only plausible mechanism of global warming is a planetary energy imbalance, with our climate system building up heat. This and the observed fingerprints left on global warming confirm the dominant role of human activities.

Fossil fuel burning is causing recent global warming

Scientists have identified two factors that drive global climate change: internal variability and external forcings. Internal variability refers to the internal processes moving heat around within the climate system. External forcings cause an energy imbalance - with the planet either building up or losing heat - and can be both natural and human caused. The only plausible mechanism accounting for the long-term temperature increase of global warming is through a buildup of heat in the climate system (Li et al., 2007).

Among the various external forcings that can cause the climate system’s energy imbalance, scientists have concluded the main cause of recent global warming is the increase of atmospheric CO2 due to fossil fuel burning.

In order to understand how scientists came to the above conclusion, it is important to understand the various drivers of climate changes.

Internal variability moves heat around the climate system

Climate change is like the motion of water in a kitchen sink with an inflow from the faucet and an outflow through the drain. The motion consists of both the water sloshing around and the rising and falling of water level. The random sloshing around is what scientists call "internal variability," while the rising and falling of water level is what scientists call "forced variability". Internal variability (e.g., ocean cycles such as El Niño South Oscillation, Pacific Decadal Oscillation, and Atlantic Multidecadal Oscillation) moves heat around to give rise to regional climate change on timescales ranging from annual to millennial timescales. Like the water sloshing around, internal variability doesn't build up or dissipate the total amount of heat in the climate system. In contrast, external forcings (e.g., 11-year solar cycle and changes in the Earth’s orbit) change the climate by causing a buildup or loss of heat, similar to the change in water level being determined by the difference between the inflow and outflow.

The single cause fallacy committed by the natural cycle myth

One climate myth argues that recent global warming is caused by natural cycles rather than human activity. The so-called “natural cycles” in the myth may include climate variation due to internal variability or external forcings. Natural external forcings, such as the 11-year solar cycle and changes in the Earth’s orbit, are part of nature and not influenced by human activities. Other external forcings like greenhouse gases and aerosol concentrations in the atmosphere are significantly influenced by human activities, and thus are excluded from natural cycles.

The argument that global warming is due to natural cycle commits single cause fallacy, by assuming there is only one driver of climate change (e.g., natural factors) when there may be others (e.g., human activity). In this case, the myth argues that the same factors, namely internal variability and natural external forcings, that drove past natural cycles must also be the same factors causing current global warming. But the fact is that humans have emitted large amounts of CO2 into atmosphere by burning fossil fuel since the industrial revolution, and it is the main cause of recent global warming. 

One version of this myth is that the natural cycles may cause cyclic climate change with timescales ranging up to millennial timescales, and therefore recent global warming is just the rising phase of such a cycle. However, this argument is ruled out by the observed fingerprints on global warming (seen in Figure 1) since no natural cycles fit all these fingerprints. For example, natural cycles cannot explain why the satellites measures less heat escaping to space at the precise wavelengths which CO2 absorbs (Philipona 2004, Wang 2009).

The observed fingerprints on global warming and the fact that only external forcings can cause a buildup in heat in the climate system work together to not only rule out natural cycles, but also confirm that the anthropogenic CO2 increase in the atmosphere is the main cause of modern global warming.

Figure 1: Schematic of the fingerprints on global warming (Skeptical Science).

Internal variability does NOT build up heat

Internal variability changes the global mean surface temperature by moving heat around inside the climate system without changing the total amount of heat for any sustained period in time. Some internal variabilities, such as the Pacific Decadal Oscillation, can transfer heat from the ocean’s upper layers to the deep ocean. As a result, more heat is moved to the deep ocean and the global mean surface temperature decreases (Douville et al., 2015). Burying all this heat in the deep ocean led to a stagnation of global warming from 2000 to 2015, known as the so-called global warming hiatus (shown in Figure 2).

However, the heat hadn't left the climate system. When ocean cycles shifted to a different phase, the buried heat in the deep ocean was released to the ocean upper layers, causing an increase in the global mean surface temperature. We saw this rebound in warming with 2014, 2015, and 2016 being the hottest years on record. Natural cycles from internal variability only results in cyclical fluctuations and are not the driver of long-term global warming.

Figure 2: This temporary plateau in temperatures has been referred to as a hiatus. Adapted from NASA Earth Observatory.

Since internal variability does not change the climate system’s energy balance and long-term warming requires a buildup in heat, the cause of the global warming can only be changes in external forcings. But which exact external forcing?

Fingerprints confirm fossil fuel burning is the main cause 

The main external forcing driving global warming has to explain the observed “fingerprints”. One of these fingerprints is the troposphere (the lowest part of the atmosphere) warming with the stratosphere (the upper levels of the atmosphere) cooling. Greenhouse gases build up heat by trapping the outgoing radiation on Earth without changing the incoming energy. As most of the greenhouse gases occupy the lower troposphere, they act like a blanket covering the surface. As a result, warming caused by increasing greenhouse gases starts from the lower atmosphere, namely troposphere (Liou 2002). This fingerprint also rules out the sun as a possible cause of warming as  increased solar energy would heat the whole atmosphere.

The amount of received solar radiation also varies with changes in the Earth's orbit. These are referred as Milankovitch cycles. They occur on very long-time scales (10,000+ years) and cannot explain the warming over the past 100 years. In addition, direct measurements show an increased greenhouse effect. The only explanation that fits the observed evidence is the increase in greenhouse gases.

The increase in greenhouse gases in the atmosphere is caused by human activities rather than natural processes. For example, CO2 emission from volcanoes is small compared to anthropogenic emissions. Although the ocean emits large amount of CO2, it actually absorbs more CO2 than it emits, including anthropogenic CO2 (Falkowski and Wilson 1992). So, the net effect of CO2 natural cycles are quite small. In addition, CO2 from fossil fuels has its own fingerprints. Fossil fuels contain less of the carbon-13 isotope, which explains why the atmospheric ratio of carbon-12 to carbon-13 has been increasing as more anthropogenic carbon dioxide gets added to the atmosphere. Additionally, atmospheric oxygen (O2) is decreasing at the same rate that CO2 is increasing, because oxygen is consumed when fossil fuels burn.

Therefore, the only cause of  global warming that both makes sense from a physics point of view and fits the observed global warming “fingerprints” is increase in CO2 from fossil fuel burning.

The climate myth viewing global warming as a natural cycle distorts the fact with a single cause fallacy. Before the 1850s when human influence on climate was almost negligible, natural cycles were the dominant drivers of the global temperature changes. But currently, with large amounts of fossil fuel burned since the industrial revolution, the global mean surface temperature is showing an obvious increasing trend apart from what can be explained by natural cycles. The natural cycles can still explain these fluctuations superimposed over the trend but fails to explain the continuously increasing trend itself. The main cause of recent global warming is the increasing anthropogenic CO2 in atmosphere.

Last updated on 14 November 2020 by Kai Huang. View Archives

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Related References

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Comments 26 to 32 out of 32:

  1. Hello,

    Have you discussed the alleged 'Atlantic multidecadal oscillation'?

    “ we
    talked about the Atlantic multidecadal
    oscillation this is the actual sea
    surface temperatures of the Atlantic and
    it goes into 60 years cycle there's 30
    up 30 down warm and cold phases warm and
    cold warm and cold if you go look at the
    data it matches the Atlantic
    multidecadal oscillation perfectly”



    [JH] Poorly disguised sloganeering snipped.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  2. Postkey @26 , thanks for the youtube video reference.

    It was the best laugh I've had this week !

    Spoiler Alert : the video is a complete waste of time.   Rubbish from beginning to end.  A rant from a crackpot who bases his opinions on the slightly-less-than-truthful info supplied/concocted/doctored by the slightly-less-than-truthful Tony Heller [ aka "Steven Goddard' ].   Plus a large dose of insane Conspiracy Theory.

    The ranter also has a bad case of AMO on the brain [Atlantic Multidecadal Oscillation].   And, from his stargazing at the charts, he predicts [on zero scientific basis] that the Earth is just about to plunge into a Grand Solar Minimum which will devastate the planet with a mini-ice-age.

    Too many other laughable points to mention here.  Yes, the Fall of the Roman Empire; the (European) Black Death Plague; and other grand historical events — all caused by cold weather.   And our ranting friend is clueless and self-contradictory about the decline of arctic ice.

    Sorry Postkey, but on climate this guy has no science and no sense.    ~ A 15-minute video of yawning [seen it all before] rubbish.

  3. "the slightly-less-than-truthful Tony Heller [ aka "Steven Goddard' ]"


    This Tony Heller???



  4. Eclectic @27.

    Thanks for your reply, I'm glad you 'enjoyed it'.

    Is there a statistical base to the 'Atlantic multidecadal oscillation'?

  5. Postkey @26,

    I would concur with the replies so far. I note the oft-repeated word "lie" that features in the YouTube you link to (narrated by "Diamond(?) from the Oppenheimer Ranch Project") which is a pretty good description of the entire video. In the main, the descriptions provided of the data presented is nothing but nonsensical verbal diarrhea, although within this nonsense description, the data presented is mainly genuine. There are however parts of the video where even the data is entirely misrepresented.

    Featuring large in the misrepresentated data is the laughable attempt by Tony Heller to graft on satellite Sea Ice Extent data onto Vinnikov et al (1980) Figure 5 (or more exactly Hoffert & Flannery (1985) fig 5.2).Vinnikov fig5.2 & Heller's crayon workNote H&F(1985)'s fig 5.1 reproduces Vinnikov et al's temperature graph. Heller would have had a more difficult time misrepresenting this temperature data, and also explaining it in light of his fictional ice record. (The image here is the same data as H&F fig 5.1 but presented by Robock 1982.) Robock (1982) fig1

    As for Fig 5.2, as presented by H&F(1985), this at first glance reproduces Fig5 of Vinnikov et al (1980) faithfully. (The original was is published in Russian in Soviet Meteorology & Hydrology Vol6.1 and isn't on-line.) But while the caption of Vinnikov et al's Fig5 is roughly reproduced by H&F(1985), the actual data presented has become misrepresented by the caption. As shown within this Vinnikov slide show, V(1980)fig5 is a plot of the annual ice coverage for the months of July, August & September and not the plot of a 12-month annual average. That is how a value of 6-7 million sq km can be plotted for the period 1925-75 and how any grown-up splicing of more recent ice coverage would be plotting levels of 4-5 million sq km over the last ten years.

    Which brings us to the AMO. The video attempts to suggest that the Arctic Ice Cover matches the wobbles of the AMO. Frankly, that is risible. Even with Heller's nonsense graph it is risible. So I can quite understand Eclectic @27 saying "It was the best laugh I've had this week !"

  6. MA Rodger @30.

    Thank you for your reply.

  7. Postkey @29 , yes that video presentation evoked both laughter & boredom, simultaneously.

    Postkey, as you increase and extend your knowledge of climate matters, you will soon discover two things :-

    (A) For all their imperfections & uncertainties, the scientists aim to present things as honestly & truthfully as they can.

    (B) The anti-science propagandists (such as Mr Heller/Goddard) do not hesitate to mislead and deceive.   They will cherrypick / "doctor" / fabricate . . . to whatever extent they think they can get away with.  They aim to outright deceive the reader — or at least get him thinking that with so much "controversy" then he might as well put the climate/AGW issue on the backburner 'cos it seems nobody knows what the hell's going on.   ~Either of those outcomes will satisfy the propaganda industry, as represented by GWPF, Heartland Institute, and other such "front" organizations.  (And you will notice, Postkey, that the more scientifically-ignorant their audience, the more these proagandists extend their lies & deceptions.  You will see that in places as diverse as Wall Street Journal op-eds and "lie & spin" websites like WattsUpWithThat or JoNova.  They are completely shameless in their disregard for truthful presentation.)

    Postkey, as for the AMO — what do you mean by "a statistical base"?   There are very short-term trends (e.g. the ENSO) having a short up-or-down effect on the global surface temperature, but which (when you think it through) are incapable of altering the long-term climate trends produced by real drivers of climate change (e.g. long-term solar activity changes / Milankovitch-cycle insolation / Northern Hemisphere ice albedo changes / continental drift positional effects / and of course Greenhouse gas alterations).

    But as for long-term (decadal) oceanic events such as the AMO — do they actually exist as some sort of real physical cycle, or are they only a collection of random natural variations that we interpret in our minds as some sort of "real" thing?   ~Interpret in a similar way as our minds "see" a Face in the Moon . . . when in reality we are only observing a random asteroidal-bombardment pattern on the Moon's surface.

    Still, whatever existence the AMO has or doesn't have — it does not and cannot cause significant climate change in the real way that Greenhouse gasses & other such "drivers" do.

    That video presenter was way off into crazy territory.  Either from his own ignorance or from his insane Conspiracy Theory beliefs or from some underlying extremist-political ideation.  And he was certainly shooting himself in the foot by using the mendacious Mr Heller as his "rock".   BTW, the presenter seemed to be "into" some form of agricultural permaculture (which in general I would say is a reasonable thing) but he hints at a Survivalist-type tendency — which is crazy-wrong in regard to apocalyptic "ice-age" threats . . . but which might well make some sense if North Korean nuclear attack occurs!   ~Alas, if the ongoing Global Warming gets very bad, then there will be no "hiding out in the mountains" for would-be Survivalists, since the climate change itself and the hordes of climate refugees will render such plans null & void.

  8. MA Rodger @30,

    I'm confused by this post, and have probably just misinterpreted it. If, as you say "Vinnikov (1980) fig5 is a plot of the annual ice coverage for the months of July, August & September" that would imply ice coverage was similar in 1935-1960 to what it is now; NSIDC data shows that July, August and September mean Arctic ice cover averages at about 6 million square kilometres in recent years, just as the Vinnikov graph does from 1935-1960. That can't be right. In fact, the idea that there was 6 million square miles of coverage for July-August-September over 1935-1960 is contradicted by the recent study Walsh et al 2016, Carbon Brief story In the study, the month September, which obviously has coverage below the July-August-September average, had an average cover of over 7 million square kilometres from 1935-1960.

    And what error has Heller made exactly in his attempt to graft the two graphs together? Has he incorrectly aligned them, or are the data between the two graphs simply showing different things?


    [BL] Link activated.

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  9. Long Knoll:

    Note that the comment you refer to from MA Rodger was made 5 years ago.

    Is this the figure you are referring to from the Carbon Brief article you mention? (I can only link to the image, not embed it here.)

    Note that the values in that figure are for sea ice extent. That is not the same as sea ice area.

    • Sea ice area in the area that is actually ice.
    • Sea ice extent is the are of ocean that has at least 15% ice cover. Up to 85% of that area is water, not ice. 1 million km2 of sea ice extent at 15% ice is only 150,000km2 of sea ice area.

    Further explanation is available here.

    So, you should not be comparing area and extent numbers. The area number will be much smaller.

    As for Heller: yes, he is simply combining two different things: full year vs. late summer.

  10. Long Knoll @33,

    If confusion is sought, the early attempts at creating an Arctic Sea Ice Extent/Area record is a good place to start.

    The 'splice' of two of these early attempts was probably not the work of Heller but of a Kenneth Richard shiown in this NoTricksZone post from 2016.

    The more recent part of the spliced graph is taken from Fig 7.20a in the first IPCC Assessment Report of 1990. A similar graph appears in the second IPCC Assessment Report of 1995 as Fig 3.8a. These Arctic Ice records do not match later records which begin to appear in Chapman & Walsh (1993). I have plotted out these various records (see here the graph posted 16/12/22) but have not had any success finding an explanation for the dip in Arctic Ice levels 1973-76. (The use of US Navy data is not something considered accurate today, but the decision not to use it or to use it differently is not something I have seen explained.)

    The earlier part of the 'spliced' graph is from Vinnikov et al (1980) which isn't on-line but note the graphic in this 2013 slide show by Vinnikov from Vinnikov et al (1999) (abstract on-line) presents a record consistent with the current records. And for good measure Walsh is one of the co-authors of Vinnikov et al (1999). So again we see a major reappraisal of the data which hasn't been explained in the literature. And without access to these early papers, the question remains of what the basis for these early records actually is. (And my assertion back in 2017 that Vinnikov et al (1980) was plotting summer ice levels is probably wrong.)

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