Gabriel Oxenstierna
For the first time, the IPCC’s doctrine of CO2 as a ‘control knob’ in our climate faces a serious challenger in the form of a comprehensive hypothesis about what drives climate and its shifts.[1][2] This article is the third in a series evaluating this new hypothesis of natural climate variability.
The Arctic [70-90°N] is a real focal point for the climate, as well as for the two competing climate hypotheses. It has warmed 3-4 times faster than the globe since 1979, and is by far the region with the highest rate of warming.[3] This phenomenon started in the late 1990s and is mainly seen during winter:
Figure 1. The AA is mainly a winter phenomenon (blue curve) in the highest latitudes, 80 – 90°N. Temperature anomalies compared to a 30-year comparison period. The ‘1997’ shift period is marked with a yellow bar. Image source: DMI
For the “Winter Gate-keeper hypothesis” [WGH], the Arctic is particularly important: The weak and sensitive polar vortex there allows for large variations in poleward heat transport that it claims regulates the climate, much like a control knob.[1, p.542] Energy is transported to the Arctic in order to get radiated from there, where radiation is as most efficient – not least due to a low green-house effect [GHE].
When heat is moved to a location where it can be more easily radiated to space, the outgoing radiation increases, leading to a reduction in the energy content of the system. Changes in transport of heat and humidity up to the Arctic explain both the strong warming trend in the Arctic and its effects on global warming, according to WGH. This is especially the case during the dark polar winter, which is why we see the pattern in figure 1. Cf. the first post in this series, here.
The Green-house Gas Forcer hypothesis says that Arctic warming primarily is caused by the increased amount of anthropogenic GHGs in the atmosphere (CO2 etc.).[5] These increase the GHE, which is assumed to cause the large temperature increase in the Arctic. The GHE-driven warming in the Arctic has even been given its own name: “Arctic Amplification” [AA]. This is IPCC’s take on the relationships:
Figure 2. The IPCC links the Arctic amplification in panel (e), to anthropogenic emissions of CO2 in panel (f), and provides a projection of the trend towards an ice-free Arctic by 2100 under two of the emission scenarios in panel (g). Source: AR6 WG1 Figure 9.14.[4]
They attribute between 50 and 70 percentof AA to human emissions of GHGs in the atmosphere (CO2 etc.), based on model runsshowing a pattern as in figure 2. IPCC writes: “…Arctic amplification, is a ubiquitous feature of the response to GHG forcing simulated by climate models.”[4] In their models, AA is attributed to a combination of radiative forcing patterns from GHGs and various feedback mechanisms.[5]
Both climate hypotheses thus emphasize the role of the GHE in global and Arctic warming, but in quite opposite ways:
The WGH says that AA is a natural variation, and that the low GHE in the Arctic is essential for its function as the prime location for regulating global warming/cooling.
The IPCC says that AA mainly is due to anthropogenic emissions of GHGs, and that the main factor that causes AA is the GHE itself via radiative forcing.
To see which hypothesis is a better representation of reality, we need to examine the GHE in some detail.
The green-house effect
The GHE is the warming of the Earth’s surface due to the Earth having an atmosphere. The effect is directly linked to the amount of GHGs in the atmosphere, first and foremost water vapour. The GHE is caused by some of the heat radiating from the Earth’s surface warming the air in the atmosphere instead of radiating into outer space. This makes the Earth on average about 33 degrees warmer than it would be if it had no atmosphere at all.
The remaining net radiation has been absorbed by the atmosphere in various ways. The thermal radiation that doesn’t disappear into space must, by definition, remain and radiate towards the Earth.
And this is what the greenhouse effect looks like, measured by satellite and calculated as absorbed radiation as a percentage of surface radiation and animated month by month: (see Appendix 1 regarding how the GHE is calculated)
Figure 3. Animation of the monthly GHE measured as a percentage of longwave (LW) radiation back to Earth. The effect is measured in each individual gridcell 1° × 1° in the unit W/m², expressed as a ratio. All measurements are made at the ToA. Grey fields in East Antarctica have negative values (as low as -6%, which isn’t on the scale). Data from Ceres Ebaf 4, averaged over the entire period March 2000 – September 2023.
The GHE is not homogeneous over the planet mainly due to the unequal distribution of water vapour. It is stronger in the wet tropics and weaker over deserts. The GHE varies between -6% in parts of Antarctica up to 56% in parts of the tropics. The global average is 39.7%.
In the animation we also see that the GHE varies strongly over the seasons, especially in the polar regions. Let’s compare the months of June and December:
Figure 4. The GHE during the months of June measured as a percentage of LW radiating back to Earth. The global average is 39.7%. For the Arctic the figure is 29.5% and for Antarctica 4.8%. Grey fields in East Antarctica have negative values. Horizontal line indicates 70°N. Data from Ceres.
The GHE is at its weakest in the very dry polar regions, which means that heat radiation can reach space most easily there. This is particularly pronounced in winter.
Above the coldest polar regions, the greenhouse gas molecules in the atmosphere are relatively warmer than the surface of the cold Earth. This means that more heat is radiated to space than would be the case if there were no greenhouse gases there.[6, p. 17] The GHE is then negative. This happens when temperature inversions make the surface colder than the atmosphere.
In much of East Antarctica we see this happen. In these areas, the upward thermal radiation is greater than the downward radiation. The extremely dry atmosphere thus makes the outgoing thermal radiation greater than it would be without greenhouse gases.[7] The negative GHE is most noticeable during the polar winter, but is also present on an annual basis (grey fields in the animation, figure 3).
When it is winter in the northern hemisphere, we get the following picture:
Figure 5. The GHE for the month of December measured as a percentage of LW radiating back to Earth. Horizontal line indicates 70°N. Data from Ceres.
During the Arctic winter the GHE becomes very weak. Greenland and northern Siberia, for example, have a GHE that is close to zero in winter, and thus have a particularly strong cooling effect – all the heat radiates out, none is captured by the atmosphere. This is because the atmosphere is both colder and drier. It is during the polar winter that energy is emitted to space most efficiently.
The greenhouse effect is strong in the tropics and weak at the poles in winter. As a result, increased heat transport to the poles makes the planet cooler because they act as cooling radiators.
The Arctic is the most important cooling region of the climate system. This is given by the massive energy import to, and radiation from, the Arctic, combined with its weak GHE. This is especially significant during winter, when the radiative cooling is even more effective than in summer.
Let’s summarize what we know about the GHE as evidenced from the satellite data shown in Figures 3-5:
1. Humidity dependent: the GHE is strong where the air is humid, and weak where the air is dry.
2. Geographically dependent: the GHE is weak over the polar regions, and over deserts. The main reason for this is low humidity. The polar regions are sometimes referred to as ‘ice deserts’.
3. Temperature and seasonal dependence: the GHE varies strongly with the seasons in the polar regions and is weakest in the polar winter. Parts of the Arctic have close to zero GHE in winter and in East Antarctica it is even negative.
Global data show a trend towards increasing GHE over the last 15 years. However, the Arctic shows no increasing trend over the same period, neither in winter nor in summer – see Appendix 2.
The Arctic paradoxes
In winter, the atmosphere in the polar regions is uniquely transparent to heat radiation. It is easier for the climate system to cool down in winter, as less of the heat radiating upwards is captured by the atmosphere. In the Arctic, the outgoing radiation is particularly high in winter because there is so much energy transported there from the south. This leads us to the following two Arctic paradoxes:
- The region with the fastest warming on Earth also cools the climate more efficiently than any other region.
- The region with the fastest warming on Earth has the (second) weakest greenhouse effect.
The Arctic’s function to cool the climate system is unique. In comparison, Antarctica has an even weaker GHE than the Arctic. But Antarctica has no warming trend in winter, and also has significantly less energy inflow than the Arctic.
Summing up
Research shows that the Arctic amplification (AA) is linked in time to increased transport of energy and moisture from the south. This explains the AA, and is fully supported by quantitative evidence.[8]
In order to accept the IPCC’s hypothesis that AA is mainly caused by increasing CO2 levels, one would expect to be given a physical explanation of how increased CO2 would lead to increased energy transport from the south. Such a theoretical explanation is not provided by IPCC, or in the literature referenced by them.[4][5] The only support the IPCC provides for its hypothesis are runs with its CO2-rigged models. That is questionable evidence.
Scientists who have analysed the climate history since the last ice age show that the impact of CO2 on meridional energy transport is “negligible”.[9] Satellite data also provide no support for an increasing GHE over time in the Arctic.
In summary, there is little support for IPCC’s hypothesis that increasing CO2 emissions and GHG forcing cause the Arctic amplification:
– There is no theory explaining how increased CO2 levels would lead to increased energy transport up to the Arctic.
– There is no support in climate history for a link between CO2 levels and energy transport to the Arctic.[9]
– There is no support in satellite data that the GHE has increased in the Arctic during the last 24 years, in spite of experiencing a shift to a warmer and wetter winter climate (see Appendix 2). The GHE is also particularly weak in the Arctic during winter.
– There is no explanation for the timing of AA: why did it start around 1997 and not earlier, if CO2 is supposed to cause it? Cf. the previous post on climate shifts.
– There is no explanation for the two Arctic paradoxes: that among all regions on Earth, the place with the strongest warming by far,
a. is the place where the planet cools more efficiently than anywhere else,
b. has the (second) lowest GHE of all regions.
In conclusion, there are good reasons to reject the IPCC’s hypothesis that the Arctic amplification is due to the increasing levels of greenhouse gases.
On the other hand, there is nothing that falsifies the Winter Gate-keeper hypothesis regarding the Arctic’s role in the climate system. There is ample physical evidence, as well as a substantial body of scientific research on meridional heat transport, all supporting its hypothesis regarding the causes of Arctic warming.
Appendix 1: On measuring the GHE
The direct approach is to measure the net of longwave radiation up from the Earth’s surface, minus the longwave radiation that is lost to space:
LWearth surface – LWTOA
Measured that way as an energy flux, the average global GHE is about 159 W/m2. However, there is a fundamental issue with the direct approach to measuring the GHE:the amount of GHE is highly dependent on changes in the surface temperature. As the surface gets warmer, it radiates more (Planck, or blackbody radiation), so more energy is absorbed by the atmosphere, which in turn increases GHE. This problem needs to be addressed wherever we have seasonal changes in temperature between summer and winter. To get around the problem of the temperature dependence of GHE, it is preferably calculated as a percentage of the surface LW radiation.[10]
(LWearth surface – LWTOA) / LWearth surface
Appendix 2. Development of the greenhouse effect in the Arctic
The IPCC and its ilk hypothesize that human GHG emissions and the GHE are responsible for the Arctic amplification (AA) that started in the late 1990s.[5] Let us test for the following:
- How does the GHE evolve over time?
- Has it increased in the Arctic in winter over the last 25 years as the AA has become stronger?
- Does the GHE increase in the Arctic with increasing levels of CO2?
On a global scale, there is a clear trend towards a somewhat higher GHE. This is mainly due to the increase in humidity that is an effect of global warming. As the air gets warmer, it increases its water vapour content, i.e. the amount of the main GHG: [11]
Figure 6. Evolution of the GHE globally, percentage of LW radiating back to Earth. Mean value 39.7%. Green curve is Loess average. 2000:3-2023:9. Calculated from spatial satellite data per gridcell, 1°x1°. Data source Ceres.
But in the Arctic, we don’t have the same trend. This is what it looks like in June and December, respectively:
Figure 7. Evolution of the GHE in the Arctic in June, percentage of LW radiating back to Earth. Mean value 29.4%. Green curve is Loess average with confidence interval (2σ). 2001:6-2023:6.
Figure 8. Evolution of the GHE in the Arctic in December, percentage of LW radiating back to Earth. Average value 23.5%. Green curve is Loess average with confidence interval (2σ). 2001:12-2022:12.
There is thus no support in the data from the period of AA that it has been caused by an increasing GHE in the Arctic.
References
[1] Vinós, Javier, Climate of the Past, Present and Future: A scientific debate, 2nd ed., Critical Science Press, 2022.
[2] Vinós, Javier. Solving the Climate Puzzle: The Sun’s Surprising Role, Critical Science Press, 2023.
[3] The Arctic has warmed nearly four times faster than the globe since 1979, Rantanen and 7 co-authors, Nature 2022, https://doi.org/10.1038/s43247-022-00498-3
[4] Ocean, Cryosphere and Sea Level Change, IPCC AR6 WG1, chapter 9.3, and quote from ch 4.5.1.1.2. See also SPM A.1.5, B.2.5.
[5] The Polar Amplification Model Intercomparison Project (PAMIP) contribution to CMIP6: investigating the causes and consequences of polar amplification, Smith and 14 co-authors, 2019, https://doi.org/10.5194/gmd-12-1139-2019
[6] Dependence of Earth’s Thermal Radiation on Five Most Abundant Greenhouse Gases, van Wijngaarden and Happer, 2020, https://arxiv.org/abs/2006.03098
[7] How increasing CO2 leads to an increased negative greenhouse effect in Antarctica, Schmithüsen and 4 co-authors, 2015, https://doi.org/10.1002/2015GL066749
[8] See chapters 10.3 and 11.5 in [1] for references to the scientific research on meridional transport into the Arctic. A fortcoming post in this series will also present the quantitative evidence.
[9] Heat Transport Compensation in Atmosphere and Ocean over the Past 22 000 Years, Yang and 5 co-authors, Nature 2015, https://doi.org/10.1038/srep16661
[10] Observational determination of the greenhouse effect, Raval and Ramanathan, Nature 1989, https://doi.org/10.1038/342758a0
[11] Revisiting the greenhouse effect—a hydrological perspective, Koutsoyiannis and Vournas, Hydrological Sciences Journal, 2023, https://doi.org/10.1080/02626667.2023.2287047
Technical note
The diagrams were created in R from NetCDF files, see the technical note in the first post.
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