From Watts Up With That?
Gabriel Oxenstierna
What drives climate change? Is it the anthropogenic emissions of CO2 and other greenhouse gases [GHG], as the established climate science and the IPCC claims with its GHG forcer hypothesis?
Or is it the natural variations in heat transport to the polar regions during winter, as the new “Winter Gate-keeper hypothesis” [WGH] claims?
The WGH asserts to be a general hypothesis for climate change, fully capable of explaining historical climate change, as well as current changes, and with explicit forecasts for our future climate. In these respects, it compares itself with the established IPCC hypothesis of climate change being driven by anthropogenic GHG emissions. The WGH is fully described in two recently published books, and has also been explained in some detail here at WUWT by its originator Javier Vinós (here, here, here), and also by Andy May (here, here).[1][2]
The WGH introduces a novel climate-forcing mechanism by proposing that changes in poleward heat transport can strongly influence climate. As the planet Earth has two such polar regions, we have one in cold season during most of the year. Temporally, planet Earth has two peaks of energy loss to space. They are when each of the polar areas is dark and cools by radiating more during the polar winter.
The two polar regions have little incoming solar energy and the green-house effect is also very small, especially during the polar winter. If, e.g., more energy would be transported polewards, we’d get a higher loss of energy at the top of atmosphere (ToA), without any compensating gain elsewhere. The energy flux of the planet would be altered by that change in transport.
Of specific significance is the regulation of the heat transport into the Arctic. The highest loss of energy is during the dark Arctic winter. Between November and February, the planet emits more energy than at any other time. It’s a complex mechanism, where five different “gate-keepers” influence the climate via the polar vortex, thus regulating meridional heat transport. This mechanism affects the radiative flux at the ToA, which changes the energy content of the entire climate system.
The WGH is a unified hypothesis that builds on a multitude of established theories regarding its contributing processes. An attempt at “definition” of the WGH by its creator formulates a whole range of testable claims:
“The Winter Gatekeeper hypothesis proposes that changes in the heat and moisture that reach the polar regions during winter, particularly the Arctic, play a major role in climate change. This is because the winter polar regions have a very low greenhouse effect due to the lack of atmospheric water vapor, the Earth’s main GHG. Combined with the lack of solar radiation, this leads to an effective loss of energy to space through outgoing infrared radiation.
Consequently, changes in the transport of heat to the polar regions during winter have an impact on the energy budget of the planet. The Arctic is particularly important in WGH because its weaker polar vortex allows for greater variations in heat transport.
Any factor that affects the atmospheric zonal circulation, the generation and propagation of planetary waves, or the strength of the polar vortex acts as a vortex gatekeeper capable of regulating the transport of heat to the Arctic during winter. These gatekeepers include theQuasi-Biennial Oscillation, El Niño-Southern Oscillation, volcanic eruptions, multi-decadal ocean oscillations(modes of variability), andsolar activity. […] The climate exhibits decades-long heat transport regimes, separated by abrupt shifts.”([2], pages 408f and 533, my emph.)
In this, and following posts I will analyze the bolded claims regarding heat transport by looking at climate data with a focus on the warming Arctic, since WGH gives the Arctic a defining role in climate change processes. Actually, the Arctic is a focal point for both the two competing hypotheses about climate change.
The Arctic has been warming almost four times faster than the global average since around 1990.[3]The established climate science (IPCC) essentially explains the warming in the Arctic with the greenhouse effect and has given it its own name: “Arctic Amplification” [AA]. The IPCC claims that 50-70 percent of the AA is caused by the increased amount of anthropogenic GHG in the atmosphere (emissions of CO2 etc.).[4] These increase the green house effect, which is assumed to cause the large temperature increase in the Arctic in winter. However, they neither provide any coherent theory how this happens, nor an explanation of the timing of the AA.
The WGH rejects the IPCC hypothesis. Instead, it claims that changes in energy flows into the Arctic are fundamental to explain the increasing temperatures there. It asks: From where comes all the additional energy that makes the Arctic winter temperature rise so sharply?
Watts in must correspond to watts out
The climate is constantly striving for a basic energy balance: the solar energy coming in must be balanced by an (approximately) equal amount of thermal energy radiating out – globally: Watts in must correspond to watts out.This has to be true as a global average, but spatially and temporally it is never met. See the animation below with the monthly sequence of the radiation balance, from January to December.
Figure 1. ToA radiation balance month by month. The animation shows the net energy exported or imported per gridcell, 1°x1°, average value per month, 2000 – 2023. Data from Ceres.
All this temporal and spatial flux is naturally driven by the Earth’s and the Sun’s various diurnal and seasonal cycles and other interactions. In spite of all the flux, there is a global balance. How is it achieved?
The Sun doesn’t shine in the polar regions during the winter polar night, thus no heat is provided from space. The main source for the outgoing radiation is the energy transported there from the tropics. The Sun irradiates so much into the tropics that it cannot all be efficiently radiated back to space. The energy is therefore transported away – advected – to the regions where it more easily can radiate to space. The resulting polewards transport of energy is achieved by advection of heat and moisture via atmospheric weather systems, and to a smaller degree by ocean currents:[5][6]
Let’s look at the the global radiation (im)balance for one month, calculated as the net incoming solar energy (solar irradiation minus reflected SW radiation) minus outgoing LW radiation (OLR) at the Top of the Atmospere (ToA). Here’s June:
In June, the maximum of solar irradiation is in the northern parts of the tropics. These parts absorb much more heat than they radiate to space, as shown by the orange and red areas. The highest levels are reached over the oceans, where humidity is high. We can also note the effect of the very dry atmosphere over desert regions in e.g. Sahara.
Some of the absorbed heat is converted into kinetic energy in weather systems. These do the job of moving the heat from the tropics to the polar regions. Solar heat accumulated in the tropics (positive values; shown in green/yellow/red colors) is thus transported polewards, where it is radiated into space (negative values; in grey/ blue/black).
The northern hemisphere up to the Arctic (except Greenland) has a positive energy balance during summer. In other words, we have a surplus of incoming solar radiation minus what is radiated back into space. But even in the summer month of June, the Arctic north of 70° latitude has a negative net radiation of energy, as seen in the figure.
In the Southern Hemisphere, it is winter in June and Antarctica is in the polar night. No solar energy comes in. To the north of Antarctica is the Southern Ocean, where the energy balance is maximally negative with up to 200 watts per m2 radiated into space (the black areas in the figure).
For the climate, water is the only significant energy carrier. The reason why most of the energy is emitted over the ocean is that the humidity is high there, so more energy is available. Energy is mainly transported by water vapor in the atmospheric weather systems. Over continental Antarctica, however, the air is extremely dry and only a fraction of the energy is available compared to the Southern ocean. This also applies to Greenland.
In December, six months later, the figure is reversed. We now have a huge wintertime radiation deficit in the Arctic, as seen by the negative values reaching almost -200 W/m2 there. That is balanced by a large surplus, mainly in the southern tropics:
Researchers have since long established the negative energy budgets for the polar regions.[7] The current average yearly heat loss in the Arctic is 114W/m2, with up to 200 W/m2 lost in the winter. This strongly negative radiation budget is a result of the dryness of the atmosphere and a very small greenhouse effect. The negative energy budget is much more pronounced in the middle of winter (fig. 3B) but applies all year round, as seen in the animation in figure 1. Three questions arise:
1. How to account for the heat that is radiated to space from the Arctic?
If we look at the Northern Hemisphere south of the Arctic, we see that the average radiation balance is almost 9W/m2 for the latitudes up to 70°N:
This excess net energy originates in the tropics and advects polewards with the weather systems via the Hadley and Ferrell cells. The amount of energy advected from the southern latitudes into the Arctic is of similar size to what is radiated from the Arctic (2.1 PW compared to 1.8 PW, as yearly averages according to the radiation data).[6][8]
Another, much smaller source of energy is latent heat released as the summer meltwater freezes. As fall transitions to winter, the Arctic cools. When the surface freezes, the latent heat stored in the water since the previous spring thaw is released. [6]
During the summer months, the Arctic energy balance is around zero as seen in figure 3A. Incoming net solar is balanced by an equally large OLR.
2. How do we know that the energy directed towards the polar regions is actually radiated out into space?
The surface in the Arctic is covered with ice and snow most of the year. Ice and especially snow have low thermal conductivities. The small energy flow through ice is also always from the warmer ocean below the ice to the colder air above the ice. Most of the net energy coming to the Arctic via the atmosphere will thus be radiated to space. Except for a few summer months with open water no significant amount of energy from the ocean can contribute to the radiation at ToA. During summer, a lot of energy is also spent on melting ice and snow. That latent heat is later released as the freeze sets in. The net energy from this cycle balances around zero on a yearly basis. [7]
3. Do changes in the energy transport coincide with the onset of AA?
The export of net energy from the tropics has a positive trend since around 2000, see figure 4. The intensity of the tropical Hadley cells have increased, and they have also significantly expanded polewards since 1997.[9] Also the Ferrel cells show similar increases.[10] The ocean also contributed to the Arctic with a net step change in 1997.[11]
The increase in net heat transport to the Arctic shown in figure 4 is almost 2 W/m2 since 2000. This is distributed between increased radiation to space and increased downward longwave radiation that warms the surface.
The outgoing heat radiation (OLR) from the Arctic is currently around 197 W/m2. The OLR has been increasing significantly with around 4 w/m2 since 1990, when the AA started, wherof around 2 W/m2 since 2000:
The energy transported to the polar regions has clearly increased over time, which has helped to increase the energy lost via AA. The result is a planetary cooling effect.
We thus have the answer both as to the amount, and the timing of AA: the increase in OLR in figure 5 in the 1990/2010 timeframe corresponds quantitatively with the increase in advected heat from the south. The data and the science fully support the Winter Gate-keeper hypothesis in this respect.
The second round brings up the topic of climate shifts.
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] IPCC AR6 WG1, chapter 9, see e.g. figure 9.14https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-9/
Forthcoming posts will analyze the greenhouse effect in the Arctic in more detail, as well as IPCC’s explanation for AA.
[5] Global ocean heat transport dominated by heat export from the tropical Pacific, Forget and Ferreira, Nature 2019, https://doi.org/10.1038/s41561-019-0333-7
[6] Decomposing the meridional heat transport in the climate system, Yang and 4 co-authors, Clim Dyn 2015, https://doi.org/10.1007/s00382-014-2380-5
[7] Peixoto, J.P. & Oort, A.H., 1992. Physics of climate. New York: American Institute of Physics. pp.353–364.
[8] 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
[9] The Hadley Circulation in Reanalyses: Climatology, Variability, and Change, Nguyen +4, 2013, https://doi.org/10.1175/JCLI-D-12-00224.1
[10] Contributions of the Hadley and Ferrel Circulations to the Energetics of the Atmosphere over the Past 32 Years, Huang and McElroy, AMS 2014, https://doi.org/10.1175/JCLI-D-13-00538.1
[11] Increased ocean heat transport into the Nordic Seas and Arctic Ocean over the period 1993–2016, Tsubouchi and 7 co-authors, Nature 2021, https://doi.org/10.1038/s41558-020-00941-3
Technical note
It’s not an easy task to knead the satellite data files so that you can select and plot the data the way you want. This note is to help others with a guidance as to which softwares and methods are workable, reliable, and accessible without too much programming.
I first download data in the NetCDF4 format, e.g. from Ceres. The data are then preprocessed in the program CDO (Climate Data Operators) in Linux (in my case Ubuntu under Windows). All the time series data are calculated as surface-weighted monthly values in CDO. (I highly recommend preprocessing data in CDO rather than attempting it in R or Python, as the command line operated CDO is very efficient, fast, and reliable.)
After preprocessing, the selected data in the resulting .nc files were read into R/Rstudio where the figures were created with GGplot. The raster map plots were created with tidyterra:SpatRaster.
All data and software are free to use/open source.
Gabriel Oxenstierna is a PhD at Stockholm University and one of the Clintel signatories.
The photo illustrating WGH in the vignette is the GateKeeper roller coaster.
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