Richard Willoughby
Summary
This article examines the seasonal variation in Earth’s reflectivity through the CERES era. Changes in solar forcing over the same period are examined with the objective of identifying possible linkages to the measured change in reflectivity.
The primary driver of the changes in solar forcing over the 15 year observational interval is identified then assessed to show why there will be a reversal of this particular change by 2037. This introduces the prospect of the reducing trend in reflectivity being reversed by 2037; noting that seasonal cycle change in solar forcing will revert to the longer term trend that has caused the NH to gradually warm over the past 300 years.
The article concludes by pointing out the Earth’s reflectivity is primarily a function of ice/snow and the available solar EMR that can be reflected. There is no reflection off ice/snow when the daily solar is zero as occurs each year in the polar regions.
Introduction
The Clouds and the Earth’s Radiant Energy System (CERES) project provides satellite-based observations sufficient to enable fair estimates of Earth’s radiation balance. The satellite based instruments have been calibrated to match the ocean heat content as determined by the Argo ocean submersible drones. The first CERES mission began in 1997 but the reflected electro-magnetic radiation (EMR) for this analysis was not available till 2004. The NASA NEO data used here only has full year data from 2007. The most recent full year is 2024. The analysis considers changes to 2024 relative to 2007.
Chart 1 displays the monthly area averaged reflected solar EMR for both hemispheres.
Both hemispheres exhibit similar annual cycles with reflected EMR peak in mid-summer. The June average in the northern hemispheres is 136.3W/m² while the December average in the southern hemisphere is 152.7W/m². These summer peaks are dominated by high reflectivity of ocean and land ice/snow rather than clouds. Also the polar regions have high monthly average solar EMR in summer.
Chart 2 examines the monthly reflected EMR over just land masses, which includes any permanent ocean ice.
The land exhibits similar annual cycle to the total but the summer peaks are somewhat higher. June average is 154.9W/m² while December average is 219.2W/m². Again the summer highs are due to the high reflectivity of permanent ice/snow.
Changes in Reflected EMR over Land
Land has a faster thermal response to changes in surface insolation than the oceans so the changes in reflected EMR over land give a more immediate response compared with the muted response of the oceans. Accordingly Chart 3 displays the change in monthly area averaged reflected EMR over land and permanent sea ice in 2024 relative to 2007.
The annual average over all land is down by 1.06W/m² but there is considerable month-to-month variation. The NH displays some cyclic regularity while the SH is more random. The November peak of 6.02W/m² is an outlier and begs closer examination per Image 1.
The higher November reflectivity in the SH is the result of increased cloud over tropical and temperate land. This leads the monsoon cycle in these regions so is related to increased moist air advection from the tropical oceans rather than convective instability over the land.
Changing Solar Forcing and Advection
Earth’s positional relationship with the Sun is not perfectly periodic over any time cycle. The two bodies have continual movement relative to each other. The positional variation changes the solar intensity reaching Earth and those changes drive changes in Earth’s climate. Chart 4 examines solar intensity at 15N and 50N through 2024 to consider how the difference in solar forcing contributes to poleward advection in the NH. The Earth to Sun positional data used for these calculations was generated by JPL’s Horizons App.
Apart from early summer, the solar intensity at 15N is higher than the solar intensity at 50N. However the oceans have slower thermal response compared with land so there will be a lagged response between poleward advection and the difference in solar intensity from low latitude to high latitude.
Chart 5 now considers how the difference in latitudinal forcing has changed in 2024 relative to 2007.
The difference curves for 2024 and 2007 appear identical on the left hand scale but the annual cycle becomes apparent when the delta is displayed against the right hand scale. The range from peak to peak over the annual cycle is slightly above 0.6W/m².
Charts 6 and 7 provide similar daily solar EMR for the SH.
The delta 2024 relative to 2007 for the SH has a similar range of 0.6W/m² while the peaks are narrower in the SH compared with the NH.
Solar and Reflectivity Changes
The delta in solar forcing peaking in October in the SH is consistent with increased cloud cover over tropical land in the SH in November. There is also some consistency in the NH between the annual cycle in the delta in solar forcing and the increase then decrease of reflectivity in the NH. Neither of these observations are compelling though. On the other hand the delta in forcing over the 15 year period is of similar magnitude to the reduction in reflectivity.
Looking ahead to 2037
If the delta in solar forcing from year-to-year is a driver of Earth’s reflectivity then the response over the past 15 years can be used as a basis for prediction. Chart 8 offers the delta in solar forcing for both hemispheres to 2037 relative to 2024.
The delta to 2037 relative to 2024 exhibits a reversal in seasons in the hemispheres compared with 2024 relative to 2007 and almost a 10-fold increase in range. This reversal is due to the movement of the Sun in and out of Earth’s orbital plane as shown in Chart 9.
In 2007 the Sun was south of Earth’s orbital plane near a minimum while in 2024 the Sun was North of Earth’s orbital plane close to a maximum. This slight movement out of plane changes the declination of the Sun relative to Earth’s axis of rotation. By 2037, the Sun will be almost in plane with Earth’s orbit and that reduces the solar intensity in the NH but increases solar intensity in the SH.
Discussion
Earth’s reflectivity depends primarily on permanent ice/snow on land, temporary ice/snow that forms on land, permanent ice/snow on oceans, temporary ice/snow on oceans and temporary ice in the atmosphere. The amount of reflected solar is a function of the solar intensity; the reflectivity of the ice or snow surface the EMR encounters and the amount of ice present across the globe on any day. Overall, the complexity involved in solar EMR not being thermalised due to Earth’s albedo cannot be overstated. Over the CERES period, Earth’s reflectivity has reduced. There appears to be some linkage between the changes in reflectivity and changes in the solar forcing that drives poleward advection. The seasonal reversal of the forcing change driving poleward advection over the next decade introduces the prospect of the reducing trend in reflectivity reversing over the next decade.
This analysis shows that permanent ice/snow is the most significant factor in summer reflectivity in both hemispheres and that is obviously linked to the high average daily intensity of the summer insolation at high latitudes. It is also apparent that there is significant year-to-year changes in seasonal solar intensity that could cause changes in advection that would change cloud cover and reflectivity but thorough analysis of that is beyond the scope of this article.
Any year-to-year changes in solar forcing have to be considered in the context of longer climate trends. Chart 10 shows how the solar EMR at 40N and 40S will change from 1850 (the year of perfect weather) to 2100.
The curves in Chart 10 are more indicative of the longer term seasonal changes in solar intensity; possibly slightly lower than the mid range of the extremes from specific year to specific year. The NH is experiencing an increase in the warming season solar intensity from March solstice to June equinox and a similar reduction in the late summer-autumn period. These changes are already apparent in the NH ocean warming and the increased early season snowfall in the NH. The increasing snowfall in the NH is presently offset by accelerating spring melt in most locations. An important exception is that the Greenland plateau is already gaining altitude; keeping in mind glaciers first form at altitude then migrate down slope.
The SH has much lower seasonal swing with the increase in spring solar EMR of about 1W/m² being the only notable change.
Conclusion
This article raises the prospect of solar forcing being a key factor in reducing Earth’s reflectivity through the CERES era but fails in making a convincing connection. It also suggests the trend could reverse in the coming decade as poleward forcing reverses seasons to the long term trend. A reversal to increasing reflectivity over the coming decade would strengthen the connection.
Understanding Earth’s reflectivity requires a comprehensive knowledge of ice formation and disappearance across the globe. That requires an understanding of how the solar intensity is changing because ice forming is energy intensive as is ice loss. All ice began life as water in an ocean. The ice that forms in the atmosphere and then settles on land had to be liberated from the ocean surface and into the atmosphere. Evaporation of water is energy intensive.
Understanding climate change on Earth is primarily based on understanding Earth’s physical relationship with the Sun and the ice forming and ice loss processes on land, oceans and atmosphere. It is also apparent that the solar “constant” is not constant and has a role in climate change.
The misdirected demonising of CO₂ has resulted in climate models that are blind to seasonal changes in solar intensity across the hemispheres and naively embody parameterisation of ice forming and ice loss processes that are disconnected from physical reality. The models have created a widely held cargo cult styled primitive belief that eliminating burning of carbon and hydro-carbon fuels will deliver perfect weather that existed on Earth in 1850. Climate models underpin the notion that eliminating use of carbon and hydro-carbon fuels will deliver perfect weather with no destructive storms; no heat waves; no blizzards; gentler cyclones; just the right amount of rain; no deserts; no floods; perfect seasons; perfect crops and so on – all things good. France would not have experienced destructive wild fires in 2025 if humans had not burnt carbon and hydro-carbon fuels. Childish, naïve beliefs.
The Author
Richard Willoughby is a retired electrical engineer having worked in the Australian mining and mineral processing industry for 30 years with roles in large scale operations, corporate R&D and mine development. A further ten years was spent in the global insurance industry as an engineering risk consultant where he developed an enduring interest in natural catastrophes and changing climate.
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