Culture

Climate change reducing Earth’s albedo

By Steve Drury First PUBLISHED ON October 4, 2021

According to a new study (Goode, P. R.et al. 2021. Earth’s albedo 1998–2017 as measured from earthshineGeophysical Research Letters, v. 48, article e2021GL094888; DOI: 10.1029/2021GL094888) the ability of the Earth to reflect solar radiation back into space has been decreasing significantly over the last two decades. The conclusion has arisen from measurements of the brightness of the lunar surface. A new Moon is barely visible, apart from a thin sliver illuminated by the Sun. Its overall faint brightness is due to sunlight reflected from the Earth’s surface that faces the Moon: so-called ‘earthshine’. New Moons occurs when it is above the lit side of the Earth, so they appear during daylight hours. Earthshine depends on the ability of the Earth’s surface and cloud cover to reflect solar radiation, or its albedo.

Albedo was high during the last ice age because of continental ice sheets and it can also occur when there is an unusually large percentage of cloud cover or a lot of dust and aerosols in the atmosphere, perhaps after a large volcanic eruption. High albedo leads to global cooling. Decreased albedo allows the atmosphere to heat up, and conspires with the greenhouse effect to produce global warming.

Philip Goode and his colleagues measured earthshine on the Moon between 1998 and 2017 to precisely determine daily, monthly, seasonal, yearly and decadal changes in terrestrial albedo. The Earth reflects roughly 30% of the solar energy that falls on it, although it varies with Earth’s rotation, depending on the proportion of land to ocean that is sunlit. Over the two decades earthshine decreased gradually by ~0.5 W m-2, indicating a 0.5% decrease in Earth’s albedo and a corresponding increase in the amount of solar energy received at the land and ocean surfaces. To put this in perspective the estimated warming from anthropogenic greenhouse emissions over the same period increased by just a little more (0.6 W m-2). Albedo decrease is reinforcing the greenhouse effect.

Sea-surface temperature anomalies over the Pacific Ocean during a ‘positive’ phase of the Pacific Decadal Oscillation – reversal to a ‘negative’ phase cools the eastern Pacific and warms the west (Credit: Wikipedia)

Although it might seem that increased seasonal melting of polar sea ice would have the main effect on albedo, this is not borne out by the earthshine data. What is strongly implicated is a decrease over the Eastern Pacific Ocean of highly reflective low-altitude clouds. That might seem counterintuitive, since warming of the sea surface increases evaporation, but the reduced low-cloud cover has been measured from satellites. Many scientists and most climate-change deniers have thought that an increase in cloud cover at low latitudes and thus albedo would moderate surface warming. The opposite seems to be happening. The key may lie in one of the Earth’s largest climate phenomena, the Pacific Decadal Oscillation (PDO). This has a major effect on global climate through long-distance connections (teleconnections) to other climatic processes. The satellite data hint at the changes in albedo of the Western Hemisphere having been related to a long-term reversal in the PDO. The Earth’s climate system increasingly reveals its enormous complexity.

See also: Earth is dimming due to climate changeScience Daily, 30 September 2021.

If you’d like to read more of Steve’s blog…….  https://earthlogs.org/homepage/

Many thanks to Steve Drury for permission to republish his article and to Bernie Bell for sending it into The Orkney News

2 replies »

  1. Albedo is an overall indicator. I would say a clear one, compared to rising temperature (which has more complex model, more diversity over the planet, faster and uncontrollable).
    Albedo includes satellites, ice shields, clouds, atmosphere clearness.

    William Shatner commented his flight emotions as looking up – is death and darkness and the Earth is bright and is life below.

    Not to diminish the necessity of the climate change awareness, but to wrap it to every day life small things that we get for granted are dimming already. And many areas are in disasters and more will come.

    Still when the full Moon shines to my open window in a clear night, I cannot sleep.

    • I don’t know where you live lariliss, but here in Orkney, last night there was a full moon. I was up in the early hours of the morning – looking out – moonlight, white clouds, many shining stars – knew that I needed to go back to sleep, but didn’t want to lose the night.