The earth is dimming. What ‘earthshine’ means for our climate system

(Credit: Unsplash)

This article is brought to you thanks to the collaboration of The European Sting with the World Economic Forum.

Author: Johnny Wood, Senior Writer, Formative Content


  • Our planet absorbs light and radiation from the sun and reflects some radiation back into space.
  • But Earth’s reflectivity is reducing over time, according to new research.
  • Rising sea temperatures have reduced reflective low-lying cloud coverage.
  • This could accelerate the impact of climate change.

Look closely at a crescent moon and you may be able to see earthshine: light from the sun reflected by earth onto the moon. But, hurry, this light source is dimming over time, new research shows.

Our planet has no light source of its own but absorbs light and radiation from the sun, while reflecting a fraction of the sun’s radiation back into space. By methodically measuring the levels of earthshine Earth reflects onto the moon, scientists have found that its reflectance – or ‘albedo’ in technical terms – is diminishing over time.

Levels of ‘earthshine’ reflected from earth to the moon are declining over time.
Levels of ‘earthshine’ reflected from earth to the moon are declining over time. Image: AGU

Measuring earth’s albedo is a challenge. The level of reflectivity is subject to daily and seasonal changes and depends on the level of snow, ice and cloud cover. Clouds reflect about 50% of light from the sun, while snow and ice reflect more, compared to just 10% reflectivity from oceans.

Measurements could only be taken when there is no direct sunlight reaching the moon, further limiting data collection.

The study, led by Philip Goode of New Jersey Institute of Technology, observed the moon’s surface from California’s Big Bear Solar Observatory over the 20-year period between1998 and 2017. Comparing like-for-like measurements while controlling for a variety of factors, the team found a “gradual but climatologically significant” decline in earthshine levels, as the chart shows.

Why is this a problem?

Study results suggest that warming ocean temperatures due to human-induced climate change are reducing the levels of low cloud cover over the eastern Pacific Ocean, which act like a mirror to reflect light and radiation from the sun back into space. The more sunlight the earth absorbs, the warmer it will be, the more of the sun’s light earth reflects, the cooler it will be.

Rise in water temperatures

If the drop in Earth’s reflectivity is a temporary effect of periodic changes in weather patterns, such as the decades-long fluctuations caused by phenomena like the Pacific Decadal Oscillation, there is no long-term problem. If, however, Earth’s reflectivity continues to decrease, there is cause for concern as the process could add to the planet’s climate instability.

a chart showing that the average sea temperatures in the world’s oceans have been increasing since 1880.
Average sea temperatures in the world’s oceans have been increasing since 1880. Image: EPA

Global surface temperatures in the world’s oceans have been increasing since 1880 and continue to rise at an average rate of 0.14°F per decade, as the chart shows. Sea temperature changes vary between regions, while most ocean zones have seen temperatures increase, the North Atlantic has experienced cooling.

Warming or cooling oceans impact plant and animal species, alter marine ecosystems and have a profound effect on climate change, including reducing the levels of reflective cloud cover in some regions.

As climate change warms the planet, melting polar caps also mean less-reflective ice cover, which could exacerbate climate change.

The largest drop in the planet’s reflectivity occurred in the last three years that data was harvested for the research paper, adding to fears that climate change is at the heart of the problem.

What’s the World Economic Forum doing about climate change?

Climate change poses an urgent threat demanding decisive action. Communities around the world are already experiencing increased climate impacts, from droughts to floods to rising seas. The World Economic Forum’s Global Risks Report continues to rank these environmental threats at the top of the list.

To limit global temperature rise to well below 2°C and as close as possible to 1.5°C above pre-industrial levels, it is essential that businesses, policy-makers, and civil society advance comprehensive near- and long-term climate actions in line with the goals of the Paris Agreement on climate change.Global warming can be beaten thanks to this simple plan

The World Economic Forum’s Climate Initiative supports the scaling and acceleration of global climate action through public and private-sector collaboration. The Initiative works across several workstreams to develop and implement inclusive and ambitious solutions.

This includes the Alliance of CEO Climate Leaders, a global network of business leaders from various industries developing cost-effective solutions to transitioning to a low-carbon, climate-resilient economy. CEOs use their position and influence with policy-makers and corporate partners to accelerate the transition and realize the economic benefits of delivering a safer climate.

Contact us to get involved.Mission Possible Platform: Delivering industry pathways t…

In 2018, the World Economic Forum created the Ocean Action Agenda to help protect ocean environments and support a range of initiatives aimed at ensuring long-term sustainable use of our oceans. Initiatives like this could help fight climate change and help make our oceans more resilient.

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