Causes: the albedo effect
Antarctica: image Sonny Whitelaw
Summary
Albedo is the measure of how much light or radiation is reflected by a surface, expressed as a number from 0 (absorbing all light) to 1 (reflecting all light). Clean ice can have an albedo as much as 0.9 or 90%. The albedo of very thick, white clouds ranges from 0.7 to 0.9 (70% to 90%). Darker surfaces such as the ocean can be as low as 6%.
When sunlight (solar radiation) reaches Earth, due to the albedo effect some of this energy is reflected back into space. But as ice caps and glaciers disappear, more heat is retained by the planet rather than escaping back into space. This adds to the increasing energy imbalance that’s resulting in rising global temperatures.
What’s covered on this page:
Sea ice
Clean ice and snow have a very high albedo, reflecting up to 90% of the sun’s incoming radiation back into space. The ocean is much darker, so it has a very low albedo, reflecting only about 6% while absorbing the other 94% (Fig. 2).
The amount, both in depth and area of sea ice in Arctic waters and around Antarctica is rapidly declining. This exposes much more of the ocean to solar radiation (heat), which it absorbs. That’s driving up the temperatures of the ocean, which, along with a warmer atmosphere, inhibits the development of sea ice over winter. This in turn exposes more ocean to solar radiation, which prevents even more sea ice from forming, so more heat is absorbed, and so on in a positive feedback effect (Figs. 2 & 3).
The effects are wide reaching and include changes to global ocean currents. Less sea ice also causes a breakdown in polar food webs because sea-ice algae lose their physical habitat, which fails to feed the microscopic grazers that feed larger animals including fish, mammals, and seabirds.
Aerosol pollution
Burning fossil fuels emits both long-lived greenhouse gases and short-lived aerosols such as sulfur dioxide (SO2) and nitrogen oxides (NO). Along with an increasing number of wildfires globally, these contribute to the formation of smog and acid rain, and are directly linked to the deaths of millions, including some 3,300 deaths in Aoteaora.
More than 8 million people died in 2018 from fossil fuel pollution, significantly higher than previous research suggested, according to new research from Harvard University. – Harvard School of Engineering
When these pollutants interact with clouds, they make them brighter and more reflective. Perversely, the resulting albedo effect has led to artificial cooling that masks around 1°C of warming (Fig. 5). The IPCC Sixth Assessment Report WG1 estimated the impact of these pollutants would be less than 1°C. Others suggested this was a dangerously conservative under-estimate, and that cutting all emissions could result in the abrupt rise of temperatures beyond 2°C. Then in 2022, International laws to reduce these toxic aerosols from shipping came into effect. The impact was immediate. By 2023 global temperatures spiked, breaking all previous records (Video 2).
Without aerosols’ cooling effect, the world would already have reached the temperature threshold of dangerous climate change… Until recently, ships’ aerosol emissions probably cooled the planet more than their greenhouse-gas emissions warmed it. – Pierce, 2024
Other pollutants include hydroxyl radicals are present in tiny quantities. While they have a lifetime of less than a second they remove about 85% of methane from the atmosphere. The abrupt reduction in these during Covid has been attributed to the sudden, abrupt rise of atmospheric methane 2021-2022 (Video 3). Due to feedback effects and a possible tipping point being breached, methane continues to rise at an alarming pace.
Volcanoes also emit sulfates. Eruptions have masked some warming over the last few hundred years, causing global temperatures to drop slightly for short periods (Fig. 5). See also ‘water vapour and clouds‘ and ‘ozone’, as both influence the amount of warming or cooling depending on the type of cloud and where they are in the atmosphere.
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Climate forcings that have contributed to climate change 1850 – 2023. The green line shows the cooling effect of natural forcings including volcanic eruptions such as Mt. Pinatubo in 1991. Aerosols (blue line) had the greatest cooling impact. But when all cooling forcings are added together (amber line), it wasn’t nearly enough to offset the main warming forcing: greenhouse gases (grey line). The black line shows the actual rise in temperatures. Image: Zeke Hausfather, January 2025.
Figure 4: Peggy Anke
Black carbon and ash blanketing ice caps and glaciers
Most aerosols in the atmosphere scatter incoming solar radiation, resulting in a net cooling effect (Fig. 5 above). But black carbon (BC) absorbs significantly more light than it reflects, radiating long-wave energy that heats the surrounding air, which results in a positive (warming) effect.
BC [black carbon] absorbs significantly more light than it reflects, resulting in a net warming effect. Light absorbing particles radiate long-wave energy that heats the surrounding air which results in a positive (warming) forcing effect. Additionally, when BC is deposited on, or precipitated with snow, it lowers the albedo (reflective properties) and the absorbed light heats the snow causing it to melt which has important implications for permanent snowpack such as the Himalayan, Arctic and Antarctic regions. – GNS Science Consultancy Report
Black carbon comes from burning fossil fuels, particularly diesel, coal, and wood—including ash and soot from wildfires. The increasing number of wildfires is leading to vast ash plumes falling on glaciers and ice caps. This isn’t just happening in the Arctic. In 2020, westerly winds send huge plumes of ash and soot from Australian bushfires onto the snow and glacier-capped Aotearoa’s Southern Alps (Figs. 6-10), reducing their albedo, and hence, increasing the rate of melting.
Impact of ash on glaciers is likely to accelerate melting. How one country’s tragedy has spillover effects. – former Prime Minister Helen Clark
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Figure 6: Soot on NZ glaciers from Australian bushfires; image: @Rachelhatesit
Algae on glaciers
The Arctic is warming four times faster than the rest of the planet. In parts of Greenland, warming has led to blooms of dark pigmented glacier ice algae on southwest Greenland, which is accelerating warming. Because these dark areas absorb heat, the ice melts, creating meltwater ponds, which in turn also absorb more heat, causing even more melting (Fig. 11). In many instances the meltwater drills down through the ice, creating fractures within the glacier and lubricating it at the base. This in turn accelerates the movement of the glaciers into the ocean, raising sea levels.
Figure 11: Eli Kintisch.
