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Causes: Black carbon and ash

Causes: black carbon and ash

Soot on NZ glaciers from Aus. bushfires: image – @Rachelhatesit

Black carbon and ash

Summary

  • Dust, black carbon (from burning fossil fuels, particularly diesel, wood, and coal), ash, and some other aerosols help cool the atmosphere by reflecting sunlight when they are in the atmosphere. But when they fall on ice and snow they lead to increased warming.
  • Fresh snow has an albedo of about 0.86, meaning it reflects 86% of sunlight. However, when aerosols like ash from volcanoes and wildfires (Figs. 1-3) and black carbon (Figs. 5-6) fall on the white ice and snow, the albedo declines, sometimes dramatically. Dark ice and snow absorbs a much higher percentage of incoming sunlight, warming the surface faster, which hastens melting, indirectly causing warming through this feedback effect.
  • The effects of ash on New Zealand glaciers is visibly evident (top image and Fig. 3).
  • Research of the impacts is now underway; contact Lynda Petherick (Victoria University of Wellington) or Phil Novis (Manaaki Whenua Landcare Research).
  • The effect of black carbon on ice caps in Greenland (Fig. 5) and Antarctica speeds melting, which directly contributes to sea level rise.

“While most aerosols in the atmosphere scatter incoming solar radiation, resulting in a net cooling effect on the atmosphere, 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

Soot on NZ glaciers from Aus. bushfires: image – @Rachelhatesit

Black carbon and ash

Summary

  • Dust, black carbon (from burning fossil fuels, particularly diesel, wood, and coal), ash, and some other aerosols help cool the atmosphere by reflecting sunlight when they are in the atmosphere. But when they fall on ice and snow they lead to increased warming.
  • Fresh snow has an albedo of about 0.86, meaning it reflects 86% of sunlight. However, when aerosols like ash from volcanoes and wildfires (Figs. 1-3) and black carbon (Figs. 5-6) fall on the white ice and snow, the albedo declines, sometimes dramatically. Dark ice and snow absorbs a much higher percentage of incoming sunlight, warming the surface faster, which hastens melting, indirectly causing warming through this feedback effect.
  • The effects of ash on New Zealand glaciers is visibly evident (top image and Fig. 3).
  • Research of the impacts is now underway; contact Lynda Petherick (Victoria University of Wellington) or Phil Novis (Manaaki Whenua Landcare Research).
  • The effect on ice caps in Greenland (Fig. 5) and Antarctica speeds melting, which directly contributes to sea level rise.

“While most aerosols in the atmosphere scatter incoming solar radiation, resulting in a net cooling effect on the atmosphere, BC [black carbon] [Fig. 4] 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

Ash: Australian bushfires blanket New Zealand glaciers

Fig. 1: Smoke plumes from bushfires in southeast Australia on January 4, 2020, as seen by the MODIS imager on NASA’s Aqua satellite. (Image: NASA Earth Observatory)
Fig. 2: Impact of Australian 2019-2020 wildifres over New Zealand (Image: Twitter/ @MetService)

Impact of ash on glaciers is likely to accelerate melting. How one country’s tragedy has spillover effects.” – former Prime Minister Helen Clark

Until 2019, Australia’s national fire-related carbon emissions averaged 439 million tonnes/year. In the first 6 weeks of 2020 alone, fires emitted 830 million tonnes.

The effects were felt in New Zealand when ash and smoke blew across the Tasman (Figs. 1 & 2). One afternoon our skies turned orange and for the next few weeks, ash fell over already retreating glaciers, reducing their albedo, leading to faster melting (Fig. 3).

As the climate warms, the weather system in the Indian Ocean, the Indian Dipole (the Pacific ‘sister’ of El Niño/La Niña) is expected see more strong “positive” events similar to the one seen in 2019 that contributed to the Australian drought and bushfires.

It will be one of the factors that is accelerating the demise of glaciers in New Zealand overall.” – Prof. Andrew Mackintosh, Monash University

Fig. 3: Franz Josef glacier. The albedo effect increases the melt rate of snow and ice on New Zealand’s glaciers. This in turn has an impact on river flows and water storage. (Image: Twitter/ @Rachelhatesit)
Fig. 4: (image: Climate coalition)
Fig. 5: Greenland. A combination of ash from increasing numbers and intensity of Northern Hemisphere forest fires + algae growth + meltwater lakes is collectively reducing the albedo effect of ice. This in turn is causing increased melting and raising sea levels. (Image: Eli Kintisch, 2017).

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