Causes: black carbon & ash

Causes: black carbon and ash

(Image: Twitter/ @Rachelhatesit – soot on NZ glaciers from Aus. bushfires )

Black carbon & ash


  • 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 about 86% of the sunlight that hits it. However, when aerosols like ash from volcanoes and wildfires (Figs. 1-3) and black carbon (Figs. 5-6)  falls 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.
  • The effects of this 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)

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)

Black carbon

“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 2018

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).


Global Warming Potential (GWP):

Is the heat absorbed by any greenhouse gas in the atmosphere, as a multiple of the heat that would be absorbed by the same mass of carbon dioxide (CO2). This is sometimes written as eCO2 or e-CO2.

 The Arctic:

Is warming at more than twice the average rate of the rest of the globe—a phenomenon known as Arctic amplification—and it is losing sea ice at a staggering pace.

The Albedo Effect:

Clean ice and snow have a very high albedo, that is, they reflect up to 90% of solar radiation back into space. The ocean is much darker, so it has a very low albedo, reflecting only about 6% of the incoming solar radiation and absorbing the other 94%, warming it much faster than the snow and ice (Fig. 10). This feedback effect then leads to more warming, then more melting, and so on.

Fig. 10: The Albedo Effect. Clean ice reflects about 90% of the sunlight that strikes it. Dark ocean water only reflects about 6%. This aerial photo shows a small portion of A-68, the iceberg that broke of Larsen C Ice Shelf in 2017 (Photo: NASA/ Nathan Kurtz)
Fig. 10: The Albedo Effect. Clean ice reflects about 90% of the sunlight that strikes it. Dark ocean water only reflects about 6%. This aerial photo shows a small portion of A-68, the iceberg that broke of Larsen C Ice Shelf in 2017 (Photo: NASA/ Nathan Kurtz)

Australian fires:

The Australian Government report states that, “The 2019-20 bushfires will have negligible impact on Australia’s progress towards its 2020 or 2030 target.” (p3) and “...affected forests are expected to recover over time, generating a significant carbon sink in the coming years.” (p9).

Evidence to support this claim is lacking and contradicts scientific concern that entire ecosystems may have been permanently lost (see for example Yale University News). While Australian forest ecosystems have indeed adapted to fire, the 2019/2020 fires were extraordinary, wiping out 186,0002km. That’s an area 30% larger than the entire South Island of New Zealand.

When ecosystems tens millions of years in the making are decimated in just a few weeks, their recovery and replacement in a progressively warmer dryer climate may be vastly different and far less capable of storing carbon. Moreover, the cumulative effect of worsening forest fires each year has been ignored. This industry-led ‘Government’ report should therefore be read in light of the Australian Government’s stance on climate change and ongoing land clearing and coal-mining policies.

Note: the figures in tonnes (above) are taken from, which use tons (Imperial). These have been converted to tonnes (metric) for consistency.

References and further reading