Black Carbon Impact on Snowpacks and Global Warming

Global warming is defined to be an increase of temperature over a long period of time, generally it is seen to have been caused by the increase in humans’ emissions. Reports have suggested that the main acknowledgment of a change was noticed when researchers for oil companies started to recognise a change in the 1950’s through to today where there has been a significant increase in temperature which has been likely to have been caused by the development in society. The demand for fuels, energy and crops has led to a large production of excess hydrocarbons as supply meets demand.

Black carbon and the occurrence of snowpacks

Black Carbon was first discovered during studies of the Arctic Haze phenomena and is a component of pure carbon within a linked formation. Black Carbon can form as a component of biomass burning aerosol of which can be broken down into two forms being: black carbon and organic carbon.

Black carbon is a by-product from the handling and consumption of many sources (diagram 1).

When incomplete combustion of such fuels in depleted oxygenated environments, larger amounts of carbon can be produced.  In 2015 it was calculated that around 6.6 million tonnes of black carbon was emitted into the atmosphere which until recent a global increase at a rate of more than 10% a year. Which is important when considering how black carbon can have a warming impact that is more than 400 times stronger per mass per unit than Carbon dioxide.

The main characteristics of black carbon is its ability to absorb solar radiation whereas organic carbon distributes solar radiation. Black carbon has a large light absorption over both UV and visible wavelengths, allowing it to absorb vast amounts of solar radiation. Black carbon converts ultraviolet to infrared, creating higher temperatures at higher altitudes having a larger impact across areas. 

However, it also has a short lifespan when compared to other gases such as carbon itself, staying in the atmosphere for only around a week on average.

Snowpacks are found within the cryosphere storing over 70% of the world’s freshwater; with only 12 percent of the world covered permanently in snow, snowpacks are more susceptible to the black carbon’s affects and more significant to the global climate when a small percentage is lost. Snow climatically has a positive albedo. The albedo of a surface is based on its ability to reflect solar radiation, the intensity can depend on the local insolation. In effect it can be said that the high albedo of the snowpacks is a way of cooling the earth as solar radiation is not absorbed instead it is reflected back into the atmosphere.

Snowpacks are considered to be of importance as it can be a large indicator of albedo feedback and can be a way of understanding the distribution and concentration of gases within the ocean and atmosphere.

Understanding the impacts of black carbon on snowpacks

Snowpacks, especially those situated within the northernly latitudes, are more vulnerable as black carbon has been shown to have a large warming effect on snow in particular. The structure of ice (without snow cover) suggests that black carbon will have a deflation of albedo to 70% of the initial value. Ice (particularly multi-year ice) is less affected by black carbon unless covered in fresh snow, which allows for a surface area which can disperse the black carbon within and make it more vulnerable to downwelling solar radiation. In order for a snowpack not to become affected by albedo the thickness needs to reach above 10 cm. Black carbon constituted within snowpacks can lower the total albedo of the area.

Snow is able to reflect more than 80% of solar radiation locally within its atmosphere. However, when black carbon is situated within the snowpack the equilibrium is offset and more solar radiation becomes absorbed warming up the local area and in snow specific areas causing a higher rate of melting due to the lower insulation.

Relatively 90% of solar radiation is reflected back into the atmosphere by snowpacks yet with the presence of black carbon within snow has the capability to lower the total albedo by around 1 – 3 %.

The global direct radiative forcing for black carbon within snow is estimated at 0.04 W m–2, with local scales varying largely, with forcing up to threefold greater after the initial trigger of black carbon darkening and decreasing albedo. Short lived climate pollutants are responsible for at least 40% of the radiative forcing.

The deposition of black carbon and incorporation into snowpacks causes a decrease in albedo through the increased absorption of downwelling solar radiation and have a positive effect on climatic radiative forcing.

When vast amounts of snow are melting it can be an indicator of global warming, due to the increase in general temperatures. When a snowpack melts the product is known as snowmelt, when the snowmelt becomes once again frozen the overall reflectivity index is lowered with larger grains of snow and trapped black carbon. By having larger grains, the surface area is increased allowing for a higher amount of solar radiation to be absorbed. The absorption of solar radiation increases the likelihood and rate of melt which forms a continuous cycle between increased melt and freeze of snow melt. As snowpacks melt there is a large contribution to sea level rise, every year the sea level has been rising about 1-2 milometers.

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As the snowpacks continue to melt the ‘brighter’ surfaces are lowered, lowering the overall albedo of the planet and increasing the absorption of solar energy across not only snowpacks but also the oceans and land disrupting higher temperature changes across the overall global climate. With the increased absorption of solar radiation over the past century, it has led to an increase of temperature of around 0.5 degrees.

Examples of Black carbons affects

In Greenland the snow-covered areas have been found to have mostly darkened over 20 years with a reduction of its albedo by 10% and continually declining. What was noticed was that as melting increased, the black carbon was released from storage within the snowpack. With some transferred into the meltwater causing for higher concentrations into the ocean circulation to then be frozen next winter as part of a continuous cycle. The rapid darkening was not necessarily linked to drastic changes in burning of fossil fuels but due to the intensity of the black carbon that was already stored within the snow that was being released and refrozen. When frozen once again in the coarser snowpacks, a larger surface area entitles it to absorb greater amounts of solar radiation. Intensifying the process and forming more darker snowpacks.

Method and observations of changes within snowpacks

In order to form data to consider whether black carbon may be causing global warming and effect on snowpacks, various studies are carried out in order to form data and provide explanation.

A snowpack can be measured using various instruments (diagram 3) such as:

Snow depth sensors - which measure the depth and the sound waves using a sensor of which uses ultrasonic pulses to target the surface measure the snow.

Snow pillows - which are used to measure the weight of the snow and volume of water within using a snow pillow which is laid on the ground, the pressure from snow above can be used as a measurement of the volume of water within.

The exposure and darkening of Black carbon can be seen through the use of infrared.

In order to work out the albedo, albedo is calculated as a ratio with the upwelling alongside the downwelling irradiance.

All instruments are used to carry out studies over various locations over periods of time in order to gather any change in temperature, melting and levels of carbon. When all compared, this can be compared to see whether there is a relation between increases in melting that of black carbon.

Uncertainties of black carbons effect on global warming

There are uncertainties whilst considering the impact of black carbon on glaobal warming. It has been shown that black carbon within snowpacks can increase the rate of which snow may melt and increase its vulnerability to solar radiation.

Remote sensing is a way of which data can be collected to understand snow surfaces and their changes over time, however the albedo in remote sensed data has been seen to disagree by multiple factors. The main difficulty is observing local temperatures and changes.

Data doesn’t always incorporate effects of clouds and other varying gases which may have negative effects on the global warming. Calculations assume that the one absorbing impurity within snow is black carbon and not taking into consideration any other substances, even including other sediments. As the locally the climate can vary alongside external forcing’s seeing what a significant indicator of global warming may be hard to distinguish. Clouds can exert a negative affect on temperature as they can reflect light into space and have a high albedo, yet they can also be a large contributor or to trapping heat and possibly increasing global warming.

Black carbon lies within the atmosphere and can have different effects on varying parts of the atmosphere. When based at the Lower stratocumulus and above, the black carbon can

stabilise the clouds that form as it blocks the sun. The black carbon can have a cooling affect.

Whereas if clouds are forming and the carbon is absorbing heat the clouds will in fact evaporate.

Black carbon interacts with multiple other compounds within the atmosphere. The mix of multiple sources of compounds can have a large effect on the climate, which makes it difficult to be certain to how one pollutant may affect global warming.  Coalescence of can affect the ability to absorb solar radiation, these can be small effects within data to be considered.

All data also depends on the time intervals chosen, some of the past data is less adequate with modern satellites and techniques, more recent recordings are more precise and reliable.

The response of how black carbon may affect snowpacks also is dependent on the type of snow, whether it be coarse, fine including the thickness of the snow itself.

Reducing black carbon emissions

With the Arctic warming at a rate twice as quickly as the rest of the planet alongside evidence showing that black carbon plays a large part in this increase in temperature, it is important to consider large reductions in the emission of black carbon.

The Paris agreement is an example of future plans to reduce emissions and reduce the future effects of global warming. In 2016 the agreement came into place with 197 signatures from varying countries. With the main response to be able to keep the global temperature this century below 2 degrees Celsius. One of the goals in place was to be able to limit the production of greenhouse gasses and by taking initiatives to focus on adaptation and strengthening societies ability to act towards the impact of global warming. As Global warming becomes a larger issue, many cities are focusing on the efforts to reduce emissions and develop upon environmentally friendly technology, becoming sustainable and environmentally friendly. A recent example in the United Kingdom being the ban of sale of new petrol/diesel and hybrid cars, this ban was recently brought forward to 2035 in order to support the plans to become a virtually zero carbon city by 2050. By being able to reduce the number of cars fuelled by diesel and petrol around a third of carbon emissions could potentially be cut, which in theory if many countries could follow with such initiatives it would be a massive impact on the reduction of overall emissions and slow down the rate of global warming.

Discussion

The intergovernmental Panel on Climate Change (IPCC) has calculated some of the largest components of radiative forcing: Carbon dioxide, methane and black carbon all contributing to global warming as warming agents.

The loss of snow continually adds to the global radiative forcing. Radiative forcing is an effective way to assess the anthropogenic contributors to global warming and with the majority of radiative forcing having a short residence time, especially when considering black carbon, by reducing black carbon it presents a large opportunity to reduce the rate of global warming.

In diagram 4, you can see the average comparison between rates of global average sea level and northern hemisphere snow cover, supporting the idea of global warming across the world with average rises across temperature and sea level as snow cover melts and becomes depleted. When considering the effects of black carbon on snow covered areas you can assume with confidence that black carbon would have increased the rate of these processes triggering a negative albedo and causing a global warming effect.

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There is uncertainty of its potential on causing global warming itself, black carbon is emitted with a range of pollutants during the combustion of fuels and the amount of black carbon becomes dependent on the source itself. When comparing to other pollutants black carbon has a 900 times higher global warming potential than carbon dioxide over a 100-year period however when put into perspective black carbon has a much smaller life and can fluctuate largely depending on the production of fuels and burning. With the reduction of black carbon there would be an almost instant cooling effect.

Conclusion

It is clear that black carbon is a dominant absorbing contaminant within snowpacks, causing for a decrease in the albedo of snowpacks and increase the absorption of solar radiation which is largely linked to an overall change in global surface albedo causing for a global rise in temperature.

By being able to curb the planets black carbon emissions there would be a reduction in global warming. However, black carbon is not the cause of global warming itself. Black carbon is a large contributor as there is clear evidence to its ability in being able to speed up the rate warming, and so black carbon can cause a global warming.

However, in the grand scheme of things carbon dioxide and other factors need to be considered especially when collecting data to support statements. Reducing black carbon within the atmosphere, as a short-lived pollutant will have a limited long-term effect on warming due to the emissions of other gases such as carbon dioxide and methane.

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