Biomass, Black Carbon, and Global warming (BBGs)!!
This blog was posted in 2014 but the logic is still valid. Hence I am sharing with those who have an interest in global climate change. According to a paper published in Energy Policy reports, a biomass resource model developed by a UK based school shows “that indigenous biomass resources and energy crops could service up to 44% of UK energy demand by 2050 without impacting food systems”. It is not clear whether this model accounts for the black carbon emitted by biomass fuel and its impact on the climate. BBGs are intimately related! One is a source of energy and the other is a source of global warming!! Over the centuries, civilizations used firewood, biomass, and dung cake to sustain lives. For both cooking and heating purposes, this was and is the cheap and easily available stock to humans, especially in rural areas. whether it is India or Ethiopia. Excess use of any such energy sources is harmful and the consequences are being felt by the current generation. In the current industrial era, besides the above fuels, fossil fuels like coal, diesel, and kerosene enhanced the black carbon (BC) content in the atmosphere!! Changing weather patterns, fast retreating glaciers, droughts, flash, and summer floods are the consequences of such uncontrolled BC emission. Carbon dioxide also plays a major role but CO2 has a long term effect while BC has a short term effect.
Coal, fuel wood, dung cake, and agricultural waste are consumed maximum in that order in India and other African countries and as published in the Energy Policy, it is also used in England. According to the recent data, 900 Mt (million) of coal, 85 000 tons of fuelwood (this number is not reliable), 121 Mt of dung cake ( this number is not reliable), and 350 Mt of agricultural waste is being used in India. The consumption of these fuels has increased by several folds due to increase since the beginning of this century due to population increase. BC (black carbon) emission factor of these fuels in that order is ~ 0.8, 1.1, 4.4 and 1.3 g/kg.
BC absorbs sunlight turning it into heat. Thus, a layer of BC in the atmosphere, while emitting a third of this absorbed heat back into space, keeps the earth’s surface warm. More BC in the atmosphere means more heat over the surface of the earth. As the BC increases the earth’s surface gets hotter and hotter!! Simple logic. Thus BC causes a change in the heat input at the top of the atmosphere. This is known as “Radiative Forcing (RF)”. According to the Intergovernmental Panel on Climate Change (IPCC) 2007 report, RF of BC is of the order of + 0.34 W/m2 while forcing of CO2 is of the order of + 1.66 W/m2.
What is Black Carbon?? The black soot, that all of us observe in our daily life, is known as black carbon (BC). BC forms due to the combustion of carbon-based fuels at high temperatures. Thus the sources of BC are fossil fuels (coal, oil, gas), biomass, agricultural waste, dung, etc. The life of BC in the atmosphere is about a week, while CO2 lingers for several decades. Both BC and CO2 have a tremendous effect on global warming and glacier retreat. BC has a strong light-absorbing property. Thus short-term control of global warming can be accomplished by controlling the BC emission. If BC emission is controlled then half our problems related to global warming are solved!! In developing countries like India and Africa, BC emission emerges mainly from rural sectors while the transport sector is the main source of BC emission in developed countries. A high percent of biomass and dung is used in rural regions for cooking, space heating, and consumption of such fuels is high during winters.
The emission values reported in the literature for BC and other related aerosols in the atmosphere varies like the climate! There is no consistency in the emission values reported. The values keep changing between the authors and sometimes with the same author!. Each author claims that their value is the best!! According to a paper published in “Atmospheric Environment” in 2002, the BC (India) emission of dung cake is 0.25 g/kg and that of crop waste is 0.47 g/kg. Another paper that appeared in the same journal in 2005 reported BC emission of dung cake from 2.2 to 6.6 g/kg and that of agricultural waste from 0.2 to 2.4 g/kg!! The value reported by the same author also varies with time!! Perhaps such discrepancies may be related to the betterment of analytical techniques and demographic data. Such uncertainties are ( E.g. see Jr. Geophy. Res., 2004) due to extrapolation of data such as population, per capita consumption ( varies by a factor of 3!), economic data, etc. and also due to over prediction of fuel-use measurements!!.
Irrespective of these numbers, the truth is, India, next to China, is the leader in BC emission!. The total BC emission by India ( 2000 base value) as reported earlier, was 600 Gg (Jr. Geophy. Res., 2003, v,108) while in 2008 this value has changed to 1343 Gg (Geophy. Res. Lett., 2008, v. 35)!!. Thus one gets two values for per capita emission of BC in India. One at 600 g and the second, just double this value!! It is safe to take the minimum value for all discussions. This data may be old but the numbers have increased now and not decreased and they are good enough for our analysis here.
In India, the maximum BC emission is from rural areas like Leh. Leh is located at an altitude of 4500 m in the Himalayas (in Ladakh province of J & K), where the temperatures fall 15 ?C below zero in winters. The combustion rate of all fuels is low at this elevation. Dung cake, biomass, and coal are extensively used to heat the homes and of course for cooking also. Guesthouses, the army, and affluent society use cooking gas or “Bukhari”, a device that uses kerosene ( or some times sawdust) to heat rooms and homes. CO, CO2, and BC are ejected out into space through an exhaust pipe. Now some are using LPG fuel source instead of “Bukhari’s”.
The population of Leh is ~ 150,000 and with the reported per capita, BC emission of 600 g (taken 2000 base value) Leh alone is contributing a minimum of about 0.09 Gg of BC annually. Similarly, Kargil with a population of 160,307 is contributing about 0.1 Gg of BC to the atmosphere around the glaciers. Similar emission figures can be assumed from other towns located at that altitude all along the higher Himalayas, extending from NW to E of India. The BC emission from the foothill Himalayas also reaches higher altitudes. During winter (where BC emission is maximum) snow brings down all the BC floating in the atmosphere. This is the reason why many Himalayan glaciers appear black. It is easy to estimate the BC content in ice. Since it is possible to date ice, BC content in the atmosphere in the past can be estimated.
The Gangotri glacier is retreating at a rate of 22 m/yr. This is alarming and this observation is not disputed. The real “component” that is responsible for this retreat is BC. Simulation studies conducted by Lawrence Berkeley National Laboratory in Feb 2010 showed that the major contributor (~90%) for the fast melting of glaciers is BC.
How does this happen? BC deposition on a white surface like snow and ice absorbs more light and becomes warmer faster than pure ice/snow and thus enhances the melting process. If one visits the Gangotri glacier, a major part of the ice body appears dirty ( black) because of small BC particles in it.
BC content in ice cores recovered from ERG glacier ( name of a glacier in the Himalayas (on the Chinese side) is about 20 ?g/kg. while the global average BC content in the snow is about 5 ?g/kg. This is alarmingly high!! 15 ?g/kg of BC in snow reduces about 1% of its albedo (fraction of light reflected by a body….here the sunlight reflected by snow).
This is a clear indication that the 22 m/year retrieval of Gangotri glacier is due to these huge BC emissions from rural Higher Himalayan villages/towns.
Also, BC from the Asian region travels to the Himalayan region contributing an additional amount to BC.
Since BC heats the atmosphere, it creates local thermal anomaly thereby disturbing the normal atmospheric convection pattern that exerts tremendous influence on the precipitation. Perhaps this could be the reason for the flash flood that devastated Leh in 2010!
The residence time of BC in the atmosphere is about a week while CO2’s is several decades. So BC does not accumulate while CO2 accumulates in the atmosphere. What it means is that through controlling BC emissions, global warming can be controlled within a short time. It is very easy to control BC emissions without compromising life comforts!! The pristine Himalayan ecosystem can be protected and fast deteriorating glaciers life can be restored by tapping the huge geothermal resources available in Leh.
Thus the Biomass model published recently should be valued in terms of the amount of BC emitted by 2050 and its effect on the arctic ice cap.
DISCLAIMER : Views expressed above are the author’s own.