“There’s so much pollution in the air now that if it weren’t for our lungs, there’d be no place to put it all.”
Robert Orben, 1927
The dawn of the industrial revolution, in the 18th century, marked the beginning of a dramatic change in the impact that humans have on the Earth. Smoke relentlessly billowed from factories, day and night, to keep up with the ever-increasing demands on growing industries such as agriculture and textiles. By the 1850s, a secondary revolution was spurred on by technological and economic progress as a result of steam-powered ships and railways. These efforts climaxed in the mid-19th century with the momentous invention of the internal combustion engine and the generation of electricity.
“It was a town of red brick, or of brick that would have been red if the smoke and ashes had allowed it; but as matters stood, it was a town of unnatural red and black like the painted face of a savage. It was a town of machinery and tall chimneys, out of which interminable serpents of smoke trailed themselves for ever and ever, and never got uncoiled. It had a black canal in it, and a river that ran purple with ill-smelling dye, and vast piles of building full of windows where there was a rattling and a trembling all day long, and where the piston of the steam-engine worked monotonously up and down, like the head of an elephant in a state of melancholy madness….”
Extract from ‘Hard Times’ by Charles Dickens, 1854.
Photo: Widnes, England, late 19th century. (Source: Wikimedia Commons)
Of course, the abundance of smoke generated during this new mechanical era didn’t just disappear into thin air. Instead, air pollution from the burning of fossil fuels had (and has) a consequential effect on the balance of the Earth’s elements. One element that has sparked interest within the Dark Snow Project is nitrogen. When fossil fuels are burned, reactive nitrogen, in the form of nitrogen oxides (NO and NO2, referred to collectively as NOX), are expelled into the atmosphere. It is these gases that can ultimately form smog and acid rain. NOX is predominantly removed from the atmosphere through the production of nitrate (Geng et al 2014). In addition to this, a second major and historic source of human generated nitrate has come from chemical fertilizers; used to assist with the ever-increasing demands on our food resources due to our growing population. These nitrogen-based compounds have been sprayed onto our fields since the advent of the Haber Bosch process (an energy demanding reaction that enables fertilizers to be synthesized) in the early 20th century (Felix and Elliott 2013). Nitrate from farmlands can become aerolised into the atmosphere, and as a result, in addition to the increased burning of fossil fuels throughout the industrial revolution, the use of fertilizers further exasperated the generation of man-made nitrate sources.
So, if all this industrial and agricultural pollution started to occur over 200 years ago, how can we possibly know about it today? Well, once aerosolized, nitrate and NOX are transported by winds through the atmosphere until they are eventually deposited onto the Earth’s surface. Depositions that occur over the Greenland ice sheet actually become encapsulated in time, buried under layer upon layer of snow. Ice core scientists can then drill out an ice core and obtain a nifty geochemical history lesson that can span thousands of years.
Photo: Bo Vinther examining an ice core as part of the NEEM drilling project, http://www.neem.ku.dk.
Human impacts on the nitrogen cycle (Galloway et al 2008) can be detected through the use of stable isotopes (variations in the atomic mass of elements due to differing numbers of neutrons within an atom’s nucleus). 14N is the natural and most common form of the stable nitrogen element, making up over 99% of the molecules that we measure on earth. However, reductions in the rarer second form of nitrogen, 15N, has been linked to increases in human-generated NOX levels; and so has become a proxy for the impact of our fuel consumption and agricultural activities on the global nitrogen cycle (e.g. Felix and Elliott 2013, Geng et al 2014, Hastings et al 2009).
Graph by Geng et al (2014) depicting how increases in ice core nitrate levels are coupled with a decrease in 15N concentrations.
With the historic global increases of nitrate concentrations in mind, and predictions that these levels will continue to rise (Liao et al 2006), this year’s Dark Snow Project participants plan to take on an alter ego as farmers, and actually fertilize the surface of the Greenland ice sheet! The idea is to add our own sources of nitrate within fertilization plots, so that we can observe the impact that nitrate elevations have on the microbial communities of surface ice. In addition, we will be looking into the implications that changes in the microbial communities have on the lowering the surface albedo, and of course, ultimately enhancing ice sheet melt rates.
Felix J D and Elliott E M 2013 The agricultural history of human?nitrogen interactions as recorded in ice core 15N?NO3? Geophysical Research Letters 40 1642-1646
Galloway J N, Townsend A R, Erisman J W, Bekunda M, Cai Z, Freney J R, Martinelli L A, Seitzinger S P and Sutton M A 2008 Transformation of the nitrogen cycle: Recent trends, questions, and potential solutions Science 320 889-892
Geng L, Alexander B, Cole-Dai J, Steig E J, Savarino J, Sofen E D and Schauer A J 2014 Nitrogen isotopes in ice core nitrate linked to anthropogenic atmospheric acidity change Proceedings of the National Academy of Sciences 111 5808-5812
Hastings M, Jarvis J and Steig E 2009 Anthropogenic impacts on nitrogen isotopes of ice-core nitrate Science 324 1288-1288
Liao H, Chen W T and Seinfeld J H 2006 Role of climate change in global predictions of future tropospheric ozone and aerosols Journal of Geophysical Research: Atmospheres 111 1984–2012