The force with you: Infrared insight to greenhouse effect

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  • Published: Mar 1, 2015
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: The force with you: Infrared insight to greenhouse effect

Forceful Fourier

The first observations of an increase in the greenhouse effect of rising carbon dioxide levels in the atmosphere has emerged from eleven years of infrared, thermal radiation absorption.

The first observations of an increase in the greenhouse effect of rising carbon dioxide levels in the atmosphere has emerged from eleven years of infrared, thermal radiation absorption.

A research team led by scientists from the Lawrence Berkeley National Laboratory have measured the increasing capacity of atmospheric carbon dioxide to absorb thermal radiation emitted from the Earth's surface and so contribute to the greenhouse effect. The data were recorded over an eleven-year period at two locations in North America - a research facility in Oklahoma and the North Slope of Alaska - and the team supports the idea that this upward trend is due to an increasing atmospheric concentration due to the burning of fossil fuels.

It was French mathematician and physicist Joseph Fourier, he of the transformations familiar to spectroscopists everywhere, who first explains why our planet does not keep getting hotter as energy from the sun hits it and conversely why if all that energy were reflected back into space the planet doesn't just freeze. His scientific successors Claude Pouillet, John Tyndall and Svante Arrhenius gradually pinned down the mechanisms quantitatively in the nineteenth century. Intriguingly, it was Alexander Graham Bell in 1917 who wrote that the unchecked burning of fossil fuels would have a sort of greenhouse effect turning our planet into a hot-house and suggested that we should find alternative energy sources that did not also come with carbon emissions.

Atmospheric influence

Today, the influence of atmospheric carbon dioxide levels on the balance between incident and radiant energy is well established, although despite this there are many people outside of science who deny that this is a real problem, political and economic motivations from those whose livelihood and lifestyles rely on perpetuating the use of fossil fuels are usually among those shouting the loudest.

Of course, until now the greenhouse effect had not been confirmed experimentally outside the laboratory, it remained a theory, albeit one that science has worked on for almost two centuries and was well beyond serious dispute. Writing in the journal Nature, the team demonstrates that their field results agree with theoretical predictions of an anthropogenic greenhouse effect. The research also provides further confirmation that the calculations used in current climate models coincide with the observations we see with regard to the effects of emissions on climate change.

Data from the sites in Oklahoma and Alaska were analysed from the year 2000 to the end of 2010 and look at the so-called radiative forcing. The data was obtained from spectroscopic instruments operated by the Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility. The instruments measure thermal infrared energy travelling downwards through the atmosphere to the surface and can reveal the unique IR spectral signature of carbon dioxide. Radiative forcing is a measure of how much the planet's energy balance is being perturbed by changes in the concentrations of atmospheric greenhouse gases. Positive radiative forcing happens when the Earth absorbs more energy from solar radiation than it emits back into space as thermal radiation.

A vernal flourish

The team reports that carbon dioxide is responsible for the significant rise in radiative forcing at both locations. Nominally, the forcing is about 0.2 Watts per square metre per decade, which the team correlates with the 22 parts per million (ppm) rise in carbon dioxide concentration over that same period. This increase is about ten percent of the trend from all sources of infrared energy such as clouds and water vapour. Tracking of fossil fuel emissions and modelling suggests that this observed forcing is due mainly to these emissions rather than natural greenhouse gas sources.

The team also explained that the measurements also reveal for the first time the influence of photosynthesis on the balance of energy at the Earth's surface as the spring flourishing takes place, carbon dioxide levels dip slightly as green plants draw in more of the gas.

"We see, for the first time in the field, the amplification of the greenhouse effect because there's more carbon dioxide in the atmosphere to absorb what the Earth emits in response to incoming solar radiation," explains Berkeley Lab's Daniel Feldman. "Numerous studies show rising atmospheric concentrations, but our study provides the critical link between those concentrations and the addition of energy to the system, or the greenhouse effect," he adds. Feldman's co-authors are Bill Collins, Margaret Torn and Jonathan Gero of the University of Wisconsin-Madison, Timothy Shippert of Pacific Northwest National Laboratory and Eli Mlawer of Atmospheric and Environmental Research.

"In terms of next steps, long-term high-quality spectra that have been recorded at  the ARM facilities can be used to explore many aspects of climate  forcing and response.," Feldman revealed to SpectroscopyNOW. "Whereas considerable attention has been devoted  to the CO2 forcing question, and thus our results agree with theoretical  predictions, this may not be the case for other greenhouse gases which  have more complex spectroscopy.  The researchers in this study look  forward to engaging with laboratory and theoretical spectroscopists on  these topics in the hopes that their efforts can be directed at the outstanding questions of climate forcing."

Related Links

Nature 2015, online: "Observational determination of surface radiative forcing by CO2 from 2000 to 2010"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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