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Scientists detect CO2 accumulation at the edge of Space

Posted on 12 November 2012

A University of York scientist is part of an international team of researchers which has reported the first direct evidence that emissions of carbon dioxide caused by human activity are propagating upward to the highest regions of the atmosphere.

The observed CO2 increase is expected to result gradually in a cooler, more contracted upper atmosphere and a consequent reduction in the atmospheric drag experienced by satellites. The team has published its findings in the latest issue of Nature Geoscience.

CO2 increases close to the Earth's surface cause temperatures to rise but, surprisingly, CO2 higher up results in just the opposite

Professor Peter Bernath

Professor Peter Bernath, from the Department of Chemistry at York, along with lead author Dr John Emmert, Dr Michael Stevens and Dr Douglas Drob from the US Naval Research Laboratory’s Space Science Division and Dr Chris Boone, from the University of Waterloo in Canada, studied eight years worth of CO2 measurements made by the Atmospheric Chemistry Experiment (ACE), a scientific satellite mission funded primarily by the Canadian Space Agency.

ACE determines vertical profiles of CO2 and many other atmospheric gases by measuring how the atmosphere absorbs sunlight at different wavelengths as the sun rises and sets relative to the spacecraft.

Carbon dioxide adds to the greenhouse effect in the Earth’s lower atmosphere, driving up temperatures. But when this gas – a significant portion of which today is the result of human activity – rises above 30 miles into the mesosphere (ca 30-50 miles high) and even higher into the thermosphere (ca 50-500 miles high), it causes temperatures there to drop.

The researchers report evidence that CO2 levels are increasing faster than expected in the upper atmosphere, which seems to be cooling and contracting at a pace that current models have not predicted. Reduction in atmospheric drag brought on by the resulting decrease in density could keep space debris in orbit longer, creating more congestion by this material.

Professor Bernath says: “CO2 increases close to the Earth’s surface cause temperatures to rise but, surprisingly, CO2 higher up results in just the opposite. In the upper atmosphere, the density of CO2 is too low to maintain greenhouse warming. Instead, the gas absorbs heat from its surroundings and radiates much of it away from Earth.”

His work with the research team derives from his role as mission scientist for the ACE satellite mission, which has been collecting important information about ozone chemistry, climate change and air pollution since 2004.

Data from ACE has set the standard for measurements of the concentrations of constituents in the Earth's middle atmosphere. Its Fourier Transform Spectrometer (FTS) routinely measures approximately 35 gas species in the atmosphere; some of these are in the parts-per-billion range of concentration.

When the research team checked measurements from 2004-12 by ACE-FTS at altitudes of about 60 miles, it found CO2 concentrations that were surprisingly high. “To date, CO2 trends have been measured only up to 35 kilometres (22 miles). Here, we present the first direct evidence that upper atmospheric CO2 concentrations – the likely primary driver of long-term thermospheric trends – are increasing,” the researchers report.

The researchers consider several possible explanations for this trend including swings in solar activity. They even estimate the amount of CO2 that may have been deposited in the upper atmosphere by the exhaust of orbital launch vehicles, but the total of 2,700 tonnes above 50 miles high cannot explain the overall trends they found.