Research shows rising carbon monoxide levels all but stopped in 1980s, likely thanks to car industry

An industry-wide change to cars in the 1980s appears to have virtually stopped decades of rising toxic gas levels across the Southern Hemisphere and led to an unintended benefit to the world’s climate, new research shows.  

A team of international researchers has plotted a complete history of carbon monoxide concentrations over Antarctica dating back 3,000 years, using ice core data as well as more recent atmospheric measurements.

Carbon monoxide is a toxic gas and pollutant. It is also considered an “indirect” greenhouse gas, because it helps to increase the lifetime of methane in the atmosphere.

Led by the French National Centre for Scientific Research and Australia’s national science agency CSIRO, the map shows carbon monoxide levels rapidly rising above their centuries-long average from about the 1940s.

But in 1985, the rising trend stops.

The researchers are confident they know why.

CSIRO atmospheric scientist David Etheridge said it fell in line with a major change to the automotive industry — the introduction of the catalytic converter.

“And despite the fact the number of vehicles being driven around the world has increased enormously over the past three decades or so, the emissions have been pulled down remarkably.”

Introduction of the catalytic converter

A catalytic converter is an exhaust emission control device that converts toxic gases, like carbon monoxide, into less-toxic pollutants.

They were first installed in cars in California, and subsequently throughout the rest of the world, during the mid-1970s and 80s to reduce local smog and other pollutants.

Th e changes took place in Australia from 1986, when stricter emission control laws on hydrocarbons, carbon monoxide, and nitrous oxide were introduced for new cars.

It’s a change former Holden project engineer Warwick Bryce remembers well.

“You had soot and deposits and all that sort of stuff making buildings dirty and grey, and brown clouds over your sky, so it was really the visual pollution and the harmful effects of unclean air.”

At the time, Mr Bryce was working in engine design and development.

He gave a lecture in 1980 in which he said catalytic converters and unleaded fuel were among the best technology options available should stricter emissions controls be introduced in Australia.

“In one fell swoop catalytic converter technology, used in conjunction with electronic fuel injection, reduced emissions of both hydrocarbons and carbon monoxide coming out the tailpipe by 95 per cent, and for nitrous oxide by 90 per cent of what the engine was producing, while at the same time fuel consumption was improved,” he said.

Mr Bryce said, as someone who had been involved in the change, learning the impact of those actions decades later was “very interesting”.

Similar observations have been made with Northern Hemisphere carbon monoxide concentrations.

A secondary climate benefit

There was always an expectation that the implementation of catalytic converters, and other emissions control devices, would reduce carbon monoxide concentrations at a local level.

But Dr Etheridge said the fact that it changed the background levels as far away as Antarctica and that it had benefited the climate on a global scale was “probably not expected”.

“I think it sheds a light on the fact that a measure that was put in place to affect local pollution actually had a much broader global hemispheric impact,” he said.

Methane is an extremely potent greenhouse gas, which has even higher global warming potential than carbon dioxide due to its efficiency in trapping heat.

Carbon monoxide indirectly increases the amount of methane in the atmosphere by reducing the abundance of hydroxyl — a natural “detergent” that helps scrub out gases like methane — from the atmosphere.

The overall benefit to the climate still needs to be quantified and will form part of the “next study”, according to Dr Etheridge.

That study would aim to properly attribute what caused the toxic gas levels to stop rising and would examine whether the trend could be maintained in the future.

Although catalytic converters do reduce carbon monoxide by converting it to carbon dioxide, Dr Etheridge said the CO2 emissions created were so small they would not outweigh the benefits to the climate.

A rare positive climate story

Dr Etheridge said stories like this, where human interaction had led to a clear and measurable positive difference in the context of climate, did not come around often in his field.

“We have to deliver the science as we do it, and they’re not all good news stories,” he said.