There have been several recent papers exploring the growth in methane that has been ongoing since 2007. In a new paper in PNAS, we explore whether changes in the global OH concentration could be playing a role. By looking at trends in methyl chloroform, we infer an intriguing rise and fall in OH over the last 20 years, which could explain some of the methane change. There are significant uncertainties remaining, and much more work is needed before we can determine with confidence the role of changes in both methane sources and sinks. This is the focus of the new UK-wide NERC-funded MOYA project which will be on-going for the next three years.
Dan Say’s work on our re-evaluation of the UK’s HFC emissions featured on the University of Bristol News. Based on an analysis of atmospheric data, we found that the UK’s estimates of the emissions of HFC-134a, used in car air conditioning, were likely too high. Dan took a closer look at the UK inventory and found that estimates of the frequency at which car air conditioning units were refilled, and the number of cars with air conditioning units in them were likely over-estimated in the inventory.
The government is now re-evaluating the assumptions that go in to their HFC-134a calculations.
“The amount of greenhouse gases that the UK produces is calculated annually by the Department for Energy and Climate Change (DECC). Researchers at the University of Bristol independently verify these estimates using atmospheric measurements, making the UK one of only three countries in the world that does so.
“Our work is used by the DECC for monitoring compliance with international and domestic legislation; identifying priorities for improving inventory accuracy; assessing the UK’s progress towards targets set in the Montreal and Kyoto Protocols; evaluating the impact of policy; and informing international negotiations.” – Professor Simon O’Doherty
The UK is signed up to the Montreal Protocol (which aims to reduce the amount of ozone depleting compounds emitted) and the Kyoto Protocol (which aims to reduce the amount of anthropogenic greenhouse gases in the atmosphere). These require the UK to report its emissions on a regular basis, but it’s not as straightforward as simply measuring the gases in the atmosphere.
Reporting the amount of man-made greenhouse gases that the UK produces annually is a challenging task. Like the other 191 countries that have signed up to the Kyoto protocol, the UK uses an inventory approach to estimate the emissions, as directly measuring anthropogenic greenhouse gases is too complicated. This involves estimating emissions from a variety of activities such as burning fossil fuels, agriculture and energy production. But the UK is one of only three countries that go one-step further, by using atmospheric measurements to validate these inventory calculations.
This independent verification is performed by researchers from the University of Bristol’s Atmospheric Chemistry Research Group which is part of the Cabot Institute and the School of Chemistry. Using a combination of physical measurement and sophisticated modelling techniques, Professor Simon O’Doherty and Dr Matt Rigby work in collaboration with Dr Alistair Manning from the UK Met Office to monitor the greenhouse gases in the atmosphere above the UK.
In order to do this, the researchers developed the UK DECC Network – a unique national greenhouse gas monitoring system comprising six stations making high-frequency measurements of key atmospheric trace gases. Analysis and interpretation of these observations using state-of-the-art modelling techniques enables the independent assessment of the UK’s adherence to the Montreal and Kyoto Protocols.
“Our work started more than 20 years ago when we provided data to the Government on the accumulation of ozone-depleting gases in the atmosphere resulting in the signing of the Montreal Protocol,” says O’Doherty. “We have been able to show how the use of chlorofluorocarbons (CFCs) has risen and fallen over the years and that direct measurement of atmospheric gases can be used to monitor the impact of legislation such as the Montreal Protocol.”
Back then O’Doherty only had one monitoring station at his disposal, but today he can use data from a network of stations across the country as well as aircraft, satellites and even ferries that measure climatically important gases such as carbon dioxide, methane and nitrous oxide. When combined with models of atmospheric gas transport, these observations provide an independent means of assessing natural and man-made emissions. As well as monitoring the UK’s compliance with international treaties, these data have been central to recent World Meteorological Office (WMO) Scientific Assessments of Ozone Depletion produced between 2007 and 2010 and to the Nobel Prize-winning Inter Governmental Panel on Climate Change (IPCC) Assessment of Climate Change published in 2007.
The data will also form the basis for negotiations of future targets for UK emissions.
“Future climate treaties will take recent emissions estimates as a baseline from which to plan emissions reductions. Therefore, it’s really important that we are able to get these estimates right, both in the UK and around the world, so that the burden for emissions reductions is shared in a fair way,” says Dr Rigby.
One of the biggest challenges for the future is distinguishing between natural and man-made greenhouse gases. O’Doherty and Rigby are now investigating new techniques that could measure different isotopic compounds and thus distinguish between anthropogenic and naturally emitted greenhouse gases.
Key facts: • The underpinning research was funded by the Department for Energy and Climate Change, the Natural Environment Research Council and NASA. • Man-made greenhouse gas emissions cannot currently be measured directly but instead are calculated by estimating emission from a number of activities such as the burning of fossil fuels. • Bristol researchers independently verify these calculations by taking atmospheric measurements and using atmospheric models to calculate the source of the emissions. • The UK now has a network of stations, managed by Professor Simon O’Doherty, that continuously monitor important atmospheric gases. • The data from the monitoring stations is used to verify if the UK is adhering to the Montreal and Kyoto protocols, as well as to inform international policy on climate change. • The UK is one of only three countries in the world that collects data and verifies emissions in this way.”
Until now, there has been little verification of the reported emissions of hydrofluorocarbons (HFCs), gases that are used in refrigerators and air conditioners, resulting in an unexplained gap between the amount reported, and the rise in concentrations seen in the atmosphere. This new study shows that this gap can be almost entirely explained by emissions from developing countries.
Currently only 42 countries are required to provide detailed annual reports of their emissions to the United Nations Framework Convention on Climate Change (UNFCCC).
The study, led by Mark Lunt from Bristol’s School of Chemistry used HFC measurements from the international Advanced Global Atmospheric Gases Experiment (AGAGE), in combination with models of gas transport in the atmosphere, to evaluate the total emissions that are reported to the UNFCCC each year.
HFCs are potent greenhouse gases; per tonne of emissions, each gas measured in this work is hundreds or even thousands of times more effective than carbon dioxide at trapping the radiation that warms the Earth.
There is currently no global agreement to regulate the emissions of these compounds, although proposals have been made to begin phasing out their use.
Mark Lunt said: “Any phase-out mechanism would likely be more stringent for the developed countries, but these results show that emissions from non-reporting countries are also highly significant.”
Meanwhile, the researchers note that although their estimates of total emissions from developed countries are broadly consistent with the reports that they compile, this does not necessarily mean that the emissions of each gas are being accurately reported.
In fact, the results suggest that the most commonly used HFC is significantly over-reported whilst some other HFCs are under-reported.
Dr Matt Rigby from the University of Bristol, who co-authored this work, said: “It appears as if the apparent accuracy of the aggregated HFC emissions from developed countries is largely due to a fortuitous cancellation of errors in the individual emissions reports.”
Professor Ron Prinn from the Massachusetts Institute of Technology (MIT), who leads the AGAGE network, added: “This study highlights the need to verify national reports of greenhouse gas emissions into the atmosphere. Given the level of scrutiny these reports are under at the moment, it is vitally important that we improve our ability to use air measurements to check that countries are actually emitting what they claim.”
In a paper published in Geophysical Research Letters, we quantify the influence of anaesthetic gases on global atmospheric radiative forcing. It turns out that inhalation anaesthetics are potent greenhouse gases, with 1 kg of emissions of desflurane (a commonly used anaesthetic) having the influence of around 2,500 kg of CO2. However, emissions of these gases are very low compared to CO2, so the influence on climate is still relatively small.
I was recently interviewed for a report on the environmental impacts of refrigerant gases on behalf of a company that makes hydrocarbon refrigerant blends. The report is called “Hydrocarbons: The Quest For A Green Solution To The Changing Future Of Refrigeration And Air-Conditioning” is available on the PriorityCool Refrigerants website.
“The total warming impact of 25 major synthetic greenhouse gases has been examined by an international team, led by researchers from the University of Bristol.
The study estimates that, without additional limits on synthetic greenhouse gas use, the resulting increase in warming could outweigh the climate benefits gained thus far from phasing down chlorofluorocarbons (CFCs).
CFCs—commonly used in refrigerators and air conditioners—garnered public attention for their role in creating a hole in the ozone layer over Antarctica. As these chemicals were phased-down thanks to international agreements limiting their use, they were replaced by other synthesized gases that can still be harmful to the ozone layer and are greenhouse gases that contribute to climate change. Despite this, synthetic greenhouse gases (SGHGs) beyond the CFCs have received relatively little attention from the research community—until now.
The study, led by Dr Matthew Rigby in Bristol’s School of Chemistry, analysed observed atmospheric levels of SGHGs from 1978 to 2012, and then used these measurements to predict the impact these gases could have on global warming through 2050.
In response to the phase-down of CFCs through the 1987 Montreal Protocol, the researchers discovered that the use of other synthetic gases as refrigerants—such as hydrofluorocarbons (HFCs)—has risen. HFCs had been limited in the now-defunct 1997 Kyoto Protocol, but there is currently no agreement restricting their use. So, using HFCs as a test case, the researchers examined the effect of phasing down HFCs by amending the Montreal Protocol to include these gases.
Dr Rigby said: “We could avoid adding the equivalent of up to another three years of carbon dioxide emissions into the atmosphere if these gases were being phased down.”
HFCs are particularly strong greenhouse gases, so even relatively small levels in the atmosphere can contribute to warming.
“Per tonne of emissions, HFCs are much more potent greenhouse gases than carbon dioxide, and are very good at trapping the radiation that heats the Earth,” Dr Rigby said.
While HFCs are currently not a major driver of climate change compared to carbon dioxide or even other SGHGs, the researchers point out that if unabated they may contribute significantly to future warming.
The study used measurements of SGHG levels from the Advanced Global Atmospheric Gases Experiment (AGAGE), a global observing system developed by Professor Ronald Prinn of the Massachusetts Institute of Technology (MIT) and colleagues, and sponsored by NASA and other agencies.
Professor Prinn, co-director of the MIT Joint Program on the Science and Policy of Global Change and a co-author of the report said: “Addressing HFCs, and other SGHGs, now will ensure that they don’t contribute significantly to warming in the future.”
Meanwhile, the researchers note that due to extensive use, CFCs will continue to warm the planet for years to come.
“CFCs have contributed the most among the synthetic greenhouse gases to warming. Their use peaked and levels are now declining, but these gases will remain in the atmosphere for many years. This is likely the trend we will see with most SGHG gases, so it is important that we address these gases now before they do more severe damage,” said Professor Prinn.”
(With particular thanks to Audrey Resutek who wrote the MIT press release that this is based on).
I’ve just returned from the 35th anniversary AGAGE meeting in Boston, MA. I’ve written a blog post for the Cabot Institute, summarising the changes AGAGE has seen during this time:
“I work on an experiment that began when the Bee Gees’ Stayin’ Alive was at the top of the charts. The project is called AGAGE, the Advanced Global Atmospheric Gases Experiment, and I’m here in Boston, Massachusetts celebrating its 35-year anniversary. AGAGE began life in 1978 as the Atmospheric Lifetimes Experiment, ALE, and has been making high-frequency, high-precision measurements of atmospheric trace gases ever since.
At the time of its inception, the world had suddenly become aware of the potential dangers associated with CFCs (chlorofluorocarbons). What were previously thought to be harmless refrigerants and aerosol propellants were found to have a damaging influence on stratospheric ozone, which protects us from harmful ultraviolet radiation. The discovery of this ozone-depletion process was made by Mario Molina and F. Sherwood Rowland, for which they, and Paul Crutzen, won the Nobel Prize in Chemistry in 1995. However, Molina and Rowland were not sure how long CFCs would persist in the atmosphere, and so ALE, under the leadership of Prof. Ron Prinn (MIT) and collaborators around the world, was devised to test whether we’d be burdened with CFCs in our atmosphere for years, decades or centuries.
ALE monitored the concentration of CFCs, and other ozone depleting substances, at five sites chosen for their relatively “unpolluted” air (including the west coast of Ireland station which is now run by Prof. Simon O’Doherty here at the University of Bristol). The idea was that if we could measure the increasing concentration of these gases in the air, then, when combined with estimates of the global emission rate, we would be able to determine how rapidly natural processes in the atmosphere were removing them.
Thanks in part to these measurements, we now know that CFCs will only be removed from the atmosphere over tens to hundreds of years, meaning that the recovery of stratospheric ozone and the famous ozone “hole” will take several generations. However, over the years, ALE, and now AGAGE, have identified a more positive story relating to atmospheric CFCs: the effectiveness of international agreements to limit gas emissions.
The Montreal Protocol on Substances that Deplete the Ozone Layer was agreed upon after the problems associated with CFCs were recognised. It was agreed that CFC use would be phased-out in developed countries first, and developing countries after a delay of a few years. The effects were seen very rapidly. For some of the shorter-lived compounds, such as methyl chloroform (shown in the figure), AGAGE measurements show that global concentrations began to drop within 5 years of the 1987 ratification of the Protocol.
Over time, the focus of AGAGE has shifted. As the most severe consequences of stratospheric ozone depletion look like they’ve been avoided, we’re now more acutely aware of the impact of “greenhouse” gases on the Earth’s climate. In response, AGAGE has developed new techniques that can measure over 40 compounds that are warming the surface of the planet. These measurements are showing some remarkable things, such as the rapid growth of HFCs, which are replacements for CFCs that have an unfortunate global-warming side effect, or the strange fluctuations in atmospheric methane concentrations, which looked like they’d plateaued in 1999, but are now growing rapidly again.
The meeting of AGAGE team members this year has been a reminder of how important this type of meticulous long-term monitoring is. It’s also a great example of international scientific collaboration, with representatives attending from the USA, UK, South Korea, Australia, Switzerland, Norway and Italy. Without the remarkable record that these scientists have compiled, we’d be much less well informed about the changing composition of the atmosphere, more unsure about the lifetimes of CFCs and other ozone depleting substances, and unclear as to the exact concentrations and emissions rates of some potent greenhouse gases. I’m looking forward to the insights we’ll gain from the next 35 years of AGAGE measurements!”
Atmospheric Scientist at the University of Bristol