Methane in the Earth System Symposium

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• John Burrows, Nic Gedney, Euan Nisbet, Matt Rigby, Philip Sargent
• Thursday 05 June 2014, 14:00-18:00
• Centre for Mathematical Sciences, meeting room MR2.

If you have a question about this talk, please contact Dr Michelle Cain.

CCfCS symposium on the topic of methane in the Earth system. A map of the venue can be found here, and further travel information here.

Open to all.

Confirmed speakers are: Prof John Burrows (University of Bremen), Dr Nicola Gedney (UK Met Office), Prof Euan G Nisbet (Royal Holloway University of London), Dr Matthew Rigby (University of Bristol), Dr Philip Sargent (DECC).

This meeting is supported by MethaneNet. If you are a UK-based early career researcher or student and wish to attend from outside Cambridge, please contact michelle.cain@atm.ch.cam.ac.uk for details of travel funds from MethaneNet.

1400	Prof Euan G. Nisbet	Is methane the canary in the mine?
1430	Dr Nicola Gedney	Modelling large-scale wetland methane emissions
1500	Tea/coffee break
1530	Prof John P. Burrows	Observing the Anthropocene from Space: Methane
1600	Dr Matt Rigby	Recent trends in atmospheric methane: what can we learn from data and models?
1630	Dr Philip Sargent	A DECC perspective on methane
1700-1830	Poster and networking session with refreshments

Abstracts:

Is methane the canary in the mine?

Prof Euan G. Nisbet

Until 1986, British coal miners took canaries underground. When the canary expired, that meant there was lethal CO in the air and probably methane also: the canary’s death implied an explosion was on its way. Curiously, atmospheric methane is in some ways the canary of climate change. It is a “first responder” to change: many feedback loops drive methane emissions when climate warms or cools, and methane is thus an early indicator of change. Because there is broadly an Arrhenius relationship between temperature and methane production, a warmer biosphere is generally a more methane-productive biosphere. Not only that, but rainfall under the convergence zones intensifies, leading to more wetland and also also more grass and tree growth, providing fuel for dry season biomass burns. Over decades to centuries of climate warming, methane hydrates decay, and thermokarst develops in permafrost yedoma: more methane is given off, though much of this is rapidly oxidised by methanotrophs.

The late glacial record shows these responses sharply, and is very instructive, though not yet fuly explained. Further back in time, the Palaeocene-Eocene Thermal maximum (about 56 Ma ago) similarly may record very sharp changes in methane emission. At the present-day, the post-2000 record may be showing fluctuating natural responses to climate events. Until 2007, methane growth was limited despite rapid human economic growth and increasing use of coal and gas. Possibly in part this stability in atmospheric methane reflected relatively dry conditions in key tropical and boreal areas. After 2007, climate shifts may have led to stronger intertropical convergence: and thus increased methane production. Over the past few years methane C isotopes have been shifting ‘light’, implying proportionately stronger biological sources despite continuing growth in energy use in East and South Asia.

Observing the Anthropocene from Space: Methane

Prof John P. Burrows

The industrial revolution, which began in the UK in the late 18th century, has been fuelled by the use of cheap energy from fossil fuel combustion. It has facilitated a dramatic rise in both the human population, now above 7 Billion with 50% now living in urban agglomerations, and its standard of living. It is anticipated that by 2050 there will be of the order of 8.3 to 10 billion people, 75% living in cities. Anthropogenic activity has resulted in pollution from the local to the global scale changes in land use, the destruction of stratospheric ozone, the modification of biogeochemical cycling, acid deposition, impacted on ecosystems and ecosystem services, destruction of biodiversity and climate change. The impact of man has moved the earth from the Holocene to the new geological epoch of the Anthropocene. To improve our understanding of the earth atmosphere system and the accuracy of the prediction of its future changes, knowledge of the amounts and distributions of trace atmospheric constituents are essential -“One cannot manage what is not measured”. An integrated observing system, comprising ground and space based segments is required to improve our science and to provide an evidence base needed for environmental policymakers.

Passive remote sensing measurements of the up-welling radiation at the top of the atmosphere from instrumentation on space borne platforms provide a unique opportunity to retrieve globally atmospheric composition. This presentation describes the approach and the results obtained from the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) which flew on the ESA Envisat 2002 to 2012. SCIAMACHY was the first instrument to use NIR and SWIR measurements to retrieve the dry mole fraction of carbon dioxide and methane from space. Its measurements yield sufficient accuracy to determine and constrain surface fluxes at the regional scale. The GOSAT Tanso instrument and its results will also be discussed as well as the objectives of the active mission MERLIN , a demonstrator LIDAR mission. The potential successors of SCIAMACHY , having capability to measure CH4 such Sentinel 5 Precursor, Sentinel 5, CarbonSat, and SCIA -ISS will also be addressed.

Recent trends in atmospheric methane: what can we learn from data and models?

Dr Matt Rigby

Long-term measurements of atmospheric methane reveal intriguing inter-annual fluctuations. These changes could be linked to perturbations in the complex mix of sources, or in the strength of atmospheric and terrestrial sinks. Atmospheric observations of methane and other species can be used to provide constraints. For example, recent measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) show that an upturn in global methane levels, beginning in 2007, is likely due to an increase in emissions, because the lifetimes of substances that also react with methane’s principal sink, the hydroxyl radical, do not appear to exhibit significant changes. I will examine our current ability to determine methane sources using atmospheric measurements at both global and regional scales, with a particular focus on new UK emissions quantification efforts being carried out by the Deriving Emissions related to Climate Change (DECC) network. I propose that our existing methods for quantify uncertainties in “inverse” modelling frameworks are likely to be inaccurate, and that new approaches are needed if our estimates are to be relevant for emissions verification purposes. I will introduce a hierarchical Bayesian framework for accounting for some unknown uncertainties in inverse frameworks, and discuss the remaining problem of quantifying the influence of transport model biases.

A DECC perspective on methane

Dr Philip Sargent

Our concern in the Science and Innovation team in DECC is ensure that methane emissions are properly taken into account in the various policies and negotiations that other parts of DECC participate in, but also that money spent on methane reduction does not seriously reduce funds available for CO2 reduction as CO2 is the long-term problem. A single, simple trade-off number – such as the GWP – is what we use but it can’t do all that we might want. We also have to be aware that government policy is to encourage “genuine carbon emission reductions” but precisely how that phrase should be interpreted depends on the timescale under consideration, which may be deliberately unelucidated for any one policy. Sometimes stronger enforcement of low methane emissions could actually reduce spending, thus enabling more to be spent on CO2 reductions, so we are particularly keen to identify those options.

What we particularly need from the research community is a wider and more considered range of options for the trade-off between methane and CO2 . What is the most appropriate period of years to use for the GWP multiplier? 100y ? 20y? Or the integral up to a specific date (such as 2050) rather than an integral over a fixed period of years? If it is to a fixed date, should that be the date at which we expect global average temperatures to peak, or the date at which regional average temperatures for the most vulnerable populations/biomes will peak? Or some internationally-agreed target date? Or should we be more interested in an integrated “date” representing the duration during which global temperatures are expected to be above 2⁰C ? We realise that properly answering these questions requires economists as well as climate scientists. We also realise that these questions particularly apply to methane as the time-constant of 12.4y means that these different metrics produce very different results for methane but not for other GHGs.

IPCC AR5 says that GWP is 28x (+/- 30% at 2 sigma) and that it should be 34x if hydroxyl feedback is included. What would be the appropriate confidence range for that hydroxyl feedback number though? And how does it vary if we are interested in 50y instead of 100y ? How appropriate is the 34x value for national policy assessment?

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