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Methane

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Methane has the second largest radiative forcing after CO2 . The concentration of CH4 has increased by a factor of 2.5 since preindustrial times, from 722 ppb in 1750 to 1803 ppb in 2011. There is very high confidence that the atmospheric CH4 increase during the industrial era is caused by anthropogenic activities [IPCC, AR5 ].

Come join us for an exciting and diverse range of talks around methane from wetland emissions to economics and policy.

1.00 to 1.40 pm Andrew Tanentzap (Cambridge): Why lakes get gassy and why it matters.

1.40 to 2.20 pm Euan Nisbet (Royal Holloway): Rising methane – wetlands? cows? hydroxyl? fossil fuels? or all of these? – is the warming feeding the warming?

2.20 to 3.00 pm Michelle Cain (Oxford): Methane’s role in the Paris Agreement and why it’s so often misunderstood

3.00 to 3.30 pm coffee break in Archaeology common room with cake!

3.30 to 4.10 pm Eleanor Burke (MetOffice): Modelling the northern high latitudes carbon cycle feedbacks in a changing climate

4.10 to 4.50 pm Paul Balcombe (Imperial): Methane emissions from natural gas: super emitters and climate metrics

5.00 to 6pm Nibbles.Archaeology common room.

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Abstracts:

Dr Michelle Cain

Oxford Martin School and Environmental Change Institute, University of Oxford

Title: Methane’s role in the Paris Agreement and why it’s so often misunderstood

For policy makers to make informed decisions to mitigate against climate change, the effects of different climate pollutants must be compared against each other. Carbon dioxide is the main driver of anthropogenic climate change. Other climate pollutants, including methane and nitrous oxide, contribute half as much warming again, and will become more important as carbon dioxide emissions are reduced.

However, many of these other pollutants are short-lived, unlike carbon dioxide. Methane has a lifetime of the order of a decade, so although the immediate effect of a molecule of methane on temperature is stronger than from carbon dioxide, in 50 years the impact will be much smaller.

How do we compare the different forcing agents when they cause different amounts of warming over different time periods? Currently, Global Warming Potential over 100 years is the most common emission metric, however it can give misleading results under ambitious mitigation scenarios (e.g. RCP2 .6). This is going to become increasingly important as the world makes plans to achieve the goals of the Paris Agreement.

In this seminar, I will discuss the problem with using GWP under ambitious emissions mitigation scenarios, with a particular focus on methane. I will go on to discuss alternatives such as a modified use of GWP , which provides a more robust link between greenhouse gas emissions and temperature response, which was first proposed in Allen et al. (2016) and demonstrated in Allen et al., (2018).

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Dr Andrew Tanentzap

Department of Plant Sciences

University of Cambridge

Title: Why lakes get gassy and why it matters.

Freshwaters are the one of the largest sources of global methane emissions and their contribution is expected to rise with global change. However, there remains large uncertainty as to how different sources of organic compounds will influence biological routes of methane production in freshwaters. In this talk, I explore how changes in vegetation cover surrounding freshwater may influence the global methane budget. I will highlight the importance of understanding variation in the age and composition of organic matter.

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Dr Paul Balcombe

Department of Chemical Engineering

Imperial College

Methane emissions from natural gas: super emitters and climate metrics

CO2 emissions from natural gas are lower than other fossil fuels, but recent studies suggest that methane emissions from the supply chain reduce this climate benefit and are highly variable. The high variability of emissions across different supply chain technologies and regions means that greater analysis is required to understand how best to minimise emissions. Additionally, the appearance of super emitters in every stage of the supply chain skews the distribution significantly. Methane is a very potent but short-lived greenhouse gas, where Global Warming Potentials are typically used to compare gases with ‘CO2 equivalences’, but there is growing acknowledgment of their limitations and a desire to use other metrics and time horizons.

Research at the Methane and Environment Programme, Sustainable Gas Institute at Imperial College London, examines the effect of the variability of methane emissions and the use of different climate metrics, and time horizons, on the potential contribution of natural gas to governmental decarbonisation pathways. The research determines the variability of supply chain emissions using a technology-rich probabilistic emissions model and then conducting life cycle assessment of different supply chains and end-uses. We assess the benefits of using different climate metrics, such as the global temperature change potential (GTP), as well as other timeframes, for different industrial, governmental and academic applications.

Results from the probabilistic assessment is that the distribution of emissions is extremely heavily skewed, resembling a log-log-logistic distribution for most supply chains: median estimates which represent typical routes are modest at 18-24 gCO2eq./MJ, but mean estimates, which account for the super emitters, are 22-107 gCO2eq./MJ, using GWP100 . Estimates vary by a factor of 100 across metrics, gas fields and supply chain routes. Placing these values into context, natural gas combustion emissions are approximately 55 gCO2/MJ. Thus, some supply chain scenarios are major contributors to total greenhouse gas emissions from natural gas. The role of natural gas in decarbonisation pathways must be managed carefully to avoid unintended consequences of increased supply chain methane emissions. Given the short-lived nature of atmospheric methane, the timing of natural gas production (and emissions) is a key consideration in energy transitions and minimising peak temperatures.

This talk is part of the Cambridge Centre for Climate Science series.

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