Developing a framework to test the sensitivity of atmospheric composition simulated by ESMs to changing climate and emissions

Climate change and air pollution are two of the biggest challenges facing humanity today. Ozone and particulate matter are pollutants that are particularly harmful to human health. Recent studies have suggested that in the UK alone they cause 50,000 extra deaths and result in a financial burden of £8-22 billion per year. Both ozone and particulate matter also play an important role in climate change. Ozone absorbs infra-red radiation resulting in a warming of the climate. Particles scatter and absorb incoming solar radiation and alter the properties of clouds. This results in complex interactions with the Earth's climate, with some types of aerosol pollution warming climate whereas others cool climate. Future air quality depends both on changes to emissions of pollutants and to changes in climate. Furthermore, a warming climate can result in worsened air pollution, which in turn can drive additional warming, meaning that complex feedbacks are possible between air pollution and climate.
To help understand these complex interactions and feedbacks scientists have developed Earth System Models that include a description of the important physical and biogeochemical processes. These models are increasingly being used by policy makers to make predictions about future air quality and climate and to guide policy decisions. It is therefore important that the models are rigorously tested.

This testing involves using detailed observations of atmospheric composition that have been made over the past few decades at locations around the world. Most model evaluation to date has involved testing whether the models simulate current average concentrations of atmospheric pollutants. Whilst this is a useful and necessary first step in model evaluation it does not test whether the model accurately simulates the change in concentration of a pollutant under changing emissions or changing climate. For example, does the model capture the real-world change in concentrations of a pollutant given a particular change in emission or under a future climate change scenario? This is particularly important as these predictions under-pin policy recommendations for air quality abatement.

In this project we will synthesis long-term (multi-decadal) observations of ozone and particulate matter and their atmospheric precursors. We will use these observations to explore trends and variability that have been observed over the past few decades. We will then develop a model-observation framework that can be used to evaluate how well models simulate observed variability and trends. We will test state-of-the-art Earth System Models using existing model output from model intercomparison exercises. Finally, we will explore the model processes that are driving simulated variability and trends.

Our results will inform the scientific community as to the fidelity of Earth System Models. This project will help improve our models and give us more confidence in our predictions.

Our project will have direct impact in 3 distinct areas:

1) Climate and Earth System Models. The project will create new metrics and design an appropriate framework to improve process-based evaluation of Earth System Models (ESMs). We will ensure that awareness of the scientific outcomes of this project is achieved through the usual channels of academic dissemination (scientific papers, conference presentations and posters). We will ensure maximum international exposure to the outcomes of the research at an academic level, through either a European Geophysical Union or American Geophysical Union special session on the topic with one of the project PIs as chair or co-chair. Specifically, user engagement will focus on the following users:
a) Met Office. Our project will develop metrics to test future Met Office climate and ESMs. The Met Office is an official project partner and this will help ensure transfer of knowledge from this project. Leeds has long-standing and well-established collaborations with the Met Office, and collaborates with the Met Office through the academic partnership, a cluster of research excellence. ICAS has been working with the Met Office for several years on the UKCA: the chemistry-aerosol-climate model that will be used for climate prediction including future Intergovernmental Policy on Climate Change (IPCC) assessments.
b) International ESM community. We will ensure that the findings from the project are made available to the international ESM community, and we will discuss in detail with stakeholders how the research may be used or refined to test Earth system or climate models. One of the PIs will attend an ESM intercomparison project meeting (e.g., Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) or Chemistry-Climate Model Initiative (CCMI)). The University of York PI leads the chemistry working group for the GEOS-Chem model which is the Chemistry module for both the NASA and the Beijing Climate Centre's ESM. This facilitates the connection between this project and those groups. We will develop a simple project webpage, hosted through University of Leeds, which will detail our project and will point to relevant the relevant data centres where our data will be archived (e.g., BADC). Finally, we will engage with providers of ESM National Capability within NERC, and will be guided in our prioritisation of interactions pending the findings of NERCs current Earth System model review.
c) ECMWF. ICAS also collaborates with the European Centre for Medium range Weather Forecasts (ECMWF) through the EU Global Monitoring for Environment and Security MACC project (http://www.gmes-atmosphere.eu/). Improved knowledge from this project will feed into future model evaluation conducted through MACC. This collaboration helps our project make a direct connection to the public and environmental agencies.

2) Climate, environmental and air quality policies. Policy impacts of our project will be achieved through development of new metrics and mechanisms to test ESMs. We will exploit existing relationships to ensure our project will directly impact the work of national and international climate prediction centres, climate and air quality policy and the IPCC. The Atmospheric Chemistry group at York hosts a joint NCAS - DEFRA staff member providing support to the DEFRA Air Quality Expert Group secretariat. The NERC-funded Atmospheric Chemistry In The Earth System (ACITES), which the York PI leads, also provides a mechanism for informing policy. We will also exploit existing links with the Met Office and their ongoing strong links with government agencies. We will hold an end of project workshop where we will invite stakeholders in ESMs and policy makers who use output from ESM and climate models (e.g., DECC and DEFRA).

3) Public outreach. We will make the results of our research applicable and accessible to the general public, via the web and through University and NERC press offices.