Resolving climate sensitivity associated with shallow mixed phase cloud in the oceanic mid- to high-latitudes (M-Phase)

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment

Abstract

Clouds containing a mixture of ice and water (mixed-phase clouds) are likely to change in response to climate change. It is expected that warming will cause an increase in the amount of water and a decrease in the amount of ice in these clouds. Because water droplets reflect more solar radiation than ice crystals (and cause less precipitation), the clouds are expected to become brighter, thereby causing a cooling effect (or negative feedback) on the climate system at mid- to high-latitudes.

The magnitude of the cloud-phase feedback is very uncertain. If the feedback is strong then global temperatures will increase more slowly in future, but if it is weak then temperatures will increase more rapidly. It was recently shown that adjusting the ratio of ice and water in a climate model to match satellite observations could increase Earth's equilibrium climate sensitivity (warming with a doubling of CO2) by 1.5 degrees; hence, Earth may warm faster than thought. The feedback process is further complicated by the fact that the special particles, ice nucleating particles (INPs), which trigger ice production, may be more abundant in a warmer world where INP sources, such as glacial valleys, will be covered in ice and snow for less time. Increased INP concentrations would mean more ice in clouds and lead to a positive feedback. These two opposing feedbacks contribute to what we refer to as the cloud-phase feedback.

This proposal will improve our understanding of how ice particles form in clouds and how this affects the cloud-phase feedback. Ice formation is the key process that controls this feedback. The problem can be broken down into two parts:
First, we will address the open questions related to the chain of processes that link initial ice formation to the reflectivity of the clouds and how the reflectivity will change with warming. We have designed an aircraft campaign targeted at conditions of most relevance to the cloud feedback problem: moderately cold clouds that will be most sensitive to changes in temperature, and where high INP concentrations are likely to influence large regions of the N Atlantic. These cold-air outbreaks clouds provide an ideal meteorological situation for studying the formation and evolution of the kinds of shallow mixed-phase clouds which are important for cloud feedbacks.
Second, we will address the paucity of knowledge on the sources, distribution and seasonal cycles of INPs at the mid- to high-latitudes. Our strategy is to use measurements to identify sources of INPs and use this information to inform the inclusion of mid- to high-latitude sources in our global model of INPs. We will perform new long-term measurements through a whole year and ship borne measurements through the key source regions in the Arctic. We have built a substantial network of Partners who will contribute INP data across the northern and southern mid- to high-latitudes which will allow us to expand our study to the globe.

The new knowledge on cloud processes and INP will be used to improve the representation of mixed-phase clouds in the Met Office weather and climate model. The model will be run at very high spatial resolution so that the individual clouds in the cold-air outbreaks can be simulated. The model will be tested and improved by comparing it to our measurements as well as against satellite observations. We will then extend this study to contrasting cases from the Southern Ocean and the other side of the Atlantic. We anticipate the new knowledge will lead to a greatly improved representation of these climatically critical clouds. We will then perform a sensitivity analysis on selected cases in order to test how these cloud systems will respond to climate change. Finally, we will use the new knowledge to develop a plan for improving how mixed-phase clouds are treated in global climate models so that this work can be carried out in a follow-on project.

Planned Impact

M-Phase is focused on reducing the uncertainty associated with equilibrium climate sensitivity through improving the representation of the cloud-phase feedback. This will lead to impact in several areas:

Climate prediction
The value of reducing uncertainties in climate sensitivity has been estimated to be in the trillions of dollars (Hope, 2014, doi:doi:10.1098/rsta.2014.0429). Climate predictions using a range of models from around the world underpin international agreements to tackle climate change. At the same time more and more national governments are using regional climate predictions to help plan mitigation measures at the country scale, as for example outlined in the National Adaptation Programme by the UK government. The impact of these predictions on society is large, ranging from changes in energy production, development of strategies and counter-measures to deal with extreme weather, to food security and spread of disease. These efforts are predicated on accurate future predictions of the climate. Therefore achieving our goal of reducing uncertainty in climate prediction will benefit all of these stakeholders.

Weather forecasting
The operational implementation of the improved representation of mixed-phase clouds will lead to more accurate weather forecasts both for polar applications (e.g. commercial shipping, community resupply) and also at mid-latitudes through demonstrable links to lower latitudes. Cold-air outbreaks have a significant impact on the UK and Europe and are associated with disruptive snow events. Forecasts underpin the weather warning system used by emergency services, infrastructure professionals, local and national government to safeguard lives, livelihoods and property. Therefore, improving weather forecast in terms of accuracy in the immediate future and extending the lead time for which useful and skilful forecasts are available has a direct impact upon different organisations ability to plan ahead and deliver more effective services. Also, forecasts at the high latitudes are likely to become more important in the future as Arctic shipping is forecast to increase with retreating sea ice. Improving the representation of Cold Air Outbreaks will improve the forecasting of situations that contain high winds (>=Beaufort force 7) and supercooled water conditions that can lead to extreme riming of superstructures

Instrument innovation and commercialisation
Murray is in the process of commercialising the PINE (Portable Ice Nucleation Experiment) chamber https://www.noell.bilfinger.com/pine/ which was developed during his ERC consolidator fellowship. This is the first portable semi-autonomous instrument for quantifying ice nucleation based on the expansion principle. It is being commercialised in partnership with Karlsruhe Institute of Technology and Bilfinger Noell GMBH. PINE will be deployed as part of the cruise. While the PINE chamber has been deployed to several land based atmospheric observatories, this will be the first time the PINE chamber has been deployed on a ship. Hence, M-Phase will help to establish the utility of PINE for autonomous INP measurements. Murray's vision for PINE is that it will become a standard instrument in all GAW style atmospheric observatories. This will not only benefit society through providing the fundamental data required to underpin climate modelling, but it will also yield significant economic impact.

Re-application of new knowledge
The M-Phase team also has a track record of using discoveries in atmospheric science and re-applying them in other areas. A good example of this is Murray's discovery that a particular mineral in desert dust is extremely effective at nucleating ice. In conjunction with Asymptote Ltd. (now part of General Electric, GE) he patented the use of this mineral for the control of ice nucleation in the cryopreservation of biological samples. This work is at the stage where it is attracting investment from GE.