IGBP Fast Track Initiative on Megacities and the coastal zone:air-sea interactions.
This is an IGBP Fast Track Initiative (FTI) linking the activities of three IGBP Core Projects IGAC (International Global Atmospheric Chemistry http://www.igac.noaa.gov/ ), SOLAS (Surface Ocean Lower Atmosphere Study ( http://www.uea.ac.uk/env/solas/ ) and LOICZ (Land Ocean Interactions in the Coastal Zone http://www.loicz.org/). IGBP Fast Track Initiatives are “focussed activities prioritised by the IGBP Scientific Committee to advance our knowledge of Earth System functioning. They should address innovative, cross-cutting issues and gaps in the programme’s research and provide means for the IGBP community to actively contribute to the IGBP synthesis”.
The focus of this FTI is on the importance of air-sea interactions in regulating environmental conditions in and around of megacities (up to several 10kms in the oceans and up to several 100s km in the atmosphere). The initiative will try to focus on generalities of megacities although it will inevitably be informed by case studies and data from specific mega cities. The initiative will bring together a group of experts to consider the scientific issues involved, leading to one or more scientific peer-reviewed publication which will be designed to inform and set the research agenda for the broad scientific community and also to assist environmental managers working in and around mega cities. There are broader issues relating to megacities and also issues that fall more within the remit of social sciences, but for this specific fast track initiative we will focus on the physical issues and specifically on air-sea interaction issues.
The world’s population has increased to about 6 billion people with more than half of these now living in urban areas. The trends of increasing population and urbanisation together lead to the development of megacities which are formally defined as cities with populations in excess of 10 million people, although the exact populations of some cities are uncertain and dependent in part on the political boundaries used. Almost 10% of the world’s urban populations currently live in megacities. Within this initiative we will consider all megacities falling within this definition, and also other very large conurbations or aggregates of conurbations, recognising that many other cities will reach the formal megacity threshold within coming decades. The concentrations of populations and associated emissions to the atmosphere, soil and adjacent waters from megacities create many environmental problems. This initiative focuses on only a subset of these issues, but one we believe to be important and to have been little studied to date, namely that of coastal zone air-sea-interactions. It will feed into a wider IGBP synthesis activity on megacities which is being developed on a longer time scale.
Many of the megacities of the world are situated adjacent to the coast and we argue that this juxtaposition leads to particular environmental consequences that have direct impacts on health and prosperity of people living in and around these cities and which we aim to consider in this initiative. There are for instance aspects of air pollution which are very different under low chloride (interior continental) and high chloride (coastal) locations, such as issues of photochemical ozone cycling. Hence, the emissions of gases and seasalt particles from the coastal zone have the potential to modify (deteriorate) the atmosphere and air quality over the mega city and adjacent areas. The outflow of polluted air from megacities (esp. NOx and VOC) transforms large regions of the marine boundary layer from ozone-destruction to ozone-production regions with potentially far-reaching effects for the oxidation capacity of the atmosphere and climate forcing. Also the interaction of urban atmospheric emissions and seasalt can affect regional climate via changes in regional scale cloud condensation nuclei numbers and size distribution and potentially more efficient cleansing of the air. These interactions between marine and urban emissions may therefore result in fundamentally different atmospheric chemistry than that arising from the same emissions from inland megacities, with attendant impacts on human health and prosperity, agricultural activity and food security and environmental integrity.
Coastal marine ecosystems’ highly complex and specialized nature makes them both biologically productive and highly sensitive to human activities. They are currently subject to multiple environmental stresses including those from run off that have been relatively well characterised scientifically, (e.g. sediment sewage, solid waste, high nutrient loads, synthetic organic chemicals, oil, and pathogens run off) even if the societal solutions to these pressures are still poorly developed. These pressures result in eutrophication and deterioration of water quality, which have adverse effects on coastal ecosystems and their living resources. Continued urbanization along coastal regions will only increase these pressures. Since many of the world’s mega cities are situated adjacent to the coastal zone, there are inevitably large sources of emissions to the atmosphere and deposition to the adjacent coastal system. These emissions include nutrient sources, such as fixed nitrogen, and contaminants such as trace metals and persistent organic contaminants as well as novel classes of contaminants such as nano-particles. The synergistic and antagonistic effects of the deposition of such a cocktail are essentially unknown. The scale of impacts from urban emissions is poorly understood and may be very different in different regions. The impacts of this deposition have the potential to increase environmental stresses on coastal ecosystems for a considerable area around mega cities, exacerbating the impact of run off which is often more local. A range of potential environmental problems can arise from such stresses including hypoxia, harmful algal blooms and the loss of coastal protection from habitats such as coral reefs and mangroves. These coastal waters are in many cases valuable resources for the local population providing food, tourism, recreation, transport, trade and possibly water supply via desalination, and the development of megacities challenge the integrity of these ecosystem services.
Hence there are important scientific issues relating to both the marine and atmospheric environment around megacities, and these are inextricably linked.
We have therefore proposed the following overall goal for this FTI
What are the impacts of coastal megacities (now and in the future) on air quality, coastal water quality, human health and prosperity and regional climate?
This leads to some more specific scientific questions to be addressed.
1. How do air-sea interactions (such as trace gas emissions and seasalt aerosol formation) within the coastal zone affect air pollution within mega cities? The scale of emissions and the key role of halogens in ozone cycling mean that these regions may have a unique chemical environment.
2. How do the interactions of large urban emissions and the marine boundary layer affect local climate? There is evidence that the interaction of marine and urban particulate matter can significantly alter cloud condensation nuclei properties and hence cloud formation and local climate, with implications for both gas-phase chemistry and aerosol micro-physics.
3. How do atmospheric deposition of both contaminants and nutrients from megacities affect the productivity of adjacent coastal waters? The atmospheric emissions from mega cities will include both nutrients, such a fixed nitrogen, and contaminants. These will be deposited down wind of the city and potentially impact the marine environment, causing eutrophication type problems, such as harmful algal blooms in regions, where large populations may be dependent on the marine environment for environmental services such as food, recreation, tourism, transport and possibly water via desalination.
4. What are the feedbacks between the marine and atmospheric impacts, such as changes in marine trace gas emissions due to changes in marine productivity and impacts of changes in air quality on marine ecosystems?
This fast track initiative cannot of course solve all of these scientific issues. The goal is rather to consider these issues within an integrative interdisciplinary framework, and identify the key research needs in terms of both scientific understanding and environmental management. Inevitably these issues are strongly dependent upon the geographic setting of particular megacities. These issues will therefore need to be addressed both in terms of the fundamental understanding of the scientific issues, scaling up with models and also case studies.
The approach to meeting these goals will be to hold one 3 day meeting to which we invite about 15 scientific specialists with diverse experience of particular aspects of this issue plus a group of 5 younger scientists from developing scientific countries. Participants will prepare material ahead of time which will be made available to participants ahead of the meeting to encourage constructive and efficient engagement at the meeting. This will probably include briefing papers within individual’s field of scientific expertise and on specific megacities. The product of the meeting will be at least one high quality high profile peer reviewed publication that will raise the profile of the scientific challenges in this field, identify the key issues involved and prioritise research needs.
We have used this approach with some success in the past with IGBP fast track initiatives for instance on dust, on iron addition experiments to the oceans and on the impacts of atmospheric nitrogen on the oceans. These each yielded a number of high profile publications e.g. Jickells et al. (2005) Science 208, 65-71, Boyd et al (2007) Science 315, 612-617, Duce et al Science 320, 893-897. There is of course no assumption that we can achieve these kind of high profile publications again but that is our aspiration.
The aim is to complete the whole cycle from initiation of the FTI to submission of the resulting papers within one and a half years.