Emily Pidgeon

Estimating Global “Blue Carbon” Emissions from Conversion and Degradation of Vegetated Coastal Ecosystems

Recent attention has focused on the high rates of annual carbon sequestration in vegetated coastal ecosystems—marshes, mangroves, and seagrasses—that may be lost with habitat destruction (‘conversion’). Relatively unappreciated, however, is that conversion of these coastal ecosystems also impacts very large pools of previously-sequestered carbon. Residing mostly in sediments, this ‘blue carbon’ can be released to the atmosphere when these ecosystems are converted or degraded. Here we provide the first global estimates of this impact and evaluate its economic implications. Combining the best available data on global area, land-use conversion rates, and near-surface carbon stocks in each of the three ecosystems, using an uncertainty-propagation approach, we estimate that 0.15–1.02 Pg (billion tons) of carbon dioxide are being released annually, several times higher than previous estimates that account only for lost sequestration. These emissions are equivalent to 3–19% of those from deforestation globally, and result in economic damages of

International Implications of Climate Change

US 6–42 billion annually. The largest sources of uncertainty in these estimates stems from limited certitude in global area and rates of land-use conversion, but research is also needed on the fates of ecosystem carbon upon conversion. Currently, carbon emissions from the conversion of vegetated coastal ecosystems are not included in emissions accounting or carbon market protocols, but this analysis suggests they may be disproportionally important to both. Although the relevant science supporting these initial estimates will need to be refined in coming years, it is clear that policies encouraging the sustainable management of coastal ecosystems could significantly reduce carbon emissions from the land-use sector, in addition to sustaining the well-recognized ecosystem services of coastal habitats.

Research Spotlight: Designing nature-based mitigation to promote multiple benefits

A number of international treaties and conventions have been developed to aid in addressing ocean issues that affect multiple jurisdictions and countries. Many of these focus either primarily on marine resources or involve them in some fashion. Exploring and strengthening synergies between these treaties and conventions would be extremely beneficial for providing increased value, better coordination, and improved focus and facilitation of the development of key priorities (Robinson et al., 2005). The following discussion includes only a subset of the larger body of international conventions and treaties.

Climate-Driven Physical and Chemical Changes in Marine Ecosystems

By promoting the conservation and restoration of natural ecosystems, policymakers have a unique opportunity to mitigate climate change while providing social and environmental benefits. Here we highlight how nature-based mitigation strategies for multiple benefits can be supported by three key areas of scientific research, drawing upon examples of research by Conservation International and its partners. First, monitoring of ecosystems can quantify the magnitude of emissions released from conversion and degradation, and can inform prioritization and planning efforts. Second, understanding the synergies and tradeoffs between climate change mitigation and other ecosystem benefits can aid in designing policy instruments, selecting management techniques and geographically targeting actions. And third, research on the design of policies, incentives and practices can enhance mitigation initiatives’ provision of both climate and noncarbon benefits. Achieving multiple benefits can in turn increase the sustainability of and investment in nature-based mitigation.

Clarifying the role of coastal and marine systems in climate mitigation

Covering more than two-thirds of the Earth’s surface, the oceans are a central component of the global climate system. The oceans help to control the timing and regional distribution of the Earth’s response to climate change, primarily through their absorption of carbon dioxide (CO2) and heat. Changes to the physical and chemical properties of the oceans are already being observed. Sea surface temperatures are warming, sea level rise is accelerating, the oceans are becoming increasingly acidic, and the rate of sea ice melt is steadily increasing. The International Panel on Climate Change (IPCC) assessment released in 2007 projects that, due to the persistence of greenhouse gases in the atmosphere, it is highly likely that the oceans will continue to warm and the impacts will be felt for centuries (IPCC, 2007a). This section focuses on the physical and chemical changes currently being observed in the Earth’s oceans, including changes in temperature, stratification, salinity, sea ice, climate regimes, ocean circulation, and ocean acidification. Knowledge gaps and research needs will be discussed throughout. The aim is to assess the current state of knowledge related to how climate change may be interacting with, and in some cases, driving, the observed physical and chemical changes in the Earth’s oceans, and what that means for the U.S.