Greenhouse gases alter the Earth's climate by absorbing infrared radiation and re-emitting a fraction of the radiation towards the Earth's surface. Carbon dioxide (CO2) and methane (CH4) are two of the most potent greenhouse gases whose atmospheric concentrations have increased from anthropogenic emissions. Concentrations of CO2 have increased by 30% since 1750, due mainly to combustion of fossil fuel and land use change. Less than half of the emitted CO2 remains in the atmosphere, and only 40% remained airborne in the 1990's. The missing CO2 is being stored as organic matter in vegetation and soils, or dissolved in the ocean. CH4 concentrations have risen dramatically by 151% since 1750 due to a combination of fossil fuel combustion, cattle farming, and rice agriculture, although its growth rate has slowed in the 1990s.
Understanding where, why, and at what rates CO2 and CH4 are exchanged with the atmosphere is essential for predicting future climate. Changes in biospheric CO2 and CH4 fluxes under climate change provide important feedbacks to the climate system. Canada plays a vital role in the global budget of CO2 and CH4: the Canadian landscape contains 10% of the world's forests and 14% of the world's wetlands, an important source of CH4.
Furthermore, knowledge of sources and sinks is necessary for Canada to meet its commitment under the Kyoto Protocol to reduce greenhouse gas emissions by 6%, relative to 1990 levels. As part of this effort, an integrated accounting system is necessary to quantify and understand the Canadian sources/sinks of CO2 and CH4.
Despite its importance, a quantitative understanding of the sources/sinks of CO2 and CH4 at the regional scale (10~1000 km) currently remains elusive. One of the main reasons for the current uncertainty is the lack of an appropriate analysis/modelling framework that can make use of the multiple observational sources.
The following figure illustrates a new analysis framework designed to infer sources/sinks of CO2:
The framework above is envisioned to merge information from multiple data sources: atmospheric concentrations, flux measurements, forest inventory, fossil fuel emissions, and satellites. The framework includes models of both 1) the biosphere, including various biological processes spanning multiple timescales; and 2) the atmosphere, which links fluxes of the greenhouse gas to the observed atmospheric concentrations.
Continued improvements and development of such modelling tools and analysis frameworks is necessary to understand current sources/sinks of greenhouse gases. Such understanding would then enable us to projecting these sources/sinks into the future and for developing a more comprehensive understanding of climate change.
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