Friday, June 6, 2008


Carbon Cycle Science
Global climate projections and regional climate forecasts depend on understanding the path of carbon through our environment.
Projecting climate into the future and forecasting regional impacts depends on our understanding of the exchange of carbon dioxide between the atmosphere, oceans and land ecosystems. The atmospheric measurements and analyses required to track the fate of carbon dioxide emissions caused by the burning of fossil fuels and biomass, and to reduce uncertainties in how the exchange of carbon responds to the variations and trends of climate and land use.
What is the Carbon Cycle?
Carbon is exchanged, or "cycled" among Earth's oceans, atmosphere, ecosystem, and geosphere. All living organisms are built of carbon compounds. It is the fundamental building block of life and an important component of many chemical processes. It is present in the atmosphere primarily as carbon dioxide (CO2), but also as other less abundant but climatically significant gases, such as methane (CH4).

Sources and Sinks
Because life processes are fueled by carbon compounds which are oxidized to CO2, the latter is exhaled by all animals and plants. Conversely, CO2 is assimilated by plants during photosynthesis to build new carbon compounds. CO2 is produced by the burning of fossil fuels, which derive from the preserved products of ancient photosynthesis. The atmophere exhanges CO2 continuously with the oceans. Regions or processes that predominatly produce CO2 are called sources of atmospheric CO2, while those that absorb CO2 are called sinks.
Why is the Carbon Cycle important?
While CO2 is only a very small part of the atmosphere (0.04%), it plays a large role in the energy balance of the planet.
CO2 in the atmosphere acts like a blanket over the planet by trapping longwave radiation, which would otherwise radiate heat away from the planet. As the amount of CO2 increases, so will its warming effect. CO2 is the largest contributor (currently 63%) to this effect by long-lived gases and its role increases each year. The additional burden of CO2 in the atmosphere will remain for a very long time, of the order of thousands of years, if we have to rely on the natural mechanixms of erosion and sedimentation to process the added CO2.
What do we know about the Carbon Cycle?
Owing primarily to the burning of fossil fuels and secondarily to changes in land-use, the amount of CO2 in the atmosphere has been increasing globally since the onset of the industrial revolution. Based on 50 years of direct observations of the atmosphere, it is clear that this trend continues and is accelerating. From observatories and cooperative sampling sites around the world, A global greenhouse gases and works with partners to improve the accuracy and reliability of these measurements in order to improve our understanding of the sources, sinks, and trends of this important gas and to improve our predictive capability. This continuing record is critical to understanding the potential evolution of global climate as well as aiding or verifying international management strategies.
fig;green house gas index

What don't we know about the Carbon Cycle?
Although we have a good sense of what is happening with CO2 on a global basis, and have a sound system for following large-scale trends, regional information is needed if society is ever to manage or verify carbon emissions. We must understand regional variations in the sources and sinks of CO2 because they help identify possible sequestration or emission management options. Ideally, these regional evalutions would be done on a global basis. Our first and perhaps most important step is to focus on the North American continent.

Impacts of increasing CO2 on other systems
Continued emission of carbon dioxide to the atmosphere will affect climate and ocean chemistry, subsequently influencing both marine and terrestrial ecosystems. The warming effects of increasing CO2 and other greenhouse gases impinge on agriculture, natural systems, and a host of environmental variables. Increasing CO2 in the atmosphere also directly translates to increasing acidity of the oceans. Carbon dioxide dissolves in water to form carbonic acid, which is corrosive to the shells and skeletal material of many marine organisms. Subsequent impacts on ecosystems are largely not understood.

What will we need to know in the future?
Anthropogenic emissions, emissions limitations, sequestration, and ocean chemistry will likely play leading roles in the future atmospheric CO2 burden. Coupled models will be required for long term projections. Answers to key questions such as the following will require careful observation and skilled modeling, all of which we aim to achieve, working together with our partners. We will also need an early warning system for potentially large, but hard to predict, changes in the carbon cycle, such as massive emissions of CO2 from frozen carbon compounds in Arctic permafrost as it warms up.
Related topics
How can we gain enough confidence in these models for them to aid in decision making?
Which features can be validated?
Can we estimate the length of time that a particular sequestration option is secure?
What are biophysical limits of biological sequestration?
How much CO2 can be stored in geological reservoirs, how much in the oceans?
What are likely environmental impacts of different strategies?
How does the effectiveness of sequestration compare to decreasing the "carbon intensity" of our activities?
How does society benefit from this knowledge?
If society is to manage or reduce carbon emissions in the future, reliable and accurate information will be needed on local, regional, and global scales. Atmospheric measurements of the spatial and temporal trends of CO2 in the atmosphere are essential for reaching quantitative understanding the sources and sinks of this gas. Without accurate measurements, the effictiveness of mitigation or verification of emission reduction become very uncertain. So is evaluation of new energy strategies. Society will be increasingly prepared to deal with the shifts of regional and global climate. In the future, coupling CO2 models with other environmental models will improve predictions and long-term stewardship strategies.

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