How does decomposition help carbon return to the atmosphere

Feedbacks can either increase or decrease the pace at which some change occurs. For example, higher temperatures can lead to more decomposition. And if climate change speeds rot, it will also speed how quickly more carbon dioxide enters the atmosphere. She is a biologist at the University of New Hampshire in Durham. And now a feedback cycle develops. In fact, the situation is more complicated, Mayes cautions.

To learn more, Mayes, Gangsheng Wang and other soil researchers at Oak Ridge National Laboratory created a computer program to model how global warming and other aspects of climate change would affect the speed at which dead things break down.

This analysis accounted for those times of the year when microbes are dormant, or inactive. It appears that after a few years, microbes may simply adjust to higher temperatures, Mayes explains. Simply put: Predicting future consequences is difficult. Outdoor experiments provide more insights. For more than two decades now, experts there have used underground electric coils to artificially warm certain soil plots. More carbon going into the air means less remains in the topsoil. The impacts of this drop in carbon on soil fertilty could be huge, says Blanchard.

It also adds nitrogen compounds to the air. Eventually, the nitrogen falls back to Earth in rain, snow or dust. Nitrogen is part of many fertilizers. That is especially true in many areas near big cities and industrial areas such as where the Harvard Forest grows.

For some of those areas, 10 to 1, times as much nitrogen gets added to the soil each year compared to back in the s.

The result: Soil levels of nitrogen continue to grow. Higher nitrogen levels seem to reduce the ability of microbes to make the enzymes needed to break down dead tissues. As a result, plant litter on the forest floor will get recycled more slowly.

Pine trees in one test area of the Harvard Forest actually died from too much added nitrogen. Pringle, at Harvard, agrees. Too much nitrogen slows decomposition in the short term, she says. Another open question: How will fungal communities change? In many areas, fungi break down most of the lignin in the woody parts of plants. The science of rot matters as much for transportation as it does for trees.

In fact, rot is key to better biofuels. Today, the big biofuel is ethanol, also known as grain alcohol. Ethanol is generally made from sugars derived from corn, cane sugar and other plants.

It could help them make biofuels less expensively. And they want to use far more than corn stalks as their plant sources. They also want to streamline the process to make their biofuels.

Those goals have led scientists on a hunt for bacteria that are up to the task of breaking down plant material quickly and reliably.

Scientists discovered this bacterium living near the Quabbin Reservoir, east of Amherst, Mass. In a one-step process, this microbe can break down hemicellulose and cellulose into ethanol. In some conditions decomposition is blocked. The plant and animal material may then be available as fossil fuel in the future for combustion.

The carbon cycle is easiest to understand in terms of its processes and how carbon is converted. The three key processes and the conversions are shown in the table below. The carbon cycle Carbon is an essential element for life on Earth. Mayes, R. Najjar, S. Reed, P. Romero-Lankao, N. Gurwick, P. Marcotullio, and J.

Field, Preface. Shrestha, R. Romero-Lankao, and Z. Zhu eds. Birdsey , R. Gurwick , K. Gurney , G. Shrestha , M. Reed, and P. RomeroLankao, Appendix D. Carbon measurement approaches and accounting frameworks. Back to top. For the past three centuries, North America has been recognized as a net source of CO 2 emissions to the atmosphere Houghton , ; Houghton and Hackler ; Hurtt et al. Now there is greater interest in including in this picture emissions of CH 4 because it has 28 times the global warming potential of CO 2 over a year time horizon Myhre et al.

The major continental sources of CO 2 and CH 4 are 1 fossil fuel emissions, 2 wildfire and other disturbances, and 3 land-use change. Globally, continental carbon sources are partially offset by sinks from natural and managed ecosystems via plant photosynthesis that converts CO 2 into biomass. Highlighted in this chapter are persistent challenges in unravelling CH 4 dynamics across North America that arise from the need to fully quantify multiple sources and sinks, both natural Warner et al.

Adding to the challenge is disagreement on whether the reported magnitudes of CH 4 sources and sinks in the United States are underestimated Bruhwiler et al. Temporal patterns indicate that fossil carbon emissions have increased from 3. However, considerable uncertainty remains in the spatial patterns of emissions at finer scales over which carbon management decisions are made. Most importantly, the sensitivity of terrestrial sources and sinks to variability and trends in the biophysical factors driving the carbon cycle is not understood well enough to provide good confidence in projections of the future performance of the North American carbon balance Friedlingstein et al.

Hayes , D. Vargas , S. Alin, R. Conant, L. Hutyra, A. Jacobson, W. Kurz, S. Liu, A. McGuire, B. Poulter, and C. Woodall, Chapter 2: The North American carbon budget.

Recorded webinars describing what is the carbon cycle, focusing on the Second State of the Carbon Cycle Report science findings and pertinent scientific and societally-relevant activities, are posted on our YouTube Channel.

The series desciption is here. Note: For the latest annual global carbon and methane budgets, please see the Global Carbon Project. The adjacent figure on the left represents recent global carbon budget estimates of annual carbon flows averaged from to , as provided in the Global Carbon Project's report.

Values in gigatons of carbon per year. The metric ton is also written as tonne in the British and French systems, as in this Global Carbon Budget figure.

View a table presenting data and source for current greenhouse gas concentrations. Read a discussion of the global carbon cycle. Find the latest carbon budget estimates. Source: Global Carbon Project. And, click here to see figures summarizing the global cycles of biologically active elements. Source: William S.

View an illustration of the major world ecosystem complexes ranked by carbon in live vegetation. Using 5. Anthropogenic CO 2 comes from fossil fuel combustion, changes in land use e. Houghton and Hackler have estimated land-use changes from , so it is convenient to use as our starting point for the following discussion.

Atmospheric CO 2 concentrations had not changed appreciably over the preceding years IPCC; The Scientific Basis so it may be safely assumed that they would not have changed appreciably in the years from to in the absence of human intervention. In the following calculations, we will express atmospheric concentrations of CO 2 in units of parts per million by volume ppmv.

Each ppmv represents 2. According to Houghton and Hackler , land-use changes from resulted in a net transfer of PgC to the atmosphere. During that same period, PgC were released by combustion of fossil fuels , and 5. Atmospheric CO 2 concentrations rose from ppmv in to The See the lastest State of the Carbon Cycle Report for details.

How much carbon dioxide is produced from the combustion of cubic feet of natural gas? If we start with cubic feet of natural gas and assuming it is pure methane or CH 4 at STP standard temperature and pressure, i. Since 1 mole of a gas occupies One mole of CO 2 has a mass of approx. A pound is about equivalent to g, so That is, the complete combustion of cubic feet at STP of natural gas results in the production of about lb of carbon dioxide.

Of course, the mass of the methane in cubic feet will vary if the temperature and pressure are NOT as assumed above, and this will affect the mass of CO 2 produced. According to the Ideal Gas Law:. Solving again at this higher relative to STP temperature, we get:. That is, at the higher temperature, a given volume of gas will contain fewer moles, and less mass. Going again through the calculation for CO 2 emitted, but using the value of moles of CH 4 , results in an answer of approximately lb of carbon dioxide.

When looking at CO 2 emissions estimates, it is important to look at the units in which they are expressed. The numbers are sometimes expressed as mass of CO 2 but are listed in all of our estimates only in terms of the mass of the C carbon. Because C cycles through the atmosphere, oceans, plants, fuels, etc. Why is the sum of all national and regional CO 2 emission estimates less than the global totals?

There are four primary reasons for this. Why do some smaller nations have larger per capita emission estimates than industrialized nations like the US? Often it is difficult to attribute emissions to a source. Many small island nations have military bases that are used for re-fueling or have large tourist industries. Who do you assign the emissions to; the US whose military planes are re-fueling on the Wake Island with aviation and jet fuel or the Wake Island?

The accounting practices used within the UN Energy Statistics Database assign this fuel consumption to the Wake Island thus elevating the Wake Island's per capita estimate. The same is true for tourist nations like Aruba who are assigned the fuels used in the commercial planes carrying tourists back to their native countries. Although this distorts the per capita emission estimates it makes it easier from an accounting standpoint than trying to trace each plane or ship to its final destination.

One should be cautious in using only the per capita CO 2 emission estimates. No, they are two different but related issues.