Economy & Energy
Year IX -No 55:
– May 2006   
ISSN 1518-2932

seta.gif (5908 bytes)No 55 Em Português  





other e&e issues

e&e No 55


Ministério do Desnvolvimanto, indústria e Comércio Exterior

Ministério da ciência e Tecnologia


Main Page

Growth of Methane
Concentration in the Atmosphere

Variation of Methane Content in the Atmosphere

Results of Macroeconomic Reference Scenario

Macroeconomic Scenario - Horizon 2026

Editorial :

 e&e : the Organization and the Periodical

 The e&e Organization

   The Economy and Energy - e&e Organization is registered as OSCIP


   Completion of the Fabrication and Assembly of the Internal Parts and Pressure Vessel of the LABGENE Reactor.


   Capital Productivity: The e&e Organization and the Ministry of Science and Technology have signed a Partnership Contract.

e&e links




Growth of Methane
Concentration in the Atmosphere

(It’s impact on the implementation
 of Kyoto Protocol)


                                                                  Carlos Feu Alvim


                                                         Omar Campos Ferreira

                                                                José Israel Vargas



Carbon dioxide (CO2) and methane (CH4) constitute the main gases responsible for the observed greenhouse effect acceleration. As well known, the concentration growth of these gases in the atmosphere was considerably accelerated after the Industrial Revolution.

Modern analytical techniques allow the estimation to be made not only of the concentration of these gases in the atmosphere but also to assay their accumulation along the remote past, trapped in snow, in the Arctic and Antarctic continents. Etheridge et ali whose results are presented below have recently revised the phenomenon. Their data suggest that the concentration of CH4 shall eventually reach stable values due to its shorter half-life.

The aim of the present study is to evaluate how this concentration saturation might contribute to the atmospheric carbon accounting as well in the returns obtainable from the clean development mechanisms adopted in Kyoto.

. The aforementioned results are presented graphically in figure 1. It displays an extraordinary acceleration of methane concentration in the beginning of the Industrial Revolution. A superficial analysis of these data would leave us to believe that the concentration increase from this period on would be exponential. However, a closer examination rather suggest that the logistic algorithm does describe both the past and the future of the system under scrutiny. This hypothesis is confirmed in figure 2 with a high precision (correlation coefficient R2 = 0,9953). However the most convenient representation is logistic as shown in figure 3.

Methane and Global Warming

The increase of methane (CH4) concentration has been identified as the second largest contributor to global warming. EPA’s (United States Environmental Protection Agency) estimates that this gas would be responsible for 22.9% of the observed effect of the total concentration accumulated since the pre-industrial era until todayii.

The characteristics of heat retention by this gas in the atmosphere is higher than that of carbonic gas (CO2) and thus lead the Kyoto Protocol to establish an equivalence between them by a factor of 21 in mass (1 ton of CH4 is equivalent to 21 tons of CO2) as regards greenhouse effect generation. Consequently carbon emitted as methane would have an effect 8 times larger than that of carbon dioxide into which it will be converted. Furthermore, this penalization naturally takes into account the half-life of CH4 in the atmosphere, (shorter than that of CO2).

This emission accounting became the current rule within the Protocol. As a consequence, the required methane emission reduction has wrongly been commercialized obeying this equivalence.

Brazil has unsuccessfully argued that the long-term effect should be considered and therefore the initial rules should continue to be followed in the carbon credit trade. Therefore the equivalence defined in the Kyoto Protocol prevails including in what concerns the Brazilian projects.

Increase of Methane Concentration in the Global Atmosphere

The knowledge of the methane content evolution in the atmosphere along time is indispensable for evaluating the contribution of human activities to its accumulation. The air captured in glaciers is an interesting source for this kind of study because there are dating processes that permit the evaluation of the age of samples colleted at different depths. Since the methane content tends to homogenize in the atmosphere, measurements of samples from a glacier are quite representative of the global content at the time when the air was captured by the ice. In recent years the measurements were directly made by collecting atmospheric air in regions free from significant local pollution.

The analysis of the present article focuses on the concentration values of methane in ice obtained by D.M. Etheridge et al.[i] that covers one thousand years. The samples were collected from glaciers in Greenland and Antarctic. The directly collected from the atmosphere were from the Grim Cape station (Tasmania). More recent ice samples from Antarctic were analyzed as well in order to test the methodology used for analyzing the possible role of methane diffusion in ice.

Results concerning methane content along the years are shown in Figure 1.

Figure 1: Methane content in the atmosphere obtained from measurements in glaciers in Antarctic and Greenland and in environmental samples collected in Tasmania.

It can be observed in Figure 1 that until 1800 methane contents remained practically constant and that concentration differences in the opposite poles were not significant.

The present analysis will be restricted to the period between 1900 and 2000, using data relative to the previous years to establish a base line for what happened in the described period. The average value obtained from data pertinent to the 1800 -1900 interval for the Antarctic data (793 ppb) was used as the base line for evaluating the subsequent period.

The adopted methodology, described in several articles by C. Marchetti and adopted by J. I. Vargas to analyze a series of natural and social phenomena, is appropriate for situations where growth of an element introduced in the system is initially accelerated and subsequently hindered or saturated by the presence of the element itself in the system under examination.

The evolution maybe described by a logistic curve obtained by the ratio between data pertinent to the initial and final states. Using the adequate algorithm (Fisher-Pry) it is possible to adjust the set of data to a straight line. For this purpose it is necessary to determine the saturation level (maximum value) that permits the best fitting, shown in Figure 2 for the set of data available for the period. This method of determining the saturation value is suitable when there is no evident physical limit for the “niche” to be occupied by the amount under study.

Figure 2:  Data fitting for methane content growth as a function of f (share of the growth “niche” already attained)

The adjustment indicates that in 1995 the methane content in the atmosphere would already have reached half of its expected growth, that is, the total growth would be 1800 ppb of methane that added to the initial value (800 ppb) would give a final concentration of 2600 ppb. Relative to year 2000 (1700 ppb of methane) the final addition would be about 50%.

The actual and adjusted content values in the atmosphere are presented in Figure 3. Furthermore it can be noted that in the last measured years it was detected a trend to apparent methane content saturation in the atmosphere. Subsequent measurements by the same laboratory (CSIRO, Australia) published by News Science concluded that methane content in the atmosphere has not grown.

It should be remembered that, in the already mentioned EPA report, the methane emission growth between 1990 and 2000 would have been only 1.1%. This reduction was mainly due to the economic crisis in some OECD countries (not USA). Reduction of the growth pace does not explain the observed reduction in the increase of methane content in the atmosphere that is supposed to be cumulative, with mean life in the atmosphere between 10 and 20 years.

Figure 3: Best fit of the methane concentration described by the logistic expression

In the Annex the fitting relative to data obtained for the interval 1940-2000 is examined leading to a saturation value smaller than the one previously obtained.


The growth of methane content in the atmosphere already indicates saturation levels as it is shown by the fitting of last century data. The equivalence adopted by the Kyoto Protocol may be inducing countries (including Brazil) to adopt measures for reducing methane emission whose efficacy concerning greenhouse effect attenuation is questionable. Incidentally, this has been the position of the Brazilian representatives in the Convention. Should it be confirmed that the methane content presently observed is not following the evaluations about its evolution then the subject should be revised.

Although the adoption of this equivalence can facilitate fulfillment of commitments by the countries that have taken them on, this practice can become unsustainable vis-à-vis scientific and technical evidence.

            Brazil also has projects for obtaining carbon credit based on methane reduction that have been approved. These projects could be impaired if the coefficient presently used for this gas is modified. However, overvaluation of methane emission reduction effects brings down the price of carbon credit by ton equivalent of CO2. So, projects in the biomass area are twice impaired: on one hand the eventual carbon credit by CO2 elimination can be reduced by the simultaneous methane emission, on the other hand the price paid by CO2 emission elimination is reduced. Besides the arguments enumerated above, overvaluation of methane emission may be giving undue relevance to phenomena like emissions from herds of cattle where the Brazilian participation is relevant.


Analysis of the 1940 -2000 period reveals that a change probably occurred in the behavior of methane accumulation in the atmosphere with saturation before that foreseen by the fitting for the XX century. Figure A1 shows the attained values and the previous adjustment.

Figure A1:  Actual values compared with fitting for the 1900 -2000 interval. It can be noticed oscillations around the adjusted values that might indicate a differentiated behavior for the period

A differential analysis of the content evolution curve shows a point of larger growth around 1975. The values of the differential curve are shown in Figure A2. One can identified a maximum value in the differential curve that corresponds to the inflexion point of the content curve around 1978. In the long- term adjustment, the maximum value of the annual content variation would correspond to the average point in the accumulation cycle under study. The value at this point would represent half of the total value of the transition between the initial and final plateaus of methane content in the atmosphere.

Figure A2: Values of methane content and average value of the annual variation that reaches a maximum point centered around 1975.

Adoption of an adjustment for the 1940-2000 period reduces the projected saturation value and anticipates the moment when the content would reach 90% of the saturation value. Results of the adjustment are shown in Figures A3 and A4

Figure A3: Adjustment of content growth for the 1940 – 2000 period relative to the average value of the previous one

Additional Methane Content in the Atmosphere

Figure A4: Adjustment for the 1940 -2004 period and projection for the additional methane content until 2005.

i Historic CH4 records from Antarctic and Greenland ice cores, Antarctic firn data, and archived air samples from Cape Grim, Tasmania D.M. Etheridge, L.P. Steele, R.J. Francey, and R.L. Langenfelds

Rapport from Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia

(firn: rounded, well-bonded snow that is older than one year)

ii Gobal Anthropogenic Non-CO2 Greenhouse Emissions:1990-2020. EPA December-2005 (Draft)

[i] Historic CH4 records from Antarctic and Greenland ice cores, Antarctic firn data, and archived air samples from Cape Grim, Tasmania D.M. Etheridge, L.P. Steele, R.J. Francey, and R.L. Langenfelds

Rapport from Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia

(firn: rounded, well-bonded snow that is older than one year)


Graphic Edition/Edição Gráfica:
Editoração Eletrônic

Monday, 09 May 2011

Contador de visitas