Advanced

Relating interannual variability of atmospheric CH<sub>4</sub> growth rate to large-scale CH<sub>4</sub> emissions from northern wetlands

Rychlik, Sophie (2009) In Lunds universitets Naturgeografiska institution - Seminarieuppsatser
Dept of Physical Geography and Ecosystem Science
Abstract (Swedish)
Metan (CH<sub>4</sub>) är en av de viktigaste växthusgaserna i atmosfären och dess kraftiga ökning har
bidragit till den uppvärmning som vi har upplevt fram till idag. Sedan mitten av 1980-talet påvisar
mätningar att metantillväxten i atmosfären har börjat fluktuera från år till år. Orsakerna till detta är
omstridda och ännu inte klargjorda. Under 2007 uppmättes en kraftig ökning i tillväxt som var
särskilt markant på högt nordliga breddgrader.
Bortsett från antropogena utsläpp, är naturliga våtmarker på global skala den enskilt
största emissionskällan av metan. Upprepade mätningar på ett flertal nordliga våtmarker visar att
marktemperatur är en viktig kontrollerande faktor för metanproduktion och utsläpp. Höga
temperaturanomalier... (More)
Metan (CH<sub>4</sub>) är en av de viktigaste växthusgaserna i atmosfären och dess kraftiga ökning har
bidragit till den uppvärmning som vi har upplevt fram till idag. Sedan mitten av 1980-talet påvisar
mätningar att metantillväxten i atmosfären har börjat fluktuera från år till år. Orsakerna till detta är
omstridda och ännu inte klargjorda. Under 2007 uppmättes en kraftig ökning i tillväxt som var
särskilt markant på högt nordliga breddgrader.
Bortsett från antropogena utsläpp, är naturliga våtmarker på global skala den enskilt
största emissionskällan av metan. Upprepade mätningar på ett flertal nordliga våtmarker visar att
marktemperatur är en viktig kontrollerande faktor för metanproduktion och utsläpp. Höga
temperaturanomalier tros därför kunna orsaka en ökning av metanutsläpp från våtmarker.
Denna studie undersöker om det finns ett samband mellan variationer i årlig tillväxt av
metan i atmosfären och storskaliga metanutsläpp från nordliga våtmarker. Data över utbredningen
av våtmarker används för att estimera utsläpp som funktion av marktemperaturanomali. Särskild
fokus läggs på tillväxttoppen som uppmärksammades 2007, men även mellanårsvariationen av
temperaturanomali och de uppskattade metanutsläppen analyseras för tidsperioden 1992-2008.
Resultaten visar på att ett samband existerar. Då en tidsserie av uppskattade
metanutsläpp från juli månad analyseras separat blir korrelationen till mellanårsvariationen av
tillväxt tydligare, och 2007 utmärker sig med en markant emissionstopp. Detta tyder på att förhöjda
marktemperaturer under växtsäsongens mitt har särskilt stor betydelse, och att de eventuellt också
kan ha inverkan på utsläpp som sker senare på hösten. Avvikelser mellan tidsserierna av
atmosfärstillväxt och de beräknade metanemissionerna tyder också på att det, under vissa år, finns
andra miljöfaktorer och emissionskällor (t.ex. skogsbränder) som begränsar betydelsen av nordliga
våtmarker.
Generellt uppnår inte de uppskattade emissionsvärdena de mängder CH4 som krävs
(uppskattas) för att förklara individuella avvikelser i årlig metantillväxt i atmosfären. Men eftersom
det finns flera osäkerheter i uppskattningsmetoden, anses det funna sambandet mellan relativ
mellanårsvariation ändå tala för att nordliga våtmarker har en nyckelroll i förklaringen till de årliga
fluktuationerna av metantillväxt i atmosfären på högt nordliga breddgrader, och kanske även
globalt. (Less)
Abstract
The increasing atmospheric concentration of the greenhouse gas methane (CH<sub>4</sub>) is highly relevant
for current and future global warming. Since the mid-1980s atmospheric measurements have
revealed large interannual fluctuations in methane growth rate. However, the causes of this feature
are still not well understood. In 2007, a peak in growth rate appears to have been particularly
strong at high northern latitudes.
Apart from anthropogenic emissions, natural wetlands are globally the single largest
source of atmospheric CH<sub>4</sub>. Studies at multiple northern wetland sites have shown that soil
temperature is a dominant controlling factor of wetland emissions. It has been suggested that strong
anomalous warming could... (More)
The increasing atmospheric concentration of the greenhouse gas methane (CH<sub>4</sub>) is highly relevant
for current and future global warming. Since the mid-1980s atmospheric measurements have
revealed large interannual fluctuations in methane growth rate. However, the causes of this feature
are still not well understood. In 2007, a peak in growth rate appears to have been particularly
strong at high northern latitudes.
Apart from anthropogenic emissions, natural wetlands are globally the single largest
source of atmospheric CH<sub>4</sub>. Studies at multiple northern wetland sites have shown that soil
temperature is a dominant controlling factor of wetland emissions. It has been suggested that strong
anomalous warming could cause an increase in wetland CH<sub>4</sub> emissions, and that northern wetlands
may be a major contributor to the observed atmospheric growth rate variability.
This study is concerned with investigating a potential relation between interannual
variations in atmospheric CH<sub>4</sub> growth rate and that of accumulated large-scale emission anomalies
from northern wetlands. With wetland distribution data for the circumpolar north between 53°N-
90°N, emissions are estimated as a function of soil temperature anomaly. Special attention is given
to the 2007 growth rate event, but the interannual variation of anomalous warming and estimated
emissions are also considered for the time period 1992-2008.
It is found that a relation does exist. When a time series of estimated July (peak
season) CH<sub>4</sub> emissions is considered separately the correlation with interannual growth rate
variability becomes more apparent, and 2007 stands out with a pronounced emission peak. The
results suggest that the impact of anomalous soil temperatures on peak season emissions is
particularly important, and that it may further have an influence on late season emissions.
Discrepancies between the atmospheric and emission time series also suggest that, in some years,
the impact of other environmental factors and emission sources (e.g. forest fires) may limit the
relevance of northern wetlands.
In general, the estimated CH<sub>4</sub> emission values do not fully correspond to the CH<sub>4</sub>
amount required (estimated) to explain the growth rate anomalies. However, due to uncertainties in
the emission estimation method, we have more confidence in the significance of the found relation
between relative interannual variations from 1992 to 2008. It is concluded that this study strongly
points at northern wetlands being a key emission source in terms of atmospheric CH<sub>4</sub> growth rate
variability in high northern latitudes, and perhaps also globally. (Less)
Please use this url to cite or link to this publication:
author
Rychlik, Sophie
supervisor
organization
year
type
H2 - Master's Degree (Two Years)
subject
keywords
temperature sensitivity, interannual variability, emission sources, CH4, northern wetlands, physical geography, July, atmospheric growth rate
publication/series
Lunds universitets Naturgeografiska institution - Seminarieuppsatser
report number
172
language
English
id
1857868
date added to LUP
2011-03-31 08:58:31
date last changed
2011-12-20 10:25:55
@misc{1857868,
  abstract     = {The increasing atmospheric concentration of the greenhouse gas methane (CH<sub>4</sub>) is highly relevant
for current and future global warming. Since the mid-1980s atmospheric measurements have
revealed large interannual fluctuations in methane growth rate. However, the causes of this feature
are still not well understood. In 2007, a peak in growth rate appears to have been particularly
strong at high northern latitudes.
Apart from anthropogenic emissions, natural wetlands are globally the single largest
source of atmospheric CH<sub>4</sub>. Studies at multiple northern wetland sites have shown that soil
temperature is a dominant controlling factor of wetland emissions. It has been suggested that strong
anomalous warming could cause an increase in wetland CH<sub>4</sub> emissions, and that northern wetlands
may be a major contributor to the observed atmospheric growth rate variability.
This study is concerned with investigating a potential relation between interannual
variations in atmospheric CH<sub>4</sub> growth rate and that of accumulated large-scale emission anomalies
from northern wetlands. With wetland distribution data for the circumpolar north between 53°N-
90°N, emissions are estimated as a function of soil temperature anomaly. Special attention is given
to the 2007 growth rate event, but the interannual variation of anomalous warming and estimated
emissions are also considered for the time period 1992-2008.
It is found that a relation does exist. When a time series of estimated July (peak
season) CH<sub>4</sub> emissions is considered separately the correlation with interannual growth rate
variability becomes more apparent, and 2007 stands out with a pronounced emission peak. The
results suggest that the impact of anomalous soil temperatures on peak season emissions is
particularly important, and that it may further have an influence on late season emissions.
Discrepancies between the atmospheric and emission time series also suggest that, in some years,
the impact of other environmental factors and emission sources (e.g. forest fires) may limit the
relevance of northern wetlands.
In general, the estimated CH<sub>4</sub> emission values do not fully correspond to the CH<sub>4</sub>
amount required (estimated) to explain the growth rate anomalies. However, due to uncertainties in
the emission estimation method, we have more confidence in the significance of the found relation
between relative interannual variations from 1992 to 2008. It is concluded that this study strongly
points at northern wetlands being a key emission source in terms of atmospheric CH<sub>4</sub> growth rate
variability in high northern latitudes, and perhaps also globally.},
  author       = {Rychlik, Sophie},
  keyword      = {temperature
sensitivity,interannual variability,emission sources,CH4,northern wetlands,physical geography,July,atmospheric growth rate},
  language     = {eng},
  note         = {Student Paper},
  series       = {Lunds universitets Naturgeografiska institution - Seminarieuppsatser},
  title        = {Relating interannual variability of atmospheric CH<sub>4</sub> growth rate to large-scale CH<sub>4</sub> emissions from northern wetlands},
  year         = {2009},
}