Trends in annual and seasonal high northern latitude CO₂ fluxes from 1986 to 2007 inferred from a time dependent inversion compared with satellite NDVI observations to identify likely regions of change

Lisa Welp, UCSD Scripps Institution of Oceanography, lwelp@ucsd.edu (Presenter)
Prabir Patra, JAMSTEC, prabir@jamstec.go.jp
Ralph Keeling, UCSD Scripps Institution of Oceanography, rkeeling@ucsd.edu
Ramakrishna R. Nemani, NASA ARC, rama.nemani@nasa.gov
Stephen Charles Piper, UCSD Scripps Institution of Oceanography, scpiper@ucsd.edu

We examine long-term trends in CO₂ fluxes in the high northern latitude regions inverted from atmospheric CO₂ concentrations using interannually varying reanalysis transport and seasonally variable fossil fuel emissions from 1986 to 2007. We then compare annual and seasonal trends in CO₂ fluxes with observations of 1x1 degree resolution NDVI from the AVHRR/MODIS satellite records over the same time period to identify where there is co-variance between CO₂ source/sink behavior and photosynthetic activity. The land zone north of 60°N, encompassing the tundra biome and excluding Europe (10°W – 63°E), had no significant long-term trend in annual CO₂ uptake. The CO₂ flux seasonal amplitude increased due to enhanced summer uptake as well as fall release, which largely canceled in the annual sum. Comparing July CO₂ uptake north of 60°N with NDVI showed the strongest temporal correlation in the tundra. According to the inversion analysis, July CO₂ uptake increased by 0.29 g C m^-2 day^-1 from 1986 to 2007. If this uptake was limited to the tundra biome only, as suggested by the NDVI trends, that would require an increased sequestration of 1.2 g C m^-2 day^-1 during the peak growing season and would imply major changes in tundra productivity over the past two decades. The land zone from approximately 50°N to 60°N, roughly corresponding to the boreal forest biome and again excluding Europe, showed a trend towards increasing annual CO₂ uptake of an extra 13 Tg C yr^-1 from 1986 to 2007. This is in spite of browning trends and increased forest fire emissions in this region. The seasonal amplitude of the flux also increased because of enhanced summer uptake. Overall, the inversion fluxes showed no indication of a large-scale positive climate-carbon feedback caused by warming temperature in high northern latitude terrestrial CO₂ fluxes as of 2007.

Presentation: 2011_Oct03_PM_Welp_338.pdf (1741k)

Presentation Type:  Plenary Talk

Session:  Poster Speed Talks:

Presentation Time:  Mon 3:35 PM  (5 minutes)