Characteristics and significance of greenhouse gas observation by GOSAT

 

CO2 changes at surface-level monitoring sites and the global CO2 mean based on those observations have long been reported by the World Meteorological Organization and several other meteorological agencies around the world. To further facilitate an understanding of overall trends for CO2 in the atmosphere, knowledge of “whole-atmosphere” CO2 mean is necessary, and for this, more CO2 information in the vertical direction is needed. In fact, from past measurements taken by aircraft, CO2 levels are known to vary with altitude. Model predictions of whole-atmosphere CO2 mean have appeared in the fifth assessment report by the Intergovernmental Panel on Climate Change, as they are important for predicting the risk of global warming due to rising greenhouse gas levels. This is where CO2 observation by GOSAT comes in useful, as the satellite measurement encompasses levels from the surface to the top of the atmosphere and provides CO2 concentration averaged over an entire atmospheric column (this is referred to as column-averaged CO2 concentration).

 

 

Whole-atmosphere monthly mean CO2 concentration based on GOSAT data

 

The whole-atmosphere mean CO2 concentration was calculated based on GOSAT measurement. Observational data collected by the satellite since April 2009 were used for this calculation. Over the analyzed period, the monthly mean CO2 concentration continually rose, with seasonal fluctuations due to photosynthetic activity by plants that intensifies and subsides over a single year in the Northern Hemisphere. The trend line of the global CO2 mean, obtained by subtracting averaged seasonal fluctuations from the monthly CO2 time series, increases monotonously 3). We note here that areas that GOSAT measurement can cover are limited to parts of the globe without cloud cover and where the local solar altitude is above a specific threshold. Therefore, the global distribution of column-averaged CO2 concentration, needed for the calculation of the whole-atmosphere mean CO2 concentration, was estimated from GOSAT data 4). Shown in the figure above are the time series of the monthly mean CO2 concentration and the trend line calculated from the monthly time series 5). The values shown here are found to be smaller by 1-2 ppm than those based on CO2 measurements at the surface level 6).

 

 

Notes:

(3) GOSAT FTS SWIR Level 2 CO2 Column Amount products (Version 02.90/02.91) are used in the calculation of whole-atmosphere monthly mean CO2 concentration.

 

(4) More details on the estimation approach used here are described at the following link:

     http://www.gosat.nies.go.jp/newpdf/Appendix_Press_20160929.pdf

 

(5) Result for January 2015 is missing due to lacking data for instrument adjustment.

 

(6) US National Oceanic and Atmospheric Administration reported that global mean CO2 concentration based on surface level measurements reached

     400 ppm in March 2015.

     Source: http://research.noaa.gov/News/NewsArchive/LatestNews/TabId/684/ArtMID/1768/ArticleID/11153/Greenhouse-gas-benchmark- reached-.aspx

 

 

 

[Contact Information]

NIES Satellite Observation Center, GOSAT Project

Phone: +81-29-850-2966