1. A Decline in the Northern Hemisphere CO 2 Sink from 1992 - 2003 John Miller 1, Pieter Tans 1, Jim White 2, Ken Masarie 1, Tom Conway 1, Bruce Vaughn 2, Jim Randerson 3, Neil Suits 4 1.NOAA/CMDL, Boulder 2.INSTAAR, University of Colorado, Boulder 3.U. of California, Irvine 4.Colorado State University, Fort Collins

2. Outline 1. Trends in NH CO 2 data indicate a change in the sink. 2. Two reasons why change originates in the terrestrial biosphere. 3. What might be causing the change?

3. Conceptual Model FF RectifierSink CO 2 = CO 2 Site – CO 2 SPO = Fossil Fuel + Sink (+ rectifier)

4. Meridional CO 2 Gradient 1998 1992 2003 Gradient increasing; big jump from 1998-2003 MBL Continental Hi-Altitude Fits to MBL

5. Sites used in study

6. Determining trends at a site SPO ICE CO2 (ppm)

7. Distribution of Trends: 1992-2003 Expected trend from FF 14/16 sites increase faster than expected: p < 0.01 Excluding 1992 and/or 2003  p < 0.05

8. Distribution of Trends: 1997-2003 Expected trend from FF Continental – Marine trend differences indicate a terrestrial origin.

9. Could continental trend signal be Fossil? 1.7 ppb/yr MBL Site Given a CO/CO2 emissions ratio of 10 ppb/ppm  max. fossil fuel contribution of 0.2 ppm/yr.

10. What about changes in N/S transport ? North/South SF 6 differences from 1997-2003 indicate a trend in inter-hemispheric exchange. North/South SF 6 differences from 1997-2003 indicate a trend in inter-hemispheric exchange. Decreasing IHE implies less fossil emissions stored in the NH. Decreasing IHE implies less fossil emissions stored in the NH. Thus, even larger sink changes are required to explain the observed gradient, 1997-2003. Thus, even larger sink changes are required to explain the observed gradient, 1997-2003.

11. Use 2D model to quantify sink changes. 1.A 2D model of atmospheric transport to quantify the flux changes, and 2.Measurements of 13 C/ 12 C in CO 2 ( 13 C) to help determine the origin.  13 C is a tracer for terrestrial fluxes. CO 2  13 C

12. Ocean Land Total 18 – 53 N Mid-latitude non-fossil Carbon Fluxes =1.5 Pg (10 15 g) C Changes in the terrestrial biosphere appear to drive the trend. Biosphere trend is relatively insensitive to C3/C4 and other parameters. p<0.01 p<0.06

13. Correlation of Flux and Climate Anomalies Zonally Averaged Climate r =-0.7 r = 0.3

14. Correlation of Flux and Climate Anomalies Eurasian Average Climate r =-0.4

15. Correlation of Flux and Climate Anomalies North American Average Climate r =-0.7

16. Conclusions 1. NH carbon sink shrunk from 1992 – 2003 by ~1.5 billion tons of C; probably driven by land. 2. Regardless of whether this persists, it demonstrates that surface uptake can change rapidly. 3. Analysis of climate anomalies hints at drought as a driver of variability in temperate NH.