Guest post by Bob Tisdale:
NOTE: This post contains 5 .gif animations that total 10MB. (below the continue reading line) Have patience. They may take a while to load.
This post is a follow-up to the recent post October to December 2010 NODC Ocean Heat Content (0-700Meters) Update and Comments. I wanted to discuss the ARGO-based period separately.
For those new to ARGO, under the heading of “What is Argo?”, the University of California, San Diego Argo webpage describes Argo as a “global array of 3,000 free-drifting profiling floats that measures the temperature and salinity of the upper 2000 m of the ocean.” The UCSD Argo website provides much more information, including an argo.avi video.
Much of the data in this post is supplied by ARGO for the upper 700 meters.
THE ARGO ERA (2003 TO PRESENT)
The NOAA NCEP webapge that presents the Global Ocean Data Assimilation System (GODAS) Input data distributions (1979-present) (Plots) allows users to plot the number of Temperature profiles at different depths for the globe, or for the Atlantic, Indian, and Pacific Oceans. An example of Global data for depths of 250 to 500 meters is shown in Figure 1. According to it, ARGO floats have been in use since the early 1990s, but they had very limited use until the late 1990s. ARGO use began to rise then, and in 2003, ARGO-based temperature readings at depth became dominant. Based on that, I’ll use January 2003 as the start month for the “ARGO-era” in this post.
Note the significant drop in samples in 2010. I have not found an explanation for this.
The NCEP GODAS Input data (Plots) webpage also allows visitors to create maps of temperature profile locations. Animation 1 is a gif animation that shows the annual data locations from 1979 to 2004. The measurements made with Expendable Bathythermographs (XBTs) are shown in red (x), the moored buoys that are parts of the TAO/ TRITON (Pacific) and PIRATA (Atlantic) projects are shown in green (+), and the blue (o) are ARGO-based measurements. Note how sparse the data is in the Southern Hemisphere prior to the early 2000s, especially south of 30S.
Unfortunately, GODAS switched map formats in 2005 and again in 2006, so an animation that included the three map formats would be difficult to watch. The format used in 2005 is unlike those in use before or after, so I’ve excluded it in both animations. Animation 2 shows the Monthly temperature profile locations from January 2006 to December 2010. Note the decline in sampling in 2009/10, especially in the Indian Ocean. Why? Dunno.
ARGO-ERA TREND VERSUS GISS PROJECTION
In past posts, when I’ve compared the NODC Global Ocean Heat Content to GISS projections, I’ve used the rate of 0.98*10^22 Joules per year for the GISS projection. This value was based on Roger Pielke Sr’s February 2009 post Update On A Comparison Of Upper Ocean Heat Content Changes With The GISS Model Predictions. The recent RealClimate posts Updates to model-data comparisons and 2010 updates to model-data comparisons have presented the projections based on Gavin Schmidt extending a linear trend of the GISS Model-ER simulations past 2003. The linear trends in both graphs are approximately 0.7*10^22 Joules per year. I’ll use this value in the comparison, but first a few more notes.
Gavin writes in the 2009 post, “Unfortunately, I don’t have the post-2003 model output handy, but the comparison between the 3-monthly data (to the end of Sep) and annual data versus the model output is still useful,” and he continues, “I have linearly extended the ensemble mean model values for the post 2003 period (using a regression from 1993-2002) to get a rough sense of where those runs could have gone.”
The only paper that I’m aware of in which GISS presented their simulations of Ocean Heat Content was Hansen et al (2005) “Earth’s energy imbalance: Confirmation and implications”. Science, 308, 1431-1435, doi:10.1126/science.1110252 (PDF). In it, they only presented their data from 1993 to 2003. Refer to their Figure 2 (not illustrated in this post).
For those who might be concerned that extending the linear trend does not represent the actual model simulations, refer to Page 8 of the .pdf file GISS ModelE: MAP Objectives and Results. The graph there presents two GISS OHC Model E simulations, one with the Russell Ocean model, the other with the HYCOM Ocean model. The simulations run to 2010 for both models. Do they extend further into the future? And for those who want to attempt to duplicate that comparison of the Model-ER and Model-EH versus the early NODC OHC data, the NODC OHC data (older version) was based on the 2005 Levitus paper “The Warming Of The World Ocean: 1955 to 2003” (Manuscript). Link for the 0 – 700 meters data.
Back to the comparison of the ARGO-era OHC data and the GISS Projection: The most recent version of the NODC OHC data is linked here for 0 – 700 meters. I’ve compared it for the period of 2003-2010 to the GISS projection in Figure 2. Note that I’ve shifted the data down so that it starts at zero in 2003. The GISS projection of 0.7*10^22 Joules per year dwarfs the linear trend of the ARGO-era NODC OHC data. No surprise there.
NOTE ABOUT THE DATA
The remainder of the data in this post was downloaded from the KNMI Climate Explorer Monthly observations webpage. The NODC OHC data there is presented in Gigajoules per square meter (GJ/m^2), not the units (10^22 Joules) provided by NODC. That’s why the scale and trends in Figures 2 and 3 are different. The NODC also provides their OHC data on a quarterly basis, but KNMI presents it as monthly data, thus allowing for comparisons to other monthly datasets. This is why the OHC data appears in 3-month tiers in Figures 3, 4 and 5.
GLOBAL AND OCEAN BASIN TRENDS
Figure 3 shows the Global NODC OHC data for the period of January 2003 to December 2010. Comparing its linear trend (0.19 GJ/m^2 per Century) to the trend of the long-term data from 1955 to 2002 shown in Figure 4 (0.52 GJ/m^2 per Century), there has been a significant flattening of the Global OHC data in recent years. And this flattening was not anticipated by the GISS models, which show a continuous rise through 2010.
Of course, the oceans are not warming uniformly. Refer to Figure 5. The trends for the North Pacific and the Southern Oceans are basically flat. The only two ocean basins with major increases in OHC during the ARGO era are the South Atlantic and the Indian Oceans, while the North Atlantic, Arctic, and South Pacific Oceans show significant declines in OHC.
Note: The coordinates for the ocean basins are:
North Atlantic = 0-75N, 78W-10E
South Atlantic = 60S-0, 70W-20E
Indian = 60S-30N, 20E-120E
North Pacific = 0-65N, 120E-90W
South Pacific = 60S-0, 120E-70W
Arctic = 65N-90N
Southern = 90S-60S
ARGO-ERA CHANGES IN NODC OHC
Figure 6 is a map that displays the change in ARGO-era OHC, from 2003 to 2010. It was created by using 2003 as the base year for anomalies, and plotting the annual OHC values for 2010. Much of the cooling in the North Atlantic has taken place at mid and lower latitudes. In the South Pacific, there was also a decline in the lower latitudes, but there appears to also have been a drop there at higher latitudes along the Antarctic Circumpolar Current (ACC).
Animations 3, 4 and 5 present the ARGO-era OHC data, using 12-month averages. The first cells are the average OHC from January to December 2003. These are followed by cells that show the period of February 2003 to January 2004 and so on, until the final cell that captures the average OHC from January to December 2010. The 12-month average reduces the noise and any seasonal component in the data. I’ve also included a graph of NINO3.4 SST anomalies (smoothed with a 12-month filter, and centered on the 6th month) since the effects of ENSO dominate the OHC data. The NINO3.4 SST anomaly graph infills with time. Animation 3 presents global maps.
Animation 4 is the North Pole stereographic view. Note the warming of the western tropical North Pacific during the 2007/08 La Niña. It’s tough to miss. There also appears to be a lagged decline in the North Atlantic OHC in response to the 2007/08 La Niña. Will we see a lagged increase there next year?
And Animation 5 is the South Pole stereographic view. Note the persistence of the warm and cool anomalies moving southward from the equatorial Pacific in waves, and also into the South Indian Ocean. I believe those would be classified as oceanic Rossby waves.
Watching the animations, it is very obvious that ENSO and the distribution of warm and cool waters caused by ENSO are major components of Global Ocean Heat Content. Refer to ENSO Dominates NODC Ocean Heat Content (0-700 Meters) Data for further discussion and illustrations. OHC studies such as Hansen et al (2005), however, do not include ENSO in their models. They assume that Anthropogenic Greenhouse Gases have a measurable impact on Ocean Heat Content. The impacts of the failure of GISS to include ENSO and other natural variables in their analysis was illustrated and discussed in detail in Why Are OHC Observations (0-700m) Diverging From GISS Projections?