Ocean Climate Variability and Change around the Cook Is. D. E. Harrison NOAA/PMEL & Univ. of Washington Mark Carson University of Hamburg International Workshop on Climate and Ocean Fisheries Rarotonga, Cook Islands Oct. 2011
Overview Historical data challenges limit confidence, especially for regional results even for temperature and sea level. The smaller the scale, the more variability is observed. Within limits of the data, multi decadal variability in trends can be larger than long term trend If behavior of recent decades continues, next few decades will be affected more by variability than by long term trend.
Summary There is near surface warming and rising sea level in much of the Cook Island region over recent decades. Can t say about salinity. Difficult to say with confidence what the rates are, because there is so much variability and regional differences. Rough estimates of trend: ~+0.0 0.2C/decade near surface ~+2 3mm/yr sea level at Rarotonga Variability amplitude likely to dominate temperature trend for next few decades and also to confound determination of increase in sea level rise. Seasonal cycle is larger than temperature variability near surface
Outline Quick overview of historical data issues for upper ocean temperature and sea level Brief progress report on global ocean observing system implementation Some global ocean heat content and sea level results and issues Some results for the Cook Islands region. Detailed regional results will be in workshop paper
Tide Gauge Distribution over Time, Church and White, 2010 1880 1889 1910 1919 1930 1939 1960 1969 1990 1999
100m 200m 100m World Ocean Atlas 2001: Number of observations for 2 x2 regions 400m 500m 300m 150 100 50 1850-2000500m 600m 1000m 2000m 1000m 2000m
% 5x5 regions meeting climate SST bias data requirement
Argo Density 3 profiles/month per 3x3 region
Global Ocean Observing System Building on WOCE, TOGA, JGOFS, etc., technology improvement and need for global climate information led to OceanObs99 meeting, development and agreement of Global Climate Observing System IP, endorsement by UNFCCC, WCRP, GOOS and GEO, and efforts to implement 1999 present. Implementation progress has stalled in recent years. OceanObs09 reaffirmed need for climate obs, and called for expansion of global efforts for ecosystems, marine biogeochemistry and marine life. Plans are proposed to be developed under new Framework for Ocean Observing (Post OO09 WG)
Important Progress in the Global Ocean Observing System for Climate We are sampling, for the first time and fairly satisfactorily, the ice free ocean surface for SST, and upper ocean for T and S. More tide gauges are now reporting in real time than ever before, and historical data sharing is improving. This is a major accomplishment and credit is due to many nations, groups and individuals. But sustainability is a big challenge, as is expansion in variables observed.
Argo Profiling Float Array, August 2011
All DBCP buoys, drifters and moorings, reporting Aug. 2010
Importance of Local Information Despite progress in observing the global ocean, many critical societal needs require local/regional information on high resolution. Local relative sea level is one example. Many places are experiencing water level change different from the global sea level rise estimate. Local variability and trends have to be observed locally. Ability to project regional conditions remains to be demonstrated.
Reconstructed Global Sea Level, Church and White (2011) 100yr trend: ~1.8mm/yr ~18cm/century
Aviso Satellite Era Mean Sea Level Smoothed Cooling/warming and changes in E P implicated in variability but is not agreed No sign of acceleration in rate of sea level rise over 20years, but satellite trend exceeds 100yr tide gauge trend.
Spatial variability of 20 year sea level trend How much results from large scale oceanic variability?
Sea Level, Marshall Is. m. m. N.Trop.Pac Altimeter era larger trends are similar in amplitude to those over some earlier periods But lots of interannual and decadal variability
Cook Island Region Satellite Era Sea Level from U. Colo Interactive Gridded Field tool NOTE: Scale is CM, not MM. (160w, 0) (160w,10s) (160w, 20s)
Annual Mean Sea Surface Height Trend ~100mm/40yr =~2.5mm/yr, but lots of variability
ENSO Decadal Variability and Trends Is there a long term trend in ENSO, and can multi decadal segments be used to reveal it? There has been much interest lately in determining which aspects of climate are undergoing long term trends, but finding the appropriate historical records for such studies can be challenging. A good proxy for ENSO state is the Darwin SLP record. There is no statistically significant trend over the full 130year record. Yet many multi decadal periods would, if treated as distinct records, present trends. It is unlikely that any 30yr subset of the record will give the correct long term trend. Harrison and Chiodi 2011, GCOS SC
Now to Oceanic Temperature Temperature Trends are harder to identify than sea level trends. Extreme spatial and temporal sampling issues Changes in observing technology Most of Southern Hemisphere inadequately sampled.
0 700m Ocean Heat Content estimates, multiple studies
Satellite Era 0 700m Ocean Heat Content Anomaly Lyman et al 2010
50 yr Temperature Trends, 90% signif 100m Harrison & Carson (2008) Carson & Harrison (2008, 2010) 300m
Some individual time series 41N, 175E 100 m 2 2 x 10 25N, 67W 300 m 3 3 x 3 3
Basin-Average Temperature (1950-2000): 50m 100m 20N 80N 20S 20N 80S 20S
20 year trends at 100m 96% of all boxes change sign at least once over the 45-year period
Upper Ocean Temperature Trends Cook Island Region Ishii et al analysis
Upper Ocean Temperature Trends Cook Island Region World Ocean Atlas 2009 analysis
Summary There is near surface warming and rising sea level in much of the Cook Island region over recent decades. Can t say about salinity. Difficult to say with confidence what the rates are, because there is so much variability and regional differences. Rough estimates of trend: ~+0.0 0.2C/decade near surface ~+2 3mm/yr sea level at Rarotonga Variability amplitude seems likely to dominate temperature trend for next few decades and to confound determination of increase in sea level rise. Seasonal cycle is larger than temperature variability near surface
Ocean Observing System STATUS At least some progress on every Action in GCOS IP, including a few completions (Argo, Sfce Drifters) Important new developments in observing technologies and feasible ECVs, although standards and metadata development issues remain Important progress in ocean reanalysis and near real time ocean analysis systems; need evaluation process & future strategy & coupling Data system needs are still many, including exchange and versioned data sets Limited progress in establishment of national institutional arrangements to sustain activities. Much work needed on coastal (incl arctic) systems and connections
Thank You