Kevin E Trenberth NCAR Kevin E Trenberth NCAR Global Warming is unequivocal  The recent IPCC report has clearly stated that “Warming of the climate system is unequivocal” and it is “very likely” caused by human activities.  Moreover, most of the observed changes are now simulated by models over the past 50 years adding confidence to future projections.  The recent IPCC report has clearly stated that “Warming of the climate system is unequivocal” and it is “very likely” caused by human activities.  Moreover, most of the observed changes are now simulated by models over the past 50 years adding confidence to future projections.

IPCC recommendations Workshop, Sydney, 4-6 October 2007 Future Climate Change Research and Observations: GCOS, WCRP and IGBP Learning from the IPCC AR4 Trenberth, K. E., 2008: Observational needs for climate prediction and adaptation. WMO Bulletin, 57 (1) GCOS-117; WCRP-127; IGBP Report No. 58 (WMO/TD No. 1418) Jan 2008

IPCC: Causes of decadal variability not well understood - cooling due to volcanism? - artefact due to temporally changing observing system? Annual ocean heat content 0-700m relative to average Ishii et al 2006 Willis et al 2004 Levitus WOA Is ocean warming accelerating? No statement on acceleration possible

Ocean warming is strongest near the surface but also penetrates to layers below, in particular in Atlantic Ocean warming > 0.025°C per decade cooling < °C per decade Zonally averaged temperature trend 1955–2003 Few regions are cooling: related to climate variability Pacific subtropical ocean circulation El Niño Changes in NAO, PDO

Most but not all parts of the Ocean are warming Ocean heat content trend corresponds to warming > 0.25 W/m 2 corresponds to cooling < W/m 2

Ocean salinities are changing, indicating changes in evaporation and precipitation Zonally averaged salinity trend 1955–1998 Tropics in upper oceans are becoming saltier, in particular in Atlantic/Indian Mid-to-high latitudes are becoming fresher, in particular in N-Pacific/N-Atlantic Consistent with increase in atmospheric water transport saltier > 0.005psu per decade fresher < psu per decade

Ocean heat content and sea level Global warming from increasing greenhouse gases creates an imbalance in radiation at the Top-Of- Atmosphere: now order 0.9 W m -2. Where does this heat go? Main sink is ocean: thermosteric sea level rise associated with increasing ocean heat content. Some melts sea ice: no change in SL Some melts land ice. SL increases much more per unit of energy from land-ice melt: ratio about 30 or 40 to 1. Sea-ice melt does not change sea level.

Land ice and Arctic sea ice are decreasing Arctic sea ice area decreased by 2.7% per decade (Summer: -7.4%/decade) 2007: 22% (10 6 km 2 ) lower than 2005 Greenland and Antarctica ice sheets and glaciers are shrinking: Accelerated rate especially from 2002 to 2006? Greenland and Antarctica ice sheets and glaciers are shrinking: Accelerated rate especially from 2002 to 2006?

Melting ice IPCC estimated melting ice contribution to SL rise was 1.2 mm/yr for 1992 to  How much is missed?  Is the Antarctic and Greenland melt a transient (mainly 2002 to 2006) or not?  Many glaciers not monitored  Ocean warming may change basal melting: poorly known  Ice sheets, buttressing by ice shelves poorly modeled  Concern future SL rise underestimated  Need process studies and improved models  Changes salinity: fresh water budget  affects ocean currents (MOC) IPCC estimated melting ice contribution to SL rise was 1.2 mm/yr for 1992 to  How much is missed?  Is the Antarctic and Greenland melt a transient (mainly 2002 to 2006) or not?  Many glaciers not monitored  Ocean warming may change basal melting: poorly known  Ice sheets, buttressing by ice shelves poorly modeled  Concern future SL rise underestimated  Need process studies and improved models  Changes salinity: fresh water budget  affects ocean currents (MOC)

Salinity Issues: Spatial and temporal observations of ocean salinity are currently not sufficient, for example in the Southern Ocean. Some issues in the current measurements include instrumental biases, a lack of deep-water salinity data (particularly at high latitudes), insufficient global data analyses and incomplete coverage of surface ocean salinities. Recommended Activities (potential lead agents: GOOS, GCOS): Maintain strong quality control of Argo salinity profiles and surface salinity data from the Ships of Opportunity Programme; Develop strategies for obtaining salinity data for the whole water column; Promote reanalyses of the temporal changes in salinity. Issues: Spatial and temporal observations of ocean salinity are currently not sufficient, for example in the Southern Ocean. Some issues in the current measurements include instrumental biases, a lack of deep-water salinity data (particularly at high latitudes), insufficient global data analyses and incomplete coverage of surface ocean salinities. Recommended Activities (potential lead agents: GOOS, GCOS): Maintain strong quality control of Argo salinity profiles and surface salinity data from the Ships of Opportunity Programme; Develop strategies for obtaining salinity data for the whole water column; Promote reanalyses of the temporal changes in salinity.

The overturning transport 26.5N above 1000 m (green line), and the five snapshot estimates from hydrographic sections by Bryden et al., (2005). All time series have been smoothed with a three-day low pass filter. As modified from Baringer and Meinen (2008). Sampling Issues

Atlantic MOC Establish and maintain long-term baseline reference networks for ocean quantities, particularly in the North Atlantic; Place a major effort on ocean data assimilation and now-casting; Improve resolution of ocean model components in global comprehensive models; Investigate ocean mixing processes and their parameterisation in coupled climate models; Explore parameter space of global models and search for possible thresholds. Establish and maintain long-term baseline reference networks for ocean quantities, particularly in the North Atlantic; Place a major effort on ocean data assimilation and now-casting; Improve resolution of ocean model components in global comprehensive models; Investigate ocean mixing processes and their parameterisation in coupled climate models; Explore parameter space of global models and search for possible thresholds.

To 700 or 800 m depth Levitus et al 2005 (3000m) Willis et al 2004 (700m) 0.4 PW into ocean implies 1.26x10 23 J/decade GECCO Spinup

Annual ocean heat content 0-700m relative to average Ishii et al 2006 Willis et al 2004 Levitus WOA Is decadal variability real? Causes of decadal variability: artefact due to temporally changing observing system ARGO problems XBT drop rate problems

Ishii et al 2008: reprocessed XBTs with revised drop rate.

Estimates of upper 700 m ocean heat content and SST. Domingues et al Nature 2008 Ocean heat content corrected for XBT drop rate: Old versions in red and blue vs new upper 700 m upper 100 m SST

Sea level is rising: from ocean expansion and melting glaciers Sea level is rising: from ocean expansion and melting glaciers Since 1992 Global sea level has risen 48 mm (1.9 inches) 60% from expansion as ocean temperatures rise, 40% from melting glaciers Steve Nerem Since 1992 Global sea level has risen 48 mm (1.9 inches) 60% from expansion as ocean temperatures rise, 40% from melting glaciers Steve Nerem

Sea level contributions” Upper 700m Deep ocean Ice sheets Glaciers/ice caps Land storage Sum of above vs Observed SL and altimeter Domingues et al 2008

Sea level Anomalies Altimeter ARGO Ocean heat content = Thermosteric GRACE Ocean mass sea level Willis, Chambers, Nerem JGR 2008

Sean Swenson

Recommendation Improving sea level rise projections requires closing the sea-level budget (with observations and models) within realistic uncertainties and monitoring sea level and ocean heat content. Measurements relevant to understanding sea level rise (i.e. satellite altimetry such as Jason and in situ observations from tide-gauges fitted with GPS receivers) should be maintained. Specifically, the Argo array needs to be maintained and extended into the ice-covered oceans and the deep and abyssal oceans using new technologies.

Other issues Ocean carbon Acidification Ocean color

Global warming is happening!

Adaptation to climate change Assess vulnerability Devise coping strategies Determine impacts of possible changes Plan for future changes Requires information Assess vulnerability Devise coping strategies Determine impacts of possible changes Plan for future changes Requires information

Future needs: Observations and Analysis  Observations: in situ and from space (that satisfy the climate observing principles);  A performance tracking system;  Climate Data Records (CDRs)  The ingest, archival, stewardship of data, data management;  Access to data  Data processing and analysis  The analysis and reanalysis of the observations and derivation of products,  Data assimilation and model initialization  Observations: in situ and from space (that satisfy the climate observing principles);  A performance tracking system;  Climate Data Records (CDRs)  The ingest, archival, stewardship of data, data management;  Access to data  Data processing and analysis  The analysis and reanalysis of the observations and derivation of products,  Data assimilation and model initialization

Future needs: Models  Data assimilation and model initialization  Better, more complete models  Assessment of what has happened and why (attribution) including likely impacts on human and eco-systems;  Prediction of near-term climate change over several decades: ensembles  Statistical models: applications  Downscaling, regional information  Responsiveness to decision makers and users.  Data assimilation and model initialization  Better, more complete models  Assessment of what has happened and why (attribution) including likely impacts on human and eco-systems;  Prediction of near-term climate change over several decades: ensembles  Statistical models: applications  Downscaling, regional information  Responsiveness to decision makers and users.

Climate Information System Trenberth, 2008 WMO Bulletin Nature 6 December 2007

Imperative A climate information system Observations: forcings, atmosphere, ocean, land Analysis: comprehensive, integrated, products Assimilation: model based, initialization Attribution: understanding, causes Assessment: global, regions, impacts, planning Predictions: multiple time scales Decision Making : impacts, adaptation Observations: forcings, atmosphere, ocean, land Analysis: comprehensive, integrated, products Assimilation: model based, initialization Attribution: understanding, causes Assessment: global, regions, impacts, planning Predictions: multiple time scales Decision Making : impacts, adaptation An Integrated Earth System Information System