# Presentation: 898759

## Global Warming is unequivocal

**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.**

## 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) 17-21.*

**GCOS-117; WCRP-127; IGBP Report No. 58**
**(WMO/TD No. 1418)**
**Jan 2008**

## Is ocean warming accelerating?

-  **cooling due to volcanism?**
** ****artefact due to temporally changing observing system?**** **

**Annual ocean heat content** 0-700m relative to 1961-90 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** < -0.025°C per decade

- Zonally averaged temperature trend 1955–2003

**Few regions are cooling:****related to climate variability**

**Pacific subtropical ocean **
**circulation**
**El Ni****ñ****o**

**Changes in NAO, PDO**

## Most but not all parts of the Ocean are warming

**Ocean heat content trend 1955-2003**

- corresponds to **warming** > 0.25 W/m2

- corresponds to **cooling**  < -0.25 W/m2

## Ocean salinities are changing, indicating changes in evaporation and precipitation

**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** < - 0.005psu 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**

## Melting ice

- IPCC estimated melting ice contribution to SL rise was 1.2 mm/yr for 1992 to 2003.
- 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.

- 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.

## To 700 or 800 m depth

- GECCO
- Spinup

## Is decadal variability real?

**Annual ocean heat content** 0-700m relative to 1961-90 average

- Ishii et al 2006
- Willis et al 2004

- Levitus WOA

**Is decadal variability real?**

## 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: 

**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

## 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!

**Notes:**
As the scientific results going into the IPCC report began to appear in the scientific literature in 2005, the popular press synthesized these results for the general public.  The message was very clear and it resonated strongly and received broad acceptance in the general public.

The combined effects of strategic insecurity due to the nation’s dependence on foreign energy sources, concerns about maintaining economic growth and competitiveness in a time of rising energy prices and rapid economic growth in China, and this clear message on global warming has galvanized the public into action at a level never seen before

## Adaptation to climate change

- 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

## 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.

## 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

**An Integrated Earth System Information System**