Warren M. WashingtonNational Center for Atmospheric

Research

April 2006

Climate Change Simulations of the 20th

and 21st Century: Present and Future

Overview• Is our climate changing?

• What is in climate models?

• How do we run the models on supercomputers?

• Verification of climate models

• Model projections of past and future climates

• Mitigation versus adaptation

• Future model developments on the path to a Earth System Model (ESM)

Global Mean Surface Temperatures Have Increased

The Land and Oceans Have Warmed

2005 Warmest or Tied forRecord Year

From GISS/NASA

Present and Future Sea Ice Change

What is the status of state-of-the-art

climate models and their transition to

earth system models?

Timeline of Climate Model Development

R15 T42

T85 T170

Model Resolutions

(300 km) (150 km)

(75) km (37 km)

CCSM method

Parallel Climate Model Method (PCM)

Global AtmosphereGlobal Atmosphere

Global Sea Surface Temperature

POP/LANL

Global and Regional Climate Aspects Using a Climate

Model

●El Niño/La Niña

●Monsoons

●North Atlantic Oscillation

●Arctic Oscillation

Sea-ice Concentration: Climatology (1979-1999)…

Mixture of Improved Physics and Resolution

Title slide

Mt Pinatubo eruption in the Philippines, June 15, 1991.

Gases and solids injected 20 km into the stratosphere. From Church, White, & Arblaster

Source: World Resources 2000-2001 Time Magazine – 9 April 2001

Natural Variations Do Not Explain Observed Climatic

Change• Climate models with

natural forcing (including volcanic and solar) do not reproduce warming

• When increase in greenhouse gases is included, models do reproduce warming

• Addition of increase in aerosols (cooling) improves agreement

Climate Change Scenarios:

At any point in time, we are committed to additional warming and sea level rise from the radiative forcing already in the system.

Warming stabilizes after several decades, but sea level from thermal expansion continues to rise for centuries.

Each emission scenario has a warming impact.

(Meehl et al., 2005: How much more warming and sea level rise? Science, 307, 1769-1772)

Heat Waves

Impacts on human health and mortality, economic impacts, ecosystem and wildlife impacts

(Meehl and Tebaldi, 2004: More intense, more frequent and longer lasting heat waves in the 21st century, Science, 305, 994-997)

Climate models can be used to provide information on changes in extreme events such as heat waves

Heat wave severity defined as the mean annual 3-day warmest nighttime minima event

Model compares favorably with present-day heat wave severity

In a future warmer climate, heat waves become more severe in southern and western North America, and in the western European and Mediterranean region

Observed

Model

Future

From Meehl and Tebaldi 2005

Tropospheric temperature increase

Stratospheric temperature decrease

Surface temperature increase Tropical troposphere warms more than

surface What do observations show?Since 1960 surface and troposphere warm

about same rateStrong decreases in stratospheric

temperature and increases in tropopause height since 1979

With more greenhouse gases climate models project

Controversy (mostly) Settled in 2005!

From T. Karl of NOAA

Sea-ice Extent in Both NH and SH

Figures based on Tebaldi et al. 2006: Climatic Change, Going to the extremes; An

intercomparison of model-simulated historical and future changes in extreme

events, in press

Five indices describe temperature-related extremes:• Total number of frost days (days with absolute minimum temperature

below 0 degrees Celsius) frost days• Intra-annual extreme temperature range (difference between the

highest temperature observation of the year and the lowest) xtemp range

• Growing season length (length of the period between the first stretch of five consecutive days with mean temperature above 5 degrees Celsius and the last such stretch of the year) growing season

• Heat wave duration index (maximum period of at least 5 consecutive days with maximum temperature higher by at least 5 degrees Celsius with respect to the climatological norm for the same calendar day) heat waves

• Warm nights (percent of times when minimum temperature is above the 90th percentile of the climatological distribution for that calendar day) warm nights

20,000 years ago 2200? ( + 5 meters)

Past and Future Rise in Sea Level

• Changes in hurricane and tropical cyclone climatology

• Most models have 100 km grids this study has 20 km.

• Eye and eye walls in the simulations

• Winds speeds increase by 8.8 m/sec, more intense storms

• Less frequent formation of storms by 30%

• Significant increase in intense storms

Oouchi, K., J. Yoshimura, H. Yoshimura, R. Mizuta, S. Kusunoki and A. Noda, 2005: Tropical cyclone

climatology in a global-warming climate as simulated in a 20km-mesh global atmospheric

model: Frequency and wind intensity analyses. J. Meteor. Soc. Japan, Accepted.

Fewer Cyclones and Hurricanes But More Intense

Oouchi et al. 2005

Ongoing and Future Climate Change Developments

●Higher resolution, especially important near mountains, river flow, and coast lines

●Full hydrological coupling including ice sheets…important for sea level changes

●Continued improvement in clouds and aerosol effects

●Better vegetation and land surface treatments with ecological interactions

●Carbon and other biogeochemical cycles

Changes That Affect Renewal Resources

● Warmer, more moist, heavier rainfall events

● Jet stream move further poleward and weaker

● Storm systems moving slower but more intense rainfall events

● Cloudiness change is largely unknown but expected to be small. Closely tied to relative humidity upper limit.

Modeling and Observational Consensus

“An increasing body of observations gives a collective picture of a warming world and other

changes in the climate system” - IPCC

• Global average surface temperature has increased over the 20th century by about 0.6°C

• The last decade of the 20th century was the warmest decade of the past millennium

• Temperatures have risen during the past four decades in the lowest 8 kilometers of the atmosphere

• Snow cover and ice extent have decreased

• Global average sea level has risen and ocean heat content has increased

Climate Change Policy Debate

NASA

Science Challenges, Uncertainties, Issues

• Physics Models– Terrestrial biochemistry– Atmospheric chemistry– New ice-sheet component

• Methods/Algorithms– Finite-volume atmospheric

dynamics• Longitude-lattitude grid with FFTs

at poles• Implement cubed-sphere grid

– Decoupled parallelism for scalability and load balance

• Atmospheric physics and dynamics

• Ocean barotropic and baroclinic on generalized grids

– Parallel I/O

• Software– Large, distributed development

team– Aggressive schedule for improving

science and performance– New coupling that allows multiple-

executable concurrent and single-executable sequential

– Regression testing with changing compiler, library, and OS versions

– Earth System Grid and analysis framework for data dissemination

• Uncertainties– Correction of model biases– Validation against observations for

terrestrial carbon models– Scalability of algorithms– Reliability of simulation

environment

The End