Arctic Climate Change: Perspectives from Observations and Global Climate Models

Arctic Climate Change: Perspectives from Observationsand Global Climate Models David Lawrence NCAR With contributions from Andrew Slater, Marika Holland, Mark Serreze, Don Perovich

Observed global climate change

Spatial pattern of warming Arctic warming at roughly twice the rate of the rest of the world

Arctic sea ice is disappearing … Stroeve et al. 2008

Glaciers are retreating …

Greenland Ice Sheet is melting … • 16% increase in melt area between 1979 and 2002 • new record in 2007 (60% increase in area)

Sea level rise from thermal expansion of ocean water and melting glaciers • Since 1993 • Global sea level • has risen 43 mm • (1.7 inches) • 60% from expansion as ocean temp. rise • 40% from melting glaciers • Steve Nerem

IPA Permafrost Distribution Map … and permafrost is degrading Long term monitoring site in Quebec, Canada 1957 1983 2003 Continuous (90 – 100%) Discontinuous (50 – 90%) Sporadic (10 – 50%) Isolated (0 – 10%) Permafrost Thermokarst Ponds Fen Vegetation Payette et al, 2004 Brown et al. 1998

Biomes are shifting (tundra to shrublands) … Shrub cover increasing at 1.2% per decade since 1950, 15% to 20% cover(Sturm et al. 2001, Tape et al. 2006)

… and snowmen are melting … Nation's Snowmen March Against Global Warming January 25, 2006 | Issue 42-04 … Centigrade told the slowly melting snowcrowd that as recently as 15 years ago, the average life span of a snowperson built in late December was three weeks to a month. Today, that same snowperson has an average life span of two weeks.

Observed Arctic Climate Change • Snow cover decreasing • River runoff to Arctic Ocean increasing • Lake and wetland distributions changing • Growing season is getting longer • More frequent forest fires • Rapid coastal erosion • …. See, e.g. Hinzman et al., Climatic Change, 2005 McGuire et al., Ann Rev Env Res, 2006 Serreze et al., Climatic Change, 2000 Arctic Climate Impact Assessment, 2004, updated in 2008

Global Climate Model Peering into the future ….

Global Climate Models Global Coupled Ocean-Atmosphere-Land-Sea Ice model Climate models are a lot like weather forecast models, but include interactive ocean, land, and sea-ice components, and can also account for changes in atmospheric constituents like greenhouse gases. They are used to study the earth's past, present and future climate states.

How does a global climate model work? Land Model

Land-Surface Model Rainfall Canopy evaporation Transpiration Stomatal conductance: solar radiation, temp, humidity deficit, soil moisture, [CO2] … Nitrogen fertilization Photosynthesis model Throughfall Sublimation Surface runoff Soil evaporation T1, Soil hydrology model T2, T3, Runoff Vertical water flow Phase change Sub-surface runoff T10, , T*, zo …

Model grids

NCAR Community Climate System Model (CCSM4) • Coupled Ocean-Atmosphere-Land- Sea Ice-Carbon cycle model • 1oresolution (~60 sq. miles) • 30 minute time step • 31 atmosphere levels • 60 ocean levels • 15 ground layers • ~5 million grid boxes • ~1.5 million lines of computer code • Archive data (monthly, daily, hourly) for over 300 geophysical fields (in land model alone)

High resolution climate model output CAM T340- Jim Hack David Lawrence National Center for Atmospheric ResearchBoulder, Colorado

History of Climate Model to Earth System Model Development 2000s 2010

CCSM Working Groups Chemistry Climate BioGeo Chemistry Atm Model Land Model Polar Climate Ocean Model Climate Change PaleoClimate Climate Variability Development Application

How do we evaluate and improve models? Compare against observations; if comparison is poor, then something is wrong

Soil (and snow) water storage (MAM − SON) GRACE (obs) CCSM4 CCSM3 GRACE satellite measures small changes in gravity which on seasonal timescales are due to variations in water storage CCSM3 and CCSM4 data from 1870 and 1850 control 300 200 100 0 -100 -200 -300 (mm)

How do we use these models to study climate change? Economists develop possible scenarios of population growth, economic growth, energy use, land use Depending on the scenario, more or less greenhouse gas emissions

Simulated global mean temperatures during last millenium and into 20th and 21st centuries Ammann et al.

Air Temperature: Typical “business as usual” scenario by 2100 Global mean warming of ~2.8oC (or ~5F);Much of land area warms by ~3.5oC (or ~6.3F)Arctic warms by ~7oC (or ~12.6F)

Abrupt reductions in the September sea ice cover September sea ice extent Ice Extent ( 106 km2 ) SSMI observed CCSM3 CCSM3 – smoothed “Abrupt” transition Holland et al., 2006

…and on broader Arctic climate … in the 1970’s D. Perovich, CRREL

Not far from today… D. Perovich, CRREL

3.5-fold increase in rate of warming over land during rapid sea ice loss September Sea- ice Extent Lawrence et al. 2008

CCSM3 Projections of Degradation of Near-Surface Permafrost Lawrence and Slater, 2005

Goal: Represent Arctic terrestrial climate-change feedbacksin the Community Climate System Model (CCSM) Carbon sequester Global warming CO2 efflux CH4 efflux Permafrost warms and thaws Enhanced [nitrogen] Expanded wetlands Arctic runoff increases Adapted from McGuire et al., 2006

Bernhard Edmaier National Geographic

Arctic Climate Change: Perspectives from Observations and Global Climate Models