text-only page produced automatically by LIFT Text Transcoder Skip all navigation and go to page contentSkip top navigation and go to directorate navigationSkip top navigation and go to page navigation
National Science Foundation Home National Science Foundation - Geosciences (GEO)
Atmospheric and Geospace Sciences (AGS)
design element
AGS Home
About AGS
Funding Opportunities
Awards
News
Events
Discoveries
Publications
Career Opportunities
Environmental Compliance
See Additional AGS Resources
View AGS Staff
GEO Organizations
Atmospheric and Geospace Sciences (AGS)
Earth Sciences (EAR)
Ocean Sciences (OCE)
Polar Programs (PLR)
Proposals and Awards
Proposal and Award Policies and Procedures Guide
  Introduction
Proposal Preparation and Submission
bullet Grant Proposal Guide
  bullet Grants.gov Application Guide
Award and Administration
bullet Award and Administration Guide
Award Conditions
Other Types of Proposals
Merit Review
NSF Outreach
Policy Office
Additional AGS Resources
AGS Data Policy
Handbook for AGS Postdoctoral Research Fellows
Proposals for Cyberinfrastructure in AGS
Other Site Features
Special Reports
Research Overviews
Multimedia Gallery
Classroom Resources
NSF-Wide Investments

Email this pagePrint this page

Discovery
Scientists Tackle Climate Model Mystery

Researchers trace a problem with a key climate model to its hydrology scheme and find a simpler scheme keeps simulations in line with real-world observations

Photo of Peter Lawrence pointing to landcover changes on a computer screen.

Peter Lawrence points to land-cover changes in a computer simulation.
Credit and Larger Version

June 19, 2009

Imagine a climate model as a black box. You put something in, you get something out. But what happens when the output is completely unexpected?

"If you don't get the results you expect, that's when you start to ask why," said climate modeler Peter Lawrence from the University of Colorado at Boulder's Cooperative Institute for Research in Environmental Sciences.

Working with Tom Chase, a colleague at the institute, the researcher compared climate simulations from the Community Land Model--part of a select group of global models used in the Intergovernmental Panel on Climate Change's 2007 climate change report--against observations.

The model simulations weren't checking out.

Despite adding more leafy vegetation to the modeled planet's land surface, Lawrence and Chase found the simulated climate consistently produced less rainfall than real-world observations revealed.

"Imagine adding more tropical rainforest to the planet and getting a drier, more desert-like climate," said Chase. "It just didn't make sense."

Their hunch? There was a snag in the model's water cycle.

Water on land eventually makes its way into the atmosphere through two processes. In one, the sun's heat directly evaporates moisture from leaf surfaces, soils and open water sources. In the other, known as transpiration, water is lost from plants during the gas exchange associated with photosynthesis. The two processes are often described together as evapo-transpiration.

According to Chase, transpiration is an important global humidifier, contributing nearly half of all evapo-transpiration worldwide. But in the Community Land Model, transpiration was contributing just 15 percent-- instead, evaporation from bare soils was putting three times as much water into the atmosphere.

"Water is a very strong climate modifier," said Chase. "It impacts surface temperature, precipitation and cloud formation. If we can't capture fundamental hydrological processes in our climate models, we have no way to determine how human activities are affecting the climate system."

Looking closely, Lawrence and Chase found that the model's hydrology was based on drainage patterns typical of small-scale watersheds a few square miles in area. Yet, a single point in a global climate model can represent several hundred square miles of the Earth's surface.

The hydrology simply wasn't scaling to size.

As a result, the model was draining too much water laterally, leaving little moisture for plants to take up through their root systems. The atmosphere, in turn, was sponging up most of its moisture from bare ground instead of from lush vegetation.

To tackle the problem, Lawrence and Chase decided to borrow a simpler hydrology scheme from another land surface model. They removed lateral drainage from the Community Land Model's soil layers and programmed the model to allow water to pond near the surface. They also changed the way plants tapped into soil water through their root systems.

With these modifications, they found they were able to simulate global temperature and precipitation patterns in line with observations. Their black box inputs and outputs finally added up.

"Complexity doesn't always get you a better large-scale simulation. If you aren't correctly representing complex interactions, you can be much better off keeping it simple," said Lawrence.

The Community Land Model is part of the Community Climate System Model (CCSM) suite developed by the National Science Foundation's (NSF) National Center for Atmospheric Research. This particular work was supported by NSF grants ATM 0639838, ATM 0001476 and ATM 0437538. The original study on which this article is based can be found here.

-- Adriana Bailey, University of Colorado adriana.bailey@colorado.edu

This Behind the Scenes article was provided to LiveScience in partnership with the National Science Foundation.

Investigators
Thomas Chase
Peter Lawrence

Related Institutions/Organizations
University of Colorado at Boulder

Locations
Colorado

Related Programs
Climate and Large-Scale Dynamics
Arctic System Science (ARCSS) Program

Related Awards
#0639838 Soil Evaporation, Transpiration and Canopy Evaporation in Community Land Model (CLM 3.0) Compared to Simple Biosphere Model (SiB 2.0)
#0437538 The Role of Tropical Asian Landcover Disturbance in Altering Large-scale Circulations: Interaction with El Nino Southern Oscillation (ENSO) and the Asian Summer Monsoon
#0001476 Collaborative Research: Land-Atmosphere Interactions in Beringia Over the Last 21,000 Years: An Investigation of Climate Feedback Using the Arctic Regional Climate System Model

Total Grants
$778,271

Related Websites
LiveScience.com: Behind the Scenes: Scientists Tackle Climate Model Mystery: http://www.livescience.com/environment/090529-bts-hydromodel.html
Community Land Model (CLM) Working Group: http://www.ccsm.ucar.edu/working_groups/Land/
Original Abstract in Journal of Hydrometeorology: http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F2008JHM987.1&ct=1

Photo of University of Colorado Engineering Professor Tom Chase working at his computer.
University of Colorado engineering professor Tom Chase works at his computer.
Credit and Larger Version



Email this pagePrint this page
Back to Top of page