NCAR Scientist Models Earth's Climate and Vegetation Patterns At Last Glacial Peak

October 30, 1996

BOULDER--Boston buried under ice? Idaho sun-dried into desert? No, this isn't Hollywood's latest foray into climate change. Benjamin Felzer, a climatologist and geologist at the National Center for Atmospheric Research in Boulder, has used NCAR computer models of climate and vegetation to find which plant types our ancestors would have wandered among during the last glacial maximum (LGM) 21,000 years ago. Felzer presented his work on Wednesday, October 30, at the annual meeting of the Geological Society of America in Denver.

These models present a world blanketed by massive ice sheets over Canada and Eurasia, with tundra covering much of Europe and North America as the Sahara Desert crept southward toward central Africa. Rain forests existed in South America and Africa, as now, but there were fewer trees globally. The whole world was colder in both summer and winter, with a global average temperature four degrees Celsius lower than now and atmospheric carbon dioxide (a greenhouse gas) at just over half of today's levels.

Felzer's study checks the NCAR model's reliability by simulating past climates and comparing its results to geological data, such as pollen deposited in lake sediments at the time, fossilized, and recently retrieved from lake cores. Once verified, the model can be used to estimate what will happen to today's plants in the next century as increasing greenhouse gases warm the climate by several degrees.

"The plants we see around us today had 21,000 years to adapt to a several- degree warming. Now these same plant types may have a hundred years or less to make the same transition," explains Felzer. Will they have time to migrate and adapt or will they die? The model may eventually shed light on such questions as Jon Bergengren, an NCAR colleague, shifts the model's gaze out of the distant past and into the next century.

In the real world, the growth and melt of the ice sheets over the past two million years has resulted from long-term cyclical changes in the earth's axial tilt, its precession (or motion around the tilted axis), and its elliptical orbit around the sun. The cold temperatures of the last glacial maximum resulted from the existence of the continental ice sheets and were intensified by reduced amounts of atmospheric carbon dioxide, which insulates the earth by trapping heat reflected from the surface toward space.

While a 4- degree global average cooling might not sound like much, it translates into regional average temperatures that were colder than today's temperatures by 2 to 20 degrees in various parts of North America. Above the ice sheets there and elsewhere, average temperatures may have plummeted to 40 degrees colder for those regions. Besides temperature, the model calculates all other climate indicators, including moisture levels (precipitation and evaporation).

To the climate model Felzer added a vegetation model that included 110 different plant types divided into 12 categories, including needle-leaf evergreen and broadleaf deciduous forests, savanna, shrub land, and desert. The model ranked the vegetation by which plant type was best adapted to which regional climate. It computed how much surface area each type occupied based on competition for light (related to canopy cover) and disturbances such as tree fall and lightning-sparked fire. The result was a global picture of vegetation 21,000 years ago.

The model shows fragile, treeless tundra covering most of Europe. Desert spread into the northern Rocky Mountains. A wetter Southwest still bore mostly desert plants, while the Pacific Northwest dried slightly. Forests gave way to tundra and polar desert in Alaska. Worldwide, the biggest vegetation changes occurred in central Asia, where needle-leaf evergreen spruces were replaced by needle-leaf deciduous larches. The Sahara expanded southward as the Asian monsoon weakened and drier conditions prevailed across Africa and Southest Asia.

Felzer checked his results against earlier LGM vegetation scenarios based on data from fossilized pollen retrieved from lake cores. His simulated vegetation matched up fairly well

with these geological reconstructions of plant life. Where differences exist, a colder simulation might help produce the correct vegetation, since there is evidence in the data for a slightly colder world than the model shows, especially in the tropics. According to Felzer, the model is accurate enough in showing past climates and vegetation that it can be a useful tool in simulating the future.

The two NCAR models used in the study were GENESIS (Global Environmental and Ecological Simulation of Interacitve Systems) created by Starley Thompson and Dave Pollard with funding from the Environmental Protection Agency, and EVE (Equilibrium Vegetation Ecology Model) developed by Bergengren and also funded by the EPA.

National Center for Atmospheric Research/University Corporation for Atmospheric Research

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to