Grappling with the Unknown: How Much of a Change Do Climate Models Project?

HUMANS HAVE BEEN tampering unwittingly with the climate of their planet for at least 100 years, and with grim results. The level of carbon dioxide has increased dramatically, causing the atmosphere to trap solar heat. Fortunately, today's computer-based climatic models allow scientists to examine and "experiment" with the Earth's climate without real-world consequences. Their climate projections may point toward solutions to the problems humans have caused.

Canadian and Hadley Models Predict Warmer Summers

A map of the predicted temperature increases in the United States. The Canadian model shows a much hotter Southeast
Source: National Assessment Synthesis Team (2001), based on models produced by NOAA's National Climatic Data Center

The Canadian and Hadley climate models both point toward hotter summer temperatures, with the Canadian model projecting a sweltering 20-degree F change in the July heat index for coastal Louisiana.
Courtesy of Union of Concerned Scientists

Because Earth's climate is formed by an intricate combination of many geological, chemical and biological processes, global climate simulations require an extensive array of data. Natural data sources include air temperatures, rainfall patterns and ocean currents, while data sources that reflect human activities include greenhouse gas emissions, population growth and changes in land use.

With computer models, it is possible to reconstruct past climates, simulate today's climate and, most importantly, predict future climatic change. An immensely difficult task, climate modeling requires supercomputers with vast amounts of memory and experts possessing a sophisticated understanding of climate processes. So far, the two models most commonly cited are the Hadley model, produced at the Hadley Centre in the United Kingdom, and the model in use at the Canadian Climate Centre, known simply as the Canadian model.

Louisiana Land Loss Projected Largest in Nation

A chart of predicted land loss by location

Sea level rise is a serious threat for Louisiana, which stands to lose more land than any other coastal area in the nation.
Courtesy of NOAA

The future climate scenarios projected by these two simulation models (see Temperatures, Sea-level Rise, Precipitation, Weather Patterns) are not identical. However, despite some differences, both strongly indicate that the Gulf Coast, and Louisiana in particular, will become significantly warmer and that the coast faces a serious threat from rising sea levels.

Models Predict Worldwide Sea-level Rise

A graph of predicted sea level rise by year Historic and projected changed in sea level based on the Canadian and Hadley model simulations. The Canadian model projection includes only the effects of thermal expansion of warming ocean waters. The Hadley projection includes both thermal expansion and the additional sea-level rise projected due to melting or accumulation of snow on Greenland and Antarctica.

Although differing in amount, both of the leading climate models predict significant increases in sea level by the end of this century.
Courtesy of NOAA

Louisiana Among Highest Risks in North America

A map of predicted sea-level rise over North America.

The Hadley model projects that ocean warming and melting of mountain glaciers will cause between 8 to 12 inches (20 to 30 cm) of sea-level rise by 2100 for much of the Atlantic and Gulf coasts of the US, depending on changes in winds and ocean current patterns.

Projections for the Northeast US and the Pacific coast range from 13 to 16 inches (32 to 40 cm). Any effects of the rising or sinking of the coastal lands must be added to these numbers.

The Canadian model projects a more complex pattern of sea-level rise by 2100.

Because of its larger warming estimate, sea level is projected to rise 20 to 24 inches (50 to 60 cm) along parts of the US Atlantic and Pacific coastlines. The orange peak in the Labrador Sea is the result of shifts in the location and intensity of ocean currents.

The leading climate models predict that Louisiana will experience one of the highest sea-level rises in North America.
Courtesy of NOAA