GFDL BROCHURE

GLOBAL CLIMATE CHANGE

In 1967, two GFDL scientists, Syukuro Manabe and Richard Wetherald, published what is now regarded as the first credible calculation of the effect of increased carbon dioxide on the climate. They calculated that a doubling of atmospheric carbon dioxide would warm the earth's surface by about 2°C. This result laid the foundation for what has become an international, multi-disciplinary research effort on global warming.

Manabe, in collaboration with oceanographer Kirk Bryan and other scientists at GFDL, has continued to lead the international effort to develop the coupled ocean-atmosphere climate models that are crucial to understanding and predicting the impact of greenhouse gases.

Three-dimensional view of projected surface air temperature and ocean warming (°C) due to greenhouse gases as calculated by a low-resolution GFDL coupled ocean-atmosphere climate model. The top panel shows the surface air temperature change over North and South America and surrounding regions. The three-dimensional box illustrates the depth to which a 1°C and 0.2°C warming has penetrated in the model's Pacific Ocean. The gray surface depicts the model's ocean floor. Note the deep mixing of the ocean warming signal in the southern hemisphere ocean near Antarctica. The temperature changes are projections of the warming due to greenhouse gases by the latter half of the twenty-first century in the absence of further increases in sulfate aerosol forcing. Results shown are based on years 61-80 of a transient CO₂ increase experiment (+1% per year compounded). [Source: adapted from Syukuro Manabe and Ronald Stouffer, Nature, 15 July 1993.]

A PROBLEM FOR CENTURIES TO COME?

In a recent paper, published 26 years after Manabe's pioneering one-dimensional CO₂ sensitivity study, he and Ron Stouffer of GFDL used a three-dimensional coupled ocean-atmosphere model to examine possible CO₂-induced climate changes over several centuries. Earlier studies had focused on shorter time horizons.

In their scenario, CO₂ quadruples over a period of 140 years, then no longer increases. This perturbation is enough to cause the ocean's global thermohaline circulation to almost disappear in the model. The global thermohaline circulation is important because it is responsible for a large portion of the heat transport from the tropics to higher latitudes in the present climate. In addition, sea level continues rising steadily for centuries after the CO₂ increase is halted. From this perspective, global warming can no longer be viewed as just as a problem of our own lifetimes, but as a legacy--with uncertain consequences--now being passed forward to many future generations.

EVALUATING CLIMATE MODELS

GFDL scientists, including Tony Broccoli and Tom Delworth, are searching for innovative ways to evaluate climate models and to distinguish between human-induced climate change and natural climate variability. Measurements of the current climate, historical observations, and glimpses of earth's climate during the ice ages and other past climates all provide opportunities to test climate models. Through research on climate models and observations, scientists at GFDL will continue to evaluate and refine the climate models that will be needed to help answer critical policy-relevant questions about global warming and its consequences.

Impact of increasing CO₂ on the earth's climate as simulated in a GFDL coupled ocean-atmosphere climate model. Shown are timeseries of: a) prescribed CO₂ concentration on a logarithmic scale in comparison to present levels; b) global mean surface air temperature (°C); c) global mean increase of sea level (cm) due to thermal expansion; and d) intensity of the North Atlantic Ocean's meridional overturning circulation (10**6 m**3/sec). The labels "Control", "2xCO₂", and "4xCO₂" refer to separate experiments where CO₂ either remains constant (Control), or increases at 1% per year (compounded) to double (2xCO₂) or quadruple (4xCO₂) the current concentration. Note that the sea level rise estimates do not include the effect of melted continental ice sheets. With this effect included, the total rise could be larger by a substantial factor. [Source: Syukuro Manabe and Ronald Stouffer, Nature, 15 July 1993.]