1995: Pinatubo's Impact on Climate

Research by students from Bronx High School of Science, John Bowne High School, Math, Science Research and Technology High School, and York College
GISS scientist: James Hansen

Summary of Previous Work

This team examined possible causes of observed global climate changes during the past several years. The project takes advantage of the natural climate experiment provided by the eruption of the Philippine volcano Pinatubo in 1991, which injected an enormous quantity, about 15 megatons, of sulfur dioxide gas into the stratosphere. Three key climate parameters were studied (temperature, winds and precipitation) to research the possibility that Pinatubo is responsible for the unusually cool summer of 1992 in North America and Asia, the almost equally cool summer of 1993 with record Midwest floods and the harsh winter of 1993-94 in the Northeast.

First the team had to test the ability of the GISS General Circulation Model (GCM) to simulate the mean climate of recent decades, with each student responsible for a different parameter. Next, the team examined the natural year to year variability of the climate parameters in the real world and in the GCM when there was no volcanic or other forcing. The final stage of the summer research was to analyze GCM runs with the Pinatubo forcing, and compare the results with observations.

Summer 1995 Objectives

Were the 1988 Midwest drought and the 1993 Midwest flood related to climate "forcings" i.e. was the likelihood (probability) of the drought/flood altered by climate boundary conditions?

Methods: Use the 25 runs of the GCM to see whether use of observed 1988 sea surface temperatures increases the frequency of droughts compared to a control run with climatological sea surface temperatures.

Did the Pinatubo aerosols have an impact on climate that would be noticeable to the person-in-the-street; more so in summer or winter?

Methods: Use the 25 GCM runs for the period following Pinatubo to look for its possible influence on the frequency/severity of both summer and winter climate anomalies.

How well can the SI94 GCM simulate drought and flood conditions?

Methods:Characterize drought and flood conditions in the real world and the model.

What are the potential causes of model inadequacies?

Methods: Based on identified model deficiencies, Pinatubo, Clouds, Impacts and Storm Tracks teams will each define GCM experiments to try to pinpoint causes, and thus help define an improved SI96 model.

Can the global cooling following Pinatubo provide information on global climate sensitivity and/or ocean mixing?

Methods: Compare observed global cooling with model results using three types of ocean: fixed SST, Q-flux ocean and dynamical ocean, designed to investigate what happens to the energy (radiative flux) perturbation introduced by Pinatubo.

Do global climate forcings have a noticeable influence on planetary scale climate features over the period 1979-1995?

Methods: Use GCM simulations with variable stratospheric aerosols and stratospheric aerosols plus ozone depletion for comparisons with observed climate change at the surface and in the upper air.