The Institute of Technology is in a strong position to help tackle many of the most vexing scientific questions about climate change

Katsumi Matsumoto: Understanding our oceans

by Richard Broderick

“I am more of a chemical oceanographer,” explains Katsumi Matsumoto, assistant professor of geology and geophysics and a contributor to the Intergovernmental Panel on Climate Change. “I use numerical models called ‘global climate models’, to simulate past climate changes to learn what happens to the carbon cycle when those changes occur.”


Assistant professor of geology and geophysics, Katsumi Matsumoto, who considers himself a chemical oceanographer, is using numerical models called “global climate models” to simulate past climate changes to learn what happens to the carbon cycle when those changes occur.

For most of the past 10,000 years during this relatively warm interglacial period, there has been a fixed ratio between the amount of carbon contained in the oceans, the atmosphere, and terrestrial plant life and soils—about 60:4:1. It was a balance that, Matsumoto said, made the oceans and the atmosphere “happy.”

Since the Industrial Revolution, and at an increasing pace over the past century, that long-time ratio of carbon has changed as the amount of atmospheric carbon—one of the principal greenhouse gases— has climbed, from about 280 parts-per-million at the dawn of industrialization to about 380 ppm today. As the amount of gas in the atmosphere has risen, the oceans have absorbed an increasing quantity.

Today, though, the upper ocean has absorbed significant amounts of atmospheric CO2, meaning that we are beginning to lose the buffer zone the earth’s waters have provided for our excess greenhouse gases. In turn, climbing temperatures are heating up the oceans. The effect of this warming is something Matsumoto is trying to calculate.

“If you heat water, it can hold less gas,” he points out. “So as the oceans warm they will be able to hold less CO2, which will return out into the atmosphere.” Then this CO2 will contribute to further warming in what Matsumoto describes as a “simple feedback system.”

Rising temperatures will ultimately also hasten the melting of glaciers and the polar ice caps drastically reducing the albedo effect—the phenomenon by which sea ice, snow, and clouds reflect sunlight back into space, helping to cool the planet—but that’s not the only untoward effect made possible by the complex interplay of changes set off by anthropogenic “forcing” of climate change.


The graphic background (below) shows a map of conventional radiocarbon age (in years) in the deep ocean. The white in the continental region is land. The white in ocean basins are midocean ridges rising above 3,000 meters water depth.

There’s also the impact on marine plant life—and its impact on CO2—especially phytoplankton, the microscopic plant life that makes up the bulk of oceanic plant life. In performing photosynthesis, phytoplankton absorbs carbon dioxide. Warmer water promotes the growth of phytoplankton and hence CO2 absorption.

That sounds like a good thing, right? Maybe not, because higher temperatures also speed up plant respiration, which produces mostly carbon dioxide. So, stimulate phytoplankton growth (and death), and ultimately you may end up with a net gain of CO2.

“Climate change is very complex and there are lot of components to it,” he explains. “But the only way we can run a numerical model that matches observations of postindustrial changes is to combine the effects of natural forces—like changes in solar temperature and reflective aerosols from volcanoes—with anthropogenic forcing like greenhouse gas emissions by humans.

Unfortunately, Matsumoto said, the climate system is slow to respond. Even if we stopped CO2 emissions today, it wouldn’t stop warming. It will take centuries before we reach equilibrium in Earth’s energy budget (and thus temperature) similar to the “happy” pre-Industrial time.

“There is already warming coming because of the CO2 we have emitted,” Matsumoto said. “We probably have a limited window of opportunity to do something to prevent dramatic changes.”