In the list of world challenges, global warming might be at once the most alarming and the most controversial. According to some predictions, climate change caused by human activity could cause mass extinction in the oceans, redraw the planet’s coastlines, and ravage world food supplies. At the same time, a significant portion of the American public questions whether global warming will really cause any major harm; many still doubt that human-driven warming is happening at all. How can we settle the debate? And can we intervene in the process or find ways to adapt to the new conditions? In conjunction with the National Science Foundation and the San Francisco Exploratorium, DISCOVER brought together four experts to discuss the reality and meaning of climate change. In a highly nuanced exchange of ideas, these researchers weighed the various scenarios and laid out a road map for navigating the warmer world to come. The conversation was moderated by DISCOVER’s editor in chief, Corey S. Powell.
POWELL: One question I hear all the time is whether the current change in climate is truly extraordinary. Even if humans are contributing to global warming, isn’t this just like the natural variations that have happened many times in the past?
A little background first. I spend a lot of time studying the ice sheets at the bottom of the planet—how they form and how they collapse. The poles are like the planet’s air conditioner. When things are working well, the poles keep the planet nice and cool and we don’t think about it. When things stop working, the poles can start to melt and there’s a puddle on the floor. Today both poles are getting warmer; in Greenland and Antarctica you can see the surface of the ice dropping, and you can see there’s less mass when you measure the ice from space. The process has been ongoing, but it looks like it’s happening faster than it was. We know the ice sheets have come and gone in the past. Why is this any different? One of the most compelling reasons is that in the past the ice sheets from the two poles didn’t move together—one would lead and the other would follow. This time, both the north and south are spewing ice into the global ocean, accelerating at the same time.
Ken Caldeira: Another indication of how unusual all this is can be seen by looking at ocean chemistry. When we drive our car and carbon dioxide comes out of the tailpipe, within a year it has spread throughout the atmosphere and is integrated with the surface ocean. When carbon dioxide dissolves in seawater, it forms carbonic acid, and in high enough concentrations carbonic acid is corrosive to the shells and skeletons of many marine organisms. To measure the impact, people go out in ships and drill holes in the ocean floor, where shells of marine organisms have settled throughout geologic history. What we see is that if we continue in our current trends in burning fossil fuels, the ocean will become more acidic than it has been at any time in the past 65 million years. The last time the ocean was as acidic as it has the potential to become in the coming decades, we saw a mass extinction event.
