Michael Oppenheimer is the Albert G. Milbank Professor of Geosciences and International Affairs and director of the Center for Policy Research on Energy and the Environment at Princeton University. He is a longtime participant in the Intergovernmental Panel on Climate Change (IPCC), which won the Nobel Peace Prize in 2007.
What is the basic science behind climate change?
Sunlight is absorbed by Earth’s surface and warms the planet. However, some of that heat is trapped as it tries to return to space in the form of infrared radiation, a process known as the greenhouse effect. This matters because it keeps the Earth in habitable conditions; otherwise it would be a frozen desert.
Unfortunately, as gases—such as carbon dioxide from burning coal, oil, and natural gas— are emitted in increasing amounts and the carbon-absorbing capacity of forests, coastal habitats, and parts of the open ocean is undermined, greenhouse gases build up in the atmosphere and increase the natural greenhouse effect, creating a continuous warming effect. This is causing a global climate change.
What is the ocean’s role in managing climate change?
We experience climate as an atmospheric phenomenon, but it ties to the rest of the Earth’s system. The climate both affects and is affected by the icy parts of Earth, primarily the northern and southern polar regions. Seventy percent of Earth’s surface is ocean water, and not only does a changing climate affect the state of the ocean, but those changes in the ocean then affect the evolution of climate change in the atmosphere.
The ocean absorbs carbon, which has helped slow the greenhouse problem. If that weren’t happening, we would yearly add twice as much carbon dioxide to the atmosphere, and it would already be a lot warmer. In addition, a lot of ice floats on the ocean in the polar regions, and that’s melting as the ocean surface warms. Reflective ice is replaced by blue ocean water that absorbs yet more heat, speeding global warming. Warmer water expands and contributes, along with melting of ice on land, to sea level rise. This means that we need the ocean to stay just about like it has been or we’ll experience a lot more warming and sea level rise. Unfortunately, the ocean is already evolving in harmful ways.
That the ocean is already evolving in harmful ways harkens to a phrase you have previously used: the “climate danger zone”—what is that threshold?
When the temperature increases, the ocean surface starts evaporating faster, and that combination of more heat and more humidity is deadly to people. Just at the 2-degree Fahrenheit warming that we’ve already seen, there’s been a significant increase in the number of very hot and very humid days in many places.
If the temperature rises 3 or 4 degrees Fahrenheit (around 1.5 to 2 degrees Celsius), we tip over into a dangerous climate situation. "Dangerous" means people dying from the effects of increased heat, heightened food insecurity with lower crop yields; hot, dry zones; and flooded communities.
Ecosystems would also run into trouble at that level. Coastal areas feel greater effects of sea level rise, particularly from storms or super tides, making areas unlivable or prohibitively expensive for many countries to protect their communities from the sea.
What can be done to avoid that critical point?
The danger zone is already very near, too close for comfort. In order to avoid it, we have to start changing the way we behave, the way our industrial society is structured, to reduce emissions, and we have to do it quickly.
One significant step is generating energy that isn’t dependent on fossil fuels—such as wind or solar energy—and using new ways of storing and transporting energy, such as smart and efficient power grids. Another big step is ending deforestation—not only does cutting and burning trees put more carbon dioxide into the atmosphere, but we rely on trees to absorb carbon. Third, we have to improve our agricultural practices, which currently release methane, nitrous oxide, and other greenhouse gases into the atmosphere. People and cities also have a big role to play in modernizing transportation—rather than using single-passenger, gas-powered automobiles, we need to turn to public transportation and electric vehicles. That will require user-friendly mass transit options, particularly in places that don’t have it now.
Much of this is already underway—we are in the middle of an energy revolution. If we don’t mishandle it, there’s a fair chance we can get where we need to go and that other countries may get there too.
How do we build more consensus on the severity of climate change and make progress on remedies?
By giving people the facts. I was an author of a special report on the ocean by the Intergovernmental Panel on Climate Change published two years ago. The most startling number we developed was that the frequency of significant floods—those that occurred historically only once a century along the world’s coastlines—would now occur at many locations once per year by 2050. That’s only 28 years away.
Our ability to deal with large-scale flooding, or any other disaster, depends on how much time we have to recover. When you have a monumental flood event, like a Hurricane Harvey or a Hurricane Sandy, communities need years, not days or months. It’s important to remember why this matters—hitting the climate change danger zone would create an ongoing disaster for societies and a biological disaster for the oceans.
But I do have some optimism. There is no silver bullet to fix the problem, but we can move quickly to improve and diffuse technologies that we know work and are already implemented in many places. Alongside that, we have to reframe the way we live as human beings so as to stop wasting so much energy. If we’re going to protect the ocean, we have to take actions at not just the international and national level, but at the local level, both to be as green as we can and to reduce the vulnerability of people to coastal flooding, heat waves, and other hazards that are on the rise due to climate change. In my view, we all share the responsibility to transform our communities.