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Peter Clark: Melting Ice, Rising Seas, and Climate Change

Peter Clark on Mt. Hood with his dog. Photo Rights: Oregon State University, 2015.

It’s the year 2100. The carbon dioxide (CO2) emitted since the industrial revolution continues to hang out in the atmosphere like some invisible ne’er-do-well. It will trap the sun’s energy for thousands of years to come. Sea levels are climbing under the gas’s influence. The oceans expand as they take on the atmosphere’s heat. Glaciers and ice sheets melt. Sea levels will continue to rise for the next 10,000 years, eventually reaching between 25 and 52 meters (82 to 171 feet) above the early twenty-first century average. 

“Sea level rise won’t stop at 2100,” said climatologist and AAAS Fellow Peter Clark. “It’s going to continue to rise. So you can’t adapt for 2100 and just call it quits.”

Clark, a researcher of both future climate change as well as the climate of our planet’s distant past, works for Oregon State University’s College of Earth, Ocean, and Atmospheric Sciences. A leading expert on sea level rise, Clark’s multiple accolades include being one of two coordinating lead authors on a far-reaching report covering climate change and sea level rise for the world’s leading climate research organization, the Intergovernmental Panel on Climate Change.

Clark specializes in the role that ice sheets, such as the Greenland and Antarctic ice sheets, play in sea level rise and the climate system. His warning: our species is not planning long term enough for the consequences of climate change.

The disquieting picture described above is illustrated in detail in a 2016 paper led by Clark and published in the journal Nature Climate Change. The paper riffs on an idea familiar to many in the climate change world: the almost magical appeal of the year 2100.

Many climate adaptation goals have set the year 2100 as a kind of planning benchmark. The initial reason was due in part to the lack of computing power available when early climate models first started simulating future projections. However, with advances in computing and improvements in our understanding of the climate system in general, many of the obstacles surrounding long-term projections are now gone.

This is Clark’s point about sea level rise: we can now predict with a high degree of confidence just how high sea levels will get if we continue emitting global warming gases at our current rate. Long story short, said Clark, planning for sea level rise for the year 2100—as has been the norm—won’t be enough.

“Ultimately,” said Clark, “we need to recognize that we are not going to save Miami by building a one-meter sea wall. Eventually we are going to have to move Miami.”

Here’s the rub: even if we were to completely stop emitting CO2 right now, the climate system would still be locked into some very long-term changes. That’s because CO2 can stay in the atmosphere for thousands of years. To conceptualize this, said Clark, imagine that you are boiling a pot of water on the stove. Flipping on the gas applies heat to the water, but the water doesn’t boil straightaway. It takes time, but as long as the heat stays on, the water stays warm. This is kind of how CO2 works in the climate system. It can effectively loiter, heating things up for ages.

What all this means is that at our current rate of CO2 emissions, we are likely looking at sea levels climbing for a period longer than all of recorded history—a dystopian scenario if ever there was one. We know this is the probable outcome of our current carbon heavy period, said Clark, because we now know from the study of paleoclimate, the study of the climate of the distant past, a lot about how changes of this magnitude occur.

“It definitely is a historical science, if you will,” said Clark of paleoclimatology. “It’s kind of a detective story. You’ve got these clues of what happened when, and you are trying to piece them together into something like a coherent history.”

Yet Clark isn’t so much a historian as a kind of journalist. In fact, becoming an investigative reporter was a one-time ambition of Clark’s, who watched the Watergate scandal and decades-long career of Richard Nixon unravel in a little over two years under the gumshoeing of two Washington Post reporters. Clark, however, would choose another career, due to his love of the outdoors.

As a young man, Clark fell in love with the landscape of the American West, hiking in countryside chiseled away by the colossal glaciers that once dominated it. His love of the outdoors would remain, as over the decades Clark would follow paleoclimate clues while doing research in some of the coldest places on Earth, in the Arctic and Antarctic. The clues this investigator would follow ended up being even more mystifying than the smoke-entangled whispers of a Deep Throat. These paleoclimate clues are called proxies.

Proxies are things that substitute for other things and that solve a problem. For paleoclimate that problem, of course, is that people weren’t taking scientific measures—or for that matter were even around—for most of Earth’s long history.

So to make up for a lack of things such as temperature measurements in the paleoclimate record, Clark and his colleagues use proxies. These include air bubbles trapped in ice that contain isotopes of carbon and oxygen, and the remains of shell-making organisms trapped in seafloor sediment. Clark’s work also relies heavily on computer models, which simulate the Earth’s complex climate system to try to understand the data painstakingly derived from proxies.

Like any good reporter, Clark’s investigative strength also comes from being plugged in, so to speak. His work studying proxies in ice has benefitted from a longtime collaboration with AAAS Fellow Edward Brook. His work deriving data from the shells of long-dead ancient organisms is thanks to his collaboration with AAAS Fellow Alan Mix. And his work with Earth system models was completed with the aid of AAAS Fellow Andrew Weaver, to name just a few of Clark’s collaborators. 

“There are lessons from the past that we can learn as to how the [climate] system works,” said Clark. “And that’s not necessarily going to inform us in exact terms as to what is going to happen in the future, but it does inform us about our understanding of the system.”

This understanding, said Clark, includes how sensitive the climate system is to a given amount warming or a given amount of added CO2. It also hints at what has been a consistent theme in Clark’s research: much like Bob Woodward and Carl Bernstein taking down Nixon, climate events that occur over short periods of time can have long-term consequences. Consider the end of the last ice age.

At the time of Last Glacial Maximum—the last time when ice sheets and glaciers reached their maximum size some 21,000 years ago—global mean sea level was approximately 130 meters (roughly 427 feet) lower than it is today. The reason was the ice that covered much of the paleo-world had effectively locked up what we think of as modern sea level in their enormous masses. Then things began to change.

CO2 levels began to rise…just slightly at first. As a consequence, temperatures also rose…again incrementally at first. Then things were set in motion.

Eventually CO2 levels would go from some 190 parts per million to 270 parts per million, leading to still more warming, producing a rise of about 4° C (7.2° F). As the atmosphere warmed, many glaciers and ice sheets melted. The oceans expanded under the warming as well. Taken together this produced hundreds of feet of sea level rise that lasted for about ten thousand years before reaching equilibrium in the dawning of the Holocene, that period of relative climate and sea level stability that has allowed human civilization to flourish.

A key lesson from this transition, said Clark, is how an initial, short-term, small change locked the planet into a larger, longer process. As in the past, ice sheets like those on Greenland and Antarctica are likely to play a key role in future sea level rise. And because we know how much of those ice sheets are likely to melt given the amount of warming we can expect—and because we know how much water is locked up in that ice—we know we are looking at change the likes of which we haven’t seen since the end of the last ice age.

“I think this should give people pause for thought on what their strategies are. It is our actions right now that are committing us to these long-term consequences,” said Clark. “Now, whether people care about that or not is another matter, but I hope they will, as we will be judged by history as the generation that determined the course of Earth’s climate and sea level for the next tens of thousands of years.”


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