Battle With The Sea: What We Know And How We Know It

Dec 11, 2014

For the past three weeks, we've brought you stories about how climate change is already affecting Rhode Island. Narragansett Bay is getting warmer. Seas are rapidly rising. Shorelines are eroding. And we're experiencing more severe weather events. As part of our new ongoing series, Battle With The Sea, we take a step back this week to look at the science of how we know these changes are happening.

More than 60 percent of Americans accept that global warming is happening, according to a study by Yale University. It's no surprise that in the Ocean State, that percentage is higher, 92 percent, as a different study by Stanford University, Resources for the Future, and USA Today found. 

At a bus stop in Providence, the handful of people we spoke to recognize human activity is driving the rapid pace of the earth's warming, but they'd like to learn more about the science of climate change. Clara Logan, for example, still has questions about how rapidly changes are happening.

"Definitely [there are] still some things that I'm still trying to understand and that I feel I could be more informed on, especially on the macro effects about how quickly things are going to devolve and what that means for our future," said Logan.

Camilla Mehdaoui said she just knows the basics. “I know it has to do with the gases that we are emitting, particularly carbon dioxide,” she said. “Aside from that, I don’t know very much about it."

But for Jonah Newman, knowing just the basics is enough. “As long as you understand that carbon is being put into the atmosphere. And the sunlight when it comes through the atmosphere can’t get back out because of the carbon and that’s what’s causing the warming of the planet,” said Newman. “That’s fundamental enough to understand.” 

And Newman is right. The issue of global warming does really come down to the energy budget of the earth: how much energy comes in and how much energy goes out. 

(Video from the website How Global Warming Works.)

Naturally occurring greenhouse gases, like carbon dioxide, methane, and water vapor, absorb energy and trap heat. They make life possible on earth, by protecting the planet from getting too hot or too cold. But since the Industrial Revolution, humans have been putting excess carbon dioxide into the atmosphere by burning fossil fuels, like oil, coal, and natural gas. That's causing the average temperature of the whole planet to warm and changing the climate system.

“And it’s pretty well established that there’s a strong relationship between greenhouse gas concentrations and global temperature,” said John King, an oceanography professor at the University of Rhode Island.

King studies climate records on timescales of decades to centuries to millions of years. He said now carbon dioxide concentrations in Earth's atmosphere are nearly 400 parts per million (ppm). 

“Usually during a warm time, the Co2 concentration is no higher than about 280 parts per million. So we are already almost 50 percent higher than the highest Co2 concentration that’s existed for the last 800,000 years," said King.

King said we have good data from ice cores on historic global temperatures and historic Co2concentrations. Scientists drill long tubes into ice sheets to gather those data.

“In these old ice cores, there are gas bubbles frozen in the ice that we can thaw the ice, analyze the concentrations of greenhouse gases in those gas bubbles and then we know what the concentration was in the atmosphere at various points back in time,” said King. “And we are way over the highest level that’s naturally observed.  So when people say, ‘Oh well, climate variation is natural.’ That’s true. But we’ve exceeded the boundaries of variation that the natural system can produce and the way that that’s happened is by combustion of fossil fuels.”

Our climate is affected by the atmosphere, ocean, and land. Changes in any one of these components can influence the overall climate system. King said the excess Co2 emissions are disrupting this system.

“When you see … Katrina, you see Sandy, you see major droughts in various parts of the country, and people say, ‘Oh well that's just the weather.’ Well they are right, if it was a single event. But once you see a higher frequency of extreme weather events, that's the climate,” said King.

Newport's tide gauge has risen 10.6 inches between 1930 and 2011. By 2100, sea level in Rhode Island is expected to rise another 3 to 5 feet above 1990 levels.
Credit Union of Concerned Scientists

 We also can project how much the seas will rise, because sea levels go up and down as we go in and out of ice ages. King said in the northern hemisphere, the waxing and the waning of ice sheets has been an important process for the last 2.6 million years. So it’s predictable.

There are two main sources of sea level rise. Warming temperatures cause the seawater to warm, and as it warms, it expands, taking up more space. And the second source is melting ice sheets, or land-based ice, in Greenland and West Antarctica. 

King said about 130,000 years ago, when the Co2 concentrations were at 280 parts per million, part of the Rhode Island coastline used to be at the base of the Charlestown, close to where Route 1 is today. 

“We're approaching 400 and we know that we get 20 feet of sea level rise if we exceed say 270, 280 parts per million for a long period of time. The sea level rose that 20 feet over thousands of years,” said King.

In other words, King said if humans continue to emit high concentrations of carbon dioxide, we're likely to melt the Greenland ice sheet in a matter of hundreds of years, rather than thousands. He said humans would be stuck with high sea levels for thousands of years, because the ice sheets don’t re-form as fast as they melt.

There are two other factors that directly affect our region, notes King. Both the Greenland ice sheet and the Gulf Stream, that warm and salty ocean current that moves through the Atlantic Ocean from the Caribbean, pull water away from our coasts, kind of like a magnet. Our region would likely get a couple of extra feet above the global sea level rise that’s expected, if the Greenland ice sheet melts and dilutes the Gulf Stream.

“So it's kind of a real concern since so much of our population and economic activity is located at the coast,” said King.

These historic records of climate, sea level, and greenhouse gas concentrations carry a message of urgency. In Rhode Island, the state has set ambitious emission reduction targets through the recently enacted Resilient Rhode Island Act, the state’s first comprehensive climate change bill. It’s also updating flood maps and conducting vulnerability assessments. Homeowners and businesses are moving or elevating their buildings in some cities and towns. But countries are still negotiating how to reduce their greenhouse gas emissions.

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