Those under the impression that climate change is advancing at a constant and predictable rate don’t understand the true dynamics of the issue. The rate of increase of the carbon dioxide concentration in the atmosphere, the main driver of climate change, went from 0.75 parts per million (ppm) per year in 1959 to about 1.5 ppm each year through the 1990s, to 2.1 ppm each year from 2002 to 2012, and finally to 2.9 ppm in 2013.
The fear is that the ability of the oceans and plants to continue to absorb half the carbon dioxide human civilization expels into the atmosphere each year may have become impaired. That means more carbon dioxide is remaining in the atmosphere where concentrations are building at the fastest rate ever recorded in the modern era.
Permafrost across the most northern reaches of land on the globe wasn’t expected to start melting until well into this century. Scientists were shocked to find gaping craters in Siberia where permafrost apparently is no longer permanent. It means carbon dioxide and methane–which absorbs about 80 times as much heat as carbon dioxide during its first 20 years in the atmosphere–will be unleashed from the melting permafrost much sooner than anticipated after being trapped for thousands of years. The release has the potential to speed up warming considerably.
Now comes what must be labeled as the most important story of the year that shows us yet more nonlinear dynamics in the world climate system. New research from James Hansen, the world’s most renown climate scientist, and 16 of his colleagues concludes that many of the world’s coastal cities could become "uninhabitable" in just 50 years due to a rapid, nonlinear rise in sea level. This is far sooner than previous findings suggested.
The new research takes into account paleoclimatological data and recent observations and modeling of ice cap and glacial melt. The research shows that rapid sea level rise has occurred in the past and is likely to happen this century because human-caused emissions are changing climate much more quickly and profoundly than during even previous periods of rapid sea level rise. The researchers state in several places that their methods may actually underestimate the speed of sea level rise.
To be fair, much depends on the assumed rate of ice melt. The researchers give a range of 50 to 200 years before water covers much of what are now the coastal cities of the world. Even 200 years is still astonishingly fast for 10 feet of sea level rise to occur. But, we should not dismiss the low estimate of 50 years. The history of climate change shows that we’ve underestimated its pace and severity at every turn.
In 1896 Svante Arrhenius, a Swedish chemist, was the first person to realize that human-created fossil fuel emissions might change the climate. He calculated that it would take 2,000 years to double the concentration of carbon dioxide in the atmosphere. The latest calculations suggest a doubling by 2050, only 154 years after Arrhenius’ realization. The Hansen research also reminds us that the pace of warming is increasing: "[T]wo-thirds of the 0.9 degrees C global warming (since 1850) has occurred since 1975."
The researchers concluded that continuing with business-as-usual would mean 700 ppm of carbon dioxide in the atmosphere by 2100 compared to 400 ppm now and about 280 ppm in 1850. That would over time result in a sea level rise of 5 to 9 meters (16 to 30 feet).* In characteristic scientific understatement they write:
It is unlikely that coastal cities or low-lying areas such as Bangladesh, European lowlands, and large portions of the United States eastern coast and northeast China plains could be protected against such large sea level rise.
The current idea that limiting the worldwide average temperature increase to 2 degrees C will prevent a rise in sea level of "several meters" is mistaken:
We conclude that the 2 degrees C global warming "guardrail", affirmed in the Copenhagen Accord (2009), does not provide safety, as such warming would likely yield sea level rise of several meters along with numerous other severely disruptive consequences for human society and ecosystems.
If Hansen’s new research is correct and possibly an underestimate as he believes, New York, London, Shanghai and myriad other low-lying coastal cities won’t just have water lapping uncomfortably against their edges in 50 years. Large portions of these cities will have long since been abandoned or moved higher as water’s edge creeps ever upward.
*If you want to get a sense of what all this means, Takepart created a set of hypothetical "before" and "after" photos of major American cities based on 25 feet of sea level rise or about 7.5 meters–which is near the middle of the range of predicted ultimate sea level rise for the business-as-usual scenario mentioned above. Climate Central did an analysis last year of how a 10-foot rise in sea level would affect American coastal communities.
Photo: The Great Mississippi Flood of 1927, U.S. Route 51 between Mounds, Illinois, and Cairo, Illinois. Via Wikimedia Commons.