Manmade Carbon CO₂ Pollution Has Already Put Us on Track for 20 Metres of Sea Level Rise

The bad news is that we’re all but certain to end up with a coastline at least this flooded: 20 metres or 69 feet.  The “good” news is that this might take 1000 to 2000 years (or longer/shorter), and the choices we make now can affect the rate of rise and whether we blow past 69 feet to beyond 200 feet.

This information should not be a surprise to anyone who follows the scientific literature.  Just last year the National Science Foundation (NSF) reported on paleoclimate research that examined rock and soil cores taken in Virginia, New Zealand and the Eniwetok Atoll in the north Pacific Ocean.

Lead author Kenneth Miller of Rutgers University said: “The natural state of the Earth with present carbon dioxide levels is one with sea levels about 70 feet higher than now.”

 

What the Past tells us about Modern Sea-Level Rise

During ice-age cycles, continental ice volume kept pace with slow, multi-millennial scale, changes in climate forcing.  Today, rapid greenhouse gas (GHG) increases have outpaced ice-volume responses, likely committing us to > 9 m of long-term sea-level rise (SLR).  Scientists portray a context of naturally precedented SLR from geological evidence, for comparison with historical observations and future projections.  This context supports SLR of up to 0.9 (1.8) m by 2100 and 2.7 (5.0) m by 2200, relative to 2000, at 68% (95%) probability.

Historical SLR observations and glaciological assessments track the upper 68% limit.  Hence, modern change is rapid by past interglacial standards but within the range of ‘normal’ processes.  The upper 95% limit offers a useful low probability / high risk value.  Exceedance would require conditions without natural interglacial precedents, such as catastrophic ice-sheet collapse, or activation of major East Antarctic mass loss at sustained CO₂ levels above 1000 ppmv.

A geological perspective on potential future sea-level rise.

This graph shows the relative amount of sea-level rise compared to the rise in atmospheric carbon dioxide (CO₂).

The symbols represent reconstructions with uncertainties for different intervals of the past 40 million years.  The black line and orange envelopes represent a probabilistic assessment that takes into account the full propagation of all uncertainties (black line is the probability maximum; dark orange is the 68% probability interval; light orange is the 95% probability interval).  The relationship averages over orbital configurations.

Hence, at any given CO₂ concentration, periods with ‘warmer/colder than average’ orbital configurations for the northern hemisphere may have had higher/lower sea level, respectively (e.g., Last interglacial sea level reached 8-9 m above Holocene values, although CO₂ concentrations were similar).

What Can We Do?

All in all, that was only slightly less worrisome than a 2009 paper in Science that found the last time CO₂ levels were this high – and sustained at those levels – the global temperatures were ~3°C to 6°C warmer and sea level 25 to 40 meters higher than present.

Glaciologist Jason Box makes this point in a Climate Desk interview with Chris Mooney: “Humans Have Already Set in Motion 69 Feet of Sea Level Rise.”  So what can we do?  For Jason Box, any bit of policy helps: “The more we can cool climate, the slower Greenland’s loss will be.  Cutting greenhouse gases slows the planet’s heating, and with it, the pace of ice sheet losses.”

 

Climate Experts Warn of Sea Peril in Latest Report

According to United Nations scientific experts’ compelling report presented at IPCC 2013, global warming will hoist sea levels higher than was previously projected six years ago, threatening millions of lives.  In a report touching on a high-stakes, contentious issue, the Intergovernmental Panel on Climate Change (IPCC) predicts sea levels to rise by between 26 and 81 centimetres (10.4 and 32.4 inches) by 2100, according to a draft seen by AFP.  These estimates outstrip projections made by the Nobel Peace Prize-winning group in 2007 of a 18-59 cm rise by 2100.

If we were truly doubly wise, “homo sapiens sapiens” as we called ourselves, the nation would join with the rest of the World in a World War II-scale effort to actually reduce the atmospheric CO₂ level from its current 394 parts per million.

Not only would that lower the ultimate sea level rise, but it would slow down the current rate of change…