Expect Warming Oceans and Rising Sea Levels
Part II in Our Series on Sea Level Rise
Our planet is entering an environmental twilight zone, where the ultimate effects of global warming are entirely unpredictable and almost certainly irreversible over human lifetimes, given “business as usual” scenarios (Hansen et al., 2008).
“Tipping points” mark the threshold of a new set of environmental parameters that are self-sustaining, leading to a unique climate condition unlike any previously experienced by humanity. Some scientists think the disappearance of sea ice across the Northwest Passage in Canada, fully navigable for the first time on record in Summer 2007, might offer a good example of such a tipping point (see also Funder et al., 2011). In this scenario, open ocean water absorbs more heat compared to high albedo of sea ice, storing more heat in water and inhibiting the formation of sea ice during subsequent years. Not only does the loss of sea ice threaten the extinction of polar bears, a progressively warming Arctic region would melt permafrost, releasing a vast reserve of methane, rapidly amplifying levels of atmospheric greenhouse gasses.
This warming condition could also lead to melting of all of Greenland’s ice, equivalent to a 5-6 m higher sea level, flooding the surface of the North Atlantic Ocean with fresh water, thereby disrupting the circulation of shallow and deeper ocean currents. This interference with thermohaline circulation could curtail or shut down global heat transfer between the Tropics and high latitudes. Such a possible “climate run amuck” scenario involves a long list of other serious implications for humanity.
A Delicate Balance
The delicate balance between CO2, ice volume and global sea level could be easily thrown off kilter by manmade greenhouse warming. The vast majority of climatologists, glaciologists, modelers and sea-level specialists, believe the main culprit is ever-increasing concentrations of atmospheric gasses including carbon dioxide (CO2), along with water vapor (H2O), methane (CH4) nitrous oxide (N2O) and chlorofluorocarbons (CFCs). These so called “greenhouse” gasses (GHG), like the glass covering a greenhouse, trap the sun’s sensible heat within the Earth’s atmosphere, rather than allowing it to escape into space. The more GHGs in the atmosphere, the warmer the planet becomes.
Increasing CO2 in the atmosphere, the biosphere, and the oceans cause physical and chemical changes in each. The ocean and the land each absorb about 25 percent of the atmospheric CO2 through physiochemical and biological processes; the latter primarily by photosynthesis, converting CO2 to organic carbon compounds. The increased CO2 and resulting ocean acidification of the oceans creates an enormous threat to carbonate-shelled marine organisms and coral reefs.
CO2 is derived from many natural and manmade sources, but historically increasing levels of CO2 are primarily due to the burning of fossil fuels, unleashing vast reservoirs of fossil carbon stored in the Earth for hundreds of millions of years. The amount of CO2 in the atmosphere has increased from about 280 ppm since 1750 AD at the beginning of the Industrial Revolution to its current 393.65 ppm in February 2012. The rate of increase in CO2 levels from 1.3 to 1.9 ppm/yr over the past four decades, along with the record 2.36 ppm/yr increase during 2010 (Peters et al., 2011) highlights the “business as usual” attitude of developed nations. It is now documented that the CO2 emissions from the top two users in 2010, the US and China, amounted to 1.5 billion tons/yr (5 tons per capita/yr), and 2.3 billion tons/yr (1.7 tons per person/yr), respectively.
Historical and Glaciological Record of CO2
The levels of greenhouse gasses and historical sea-level changes have been measured for decades by a variety of sophisticated techniques. The greater than 110 ppm increase over the past 250 years has been largely attributed to increasing combustion of plant material and fossil fuels by humans. From a geological perspective, gas bubbles in cores of Antarctic ice reveal that a natural 110 ppm shift is about the equivalent as that between a full glacial (about 180 ppm) and full interglacial (about 290 ppm) cycle (Figure 3 same graph as in Part I) over a period of about 100,000 years! The micro-samples of ancient atmosphere compressed in fossil ice also reveal that our industrial age CO2 levels approaching 400 ppm have not been equaled over at least the past 800,000 years. The maximum level of CO2in nature during this period was ~300 ppm was at 400,000 years ago during a warm interglacial called marine isotope stage (MIS) 11. See the chart above.
The atmospheric CO2 value of 400 ppm is an inauspicious and ominous benchmark that humanity will exceed in the next few years. 400 ppm was typical of the Pliocene atmosphere some 3 million years ago. In that ancient 400 ppm world, sea level is estimated to have been 10 to 40 m higher than it is now (e.g., Dowsett and Cronin, 1999). Although these sea-level estimates are highly variable, they point to dynamic changes in the volume of polar ice sheets under a global climate 2-3°C warmer than present.
The Antarctic ice core data also show that past glacial and interglacial sea-level and climate cycles parallel CO2 levels (Figure 3), along with an intricate mixed bag of feedback leads and lags. We can expect these essential variables to operate in tandem into the future – where CO2 goes, warming climate and sea level will follow.
Sea-level Changes and the Intergovernmental Panel on Climate Change (IPCC)
Given the apparent bad behavior of ice sheets in the past, can we be confident of the accuracy of the predictions of sea level rise by IPCC (2007)? Current estimates of a 0.5 to 1.5 m rise by 2100 are based largely on the thermal expansion of seawater as the ocean surface heats up. However, the possibility of a significant contribution from melting of ice sheets in Greenland and East and West Antarctic is not currently an important factor in IPCC predictions. We know from geological studies along the world’s coastlines that past slightly warmer (1-2°C) or longer than present (> 10,000-30,000 yrs) interglacial periods 125,000 and 400,000 years ago are associated with sea levels several meters higher than present (stay tuned for Part III “The Rock Record of Sea Level Changes”). These higher sea levels are almost certainly tied to melting or collapse of either or both the Greenland and West Antarctic ice sheets. Thus, a similar response of these ice sheets in future global warming scenarios of similar magnitude cannot be ruled out (see Joughin and Alley, 2011).
In a nutshell, the extreme atmospheric and oceanic fluctuations over the past two centuries are unrivaled over at least 3 million years, long before the rise of industrial Homo sapiens. Only in the last 200 years have machines and factories accelerated the pumping of CO2 and other greenhouse gasses into the atmosphere. Even the most skeptical skeptic or climate denier in denial cannot claim that a 110 ppm increase in CO2 in two centuries, exceeding any known rate or level reached in nature over the past 3 million years, is part of a “natural cycle” of climate change. But given the current global attitude of business as usual, it appears that we may have a ‘world of change’ in store for us for decades and centuries to come.
Paul J. Hearty, Ph.D.
Ecology Global Network, Earth Science Advisor
Funder, S., and 11 authors. A 10,000-Year Record of Arctic Ocean Sea-Ice Variability—View from the Beach. Science, v. 333, no. 6043, p. 747-750. DOI: 10.1126/science.1202760.
Hansen, J., M. Sato, P. Kharecha, D. Beerling, R. Berner, V. Masson-Delmotte, M. Pagani, M. Raymo, D.L. Royer, and J.C. Zachos, 2008: Target atmospheric CO2: where should humanity aim? Open Atmos. Sci. J., 2, 217-231.
Hearty, P.J., 2011. Global Warming and Rising Ocean Waters. The Bahamas Handbook, 2011, Etienne Dupuch Jr Publications Ltd., Nassau, Bahamas.
Hearty, P.J., and Kaufman, D.S., 2000. Whole-Rock Aminostratigraphy and Quaternary Sea-Level History of the Bahamas Quaternary Research, 54, 163-173.
IPCC, 2007. Intergovernmental Panel on Climate Change, fourth assessment report, available at: http://www.ipcc.ch/ipccreports/ar4-syr.htm.
Joughin, I., and Alley, R.B., 2011. Stability of the West Antarctic ice sheet in a warming world. Nature Geoscience 4, 506–513, doi:10.1038/ngeo1194.
Olson, S.L., and Hearty, P.J., 2009. A sustained +21 m highstand during MIS 11 (400 ka): direct fossil and sedimentary evidence from Bermuda. Quaternary Science Reviews 28, 271-285.
Peters, G.P., Marland, G., Le Quéré, C., Boden, T., Canadell, J.G., Raupach, M.R., 2011. Rapid growth in CO2 emissions after the 2008-2009 global financial crisis. Nature Climate Change, doi. 10.1038/nclimate1332. (http://dx.doi.org/10.1038/nclimate1332).
Petit, J.R., et al. 1999. Climate and Atmospheric History of the Past 420,000 years from the Vostok Ice Core, Antarctica, Nature, 399, p.429-436.
- Sea-level rise
- Global warming
- Temperature records
- Carbon dioxide
- Oceans and climate change
- Climate skeptics
- Acidification of ocean