Friday, 5 February 2016

Rapid acceleration in sea level rise

Rapid Acceleration in Sea Level Rise — From 2009 Through October 2015, Global Oceans Have Risen by 5 Millimeters Per Year


The evidence that a human-forced warming of the globe is hitting a much higher gear in terms of both added heat and ramping impacts just keeps streaming on in. Today, an update in the satellite monitor tracking global sea level rise provides yet one more ominous marker. The world’s oceans are rising at an unprecedented rate not seen since the end of the last Ice Age. A rate that appears to be rapidly accelerating.
(Surface melt visible across the Zachariae Isstrom Glacier in Greenland on July 20th of 2015. Melt like that occurring on this glacier has become more and more widespread over Antarctica and Greenland. It’s an ongoing heat accumulation in the world’s great ice mountains that is contributing to increasing melt water outflows into the rising world ocean system. Image source: LANCE MODIS.)

It’s a tough bit of evidence that the world is swiftly accumulating heat. For aside from atmospheric temperature readings, the rate of sea level rise is probably the best marker for how fast the world is warming. It’s a sign of heat build-up that’s thermally expanding the ocean. And, far more ominously,it’s a sign that the great glaciers of the world are starting to accumulate enough heat to go into a more and more widespread melt and destabilization.

Ocean Rise Begins with Ramp-up in CO2 Emissions

Ever since the Holocene climate era began about 10,000 years ago, ocean levels and shorelines have remained remarkably stable. At the close of the 19th Century, and in conjunction with a build-up of heat-trapping gasses in the atmosphere through the extraction and burning of fossil fuels, sea levels began a rise that would start to mark a departure from the stable coastlines human civilizations had enjoyed for so long.

(Global sea level rise has ramped higher and higher — an upward curve that follows increasing volumes of CO2 in the atmosphere and rising global temperatures. Image source: Dr. James Hansen.)

At first the rise in global waters, driven by a then slow accumulation of heat in the world ocean system, was slight and gradual. Beginning in 1870, and continuing on through 1925, sea levels across the world increased by about 0.8 millimeters per year. The increase was likely driven by heat accumulating in the atmosphere and then transferring to the surface waters of the oceans. From 1870 through 1925, atmospheric carbon dioxide levels had increased from around 280 parts per million to 305 parts per million — into a range about 25 parts per million above the typical interglacial peak CO2 level of the last 2 million years. A volume of heat trapping gasses that began to slowly upset the Holocene’s relative stability.
If scientists and researchers at the time were paying closer attention, they would have noted this mild but consistent increase in the height of global surface waters as the first hint that the human emission of greenhouse gasses was starting to alter the Earth environment. Sadly, it took many more decades to begin to understand the profound changes that were starting to take place.
The First Acceleration — 1925 to 1992

While climate science was still in its infancy during 1925, a human forced warming of the globe was starting to kick into higher gear. A signal of atmospheric warming since the 1880s was beginning to develop. Though unclear, it was becoming apparent that the airs of the world were building up heat. But the waters of the world were providing a strong signal that the Earth was accumulating that heat more and more rapidly.
Sea level rise, at that time driven by thermal expansion and by a later small but growing contribution from glacial melt, took its first leap higher. And from 1925 through 1992, the average rate of sea level rise more than doubled to 1.9 millimeters per year. It was a sign that the Earth was warming more and more rapidly and that the heat was showing up in still more thermal expansion of the world’s waters.
(Globally, CO2 began to increase in the atmosphere starting with the widespread burning of coal in England during the 17th and 18th Century. As new fossil fuels like natural gas and oil were added to the mix and as fossil fuel based burning greatly expanded during the 19th, 20th, and 21st Centuries, concentrations of this key greenhouse gas sky-rocketed. By the decade of the 2010s, the rate of atmospheric greenhouse gas accumulation was about 6 times faster than at any time in the geological record. A human emission that, if it continues for just a blink in geological timescales, is the equivalent to multiple clathrate guns firing off at the same time. Image source: The Keeling Curve.)

During the same period, atmospheric greenhouse gasses increased from 305 parts per million in 1925 to around 350 parts per million by 1992. This jump by 45 parts per million in just 67 years pushed the Earth’s climate well outside the range of past interglacials — exceeding the previous peak of 280 parts per million CO2 by more than 70 parts per million overall. Atmospheric temperatures, by 1992, had also increased into a range about 0.5 C above 1880s values.
We had started to enter a period where the context of the human-driven warming (primarily enforced by a monopolization of energy markets by fossil fuels) was being pushed far outside the range of the Holocene and into time periods tens of thousands to hundreds of thousands of years in the geological past. The Earth System, in other words, was entering a period of increasingly dangerous imbalance.
The Second Acceleration 1992 to 2009

During the 17 years from 1992 through 2009, atmospheric carbon dioxide levels rose by 40 parts per million to about 390 parts per million in total. That’s a rate of accumulation nearly four times faster than the entire period from 1925 through 1992. An accumulation that by 2009 had pushed the world into a climate context more similar to the Pliocene of 3 million years ago, than of the geological epoch in which human civilization emerged and thrived. For the Holocene was then starting to look like some fond memory fading off into an increasingly murky and smoke-filled far horizon.
Rates of sea level rise again increased — hitting a ramp up to around 3 millimeters per year. More ominously, scientific studies were beginning to indicate that the Greenland Ice Sheet and West Antarctica were starting to significantly contribute to the rising waters. The great glaciers were showing their first signs of a mass seaward movement called a Heinrich Event. And with the world hitting 0.8 degrees Celsius above 1880s temperature values and rising, such an event was starting to look more and more likely.

Sea Level Rise at 5 Millimeters Per Year Since 2009

Now, by early 2016, with the world at 1.1 C warmer than 1880s averages and with CO2 levels likely to peak at around 407 parts per million this year, it appears that rates of sea level rise have again jumped markedly higher. For according to satellite altimetry data from AVISO, global sea levels rose by 36 millimeters from the end of 2009 through October of 2015. That’s an annual rate of around 5 millimeters per year and one far above the longer term range of 3.1 mm per year established from 1992 through 2012.

(Global sea level rise as measured by satellite altimetry hits a noticeably higher ramp from 2009 through late 2015. Image source: AVISO.)

We can clearly see the departure from the trend line starting post 2011 in the above graph. And if we were to cherry pick that particular departure zone, the rate from trough-to-peak would be 7 millimeters per year. However, since a La Nina occurred during 2011-2012 and a record strong El Nino is occurring now, that particular trend line is probably a bit exaggerated. The reason being that La Nina tends to dampen rates of sea level rise through variable cooling and El Nino tends to spike rates of sea level rise as world surface waters warm during such events.
However, even when correcting for La Nina and El Nino variation, it appears that sea level rise since 2009 is tracking in a range of 4 to 5 millimeters each year — which is yet another significant departure from the trend. A rate that, if it were to further solidify, would be 5 to 6 times faster than initial rates of sea level rise at the start of the 20th Century or two and a half times faster than the sea level rise rates from 1925 through 1992.
Open water and no snow in south Greenland on February 2, 2016
(Open water and no snow in Southern Greenland on February 2 of 2016. Zero sea ice and no snow in southern Greenland during Winter is a strong sign that the island is falling deeper and deeper into the grips of a severe warming event. Image source: Greenland Today.)

Spiking rates of heat accumulation and related thermal expansion of the world’s oceans is likely playing a part in the current increase. But, all-too-likely, the numerous destabilized glaciers now rushing seaward — which in total contain at least enough water to raise seas by 15-20 feet — are also starting to add greater and great contributions. And, unfortunately, with global temperatures now pushing into a very dangerous range between 1 and 2 degrees Celsius above 1880s averages, we are likely to see more and more of these glaciers go into a rapid seaward plunge. It looks like we’ve already locked in a ramping rate of sea level rise for decades to come and at least 15-20 feet long term. But that pales in comparison to what happens if we keep burning fossil fuels.
Hat Tip to Catherine Simpson

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