Antarctica linked to Arctic

Waters in the Arctic Ocean continue to warm up. Very warm waters from the North Atlantic and Pacific Ocean are invading the Arctic Ocean.

Waters in the North Atlantic and in the North Pacific are very warm, due to a number of reasons.

What is happening in the oceans is very important in this respect. As discussed in earlier posts, most of the extra heat caused by people's emissions goes into the oceans.

The great ocean conveyor belt (Thermohaline Circulation), brings warm water from the southern hemisphere to the northern hemisphere.

The Gulf Stream is the North Atlantic leg of the great ocean conveyor belt, and it brings dense, salty water from the North Atlantic into the Arctic Ocean.

Saltier water is denser than fresher water because the dissolved salts fill interstices between water molecules, resulting in more mass per unit volume.

Very dense ocean water can be found in the North Atlantic because the North Atlantic has high salinity, due to high evaporation rates, while salty water is also coming from the Mediterranean Sea.

As also discussed in an earlier post, this dense, saltier water sinks in the North Atlantic, accumulating in deeper water.

By contrast, much of the Arctic Ocean has low salinity, due to ice melt and river runoff.  As it enters the Arctic Ocean, the warm and dense water from the Atlantic thus dives under the under the sea ice and under the less salty surface water in the Arctic Ocean.

In conclusion, much of the heat resulting from people's emissions accumulates in the North Atlantic and also ends up in the Arctic. This partly explains why surface temperatures are rising much faster at the poles, as illustrated by the NOAA image below.

There are further reasons why surface air temperatures elsewhere (other than at the poles) are rising less rapidly than they did, say, a decade ago. As also discussed by Andrew Glikson in the post No Planet B, the increased amounts of sulphur emitted by the growing number of coal-fired power plants and by the burning of bunker fuel on sea is (temporarily) masking the full wrath of global warming.

Another reason is the growth of the sea ice around Antarctica, as illustrated by the CryosphereToday image on the left.

Melting takes place both in the Arctic and on Antarctica, but more so in the Arctic. Recent research of CryoSat-2 data reveals that Greenland alone is now losing about 375 cubic kilometers of ice annually, while in Antarctica the annual volume loss now is about 125 cubic kilometers.

Currents also distribute ocean heat in ways that make the Arctic warm up more than twice as rapidly as the Antarctic. In a recent paper, John Marshall et al. further suggest that ozone depletion also contributes to this.

All this makes that, while the jet streams on the northern hemisphere are circumnavigating the globe at a slower pace, jet streams on the southern hemisphere are getting stronger, making it more difficult for warm air to enter the atmosphere over Antarctica, while the stronger winds also speed up sea currents on the southern hemisphere. This makes the sea ice around Antarctica grow, and as the sea ice spreads further away from Antarctica, temperatures of surface waters around Antarctica are falling.

Growth of the sea ice around Antarctica makes that more sunlight is reflected back into space. There now is some 1.5 million square kilometers more sea ice around Antarctica than there used to be. The albedo change associated with sea ice growth on the southern hemisphere can be estimated at 1.7 W/sq m, i.e. more than the total RF of all CO2 emission caused by people from 1750 to 2011 (IPCC AR5).

The rapid growth of sea ice on the southern hemisphere alone goes a long way to explain why, over the past three months, surface air temperatures have not been much higher than they used to be, both globally and in the Arctic, as illustrated by above NOAA image. What has also contributed to warmer temperatures around latitude 60 on the northern hemisphere is the fact that methane has accumulated in the atmosphere at that latitude, as discussed in earlier posts.

Arctic SST far exceed anything ever seen in human history

So, does the sea ice on the southern hemisphere constitute a negative feedback that could hold back global warming? It doesn't.

It may temporarily keep surface temperatures close to what they used to be, as the sea ice reflects lots of sunlight back into space, but at the same time ocean temperatures are rising strongly, as the sea ice also prevents heat from radiating out of the waters around Antarctica.

The latter also helps explaining the colder surface temperatures over those waters.

Much of this additional ocean heat has meanwhile been transported by the great ocean conveyor belt to the northern hemisphere.

No time before in human history has such a huge amount of ocean heat accumulated in the North Atlantic and the North Pacific. This heat is now threatening to invade the Arctic Ocean and trigger huge temperature rises due to methane eruptions from the seafloor.

The situation is dire and calls for comprehensive and effective action, as dicussed at the Climate Plan blog.

UK MET Office keeps downplaying significance of events in the Arctic

One of the most respected datasets on Arctic sea ice volume is produced by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS, Zhang and Rothrock, 2003) developed at the Polar Science Center, Applied Physics Laboratory, University of Washington. The graph below shows PIOMAS data for annual minimum Arctic sea ice volume (black dots) with an exponential trend added (in red).

The Arctic Methane Emergency Group (AMEG), in a February 12, 2012, written submission to the U.K.  Environmental Audit Committee (EAC), pointed at the graph:

. . summer volume [is] less than 30% of its value 20 years ago. The trend in volume is such that if one extrapolates the observed rate forward in time, by following an exponential trend line, one obtains a September near-disappearance of the ice by 2015.

The MET Office, in a March 8, 2012, written submission:

Climate models project the Arctic will become ice-free during summer at some point this century – though likely not before 2040. . . In September 2007, sea ice extent reached an all-time low, raising the question of whether the sea ice is likely to melt more quickly than has been projected. There is, however, no evidence to support claims that this represents an exponential acceleration in the decline. Indeed, modelling evidence suggests that Arctic sea ice loss would be broadly reversible if the underlying warming were reversed.

Professor Slingo, Chief Scientist, MET Office, elaborated on this in a March 14, 2012, oral submission:

Q114 Chair: . . when the Arctic will be ice free in summer. . . Professor Slingo: . . Our own model would say between 2040 and 2060 . . Q115 Chair: You would rule out an icefree summer by as early as 2015, for example? Professor Slingo: Yes we would . . . Q117 Chair: . . In terms of the modelling that you are using, does that cover . . . volume of ice? Professor Slingo: We run quite a sophisticated sea ice model. . . and we are looking forward now to the new measurements from CryoSat-2. Q118 Chair: . . evidence that we had suggested that the volume of ice had already declined by 75%, and that further decreases may cause an immediate collapse of ice cover. Professor Slingo: I wouldn’t [give credence to that]. We don’t know what the thickness of ice is across the whole Arctic with any confidence. . . I probably would [rule it out altogether] . . . to say we have lost 75% of the volume is inconsistent with our assessments.

Professor Laxon, director of Centre for Polar Observation and Modelling, where CryoSat-2 data is being analysed, in an August 24, 2012, written submission:

. . [analysis of] CryoSat-2 and ICESat data . . suggest a decrease in ice volume over the period 2003–12 at least as large as that simulated by PIOMAS, and possibly higher.

The Met Office, in an August 31, 2012, supplementary written submission:

The changes in observed sea-ice volume only extends [sic] over a few years and cannot in isolation be interpreted as representative of a long term trend. . . . The extrapolation of short-term trends in ice volume is not a reliable way to predict when the Arctic will be seasonally ice free as negative feedbacks and changing weather patterns may slow the rate of ice loss. . . it is worth noting that climate models can show a period of recovery in ice volume following periods of large ice volume loss.

For some curious reason, some people seek to downplay the significance of the events taking place in the Arctic, as well as the risk of methane releases. Here's more on that.

AMEG added, in its above February 12, 2012 written submission:

The catastrophic risk of global warming leading to very large emissions of methane from large Arctic carbon pools, especially from subsea methane hydrate, is documented in the 2007 IPCC assessment. By collaborating with others to protect the Arctic, a climate of cooperation can be engendered to protect the whole planet for the benefit of ourselves and future generations.

Professor Lenton, in a Feb 21, 2012, oral submission:

. . the Hadley Centre [has] permafrost in the latest state-of-the-art model . . . their best estimate is we may get 0.1°C of extra warming at the end of the century from the loss of methane from the northern high latitudes.

Professor Slingo, in the above March 14, 2012, oral submission:

Q126 Dr Whitehead:. . what sort of modelling factors may be accounted for by the possibility of tipping points or feedback attached to these? For example, the argument that follows very substantially from the extent of continental shelf that there is within the Arctic Basin and, therefore, the particular relationship that warming on that relatively shallow sea has on trapped methane-for example, the emergence of methane plumes in that continental shelf, apparently in quite an anomalous way-leading possibly to the idea that there may be either tipping points there or catastrophic feedback mechanisms there, which could then have other effects on things, such as more stabilised caps like the Greenland ice cap and so on. I rapidly collated all the possible catastrophe theories, but I mean how are those factored into the modelling process? Professor Slingo: . . we are not looking at catastrophic releases of methane. . . We don’t see catastrophic change in the Arctic that would lead to catastrophic releases of methane, or very large changes in the thermohaline circulation, within the next century. Our understanding of the various feedbacks-and it is a very complex system-both through observations and modelling, suggests that we won’t see those catastrophic changes, in terms of the physical system.

Note that the above are excerpts, to make things easier to read. For the full text, click on the respective links.

Below an update of the image, produced earlier this month, with recent volume data for 2012 added. On September 2, 2012, PIOMAS recorded a volume of 3407 cubic km of ice, i.e. very close to what the exponential line projected. The volume is likely to continue to fall further before reaching its final 2012 minimum.

The image below shows Arctic sea ice extent (total area of at least 15% ice concentration) for the last 7 years, compared to the average 1972-2011, as calculated by the Polar View team at the University of Bremen, Germany.

CryoSat

The image below shows how much the older, thicker sea ice has declined over the years. This decline doesn't become apparent when focusing on sea ice extent; volume measurements are needed to reveal this decline.

Old versus new ice in Arctic: The maps show the median age of sea ice in March 1985 (left) and March 2011 (right).
Overall, the proportion of old ice has decreased. By March 2011, ice over 4 years old accounts for less than
10% of the Arctic ice cover. Credit: National Snow and Ice Data Center, University of Colorado, Boulder.

The screenshot below shows GHRSST volume measurements from National Centre for Ocean Forecasting website.

The European Space Agency's CryoSat promises to deliver an even clearer picture. One of the scientists analyzing the CryoSat data, Dr Seymour Laxon, said in April 2012 that CryoSat's volume estimate is very similar to that of PIOMAS, the model developed at the Polar Science Center at the University of Washington.

In a recent interview, Dr Laxon said that if the current trend continues, the Arctic could be ice-free at the height of summer by the end of the decade.

John Nissen, Chair of the Arctic Methane Emergency Group (AMEG), comments: "Dr Laxon failed to mention the data on sea ice thickness that has been collected over many years by sea ice expert Professor Peter Wadhams of the University of Cambridge, who now considers that the Arctic Ocean will be seasonally free of sea ice most probably by September 2016. PIOMAS sea ice volume data suggest that a collapse in sea ice area could occur even sooner, as discussed on the AMEG blog posting."