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.

Is the permafrost's integrity breaking down?

The chart below shows very high methane levels over Antarctica in April and May 2013. High levels of methane over Antarctica were recorded before in 2013, as described in an earlier post at the methane-hydrates blog.

Meanwhile, a methane reading of 2475 ppb was recorded on April 26, 2013, appearing to originate from the Himalayan Plateau, as illustrated by the image below.

Recurring high readings could indicate that methane is bubbling up through the permafrost, both in Antarctica and on the Himalayan Plateau.

Loss of the integrity of the permafrost is particularly threatening in the Arctic, where the sea ice looks set to disappear within years, resulting in huge albedo changes in summer. Decrease of surface reflectivity results in increases in absorption of energy from sunlight and decreases in shortwave radiation in the atmosphere. The latter results in lower photo-dissociation rates of tropospheric gases. Photo-dissociation of the ozone molecule is the major process that leads to the production of OH (hydroxyl radical), the main oxidizing (i.e., cleansing) gas species in the troposphere. A 2009 NASA study projects this to lead to a decrease in OH concentrations and a weakening of the oxidizing capacity of the Arctic troposphere, further increasing the vulnerability of the Arctic to warming in case of additional methane releases.

Levels of greenhouse gases such as carbon dioxide and methane are already very high in the Arctic atmosphere, while large quantities of black carbon get deposited on snow and ice, further contributing to the albedo changes. This threatens to result in rapid summer warming of many parts of the Arctic Ocean with very shallow waters. Additionally, rivers can bring increasingly warm water into those shallow seas in summer, adding to the threat that heat will penetrate the seabed that contains huge quantities of methane.



Above image, earlier included in an animation at the Arctic-news blog, shows methane concentrations on January 23, 2013, when a reading of 2241 ppb was recorded in the Arctic.

Analysis of sediment cores collected in 2009 from under ice-covered Lake El'gygytgyn in the northeast Russian Arctic suggest that, last time the level of carbon dioxide in the atmosphere was about as high as it is today (roughly 3.5 to 2 million years ago), regional precipitation was three times higher and summer temperatures were about 15 to 16 degrees Celsius (59 to 61 degrees Fahrenheit), or about 8 degrees Celsius (14.4 degrees Fahrenheit) warmer than today.

As temperatures rose back in history, it is likely that a lot of methane will have vented from hydrates in the Arctic, yet without causing runaway warming. Why not? The rise in temperature then is likely to have taken place slowly over many years. While on occasion this may have caused large abrupt releases of methane, the additional methane from such releases could each time be broken down within decades, also because global methane levels in the atmosphere were much lower than today.

In conclusion, the situation today is much more threatening, particularly in the East Siberian Arctic Shelf (ESAS), as further described in the earlier post methane hydrates.

Above post is an extract of the full post at the methane-hydrates blog. 

1250 - New group calls for action on methane

A new group, named 1250, calls for governments around the world to take action on methane.

Just like 350 parts per million has become a popular target for carbon dioxide, the group similarly advocates a target for methane, aiming for a reduction of methane to 1250 parts per billion (ppb).

On several occasions in April, 2013, the hourly average carbon dioxide concentration in the atmosphere of Mouna Loa, Hawaii, surpassed 400 parts per million (ppm). On May 9, 2013, the daily mean concentration of carbon dioxide in the atmosphere of Mauna Loa also surpassed 400 ppm. The National Oceanic and Atmospheric Administration (NOAA) comments that before the Industrial Revolution in the 19th century, global average carbon dioxide was about 280 ppm. During the last 800,000 years, carbon dioxide fluctuated between about 180 ppm during ice ages and 280 ppm during interglacial warm periods. Today’s rate of increase is more than 100 times faster than the increase that occurred when the last ice age ended.

On May 9, 2013, at another place on Earth, another significant event took place. Methane levels above Antarctica reached a peak of 2249 ppb, highlighting the need for action on methane.

The group 1250 advocates a similar target for methane, i.e. a reduction of methane to 1250 parts per billion.

“Methane is far more potent than carbon dioxide as a greenhouse gas, making it important to reduce levels of methane in the atmosphere,” explains founder Nathan Currier; “1250 is not just an advocacy group for methane cuts, however. Rather, it is a group focusing on near-term climate as a whole, and on practical pathways to constructing a ‘climate bridge’ towards a stable and sustainable future.”

The launch of the group is accompanied by the release of the chart below showing the very high methane levels that have been recorded over Antarctica recently. The chart was prepared by Sam Carana, who also is a founding member of 1250.

These very high methane emissions occur on the heights of East Antarctica. Antarctica is covered in a thick layer of ice. It appears that these very high emissions are caused by methane from hydrates that is escaping in the form of free gas bubbling up through the ice sheet.

The danger is that such emissions will escalate, not only over Antarctica, but also on the Qinghai-Tibet Plateau and in the Arctic. For more on this, see the methane-hydrates blog.

The group 1250 was set up specifically to address to need for a comprehensive approach to the challenges posed by climate change. The group now invites other groups to a dialogue regarding the details.

The group has a website at http://1250now.org/ and encourages people to join its mailing list and sign its petition.