Maps showing areas where melting took place on the 10-11th April. Graph shows standard deviation - percentage of total area where melting occurred. Source: DMI, 2016

Depending on the doubling time, the amount of time it would take for ice loss from the ice sheets to double, say if it's as short as 10 or 20 years like Hansen has proposed we could come to see several meters of sea level rise already by 2050. Perhaps its not likely but its possible. 

Climate change can give rise to abrupt and unexpected outcomes in the Earth system. Last week, a new article in Nature Scientific Reports claimed that a collapse of the Atlantic Meridional Overturning Circulation (AMOC) could lead to a rapid cooling in the Northern Hemisphere, and that this cooling in turn could obliterate global warming for a period of 15-20 years. Only to revert to a warming pattern some 40 years later.

According to professor Sybren Drijfhout, his model showed that “The planet earth recovers from the AMOC collapse in about 40 years when global warming continues at present-day rates, but near the eastern boundary of the North Atlantic (including the British Isles) it takes more than a century before temperature is back to normal”.

What is so scary about this study is that the effect of atmospheric cooling due to an AMOC collapse is associated with heat flow from the atmosphere into the oceans, which has actually occurred during the last 15 years. A well known fact to many scientists but somewhat unclear to the public which has been bombarded with climate deniers "warming hiatus" nonsense.

According to Drijfhout, when there is a net cooling effect heat flows from the oceans to the atmosphere but when there is net warming effect then this energy flow is reversed. In other words, the world’s oceans have acted as giant heat sinks, counteracting the greenhouse effect in regards to atmospheric temperatures, for the last decade. But this period is now over, according to Drijfhout. The oceans are again releasing heat, amongst others due to shifting ocean and wind patterns and a strong El Niño.

Permafrost is soil at or below the freezing point of water 0 °C that stays frozen for two or more years. Permafrost comprises 24% of the land surface in the Northern Hemisphere and can be found at Arctic ocean shelves and floor. It contains large quantities of trapped greenhouse gases such as methane and carbon dioxide, and is usually regarded as a carbon sink. Researchers have become increasingly worried that with climate change large permafrost areas could start to thaw and ultimately melt, releasing massive amounts of carbon that would exacerbate global warming. 

A small team of scientists working in Greenland have now found evidence that as microbes become active in permafrost, they produce heat, which can increase the rate of permafrost melt. In their paper published in Nature Climate Change, Hollesen et al. (2015) describes computer simulations that showed possible impacts of microbe activation in permafrost areas. Previous attempts at predictions for permafrost melt through modeling are now looking like they will have to be revised. 

Suspecting that microbes in the soil might have an impact on warming permafrost, Hollesen et al. collected 21 samples of permafrost soil from six locations across Greenland. They then exposed the samples to different temperatures in a laboratory. By monitoring the heat production from microbes they were able to gather enough information to create a computer simulation. That simulation revealed that as global temperatures rise, a feedback loop occurs in permafrost areas. Heat causes melting which stimulates the microbes that start decomposing organic material, and producing heat, which adds to the increased temperatures, on and on until the permafrost melts, releasing massive amounts of carbon into the atmosphere far earlier than previous models have predicted. 

One immediate consequence of thawing permafrost in Greenland is the potential for destruction of unexcavated archeological findings. The National Museums of Denmark and Greenland have now started several projects where decomposing wooden artifacts and bones from the first people on Greenland will help identify areas most threatened. This is mainly happening because the average temperature has risen by 2-3°C in Greenland. Thawing of protective permafrost leads to archaeological material rotting because the amount of oxygen rises and the decomposition process accelerate. Other concerns are related to coastal erosion, resettlement and infrastructure damage.

More long-term consequences of permafrost thaw is of course increasing greenhouse gas concentration in the atmosphere, and in turn a warmer climate. Previous estimates have pointed to 120 ± 85 Gigatonne of carbon emissions from thawing permafrost by 2100, which could increase global temperatures by 0.29 ± 0.21 °C. However, we now know that permafrost starts to thaw much earlier than expected, so we need to start including this knowledge into climate models or we risk overshooting the 2°C warming limit. For example, the most recent knowledge on permafrost/carbon feedbacks are not included into IPCC climate projections.

According to the US National Oceanic and Atmospheric Administration (NOAA) the first ten months of 2014 (January-October) were the warmest such period since record keeping began in 1880. Global land and ocean average surface temperature reached 0.68 °C above the 20th century average of 14.1°C. Making 2014 on track to become the warmest year on record. Record warmth for the year so far has been particularly notable across much of northern and western Europe, parts of far east Russia, and large areas of the northeastern and western equatorial Pacific Ocean.

Source: NOAA, 2014

Sweden was warmer than average during October, with the southern half of the country experiencing temperatures 2-4°C above their October averages (SMHI). On October 28, the daily temperature in Stockholm was 14.2°C, the highest daily average observed so late in the year since records began in 1756. 

Looking at historical records  of Land and Ocean surface mean temperature anomalies we can see that the northern hemisphere is warming much faster, with some of the most rapid warming rates on Earth located in the Arctic, where sea and land ice is shrinking and thinning.

Source: NOAA, 2014

Changes in albedo (i.e. reflectivity) difference between the Arctic and Antarctic and global ocean currents contribute to the Northern Hemisphere’s rapid warming, according to researchers from Potsdam Institute for Climate Impact (Feulner et al. 2013). Currents transport heat away from southern waters and into the North Atlantic and North Pacific, helping to warm nearby land areas in the north even more. For example, the Gulf Stream, which carries heat from the tropics far into the North Atlantic, along the Scandinavian west coast (see map).

Source: Tellus

Melting Arctic = More Extreme Weather?

Temperatures in the Arctic have risen twice as fast as the rest of the world, a phenomenon known as Arctic amplification (Cohen et al. 2014). Scientists have linked the rapid rise in Arctic temperatures over the past two decades to weather extremes in the Northern Hemisphere such as heatwaves in the US and flooding in Europe (Coumou et al. 2014, Francis 2014). Rapid warming in the Arctic can have triggered changes to global wind patterns, which have brought extreme weather to lower latitudes. Extreme weather events have almost doubled over the last two decades. Now researchers think that this can be linked with unusual weather patterns in the upper atmosphere, influenced by warmer Arctic temperatures. They believe that the loss of sea ice in the Arctic may be contributing to the appearance of wide north-south swings in the high-altitude winds flowing globally west to east around the polar region, causing them to “get stuck” and amplified in a quasi-stationary pattern known as a “standing wave”. When interviewed by the Independent one of the researchers, Stefan Rahmstorf, said “Evidence for actual changes in planetary wave activity was so far not clear. But by knowing what patterns to look for, we have now found strong evidence for an increase in these resonance events” (Professor of Physics and co-chair of Earth System Analysis at Potsdam University). The possibility of a link between Arctic change and mid-latitude weather has spurred research activities that reveal three potential dynamical pathways: changes in storm tracks, the jet stream, and planetary waves and their associated energy propagation (Cohen et al. 2014).

A study from Berkeley has projected that if emissions remain on their present upward trajectory, the average temperature difference between the two hemispheres could be about 1.6°C. This would be sufficient to alter tropical rainfall patterns, which could affect everything from rice cultivation in India to the health of the Amazonas Rainforest (Friedman et al. 2013). According to the authors, tropical rain bands that form near the equator where trade winds collide to build up thunderstorms may shift northward, drying out parts of the Southern Hemisphere, while causing more precipitation in the North.