But — not all parts of it are heating up at the same rate. Temperature in the Arctic in particular is rising faster than the global average. The Arctic, according to NASA data, warmed by about 2.2 °C (4 °F) between 1900 and 2015.

Their estimate of Arctic heating is considerably bigger than NASA's. It indicates that between 1900 and 2015, Arctic temperature has risen about 2.9 °C (5.3 °F).

Sea ice volume is a measurement of ice extent and its thickness. Understanding how fast the ice is being depleted by volume is crucial to working out how quickly we are approaching an ice-free Arctic summertime because thinner ice can be more vulnerable to future melting. As one expert noted, “there comes a point when large parts of the ice pack become so thin that it doesn't matter what the weather does…the train keeps chugging along, even when the weather isn't so great for melt”. NOAA has said that the Arctic “has reached a new state…characterised by less sea ice (both extent and thickness),” adding that “the decline in total sea ice extent has been accompanied by an unprecedented loss of old, thick multiyear ice.” Or, as one commentator noted, Arctic sea ice loss is now “being driven by human emissions".Click here for the source

The extremity of the last couple of months might be even more visible in a plot of monthly average sea ice anomaly (the difference between the month's value, and what's “typical” for that month of the year)

Although more Arctic sea ice survived this year [2014] than in the record-shattering melt of 2012, in 2014 the ice was nevertheless at its 6th-lowest level in thousands of years. About 70% of the sea ice in the Arctic has disappeared over the past three decades, mainly due to human-caused global warming. This rapid decline is well outside “the normal range” of Arctic sea ice extent and volume.

More heat generally means less ice. This is rather obvious in the Arctic lately, as 6 out of 10 months so far this year have set new record lows for the extent of sea ice (2016 values shown in red)

Permafrost temperatures are increasing over Alaska and much of the Arctic. Regions of discontinuous permafrost in interior Alaska (where annual average soil temperatures are already close to 32°F) are highly vulnerable to thaw. Thawing permafrost releases carbon dioxide and methane – heat-trapping gases that contribute to even more warming. Recent estimates suggest that the potential release of carbon from permafrost soils could add as much as 0.4ºF to 0.6ºF of warming by 2100.150 Methane emissions have been detected from Alaskan lakes underlain by permafrost, 151 and measurements suggest potentially even greater releases from thawing methane hydrates in the Arctic continental shelf of the East Siberian Sea.152 However, the response times of Arctic methane hydrates to climate change are quite long relative to methane’s lifetime in the atmosphere (about a decade).153 More generally, the importance of Arctic methane sources relative to other methane sources, such as wetlands in warmer climates, is largely unknown. The potential for a self-reinforcing feedback between permafrost thawing and additional warming contributes additional uncertainty to the high end of the range of future warming. The projections of future climate shown throughout this report do not include the additional increase in temperature associated with this thawing.

Figure 2.29. Model simulations of Arctic sea ice extent for September (1900-2100) based on observed concentrations of heat-trapping gases and particles (through 2005) and four scenarios. Colored lines for RCP scenarios are model averages (CMIP5) and lighter shades of the line colors denote ranges among models for each scenario. Dotted gray line and gray shading denotes average and range of the historical simulations through 2005. The thick black line shows observed data for 1953-2012. These newer model (CMIP5) simulations project more rapid sea ice loss compared to the previous generation of models (CMIP3) under similar forcing scenarios, although the simulated September ice losses under all scenarios still lag the observed loss of the past decade. Extrapolation of the present observed trend suggests an essentially ice-free Arctic in summer before mid-century.139 The Arctic is considered essentially ice-free when the areal extent of ice is less than one million square kilometers. (Figure source: adapted from Stroeve et al. 2012136).

Sea ice extent is affected by winds and ocean currents as well as temperature. Sea ice in the partly-enclosed Arctic Ocean seems to be responding directly to warming, while changes in winds and in the ocean seem to be dominating the patterns of climate and sea ice change in the ocean around Antarctica.