The latest accumulated wisdom, from our best and most dedicated,
shows continued Arctic warming at about twice the rate of the overall global rate of warming.
FOURTH NATIONAL CLIMATE ASSESSMENT Volume II: Impacts, Risks, and Adaptation in the United States: https://nca2018.globalchange.gov
“The rate at which Alaska’s temperature has been warming is twice as fast as the global average since the middle of the 20th century. Statewide average temperatures for 2014–2016 were notably warmer as compared to the last few decades, with 2016 being the warmest on record. Daily record high temperatures in the contiguous United States are now occurring twice as often as record low temperatures. In Alaska, starting in the 1990s, high temperature records occurred three times as often as record lows,
and in 2015, an astounding nine times as frequently.
” –Ch.26 (Alaska: Climate)
“Changes in ocean chemistry and increased corrosiveness are exacerbated by sea ice melt, respiration of organic matter, upwelling, and glacial runoff and riverine inputs, thus making the high-latitude North Pacific and the western Arctic Ocean (and especially the continental shelves of the Bering, Chukchi, and Beaufort Seas) particularly vulnerable to the effects of ocean acidification.
More recent research suggests that corrosive conditions have been expanding deeper into the Arctic Basin over the last several decades.”
“Aragonite saturation is a metric used to assess ocean acidification and the ability for organisms to build shells and skeletons. The annual average saturation state for the Beaufort Sea surface waters likely crossed the saturation horizon
—a tipping point—around 2001, meaning it is currently undersaturated and its marine ecosystems are vulnerable to the impacts of ocean acidification during most of the year. The Chukchi Sea is projected to first cross this threshold around 2030 and then likely remain under the threshold after the early 2040s; the Bering Sea is projected to be a concern after 2065. Source: adapted from Mathis et al. 2015.” –Ch.26 (Alaska: Ocean Acidification)
“Younger, thinner sea ice is more susceptible to melt, therefore Climate Science Special Report
, Fourth National Climate Assessment (NCA4), Volume I [the science]
“The world’s oceans have absorbed about 93% of the excess heat caused by greenhouse gas warming since the mid-20th century, making them warmer and altering global and regional climate feedbacks.” “Ocean heat content has increased at all depths since the 1960s and surface waters have warmed by about 1.3° ± 0.1°F (0.7° ± 0.08°C) per century globally since 1900 to 2016.”
“Accelerated melting of multiyear sea ice cover, mass loss from the Greenland Ice Sheet, reduced snow cover, and permafrost thawing are stark examples of the rapid changes occurring in the Arctic.”"Arctic Ocean acidification is occurring at a faster rate than the rest of the globe (see also Ch. 13: Ocean Changes).” “Global-scale modeling studies suggest that the largest and most rapid changes in pH will continue along Alaska’s coast, indicating that ocean acidification may increase enough by the 2030s to significantly influence coastal ecosystems."
"Arctic Sea Ice Loss Since the early 1980s, annual average arctic sea ice has decreased in extent between 3.5% and 4.1% per decade, has become thinner by between 4.3 and 7.5 feet, and is melting at least 15 more days each year. September sea ice extent has decreased between 10.7% and 15.9% per decade. (Very high confidence)"
reductions in age and thickness imply a larger interannual variability of extent.”
“September sea ice extent and age is shown for (top) 1984 and (middle) 2016, illustrating significant reductions in sea ice extent and age (thickness). The bar graph in the lower right of each panel illustrates the sea ice area (unit: million km2) covered within each age category (> 1 year), and the green bars represent the maximum extent for each age range during the record. The year 1984 is representative of September sea ice characteristics during the 1980s. The years 1984 and 2016 are selected as endpoints in the time series; a movie of the complete time series is available at http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4489.”
"Arctic sea ice loss is expected to continue through the 21st century, very likely
resulting in nearly sea ice-free late summers by the 2040s. (Very high confidence) --11.2.1"