|Abstract or Summary
- For the first time in several years, the El Niño-Southern
Oscillation did not dominate regional climate conditions
around the globe. A weak La Niña dissipated to ENSOneutral
conditions by spring, and while El Niño appeared
to be emerging during summer, this phase never fully
developed as sea surface temperatures in the eastern equatorial Pacific uncharacteristically returned to neutral
conditions. Nevertheless, other large-scale climate patterns
and extreme weather events impacted various regions
during the year. A negative phase of the Arctic Oscillation
from mid-January to early February contributed to frigid
conditions in parts of northern Africa, eastern Europe, and
western Asia. A lack of rain during the 2012 wet season
led to the worst drought in at least the past three decades
for northeastern Brazil. Central North America also
experienced one of its most severe droughts on record.
The Caribbean observed a very wet dry season and it was
the Sahel's wettest rainy season in 50 years.
Overall, the 2012 average temperature across global
land and ocean surfaces ranked among the 10 warmest
years on record. The global land surface temperature alone
was also among the 10 warmest on record. In the upper
atmosphere, the average stratospheric temperature was
record or near-record cold, depending on the dataset.
After a 30-year warming trend from 1970 to 1999 for
global sea surface temperatures, the period 2000-12 had
little further trend. This may be linked to the prevalence
of La Niña-like conditions during the 21st century. Heat
content in the upper 700 m of the ocean remained near
record high levels in 2012. Net increases from 2011 to
2012 were observed at 700-m to 2000-m depth and even
in the abyssal ocean below. Following sharp decreases in
global sea level in the first half of 2011 that were linked to the effects of La Niña, sea levels rebounded to reach
records highs in 2012. The increased hydrological cycle
seen in recent years continued, with more evaporation
in drier locations and more precipitation in rainy areas.
In a pattern that has held since 2004, salty areas of the
ocean surfaces and subsurfaces were anomalously salty on
average, while fresher areas were anomalously fresh.
Global tropical cyclone activity during 2012 was near
average, with a total of 84 storms compared with the
1981-2010 average of 89. Similar to 2010 and 2011,
the North Atlantic was the only hurricane basin that
experienced above-normal activity. In this basin, Sandy
brought devastation to Cuba and parts of the eastern
North American seaboard. All other basins experienced
either near- or below-normal tropical cyclone activity. Only
three tropical cyclones reached Category 5 intensity-all in
the Western North Pacific basin. Of these, Super Typhoon
Bopha became the only storm in the historical record to
produce winds greater than 130 kt south of 7°N. It was
also the costliest storm to affect the Philippines and killed
more than 1000 residents.
Minimum Arctic sea ice extent in September and
Northern Hemisphere snow cover extent in June both
reached new record lows. June snow cover extent is
now declining at a faster rate (-17.6% per decade) than
September sea ice extent (-13.0% per decade). Permafrost
temperatures reached record high values in northernmost
Alaska. A new melt extent record occurred on 11-12 July
on the Greenland ice sheet; 97% of the ice sheet showed
some form of melt, four times greater than the average
melt for this time of year.
The climate in Antarctica was relatively stable overall.
The largest maximum sea ice extent since records
began in 1978 was observed in September 2012. In the
stratosphere, warm air led to the second smallest ozone
hole in the past two decades. Even so, the springtime
ozone layer above Antarctica likely will not return to its
early 1980s state until about 2060.
Following a slight decline associated with the global
Financial crisis, global CO2 emissions from fossil fuel
combustion and cement production reached a record 9.5
± 0.5 Pg C in 2011 and a new record of 9.7 ± 0.5 Pg C
is estimated for 2012. Atmospheric CO2 concentrations
increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012,
for the first time, the atmospheric CO2 concentration
exceeded 400 ppm at 7 of the 13 Arctic observation sites.
Globally, other greenhouse gases including methane and
nitrous oxide also continued to rise in concentration and
the combined effect now represents a 32% increase in
radiative forcing over a 1990 baseline. Concentrations of
most ozone depleting substances continued to fall.
- Blunden, J., & Arndt, D. S. (2013). State of the Climate in 2012. Bulletin of the American Meteorological Society, 94(8), S1-S238. doi:10.1175/2013BAMSStateoftheClimate.1
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