State of the climate in 2011: Special supplement to the Bulletin of the American Meteorological Society

Large-scale climate patterns influenced temperature
and weather patterns around the globe in 2011. In particular,
a moderate-to-strong La Niña at the beginning of the
year dissipated during boreal spring but reemerged during
fall. The phenomenon contributed to historical droughts
in East Africa, the southern United States, and northern
Mexico, as well the wettest two-year period (2010–11)
on record for Australia, particularly remarkable as this
follows a decade-long dry period. Precipitation patterns
in South America were also influenced by La Niña. Heavy
rain in Rio de Janeiro in January triggered the country’s
worst floods and landslides in Brazil’s history.
The 2011 combined average temperature across global
land and ocean surfaces was the coolest since 2008, but
was also among the 15 warmest years on record and
above the 1981–2010 average. The global sea surface
temperature cooled by 0.1°C from 2010 to 2011, associated
with cooling influences of La Niña. Global integrals
of upper ocean heat content for 2011 were higher than
for all prior years, demonstrating the Earth’s dominant
role of the oceans in the Earth’s energy budget. In the
upper atmosphere, tropical stratospheric temperatures
were anomalously warm, while polar temperatures
were anomalously cold. This led to large springtime
stratospheric ozone reductions in polar latitudes in both
hemispheres. Ozone concentrations in the Arctic stratosphere
during March were the lowest for that period since
satellite records began in 1979. An extensive, deep, and
persistent ozone hole over the Antarctic in September
indicates that the recovery to pre-1980 conditions is
proceeding very slowly.