The five-year period from 2011 to 2015 has been the warmest five-year period on record globally, with 2015 being the warmest year on record to date.(1) The period 2011–2015 was also the warmest on record for every continent except Africa. During this period, concentrations of the major greenhouse gases continued to rise and reached record levels for the instrumental period.
The record high temperatures from 2011 to 2015, along with the annual record set in 2015, are consistent with established long-term warming trends, the dominant cause of which is the emission of anthropogenic greenhouse gases. Year-to-year temperature fluctuations occur against the backdrop of the long-term warming trend, in particular as a result of El Niño and La Niña events. High temperatures have been accompanied by the continuation of long-term trends in other indicators that are consistent with warming, such as rising sea levels and declines in Arctic sea-ice extent and in continental glaciers and ice sheets in Arctic and high-mountain regions.
The single most significant event of the period in humanitarian terms was the 2011–2012 famine in the Horn of Africa, to which drought in late 2010 and 2011 was a major contributor. More than 250 000 excess deaths in the Horn of Africa were attributed to this event by the Famine Early Warning Systems Network. On shorter timescales, no single climate-related disaster in the period 2011–2015 was associated with short-term casualties on the scale of some of the worst events of the previous decade, such as the 2003 European heatwave and Cyclone Nargis in Myanmar in 2008. However, many of the worst disasters of the period 2011–2015 still involved extreme weather and climate. Three tropical cyclones – including one implicated in the period’s worst single meteorological disaster, Typhoon Haiyan (Yolanda) – were each associated with over 1 000 deaths in the Philippines.(2)
Casualties were on a comparable scale in India and Pakistan due to flooding in 2013 and heatwaves in 2015. The South-East Asian flooding of 2011 and Hurricane Sandy in the Caribbean (especially Haiti) and the United States of America in 2012 both resulted in economic losses in excess of US$ 40 billion.(3)
Scientific assessments have found that many extreme events in the period 2011–2015, especially those involving extreme high temperatures, have had their probabilities sub- stantially increased, by a factor of 10 or more in some cases, as a result of anthropogenic climate change. More than half the events assessed scientifically manifested some degree of anthropogenic climate change signal. In addition, there have been longer-term events that have not yet been the subject of formal attribution studies but that are consistent with projections of near- and long-term climate change. These include, for example, increased incidence of multi-year drought in the subtropics, as manifested during the period in the southern United States, parts of southern Australia and, towards the end of the period, southern Africa. There also have been events, such as the unusually prolonged, intense and hot dry seasons in the Amazon basin of Brazil, in both 2014 and 2015 (especially the latter). While they cannot yet be stated with confidence to be part of a long- term trend, these are of considerable concern in the context of potential “tipping points” in the climate system as identified by the IPCC Fifth Assessment Report.
The present assessment describes the state of the key components of the climate system in the period 2011–2015.4 It focuses on events such as multi-year droughts that require a longer-term perspective than is possible in an annual report.
(1) At the time of writing, it is likely that the 2015 record high annual temperature will be exceeded in 2016.
(2) Unless otherwise stated, casualty figures in this publication are sourced from the EM-DAT Emergency Events Database maintained by the Centre for Research on the Epidemiology of Disasters at the Université catholique de Louvain, Belgium.
(3) Economic loss estimates for this event are from the World Bank for the South-East Asian flooding in 2011, and from the National Oceanic and Atmospheric Administration National Centers for Environmental Information (NOAA NCEI) for Hurricane Sandy.
(4) Some information is also included from events in late 2010 that extended into 2011, likewise 2015 events that extended into early 2016.