Climate Change 2014: Synthesis Report, Summary for Policy Makers

This Synthesis Report is based on the reports of the three Working Groups of the Intergovernmental Panel on Climate Change (IPCC), including relevant Special Reports. It provides an integrated view of climate change as the nal part of the IPCC’s Fifth Assessment Report (AR5).

This summary follows the structure of the longer report which addresses the following topics: Observed changes and their causes; Future climate change, risks and impacts; Future pathways for adaptation, mitigation and sustainable development; Adaptation and mitigation.

In the Synthesis Report, the certainty in key assessment ndings is communicated as in the Working Group Reports and Special Reports. It is based on the author teams’ evaluations of underlying scienti c understanding and is expressed as a qualitative level of con dence (from very low to very high) and, when possible, probabilistically with a quanti ed likelihood (from exceptionally unlikely to virtually certain)1. Where appropriate, ndings are also formulated as statements of fact with- out using uncertainty quali ers.

This report includes information relevant to Article 2 of the United Nations Framework Convention on Climate Change (UNFCCC).

Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. The period from 1983 to 2012 was likely the warmest 30-year period of the last 1400 years in the Northern Hemisphere, where such assessment is possible (medium con dence). The globally averaged combined land and ocean surface temperature data as calculated by a linear trend show a warming of 0.85 [0.65 to 1.06] °C 2 over the period 1880 to 2012, when multiple independently produced datasets exist (Figure SPM.1a). {1.1.1, Figure 1.1}

In addition to robust multi-decadal warming, the globally averaged surface temperature exhibits substantial decadal and interannual variability (Figure SPM.1a). Due to this natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general re ect long-term climate trends. As one example, the rate of warming over the past 15 years (1998–2012; 0.05 [–0.05 to 0.15] °C per decade), which begins with a strong El Niño, is smaller than the rate calculated since 1951 (1951–2012; 0.12 [0.08 to 0.14] °C per decade). {1.1.1, Box 1.1}

Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high con dence), with only about 1% stored in the atmosphere. On a global scale, the ocean warming is largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C per decade over the period 1971 to 2010. It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971. {1.1.2, Figure 1.2}

Averaged over the mid-latitude land areas of the Northern Hemisphere, precipitation has increased since 1901 (medium con dence before and high con dence after 1951). For other latitudes, area-averaged long-term positive or negative trends have low con dence. Observations of changes in ocean surface salinity also provide indirect evidence for changes in the global water cycle over the ocean (medium con dence). It is very likely that regions of high salinity, where evaporation dom- inates, have become more saline, while regions of low salinity, where precipitation dominates, have become fresher since the 1950s. {1.1.1, 1.1.2}

Since the beginning of the industrial era, oceanic uptake of CO2 has resulted in acidi cation of the ocean; the pH of ocean surface water has decreased by 0.1 (high con dence), corresponding to a 26% increase in acidity, measured as hydrogen ion concentration. {1.1.2}

Over the period 1992 to 2011, the Greenland and Antarctic ice sheets have been losing mass (high con dence), likely at a larger rate over 2002 to 2011. Glaciers have continued to shrink almost worldwide (high con dence). Northern Hemisphere spring snow cover has continued to decrease in extent (high con dence). There is high con dence that permafrost tempera- tures have increased in most regions since the early 1980s in response to increased surface temperature and changing snow cover. {1.1.3}

The annual mean Arctic sea-ice extent decreased over the period 1979 to 2012, with a rate that was very likely in the range 3.5 to 4.1% per decade. Arctic sea-ice extent has decreased in every season and in every successive decade since 1979, with the most rapid decrease in decadal mean extent in summer (high con dence). It is very likely that the annual mean Antarctic sea-ice extent increased in the range of 1.2 to 1.8% per decade between 1979 and 2012. However, there is high con dence that there are strong regional differences in Antarctica, with extent increasing in some regions and decreasing in others. {1.1.3, Figure 1.1}

Over the period 1901 to 2010, global mean sea level rose by 0.19 [0.17 to 0.21] m (Figure SPM.1b). The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high con dence). {1.1.4, Figure 1.1} 

Data type
Research report
Research and monitoring

Sand temperatures for nesting sea turtles in the Caribbean: Implications for hatchling sex ratios in the face of climate change

A 200-year time series of incubation temperatures and primary sex ratios for green (Chelonia mydas), hawksbill (Eretmochelys imbricata) and leatherback (Dermochelys coriacea) sea turtles nesting in St. Eustatius (North East Caribbean)was created by combining sand temperature measurementswith historical and current environmental data and climate projections. Rainfall and spring tides were important because they cooled the sand and lowered incubation temperatures. Mean annual sand temperatures are currently 31.0 °C (SD = 1.6) at the nesting beach but show seasonality, with lower temperatures (29.1–29.6 °C) during January–March and warmer temperatures (31.9–33.3 °C) in June–August. Results suggest that all three species have had female-biased hatchling production for the past decades with less than 15.5%, 36.0%, and 23.7% males produced every year for greens, hawksbills and leatherbacks respectively since the late nineteenth century. Global warming will exacerbate this female-skew. For example, projections indicate that only 2.4% of green turtle hatchlings will be males by 2030, 1.0% by 2060, and 0.4% by 2090. On the other hand, future changes to nesting phenology have the potential to mitigate the extent of feminisation. In the absence of such phenological changes, management strategies to artificially lower incubation temperatures by shading nests or relocating nest clutches to deeper depths may be the only way to prevent the localised extinction of these turtle populations. 

Data type
Scientific article
Research and monitoring
Geographic location
St. Eustatius