Climate change

Ocean temperatures chronicle the ongoing warming of Earth

To the Editor — e global ocean has absorbed 93% of the extra heat trapped by the Earth since 19701 and the rate of change in ocean heat content is a good estimate of the radiation imbalance at the top of the atmosphere2. Previously we reported3 a robust warming rate over the Earth’s area of 0.5–0.7 W m–2 during 2006–2014 using the global ocean data from the Argo array and three contrasting mapping methods: an optimal interpolation (OI), reduced space optimal interpolation (RSOI) and robust parametric t (RPF). We have extended these analyses over the additional 23 months of data from Argo to probe ocean heat content evolution through to November 2015.

Date
2016
Data type
Scientific article
Theme
Research and monitoring

A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2.

Recent research has highlighted the valuable role that coastal and marine ecosystems play in sequestering car- bon dioxide (CO2). The carbon (C) sequestered in vegetated coastal ecosystems, specifically mangrove forests, seagrass beds, and salt marshes, has been termed “blue carbon”. Although their global area is one to two orders of magnitude smaller than that of terrestrial forests, the contribution of vegetated coastal habitats per unit area to long-term C sequestration is much greater, in part because of their efficiency in trapping suspended matter and associated organic C during tidal inundation. Despite the value of mangrove forests, seagrass beds, and salt marshes in sequestering C, and the other goods and services they provide, these systems are being lost at critical rates and action is urgently needed to prevent further degradation and loss. Recognition of their C sequestration value provides a strong argument for their protection and restoration; however, it is necessary to improve scientific understanding of the underlying mechanisms that control C sequestration in these ecosys- tems. Here, we identify key areas of uncertainty and specific actions needed to address them. 

Date
2011
Data type
Scientific article
Theme
Research and monitoring
Document

Western Antarctic Peninsula physical oceanography and spatio–temporal variability

This study focuses on 12 years of physical oceanography data, collected during the Palmer, Antarctica, Long-Term Ecological Research program (PAL LTER) over the continental margin of the western Antarctic Peninsula (WAP). The dataset offers the most long-lived consistent CTD-gridded observations of Antarctic waters collected anywhere in the Southern Ocean. The physical characteristics, water column structure and spatio–temporal variability of the various properties are examined for physically consistent and ecologically important patterns and modes of variability. Unique findings of note include: (1) The average annual ocean heat flux (to the atmosphere) over the continental shelf shows a decreasing trend through time averaging 0.6 W m−2 yr−1, with an annual average ocean heat flux of ∼19 W m−2. The ocean heat content over the shelf shows a linearly increasingtrend of 2.6×107 J m−2yr−1, due predominantly to increased upwelling of warm Upper Circumpolar Deep Water (UCDW) onto the shelf with a small contribution due to a slight warming of UCDW (but over longer time scales (50 yr), the warming of UCDW dominates), (2) optimal multi-annual average vertical turbulent diffusivity coefficient (kz) is ∼8.5×10−5 m2s−1, determined by inversion considering warming of trapped remnant winter mixed layer water, (3) the water masses in the grid are well separated according to bathymetrically controlled features, dividing the sample domain into 3 sub-regions: slope, shelf and coastal waters; (4) the Antarctic Circumpolar Current (ACC) was always present along the shelf-break (consistent with the Orsi et al. [1995. On the meridional extent and fronts of the Antarctic Circumpolar Current. Deep-Sea Research I 42 (5), 641–673.] climatology) where UCDW shows its farthest southern extent and forms the Southern ACC Front (SACCF). The spatio–temporal variability of the delivery and distribution of ocean heat is dictated by the dynamics that are consistent with changes in the state of ENSO (La Niña drives enhanced upwelling in this region) and in the strength of the Southern Annular Mode (SAM; +SAM drives a local response similar to that of La Niña). The large 1997–1998 El Niño, followed by the transition to the strong La Niña of 1998–1999 (amplified by a large +SAM) introduced a regime shift on the shelf, resulting in the elimination of ∼0.5 m of sea ice melt (presumably from the loss of sea ice being grown). 2002 was an anomalous year coinciding with an extraordinary storm forcing driving a 4.5σ increase in the heat content on the shelf. These jumps coincide with considerable changes in sea ice distribution as well. Pure UCDW on the shelf is primarily restricted to the deep canyons, with occasional appearances on the shelf floor near the middle of the grid. Anomalies in summer sea surface temperatures reflect wind strength (stronger winds mixing more cold winter water to the surface, with cooler SST; light winds, the opposite).

Date
2008
Data type
Scientific article
Theme
Research and monitoring

Climate change impact on Balearic shearwater through a trophic cascade

A recent study showed that a critically endangered migratory predator species, the Balearic shear- water Puffinus mauretanicus, rapidly expanded northwards in northeast Atlantic waters after the mid-1990s. As a significant positive correlation was found between the long-term changes in the abundance of this seabird and sea temperature around the British Isles, it was hypothesized that the link between the biogeographic shift and temperature occurred through the food web. Here, we test this conjecture and reveal con- comitant changes in a regional index of sea temperature, plankton (total calanoid copepod), fish prey (anchovy and sardine) and the Balearic shearwater for the period 1980–2003. All three trophic levels exhibit a significant shift detected between 1994 and 1996. Our findings therefore support the assertion of both a direct and an indirect effect of climate change on the spatial dis- tribution of post-breeding Balearic shearwater through a trophic cascade. 

Date
2017
Data type
Scientific article
Theme
Research and monitoring
Journal

Climate change and temperature-linked hatchling mortality at a globally important sea turtle nesting site

The study of temperature-dependent sex determination (TSD) in vertebrates has attracted major scientific interest. Recently, concerns for species with TSD in a warming world have increased because imbalanced sex ratios could potentially threaten population viability. In contrast, relatively little attention has been given to the direct effects of increased temperatures on successful embryonic development. Using 6603 days of sand temperature data recorded across 6 years at a globally important loggerhead sea turtle rookery—the Cape Verde Islands—we show the effects of warming incubation temperatures on the survival of hatchlings in nests. Incorporating published data (n = 110 data points for three species across 12 sites globally), we show the generality of relationships between hatchling mortality and incubation temperature and hence the broad applicability of our findings to sea turtles in general. We use a mechanistic approach supplemented by empirical data to consider the linked effects of warming temperatures on hatchling output and on sex ratios for these species that exhibit TSD. Our results show that higher temperatures increase the natural growth rate of the population as more females are produced. As a result, we project that numbers of nests at this globally important site will increase by approximately 30% by the year 2100. However, as incubation temperatures near lethal levels, the natural growth rate of the population decreases and the long-term survival of this turtle population is threatened. Our results highlight concerns for species with TSD in a warming world and underline the need for research to extend from a focus on temperature-dependent sex determination to a focus on temperature-linked hatchling mortalities.

Date
2017
Data type
Scientific article
Theme
Research and monitoring

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} 

Date
2014
Data type
Research report
Theme
Governance
Research and monitoring
Author

Coral reefs under rapid climate change and ocean acidification

Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2°C by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse. This review presents future scenarios for coral reefs that predict increasingly serious consequences for reef-associated fisheries, tourism, coastal protection, and people. As the International Year of the Reef 2008 begins, scaled-up management intervention and decisive action on global emissions are required if the loss of coral-dominated ecosystems is to be avoided. 

Date
2007
Data type
Scientific article
Theme
Research and monitoring
Journal

One-Third of Reef-Building Corals Face Elevated Extinction Risk from Climate Change and Local Impacts

The conservation status of 845 zooxanthellate reef-building coral species was assessed by using International Union for Conservation of Nature Red List Criteria. Of the 704 species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction. Declines in abundance are associated with bleaching and diseases driven by elevated sea surface temperatures, with extinction risk further exacerbated by local-scale anthropogenic disturbances. The proportion of corals threatened with extinction has increased dramatically in recent decades and exceeds that of most terrestrial groups. The Caribbean has the largest proportion of corals in high extinction risk categories, whereas the Coral Triangle (western Pacific) has the highest proportion of species in all categories of elevated extinction risk. Our results emphasize the widespread plight of coral reefs and the urgent need to enact conservation measures. 

Date
2008
Data type
Scientific article
Theme
Research and monitoring
Journal

Long-term responses of North Atlantic calcifying plankton to climate change

The global increase in atmospheric carbon dioxide concentration is potentially threatening marine biodiversity in two ways. First, carbon dioxide and other greenhouse gases accumulating in the atmosphere are causing global warming. Second, carbon dioxide is altering sea water chemistry, making the ocean more acidic. Although temperature has a cardinal influence on all biological processes from the molecular to the ecosystem level, acidification might impair the process of calcification or exacerbate dissolution of calcifying organisms. Here, we show however that North Atlantic calcifying plankton primarily responded to climate-induced changes in temperatures during the period 1960–2009, overriding the signal from the effects of ocean acidification. We provide evidence that foraminifers, coccolithophores, both pteropod and non-pteropod molluscs and echinoderms exhibited an abrupt shift circa 1996 at a time of a substantial increase in temperature and that some taxa exhibited a poleward movement in agreement with expected biogeographical changes under sea temperature warming. Although acidification may become a serious threat to marine calcifying organisms, our results suggest that over the study period the primary driver of North Atlantic calcifying plankton was oceanic temperature.

Date
2013
Data type
Scientific article
Theme
Research and monitoring

Global analysis of the effect of local climate on the hatchling output of leatherback turtles

The most recent climate change projections show a global increase in temperatures along with precipitation changes throughout the 21st century. However, regional projections do not always match global projections and species with global distributions may exhibit varying regional susceptibility to climate change. Here we show the e ect of local climatic conditions on the hatchling output of leatherback turtles (Dermochelys coriacea) at four nesting sites encompassing the Paci c, Atlantic and Indian Oceans. We found a heterogeneous e ect of climate. Hatchling output increased with long-term precipitation in areas with dry climatic conditions (Playa Grande, Paci c Ocean and Sandy Point, Caribbean Sea), but the e ect varied in areas where precipitation was high (Pacuare, Caribbean Sea) and was not detected at the temperate site (Maputaland, Indian Ocean). High air temperature reduced hatchling output only at the area experiencing seasonal droughts (Playa Grande). Climatic projections showed a drastic increase in air temperature and a mild decreas in precipitation at all sites by 2100. The most unfavorable conditions were projected for Sandy Point where hatching success has already declined over time along with precipitation levels. The heterogeneous e ect of climate may lead to local extinctions of leatherback turtles in some areas but survival in others by 2100. 

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Document