Download Antarctic Climate Change Report Card

IP 81
Agenda Item:
CEP 7a
Presented by:
ASOC
Original:
English
Submitted:
25/04/2016
Antarctic Climate Change Report Card
1
IP 81
Antarctic Climate Change Report Card
Submitted by ASOC1
Summary
Overview of
research focus
In Sum
Changes from Last Year
Temperature
Observations and
models
Antarctica is warming,
particularly on the Antarctic
Peninsula
Consistent
Ice Sheets and
Glaciers
Paleoclimatic
studies,
observations,
models
A major improvement in ice
sheet modelling suggests a
potential 1m SLR by 2100
Improved research: major
climate impact
Sea Ice
Observations and
models
Antarctic sea ice is increasing
Consistent: research continues
Ocean
Acidification
Observations and
models
Onset of widespread ocean
acidification will be abrupt
Consistent, with indications OA
is already underway
Blue Carbon
Observations
Impact of benthic species as a
carbon sink is significant but
relatively understudied
Improved understanding of role
of benthos in carbon
immobilization
Impacts on
Antarctic
Species
Observations
Changing sea ice conditions
could have direct impacts on
benthic species as well as
seabirds
Consistent, with documentation
of impact of extreme climate
events on Antarctic species
Introduction
For the fourth year, ASOC presents its Climate Change Report Card, a summary of notable scientific
breakthroughs and climate events related to anthropogenic climate change in the Antarctic. We track
scientific publications and science reporting to bring up-to-date findings to the ATCM and provide policy
advice connecting Antarctic climate science to Antarctic environmental management decisions.
Temperature
The Antarctic continent overall has been warming since the late 1950s, though some areas, especially in the
Antarctic Peninsula, are warming rapidly, others, such as the interior are warming at a much lower rate or
cooling.2
1
Lead authors Jessica O’Reilly and Claire Christian.
Steig, E. J., Schneider, D. P., Rutherford, S. D., Mann, M. E., Comiso, J. C., & Shindell, D. T. (2009). Warming of the
Antarctic ice-sheet surface since the 1957 International Geophysical Year. Nature, 457(7228), 459-462.
2
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Antarctic warming is consider through two primary sources: global atmospheric warming and in relation to
the warming of the Southern Ocean. For the planet as a whole, temperatures are warming and this warming
is “extremely likely” to be caused by anthropogenic activities.3 In an update of the Goddard Institute for
Space Studies (GISS) global temperature analysis, the data suggest that 2015 was the warmest year recorded,
showing a global surface temperature 0.87°C warmer than 1951-1980, the base period for this analysis.4 Part
of this increase may be attributed to the strong El Nino last year.5
Antarctic warming is likely to be anthropogenic, though expert assessors express low confidence in this, due
to the more scattered temperature measurement instruments over Antarctica compared to the rest of the
planet.6 Further research on detection, attribution, and the long term persistence of Antarctic surface
temperatures continues to example the significance and uncertainties surrounding Antarctic temperature
records.7
In models, a warming Southern Ocean can explain up to 2°C of continental warming through heat exchange
between the ocean and atmosphere.8 Pedro et al.’s findings suggest a 50-year lag between ocean warming
and continental temperature response. These open ocean deep convection events are rare in the contemporary
Southern Ocean, so this study proposes further paleoclimatic research, which indicates that such convection
processes may have been more common in the past.9
In sum: On a planetary scale, 2015 was the warmest year since instrumental measurements began. The
Earth is warming due to anthropogenic forcings: the same is happening in the Antarctic, with less
confidence. Research continues around the significance of Antarctic warming data due to patchy
instrumentation. The role of the Southern Ocean is considered as influencing continental warming.
Changes from last year: consistent.
Ice Sheets And Glaciers
Research on the Antarctic Ice Sheets is dynamic, with regular new findings and discoveries. The West
Antarctic Ice Sheet (WAIS), as a marine-grounded ice sheet, is inherently unstable. The East Antarctic Ice
Sheet (EAIS) is grounded on the continent and is generally considered stable. The Antarctic Ice Sheets,
combined, are losing mass, this loss is accelerating, and the resulting increase in global sea level is
significant to much of society.10
DeConto and Pollard published findings based on their improved model. Modeling ice sheets, especially
instabilities caused by a marine grounding line, has been challenging, though innovations are continuous. A
major success of DeConto and Pollard’s model is that it is able to adequately reproduce paleoclimatic ice
behavior of the ice sheets from the Last Interglacial (130,000-115,000 years ago) and the Pliocene epoch
(approximately 3 million years ago).11 Inability to reproduce past glacial events was a major limitation in
verifying older ice sheet models, so this model marks a significant step forward in modeling ice sheets, and
therefore, projecting future sea level change.
3
Intergovernmental Panel on Climate Change (IPCC). 2014. Climate Change 2014: Synthesis Report. Contribution of
Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Core
Writing Team, R.K. Pachauri and L.A. Meyer, eds. Geneva, Switzerland: IPCC.
4
Hansen, J., Sato, M., Ruedy, R., Schmidt, G. A., & Lo, K. (2016). Global Temperature in 2015.
5
Hansen et al., 2016.
6
IPCC 2014.
7
Ludescher, J., Bunde, A., Franzke, C. L., & Schellnhuber, H. J. (2015). Long-term persistence enhances uncertainty
about anthropogenic warming of Antarctica. Climate Dynamics, 1-9.
8
Pedro, J. B., Martin, T., Steig, E. J., Jochum, M., Park, W., & Rasmussen, S. O. (2016). Southern Ocean deep
convection as a driver of Antarctic warming events. Geophysical Research Letters, 43(5), 2192-2199.
9
Pedro et al. 2016.
10
IPCC 2014.
11
DeConto, R. M., & Pollard, D. (2016). Contribution of Antarctica to past and future sea-level rise. Nature, 531(7596),
591-597.
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DeConto and Pollard state that, “Antarctica has the potential to contribute more than a metre of sea-level rise
by 2100 and more than 15 metres by 2500, if emissions continue unabated.”12 They also note that,
“atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will
delay its recovery by thousands of years.”13 While these results suggest that Antarctic ice loss is not
inevitable, it is important to note that ice loss is fundamentally irreversible on a human timescale.
A collapse of WAIS, according to models by Steig et al., could influence surface climate for the rest of the
continent. These simulations suggest that areas of the EAIS adjacent to WAIS would warm, while the coastal
portions of Marie Bryd Land would warm.14
In paleoclimate research on the ancient Antarctic Ice Sheet, Galeotti et al. found that the stable Antarctic Ice
Sheet formed about 32.8 million years ago, when atmospheric carbon dioxide concentration levels fell below
600 ppm.15 This suggests a threshold for the contemporary continental Antarctic Ice Sheet, with marine
portions of the Antarctic Ice Sheet vulnerable at lower carbon dioxide levels.16
In sum: An improved model suggests an unstable Antarctic Ice Sheet that could significantly
contribute to global sea levels by the end of this century and beyond, with recovery taking thousands
of years due to a lag in ocean warming.
Changes from last year: new research that underscores need for prompt abatement of carbon emissions.
Sea Ice
Sea ice in Antarctica is increasing and has been doing so for several decades. Indeed there are increasing sea
ice accumulations annually as well as during all Antarctic seasons.17 Given what we know about Antarctic
surface temperature increase and changes in the ice sheets, there are several lines of inquiry to follow in the
case of Antarctic sea ice.
First, models suggest a decrease in Antarctic sea ice extent (SIE), which does not conform to observed
changes.18 This most plausible explanation to this is that the physics in the models is incorrect: Simmonds
suggests that polar sea ice physics in models is based upon Arctic sea ice behavior, which the models
adequately capture.19
Second, and related to physics in models, is the relationship between changes in atmospheric circulation,
wind patterns, and atmospheric chemistry and the patterning and accumulation of sea ice.20,21 Simmonds
notes that, in contrast to the Arctic, “the high southern latitudes SLPs [sea level pressures] have exhibited
strong and significant changes in the 35 years considered here [1979-2013].”22
12
DeConto and Pollard 2016, page 591.
Ibid.
14
Steig, E. J., Huybers, K., Singh, H. A., Steiger, N. J., Ding, Q., Frierson, D. M., ... & White, J. W. (2015). Influence
of West Antarctic Ice Sheet collapse on Antarctic surface climate. Geophysical Research Letters, 42(12), 4862-4868.
15
Galeotti, S., DeConto, R., Naish, T., Stocchi, P., Florindo, F., Pagani, M., ... & Sandroni, S. (2016). Antarctic Ice
Sheet variability across the Eocene-Oligocene boundary climate transition. Science, 352(6281), 76-80.
16
Ibid.
17
Simmonds, I. (2015). Comparing and contrasting the behaviour of Arctic and Antarctic sea ice over the 35 year
period 1979–2013. Annals of Glaciology, 56(69), 18-28.
18
Simmonds 2015.
19
Ibid.
20
Gagné, M. È., Gillett, N. P., & Fyfe, J. C. (2015). Observed and simulated changes in Antarctic sea ice extent over the
past 50 years. Geophysical Research Letters, 42(1), 90-95.
21
Kohyama, T., & Hartmann, D. L. (2016). Antarctic Sea Ice Response to Weather and Climate Modes of Variability.
Journal of Climate, 29(2), 721-741.
22
Simmonds 2015, brackets added.
13
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Third, investigators are studying the relationship between freshening of the sea near the continent as the ice
sheets melt, which could lead to positive accumulation of sea ice.23
Finally, some experts suggest that the increase in Antarctic SIE is due simply to internal variability. Gagne et
al. used data from the Nimbus Data Rescue Project at the National Snow and Ice Data Center (NSIDC) to
extend analysis of sea ice extent beyond the continuous satellite observations that began in 1979. Their data
stretches to 1960 to test their hypothesis: “if the observed increase in SIE were largely driven by greenhouse
gas increase or stratospheric ozone depletion, then a positive trend before 1979 would also be expected,
whereas if it were largely driven by internal variability, then a negative trend prior to 1979 would be more
likely.”24 Their results showed a negative trend between before 1979, suggesting that while there is
inconsistency of SIE in the recent short term, a longer time period of analysis provides more consistency
with the CMIP5 ensemble mean.25
In sum: Sea ice in Antarctica is increasing. Research continues to investigate improving models and
factors contributing to this, including atmospheric circulation, the contribution of fresh water from
melting ice, and internal variability.
Changes from last year: similar, research continues.
Ocean Acidification
Ocean acidification is expected to impact large swaths of the Southern Ocean within the next few decades.
The overall impact of this phenomenon on ecosystems remains unknown. Despite growing worldwide
concerns about what OA means for ocean life, however, the amount of biological research on OA effects
remains low according to a recent analysis, with only 12 papers out of 539 focusing on the Southern Ocean.26
The polar regions are expected to experience widespread acidification sooner than other parts of the world.27
Furthermore, as much as 98% of the pelagic region is predicted to be undersaturated in aragonite until 2100
if emissions continue at their current rate.28 Researchers have recently predicted that occurrences of
undersaturation will be “abrupt”, starting in 2030, and will last for six months by 2050.29 With this in mind,
the relative lack of information on SO acidification is troubling. Although their data have not yet been
published, researchers studying shell-forming pteropods in the Southern Ocean reported that they have
collected numerous specimens with evidence of shell dissolution.30 This suggests that OA may already be
having impacts on organisms that could impact the entire food web.
In sum: Research is clear that widespread ocean acidification will affect broad swaths of the Southern
Ocean in the next two decades. Preliminary results suggest ocean acidification is already having an
effect on the Southern Ocean, but there is not enough research occurring to understand the full
ecosystem impacts of these changes.
Changes from last year: Similar, with preliminary findings indicating OA is already having a demonstrable
impact on some species.
23
Bintanja, R., Van Oldenborgh, G. J., Drijfhout, S. S., Wouters, B., & Katsman, C. A. (2013). Important role for ocean
warming and increased ice-shelf melt in Antarctic sea-ice expansion. Nature Geoscience, 6(5), 376-379.
24
Gagné et al. 2015, page 91.
25
Ibid, page 94.
26
Y. Yang, L. Hansson, and J.-P. Gattuso. (2015). Data Compilation on the Biological Response to Ocean
Acidification: An Update. Earth System Science Data Discussions 8(2): 889–912, doi:10.5194/essdd-8-889-2015.
27
J.C. Orr et al. (2005). Anthropogenic Ocean Acidification over the Twenty-First Century and Its Impact on Calcifying
Organisms. Nature 437 (7059): 681–6, doi:10.1038/nature04095.
28
J. Gutt et al. (2015). The Southern Ocean Ecosystem under Multiple Climate Change Stresses - an Integrated
Circumpolar Assessment. Global Change Biology 21(4): 1434–1453, doi:10.1111/gcb.12794.
29
C. Hauri, T. Friedrich, and A. Timmermann (2015). Abrupt Onset and Prolongation of Aragonite Undersaturation
Events in the Southern Ocean. Nature Climate Change 6(2): 172–176, doi:10.1038/nclimate2844.
30
“The Antarctic Sun: News about Antarctica - The Dissolving Sentinels of the Southern Ocean (cont.),” accessed April
5, 2016, http://antarcticsun.usap.gov/science/contentHandler.cfm?id=4209.
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Impacts on Antarctic species
Changing ice conditions in the Antarctic have regional and local implications as well as global ones, with
many species sensitive to even small shifts in environmental conditions. Increased sea ice cover in the
Antarctic is often identified by climate change skeptics as a positive sign that global warming, but this
ignores the massive implications that such shifts could have for the ecosystem. For example, a dramatic
increase in sea ice cover in the Dumont D’Urville Sea region of East Antarctica during January and February
2014 has been linked to equally dramatic breeding failures for several local bird species, with Adélie
(Pygoscelis adeliae) and Wilson’s storm petrel (Oceanites oceanicus) producing no viable offspring that
season.31 The researchers note that predicted decreases in sea ice towards the end of the century will also
have a negative impact on many Antarctic species.32
Sea ice extent is not the only consideration, however. Fast ice in the West Antarctic Peninsula has been
disappearing earlier over the past 30 years, and this may put coastal benthic ecosystems at risk, since the
absence of ice will change environmental conditions, increasing light, water turbulence, and iceberg scouring
events.33 The invertebrates that make up these relatively rare but diverse ecosystems will be at significant
risk.34
The decline in Adélie penguins and increase in gentoos in the West Antarctic Peninsula have been linked to
climate change, although it is not certain which specific factors are the most influential. New research
comparing the foraging behavior of gentoo and Adélie penguins indicates that these species are not in
competition for prey that in turn are declining due to climate change, since they do not forage in the same
places (other research shows that prey populations are not decreasing in size).35 However, other factors
related to climate change are still the most likely cause for these population trends in the WAP.36
In sum: It is clear that changes to sea ice have variable, but sometimes dramatic, impacts on Antarctic
species. Adélie penguin declines are almost certainly linked to climate change impacts, but it remains
unclear which factors are responsible.
Changes from last year: Greater understanding of the impact of extreme climate events and sea ice
variations, ruling out competition for prey as a reason for Adélie penguin declines.
Blue Carbon
Although declines in sea ice will likely disrupt Antarctic ecosystems in shallow waters, research has shown
that this may result in increased carbon uptake by benthic organisms living at greater depths.37 Indeed,
researchers have identified the South Orkney Islands Marine Protected Area (MPA) as a ‘carbon
immobilization hotspot’ due to the fact that bryozoan species there sequestered more carbon than those at
other sites due to the abundance of phytoplankton.38 If sea ice continues to break up at earlier dates in the
Antarctic summer, it is possible that the resulting phytoplankton blooms could increase carbon accumulation
31
C. Barbraud, K. Delord, and H. Weimerskirch (2015). Extreme Ecological Response of a Seabird Community to
Unprecedented Sea Ice Cover. Royal Society Open Science 2 (5): 140456, doi:10.1098/rsos.140456.
32
Ibid.
33
G. F. Clark et al. (2015). Vulnerability of Antarctic Shallow Invertebrate-Dominated Ecosystems. Austral Ecology
40(4): 482–491, doi:10.1111/aec.12237.
34
Ibid.
35
M. A. Cimino et al. (2016). Climate-Driven Sympatry May Not Lead to Foraging Competition between Congeneric
Top-Predators. Scientific Reports 6: 18820, doi:10.1038/srep18820.
36
Ibid.
37
D. K. A. Barnes. Antarctic Sea Ice Losses Drive Gains in Benthic Carbon Drawdown. (2015). Current Biology:
25(18): R789–90, doi:10.1016/j.cub.2015.07.042.; D. K. A. Barnes et al. (2016). Why Is the South Orkney Island Shelf
(the World’s First High Seas Marine Protected Area) a Carbon Immobilization Hotspot? Global Change Biology 22 (3):
1110–20, doi:10.1111/gcb.13157.
38
Barnes et al. 2016.
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in other areas as well.39 This phenomenon will not be sufficient to impact global climate change in any
significant way, but it is important to understand how these processes function.
In sum: Scientists are still learning about the impact of marine species on the carbon cycle. Warming
trends in the Antarctic may result in increased carbon sequestration in some benthic species due to
increased growth resulting from increased food supplies.
Changes from last year: Deepening our knowledge of the carbon system in Southern Ocean ecosystems.
Conclusions and Recommendations
The predictions about how climate change will affect Antarctica have grown increasingly serious. The recent
meeting of the United Nations Framework Convention on Climate Change (UNFCCC) indicated that
policymakers may finally have appreciated the need for action to prevent further increases in warming by
limiting carbon emissions. Nevertheless, we can expect that the significant changes already seen in parts of
the Antarctic will continue into the near future. Antarctic science, already so crucial to our understanding of
global climate change, will only grow in importance over the next several decades. ASOC therefore strongly
recommends:
• That all ATCPs make clear commitments to funding research into the impacts of climate change and
ocean acidification, and the possible ramifications for Antarctica and the rest of the world.
• That all ATCPs work closely with officials responsible for implementation of UNFCCC pledges to
reinforce scientific findings about the serious impact on sea level rise that melting Antarctic ice
sheets are predicted to have.
39
Barnes 2015.
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