GPHY 314 Quiz: Week 9

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29 Dec 2020
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WEEK 9: Climate Change Adaptation
Climate Tipping Points
Tipping points: critical thresholds in a system that, when exceeded, can lead to a
significant change in the state of the system, often with an understanding
that the change is irreversible (IPCC definition)
Climate tipping points can be regional or global (known as large-scale singular events)
o Impact ecosystems, people, function on overall climate system
o Regional events do matter, but large-scale singular events are the ones that are
often discussed for particular climate targets and tipping points to avoid
o Regional tipping points may impact global systems less but more likely to occur
Graphic depicting whole host of potential tipping points
o Some theoretical, some identified in past but not ongoing or
expected to occur in near future, but still worth considering
impacts of these low-probability events if they were to occur
o Regional examples -> Yedoma permafrost
Period in past where permafrost [in Siberia] had
dramatic impact on climate but doesn’t mean we’re at
severe risk of crossing that threshold in the near future
Regional impact, but if we warm up enough, can lead to global impact by
impacting carbon system
o Uncertain -> Jet stream, Sahara greening, Sahel drying
o Not speculative -> Tropical coral reefs, West Antarctic ice sheet, Arctic sea ice
If Arctic sea ice shrunk so much there wasn’t much left in September
months (at its minimum), would lead to so much absorption of heat that it
would be difficult to form ice, impacting climate system
Irreversibility of this impact called into question recently
A few fairly cool years should be enough to stabilize this situation
Worrying tipping points
o Amazon rainforest -> Frequent droughts
o Arctic sea ice -> Reduction in area
o Atlantic circulation -> Slowing down since 1950s
o Boreal forest -> Fires and pests changing
o Coral reefs -> Large-scale die-offs
o Greenland ice sheet -> Ice loss accelerating
o Permafrost -> Thawing
o West Antarctic ice sheet -> Ice loss accelerating
o Wilkes Basin, East Antarctica -> Ice loss accelerating
Looking at large-scale singular events, graphic depicting
amount of change relative to pre-industrial times, whether we
can detect an impact and how much impact we would get
o Grey shading where we were at the time IPCC put out report
o Start going from minimal to moderate to high risk as we pass certain thresholds
o ~1°C when we start to see risks associated with large-scale events
o +2°C have more of a high risk any of the thresholds will be crossed
o Speaks to importance of maintaining temperatures at lower level
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Interesting thing that above graphic aggregates them all together, but if
we disaggregate, there’s quite a difference between varying tipping
points [regardless of regional or global], when they start to initiate,
and when elements start to be at risk
o Potential to lose Arctic summer sea ice and alpine glaciers with
1-3°C change
o Slow moving processes (3-5°C) like expansion of Boreal
forest, El Niño, some more theoretical ones
o +5°C risk losing sea ice, permafrost, and East Antarctic ice sheet
Tipping Points: Corals
Closest to being large-scale events happening throughout our lifetimes -> Coral bleaching
Coral reefs among most biodiverse ecosystems on Earth
Coral reefs cover <1% of ocean floor but 25% of all marine life
o Loss a major tipping point for ecosystems on earth -> Die-offs and subsequent
large-scale impact on not only marine life, but human systems reliant on it
Losses typically occur due to bleaching events
Global distribution of systems -> Warm-water reefs predominantly in low-latitude
regions around equatorial zone, with more cold-water ecosystems farther north
o Warm water reefs the most at risk in context of future climate change (distinct)
Reefs made up of coral and algae (symbiotic relationship)
o Corals allow algae to live in them, feed off and get colour from algae
o When reefs become under [heat] stress, algae tend to leave coral, resulting in
bleached appearance and losing primary food source
Leaves them vulnerable, potential to die
o Caused mostly by heat but also low tides, pollution, sometimes sun exposure
Great Barrier Reef video
o Cameras take high numbers of 360° photos at bottom of sea, mapping seafloor
o Establish baseline for coral reefs to figure how much lost after bleaching event
o Reefs currently thriving but impacts of stress at other reefs will soon carry over
o First mass bleaching event early 1980s, 1998 had first global event, then again in
2010s with intervals between events shortening and intensity increasing
o Now in third global mass bleaching event -> Very warm conditions coming into
the summer and strong El Niña pushing sea temperatures to the limit
Mass heat events in terms of duration and intensity can have a huge impact on coral reefs
o Areas that experienced severe/moderating bleaching across 2015 and 2016 ------>
Over past century, increase in number and duration of marine heat waves
o Last 120 years seen increase in frequency, average duration, total number of days
marine heat waves are occurring
o A lot occurring over areas quite susceptible to bleaching events
Looking into future and potential for marine heat waves over 21st C, certain
climate scenarios move us up into significant amounts of heat waves per
day, even under moderating warming like RCP 4.5
o Getting past 2050, get new category of extreme marine heat waves
o By 2040-2050, a lot of warm-water corals under more realistic scenario like RCP
4.5 expected to have gone heat wave events and significant bleaching events
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