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Effects of Climate Change on 1.5° Temperature Rise Relevant to the Pacific Islands

Countries
Solomon Islands
+ 7 more
Sources
Govt. UK
Publication date
Origin
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Patrick Pringle, Climate Analytics, Samoa

EXECUTIVE SUMMARY

This report synthesizes the emerging evidence of climate impacts at different temperature thresholds for Pacific islands. All evidence points to vast differences in impacts in a 1.5˚C world, compared to the +3˚C world to which our current policies and climate change pledges are leading us. For Pacific islands and marine and coastal ecosystems in the region, these differences cannot be overstated; even a 0.5˚C difference (between 1.5˚C and 2˚C) may mean that critical tipping points are crossed. Some of the most critical impacts for marine and coastal ecosystems and communities in the region include:

• At 2˚C global sea levels could increase by approximately 50cm by 2100 (5.5mm p/a), compared to 40cm under a 1.5˚C scenario (4mm p/a). As polar ice dynamics are better reflected in projections it is evident that sea level rise (SLR) of 1m+ by 2100 is a real risk, especially given we are currently heading towards a +3˚C world.

• Warming exceeding 1.5°C is expected to greatly increase the probability of reaching critical tipping points for the Greenland and Antarctic ice sheets, with the former facing irreversible decline most likely around 1.6°C of warming. This would lead to multi-metre SLR for centuries and millennia ahead. This is consistent with recent projections of SLR which illustrate that above 2˚C of warming the impacts of Antarctic ice melt become increasingly apparent by the end of the current century.

• The frequency of tropical cyclones is expected to decrease, while the intensity of these storms is projected to increase with global temperature. Research indicates a greater increase in monthly sea-surface temperature (SST) for the months of the main Pacific cyclone season under a 2˚C scenario compared to 1.5˚C. SSTs are an important driver for the formulation of intense cyclones in the region.

• At 2˚C virtually all coral reefs in the region may be lost (98% loss) with severe implications for biodiversity and island communities, economies and cultures. Reef degradation at 1.5˚C is still catastrophic (90%) but significant reef ecosystems could remain.

• Ocean acidification will impact upon reefs, fisheries and biodiversity with knock-on impacts for communities and economies. Only by limiting warming to 1.5°C can ocean acidification be halted and the worst impacts avoided.

• Deoxygenation of the ocean will increase with a rise in global temperatures. Under warming scenarios exceeding 4°C, ocean oxygen levels in coastal seas could reduce by more than 40%. At 1.5°C this reduction would be limited to less than 10% and, critically, may allow for stabilization and eventual recovery of oxygen levels.

Impacts at different temperature thresholds must be set in the context of the full range of pressures already placed upon ocean and coastal systems.