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Climate change effects on ocean and ice – Expert Reaction

Climate change effects on ocean and ice – Expert Reaction

A new report has highlighted the urgent need to address climate change to protect the world's oceans and frozen places.

The Intergovernmental Panel on Climate Change finalised its special report on the ocean and cryosphere this week in Monaco, concluding that urgent reduction of greenhouse gases is required to limit the effects of climate change on these environments.

The SMC gathered expert comment on the special report.

Professor Christina Hulbe, School of Surveying, University of Otago, comments:

"Hanging over the technical details in the Special Report on the Ocean and Cryosphere report are two broad messages: first, the climate change drumbeat isn’t in the distance, it’s here and it’s loud, and second, the processes and impacts are highly interconnected. This means a number of climate change consequences are locked in but it also means that some of the most serious outcomes can still be avoided and, no matter what, the time we have available to get ready for the inevitable changes depends on how hard we keep pushing the climate system.

"Another important attribute of the special report is that confidence in the conclusions is getting higher as the global climate science focus has been intensifying and the methods and tools available to monitor the cryosphere continue to develop.

"With the polar cryosphere, we know where change is happening and we know, broadly, why a lot of it is happening. But if you read the details of the report you will also see that this is where some of the lower confidence statements are found. For example, there is a potential for large, irreversible retreat of the West Antarctic Ice Sheet but whether or not it is realised depends on whether or not a threshold in the physics that governs the ice sheet is passed. We don’t know if that has happened yet. Item B3.1 states 'The uncertainty at the end of the century is mainly determined by the ice sheets, especially in Antarctica', and item B3.3 states 'Processes controlling the timing of future ice-shelf loss and the extent of ice sheet instabilities could increase Antarctica’s contribution to sea level rise to values substantially higher than the likely range on century and longer time-scales (low confidence)'.

"The best available computer models suggest the threshold for large, irreversible change is nearby — somewhere between 1.5 and 2 degrees global mean warming. So while there is certainly change locked in, it may still be possible to avoid some of the largest consequences of global warming. The low-emission RCP2.6 pathways show this option."

No conflict of interest.

Professor Cliff Law, NIWA; University of Otago, comments:

"The IPCC SROCC report confirms that the oceans provide us with an amazing buffer against climate change. By absorbing 20%-30% of the CO2 we’ve released and an incredible 90%+ of the additional heat retained in the global climate system, it's prevented the planet overheating.

"However, these benefits have come at a cost, and the ocean is exhibiting changes in currents, chemistry and ecosystems that are projected to worsen. Poleward shifts in the distribution of many marine species in response to warming will cause major shifts in ecosystems across the oceans, with significant implications for fishing and food security. The decrease in dissolved oxygen and nutrients, and also the acidification, of some productive oceanic regions is further cause for concern.

"That extreme sea levels which formerly occurred once-a-century may now become annual events should ring alarm bells. Coastal zones are where we interact with and gain most benefit from the oceans, yet these regions are in the front line of climate change, being impacted by a number of different stressors.

"Here, the report also offers hope that, if we can manage natural resources, increase adaptation, and reduce other stressors, in addition to the all-important emission reductions, then we can sustain marine ecosystems and the services they provide. The SROCC report is not just a review of the current state of the marine realm and cryosphere, it’s a call for action – one we need to prioritise if we value our oceans."

Conflict of interest statement: I acted as an expert reviewer for the first draft of the SROCC report.

Professor James Renwick, Victoria University of Wellington, comments:

"The Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) explains very clearly the consequences of melting ice and rising seas, and spells out yet again why we need urgent action on climate change.

"Over one billion people depend on glacier ice for their water supply, and those communities will be increasingly put at risk as the ice melts away. Tens of millions of people live in low-lying small island nations and millions more live very close to sea level. Unless we take urgent action to reduce greenhouse gas emissions, vast populations will be displaced by rising seas. If no action is taken, sea level rise could easily exceed one metre by 2100 and be on the way to several metres more, as large parts of the ice sheets in Antarctica and Greenland melt.

"Every 10cm of sea level rise triples the occurrence of coastal inundation. One metre of sea level rise would threaten cities and communities all over the world, including New Zealand. The economic costs would be measured in the tens of billions here in New Zealand, and in the trillions worldwide.

"The oceans are absorbing over 90% of the heating from increased atmospheric greenhouse gases, and they are absorbing about a quarter of the carbon dioxide we emit. The oceans are getting hotter, and more acidic, with potentially dire consequences for marine life through the world’s oceans.

"The SROCC calls once again for 'unprecedented transitions in all aspects of society'. To stop global warming at 1.5C above pre-industrial levels, a hard enough future to deal with, we need to see global emissions of carbon dioxide halved in the next 10 years, and go to zero by 2050. If the wholesale transition to renewable energy does not start by 2020, we will miss that limit and be well on the way to two degrees of warming and beyond. Such a warm future would bring serious disruption to global food security and water availability and would displace hundreds of millions of people. The economic and human costs are virtually incalculable."

Conflict of interest statement: Prof. Renwick is a coordinating lead author for the IPCC 6th Assessment Report.

Dr Judy Lawrence, Senior Research Fellow, Climate Change Research Institute, Victoria University of Wellington, comments:

"The Special Report on the Ocean and Cryosphere has highlighted new evidence about the impacts of climate change and the increasing costs and risks of delayed action because past and current emissions are resulting in profound consequences for ecosystems and people. Oceans are becoming more acidic and less productive, sea levels are accelerating due to polar ice melt, coastal extreme sea level rise (SLR) events are becoming more severe at high tides and, when intense storms hit the coast, globally a once in one hundred year event becomes a once a year event by mid-century; so locally these will be more frequent. There is high confidence that these are projected to exacerbate risks for human communities in low-lying coastal areas.

"The benefits of reducing our carbon emissions to the lowest possible levels to reduce the scale of impacts are highlighted. The report states that we will only keep below 2 degrees if we effect unprecedented transitions in all aspects of society; energy, land and ecosystems, urban and infrastructure and industry. But the report also warns that [under this scenario] impacts will still be challenging, although potentially more manageable for the most vulnerable.

"There is a call for embedding this new knowledge of unavoidable change and plausible futures into each country context to limit the scale of risks and climate impacts. This means that, the more decisively and the earlier we act, the more able we will be to address unavoidable changes, manage risks, improve lives and achieve sustainability for ecosystems and people today and in the future.

"The governance and adaptation implications of the impacts are discussed. The temporal differences between the changes and our ability to respond are highlighted. This is because of fragmented administration of the risks across governments and sectors, lack of coordination and adaptive capacity of humans and ecosystems due to financial, technological and institutional barriers, the rate and scale of climate changes and the ability of societies to turn their adaptive capacity into effective adaptation responses.

"The effectiveness of different adaptation options and their combinations are canvassed for different rates and scale of changes. This is helpful for decision makers when making adaptation choices especially for judgments about investments today and their effectiveness over the investment lifetime. Despite large uncertainties around scale and rate of change, many coastal decisions being made now can be improved by taking relative sea-level rise into account, favouring flexible responses that can be adapted over time using adaptive decision making, supported by robust decision making, expert judgments and scenarios tools. However, the report stresses that for effective adaptation, the following enabling conditions are needed; a long term perspective, cross scale coordination, addressing vulnerability and equity, inclusive public participation, and the capability to address complexity.

"In New Zealand we have the tools already embedded into our national Coastal Hazards and Climate Change Guidance for use by decision makers and the enablers for effective adaptation were spelled out in the Recommendations from the Climate Change Adaptation Technical Working Groups 2018 report to the Government. We now need these to be fully acted upon to address the warnings in the Special Report."

Conflict of interest statement: I am currently coordinating lead author for the IPCC Sixth Assessment Report Working Group 2 Chapter 11 Australasia. I contributed to one box in the sea level rise chapter of the SROCC. I co-chaired the Climate Change Adaptation Technical Working Group 2016-18. I was a co-author of the Coastal Hazards and Climate Change Guidance 2018.

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