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By Antonia Bryce 30 May 2018 6 min read

A gathering storm, Northern Territory. ©  Shutterstock

THE ocean is a yardstick of climate change. As the earth warms, the large carbon sink swells.

Hourly sea level data, water temperatures, and rainfall measurements are just some of the indicators used with complex models to help predict where water might inundate cities, suburbs, villages and farms.

Or, which eco-systems are at most risk from marine heat waves, extreme weather or arguably worse – coinciding events.

But secrets like those locked away in the polar ice caps have left the world waiting for more clues about just how hot, and how high - and when and where - the water could go.

The information is needed urgently, so the United Nation’s Intergovernmental Panel on Climate Change (IPCC) ordered a special report to be delivered by the end of next year.

It will include new research and modelling.

Intergovernmental Panel on Climate Change

CSIRO senior researcher, Dr Kathy McInnes is a lead author on the special report, Oceans and Cryosphere in a Changing Climate for the UN Panel, due to be delivered by the end of next year.

Among other topics, she is assessing how compound events contribute to multi-risk cascading impacts in the context of climate change.

“We are interested in not only single extreme hazards but also coincident or sequential events that can create compounding or cascading climate change events,” she says.

The Panel has commissioned two other special reports, Climate Change and Land and Global Warming of 1.5 Degrees.

McInnes is also a contributing author on the latter, where she’s focussing on how climate change may affect wind.

“On each chapter, there are physical scientists as well as social scientists. So, they are looking at the topics from an end-to-end perspective, which I think is really good for understanding not just the physical implications of the changes, but how they are going to feed through socio-economic systems and impact society,” says McInnes.

And, as in previous IPCC special reports, the authorship involves scientists from disciplines from the three main working groups. Working Groups 1 and 3 examine the physical basis of climate change and mitigation, and Working Group 2 examines impacts and adaptation to climate change.

McInnes’s colleague at CSIRO Oceans and Atmosphere, Kevin Hennessey is a Lead Author on Working Group 2, while Dr Simon Marsland from CSIRO’s Climate Science Centre is a Review Editor on Working Group 1.

In addition to the publication of the three special reports, the material from these reports will be considered in the Sixth Assessment Report by the IPCC, the international body set up by the UN and World Meteorological Organization in 1988 to assess the science and options relating to climate change.

Climate change puzzle

McInnes points to her scientific colleagues’ important work in finding more pieces to the climate change puzzle.

“There are a bunch of processes that are starting to be observed that suggest that Antarctica could be contributing a lot more to sea level rise than was previously understood. But, those processes weren’t well understood enough to quantify the effect at the last IPCC report.”

The 2014 IPCC report found the ocean’s absorption of heat and CO2 could push sea levels up by 52- 98 cm by 2100 under a “business as usual” emissions scenario, but that poorly understood Antarctic processes could lead to a rise of several tens of centimetres more.

Mean sea level rise is a key factor in creating hydrodynamic simulations to understand the effect of climate variability on severe weather events, extreme sea levels and coastal impacts.

McInnes’s research involves tipping points, tropical cyclones, storm tracks, storm surges, governance, along with compound events and cascading impacts and marine heat waves.

“We are seeing more and more heat waves as the ocean temperatures increase. There’s a lot of heat energy being stored in the ocean and we are seeing the manifestation of that particularly on continental shelves, where the rate of rise can be a lot higher,” says McInnes.

Figure: Projections of global sea level rise. The red line indicates a 'business-as-usual' scenario; the blue line indicates projections at ~2 degrees C increase. Source: IPCC AR5, Working Group 1 chapter 13 on sea level rise.

The ocean has absorbed 93 per cent of the excess heat in the climate system and about 30 per cent of CO2 released into the atmosphere, increasing acidification and damaging ecosystems.

Scientists are also working to clarify the extent to which coral bleaching on the Great Barrier Reef can be attributed to climate change.

The IPCC Special Report will examine the increasing number and broadening scope of studies involving the detection and attribution of climate change in extreme events.

“The science has evolved now so that we can attribute some portion of the likelihood of extreme events to climate change,” says McInnes.

So far, 65 per cent of these detection and attribution studies have found climate change has played a role in extreme events, such as in Hurricane Harvey in the Caribbean last year.

“A number of studies say the rainfall was increased because of the extra holding capacity of the warmer atmosphere and the sea surface temperatures over which the hurricane travelled,” says McInnes.

Complex compound events

McInnes’s IPCC work goes beyond single extreme hazards to those involving coincident or sequential events that lead to cascading impacts.

The IPCC reports will include new climate model analysis for compound events, feeding in sea rise scenarios, along with weather and circulation changes to help predict the likelihood and severity of coincident or sequential hazards.

Australia offers several recent examples, from coral bleaching to the Brisbane floods.

In 2015, the nation was experiencing its warmest October, one of the strongest El Nino events and record dry conditions when lightning strikes triggered bushfires in Tasmania.

There were cascading impacts on natural systems, agriculture, infrastructure and communities.

In the same year in northern Australia, high temperatures, low rainfall and low sea levels associated with the El Nino caused mangrove die-back. The loss of recruitment habitat could affect the 30-million-dollar fishing industry.

Extreme storms can also cause cascading impacts.

“Tropical cyclones, while they are not oceanographic, impact the ocean and cause extreme sea levels and do cause changes in the ocean system and do a lot of damage to things like coral reefs because they generate such strong winds and waves,” says McInnes.

Being a climate scientist

McInnes is one of several thousand scientists responsible for researching and analysing climate change, and providing advice that will ultimately flow to world leaders.

She’s keenly aware of the responsibility they carry.

“The literature can be really complex, and there can be many different studies: we want to see the weight of evidence. And, we have to get the messages as policy relevant as possible. Because it is also a communication challenge and it can be quite daunting for people to really take on this information if it is not communicated in a way that really resonates with them.”

McInnes is heartened by the insurance industry’s engagement at the recent Climate Adaptation 2018 conference.

“They are interested in what kind of information we are developing, and they are definitely changing their thinking on what sort of products they will be offering and how they can price risk and in doing so, perhaps send that signal that people need to stop and think about where they build or live.

“It is another line of evidence that the average, every day person who might not have been that engaged with the science gets the messaging that there is something going on out there.”

In the not-too-distant past, a climate change conference would not have attracted so many people from the private sector.

“They’re recognising it impacts their sector and they are taking it so seriously that I sort of feel this ground swell of change is afoot to try and meet the Paris agreement and I actually felt very inspired. That for me is the way that helps me to cope with it.”

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