Tag Archives: Sophie Lewis

It’s official: 2016’s Great Barrier Reef bleaching was unlike anything that went before

The Conversation

Sophie Lewis, Australian National University and Jennie Mallela, Australian National University

It is no longer news that the Great Barrier Reef has suffered extreme bleaching.

In early 2016, we heard that the reef had suffered the worst bleaching ever recorded. Surveys published in June that year estimated that 93% of coral on the vast northern section of the reef was bleached, and 22% had already been killed.

Further reports from this year show that bleaching again occurred. The back-to-back bleaching hit more than two-thirds of the Great Barrier Reef and may threaten its UNESCO World Heritage listing.

After recent years of damage, what does the future hold for our priceless reef?

Our new research, published in the Bulletin of the American Meteorological Society’s special report on climate extremes, shows the news isn’t good for the Great Barrier Reef’s future.


Read more: How to work out which coral reefs will bleach, and which might be spared


Coral reefs are complex ecosystems that are affected by many factors. Changes in sea surface temperatures, rainfall, cloudiness, agricultural runoff, or water quality can affect a reef’s health and resilience to stress.

Early analysis of the 2016 bleaching suggested that the Great Barrier Reef was suffering from thermal stress brought on by human-caused climate change.

Our study took a new and comprehensive approach to examine these multiple climatic and environmental influences.

We set out to answer the crucial question: could anything else have bleached the Great Barrier Reef, besides human-induced climate change?

Clear fingerprint

The results were clear. Using a suite of climate models, we found that the significant warming of the Coral Sea region was likely caused by greenhouse gases from human activities. This warming was the primary cause of the extreme 2016 bleaching episode.

But what about those other complex factors? The 2016 event coincided with an El Niño episode that was among the most severe ever observed. The El Niño-Southern Oscillation system, with its positive El Niño and negative La Niña phases, has been linked to bleaching of various coral reefs in the past.

Our study showed that although the 2016 El Niño probably also contributed to the bleaching, this was a secondary contributor to the corals’ thermal stress. The major factor was the increase in temperatures because of climate change.

We next analysed other environmental data. Previous research has found that corals at sites with better water quality (that is, lower concentrations of pollution particles) are more resilient and less prone to bleaching.

Pollution data used in our study show that water quality in 2016 may have been better than in previous bleaching years. This means that the Great Barrier Reef should have been at lower risk of bleaching compared to long-term average conditions, all else being equal. Instead, record bleaching hit the reef as a result of the warming temperature trend.

Previous events

The final part of our investigation involved comparing the conditions behind the record 2016 bleaching with those seen in previous mass bleaching episodes on the Great Barrier Reef, in 1997-98 and 2010-11.

When we analysed these previous events on the Reef, we found very different factors at play.

In 1997-98 the bleaching coincided with a very strong El Niño event. Although an El Niño event also occurred in 2016, the two were very different in terms of the distribution of unusually warm waters, particularly in the eastern equatorial Pacific. In 1997-98, the primary cause of the bleaching – which was less severe than in 2016 – was El Niño.

In 2010-11, the health of the Great Barrier Reef was impaired by runoff. That summer brought record high rainfall to eastern Australia, causing widespread flooding across Queensland. As a result of the discharge of freshwater onto the reef reducing the salinity, bleaching occurred.


Read more: Feeling helpless about the Great Barrier Reef? Here’s one way you can help


There have been many reports in recent years warning of trouble for the Great Barrier Reef. Sadly, our study is yet another warning about the reef’s future – perhaps the most comprehensive warning yet. It tells us that the 2016 bleaching differed from previous mass bleaching events because it was driven primarily by human-induced climate warming.

This puts the Great Barrier Reef in grave danger of future bleaching from further greenhouse warming. The local environmental factors that have previously helped to protect our reefs, such as good water quality, will become less and less able to safeguard corals as the oceans warm.

The ConversationNow we need to take immediate action to reduce greenhouse gas emissions and limit further warming. Without these steps, there is simply no future for our Great Barrier Reef.

Sophie Lewis, Research fellow, Australian National University and Jennie Mallela, Research Fellow in Coral Reef Monitoring and Reef Health Appraisal, Australian National University

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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Climate change has changed the way I think about science. Here’s why

The Conversation

File 20170810 4244 oydjjn
Science is a human approach to understanding the world. Nitirak Rakitiworakun/shutterstock

Sophie Lewis, Australian National University

I’ve wanted to be a scientist since I was five years old.

My idea of a scientist was someone in a lab, making hypotheses and testing theories. We often think of science only as a linear, objective process. This is also the way that science is presented in peer reviewed journal articles – a study begins with a research question or hypothesis, followed by methods, results and conclusions.

It turns out that my work now as a climate scientist doesn’t quite gel with the way we typically talk about science and how science works.

Climate change, and doing climate change research, has changed the way I see and do science. Here are five points that explain why.


Read more: Australia needs dozens more scientists to monitor climate properly


1. Methods aren’t always necessarily falsifiable

Falsifiability is the idea that an assertion can be shown to be false by an experiment or an observation, and is critical to distinctions between “true science” and “pseudoscience”.

Climate models are important and complex tools for understanding the climate system. Are climate models falsifiable? Are they science? A test of falsifiability requires a model test or climate observation that shows global warming caused by increased human-produced greenhouse gases is untrue. It is difficult to propose a test of climate models in advance that is falsifiable.

Science is complicated – and doesn’t always fit the simplified version we learn as children. FoxyImage/shutterstock

This difficulty doesn’t mean that climate models or climate science are invalid or untrustworthy. Climate models are carefully developed and evaluated based on their ability to accurately reproduce observed climate trends and processes. This is why climatologists have confidence in them as scientific tools, not because of ideas around falsifiability.

2. There’s lots of ways to interpret data

Climate research is messy. I spent four years of my PhD reconstructing past changes in Australian and Indonesian rainfall over many thousands of years. Reconstructing the past is inherently problematic. It is riddled with uncertainty and subject to our individual interpretations.

During my PhD, I submitted a paper for publication detailing an interpretation of changes in Indonesian climates, derived from a stalagmite that formed deep in a cave.

My coauthors had disparate views about what, in particular, this stalagmite was telling us. Then, when my paper was returned from the process of peer review, seemingly in shreds, it turns out the two reviewers themselves had directly opposing views about the record.

What happens when everyone who looks at data has a different idea about what it means? (The published paper reflects a range of different viewpoints).

Another example of ambiguity emerged around the discussion of the hiatus in global warming. This was the temporary slowdown in the rate of global warming at the Earth’s surface occurring roughly over the 15 year period since 1997. Some sceptics were adamant that this was unequivocal proof that the world was not warming at all and that global warming was unfounded.

There was an avalanche of academic interest in the warming slowdown. It was attributed to a multitude of causes, including deep ocean processes, aerosols, measurement error and the end of ozone depletion.

Ambiguity and uncertainty are key parts of the natural world, and scientific exploration of it.

3. Sometimes the scientist matters as well as the results

I regularly present my scientific results at public lectures or community events. I used to show a photo depicting a Tasmanian family sheltering under a pier from a fire front. The sky is suffused with heat. In the ocean, a grandmother holds two children while their sister helps her brother cling to underside of the pier.

After a few talks, I had to remove the photo from my PowerPoint presentation because each time I turned around to discuss it, it would make me teary. I felt so strongly that the year we were living was a chilling taste of our world to come.

Just outside of Sydney, tinderbox conditions occurred in early spring of 2013, following a dry, warm winter. Bushfires raged far too early in the season. I was frightened of a world 1°C hotter than now (regardless of what the equilibrium climate sensitivity turns out to be).

At public lectures and community events, people want to know that I am frightened about bushfires. They want to know that I am concerned about the vulnerability of our elderly to increasing summer heat stress. People want to know that, among everything else, I remain optimistic about our collective resilience and desire to care for each other.


Read more: Distrust of experts happens when we forget they are human beings


Communicating how we connect with scientific results is also important part of the role of climate scientists. That photo of the family who survived the Tasmanian bushfire is now back in my presentations.

4. Society matters too

In November 2009, computer servers at the University of East Anglia were illegally hacked and email correspondence was stolen.

A selection of these emails was published publicly, focusing on quotes that purported to reveal dishonest practices that promoted the myth of global warming. The “climategate” scientists were exhaustively cleared of wrongdoing.

On the surface, the climategate emails were an unpleasant but unremarkable event. But delving a little deeper, this can be seen as a significant turning point in society’s expectations of science.

While numerous fastidious reviews of the scientists cleared them of wrongdoing, the strong and ongoing public interest in this matter demonstrates that society wants to know how science works, and who “does” science.

There is a great desire for public connection with the processes of science and the outcomes of scientific pursuits. The public is not necessarily satisfied by scientists working in universities and publishing their finding in articles obscured by pay walls, which cannot be publicly accessed.

A greater transparency of science is required. This is already taking off, with scientists communicating broadly through social and mainstream media and publishing in open access journals.

5. Non-experts can be scientists

Climate science increasingly recognises the value of citizen scientists.

Enlisting non-expert volunteers allows researchers to investigate otherwise very difficult problems, for example when the research would have been financially and logistically impossible without citizen participation.


Read more: Exoplanet discovery by an amateur astronomer shows the power of citizen science


The OzDocs project involved volunteers digitising early records of Australian weather from weather journals, government gazettes, newspapers and our earliest observatories. This project provided a better understanding of the climate history of southeastern Australia.

Personal computers also provide another great tool for citizen collaborators. In one ongoing project, climate scientists conduct experiments using publicly volunteered distributed computing. Participants agree to run experiments on their home or work computers and the results are fed back to the main server for analysis.

While we often think of scientists as trained experts working in labs and publishing in scholarly journals, the lines aren’t always so clear. Everyone has an opportunity to contribute to science.

My new book explores this space between the way science is discussed and the way it takes place.

The ConversationThis isn’t a criticism of science, which provides a useful way to explore and understand the natural world. It is a celebration of the richness, diversity and creativity of science that drives this exploration.

Sophie Lewis, Research fellow, Australian National University

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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