Posts Tagged ‘australia’

Around 55 million years ago, an abrupt global warming event triggered a highly corrosive deep-water current to flow through the North Atlantic Ocean. This process, suggested by new climate model simulations, resolves a long-standing mystery regarding ocean acidification in the deep past.

The rise of CO2 that led to this dramatic acidification occurred during the Paleocene-Eocene Thermal Maximum (PETM), a period when global temperatures rose by around 5°C over several thousand years and one of the largest-ever mass extinctions in the deep ocean occurred.

The PETM, 55 million years ago, is the most recent analogue to present-day climate change that researchers can find. Similarly to the warming we are experiencing today, the PETM warming was a result of increases in atmospheric CO2. The source of this CO2 is unclear, but the most likely explanations include methane released from the seafloor and/or burning peat.

During the PETM, like today, emissions of CO2 were partially absorbed by the ocean. By studying sediment records of the resulting ocean acidification, researchers can estimate the amount of CO2 responsible for warming. However, one of the great mysteries of the PETM has been why ocean acidification was not evenly spread throughout the world’s oceans but was so much worse in the Atlantic than anywhere else.

This pattern has also made it difficult for researchers to assess exactly how much CO2 was added to the atmosphere, causing the 5°C rise in temperatures. This is important for climate researchers as the size of the PETM carbon release goes to the heart of the question of how sensitive global temperatures are to greenhouse gas emissions.

Solving the mystery of these remarkably different patterns of sediment dissolution in different oceans is a vital key to understanding the rapid warming of this period and what it means for our current climate.

A study recently published in Nature Geoscience shows that my co-authors Katrin Meissner, Tim Bralower and I may have cracked this long-standing mystery and revealed the mechanism that led to this uneven ocean acidification.

We now suspect that atmospheric CO2 was not the only contributing factor to the remarkably corrosive Atlantic Ocean during the PETM. Using global climate model simulations that replicated the ocean basins and landmasses of this period, it appears that changes in ocean circulation due to warming played a key role.

55 million years ago, the ocean floor looked quite different than it does today. In particular, there was a ridge on the seafloor between the North and South Atlantic, near the equator. This ridge completely isolated the deep North Atlantic from other oceans, like a giant bathtub on the ocean floor.

In our simulations this “bathtub” was filled with corrosive water, which could easily dissolve calcium carbonate. This corrosive water originated in the Arctic Ocean and sank to the bottom of the Atlantic after mixing with dense salty water from the Tethys Ocean (the precursor to today’s Mediterranean, Black, and Caspian Seas).

Our simulations then reproduced the effects of the PETM as the surface of the Earth warmed in response to increases in CO2. The deep ocean, including the corrosive bottom water, gradually warmed in response. As it warmed it became less dense. Eventually the surface water became denser than the warming deep water and started to sink, causing the corrosive deep water mass to spill over the ridge – overflowing the “giant bath tub”.

The corrosive water then spread southward through the Atlantic, eastward through the Southern Ocean, and into the Pacific, dissolving sediments as it went. It became more diluted as it travelled and so the most severe effects were felt in the South Atlantic. This pattern agrees with sediment records, which show close to 100% dissolution of calcium carbonate in the South Atlantic.

If the acidification event occurred in this manner it has important implications for how strongly the Earth might warm in response to increases in atmospheric CO2.

If the high amount of acidification seen in the Atlantic Ocean had been caused by atmospheric CO2 alone, that would suggest a huge amount of CO2 had to go into the atmosphere to cause 5°C warming. If this were the case, it would mean our climate was not very sensitive to CO2.

But our findings suggest other factors made the Atlantic far more corrosive than the rest of the world’s oceans. This means that sediments in the Atlantic Ocean are not representative of worldwide CO2 concentrations during the PETM.

Comparing computer simulations with reconstructed ocean warming and sediment dissolution during the event, we could narrow our estimate of CO2 release during the event to 7,000 – 10,000 GtC. This is probably similar to the CO2 increase that will occur in the next few centuries if we burn most of the fossil fuels in the ground.

To give this some context, today we are emitting CO2 into the atmosphere at least 10 times faster than than the natural CO2 emissions that caused the PETM. Should we continue to burn fossil fuels at the current rate, we are likely to see the same temperature increase in the space of a few hundred years that took a few thousand years 55 million years ago.

This is an order of magnitude faster and it is likely the impacts from such a dramatic change will be considerably stronger.

Written with the help of my co-authors Katrin and Tim, as well as our lab’s communications manager Alvin Stone.

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I don’t really care about the panda bears. But that’s not saying this problem [climate change] isn’t serious. This is a people problem, this is a billion dead people problem. This is a national security problem. This is rewinding the clock 300 years to a time we don’t want to go back to.

– Nick Wood (spoken at a presentation I attended, and possibly slightly paraphrased as I scrambled to write it down; his profile is here)

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My supervisors are so distinguished that they now exist in cartoon form! If that’s not the mark of a successful science communicator, I’m not sure what is.

Here is Katrin:

And here is Matt:

A former supervisor of mine also got a cartoon:

There are 97 cartoons like this over at Skeptical Science, a site which is quickly becoming a force of nature. This campaign reached millions of people through Twitter alone, and was even retweeted by President Obama.

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It has been a very busy few months. Here are some of the things I have done since I last wrote:

  • Moved out of our apartment in Canada
  • Spent three weeks in Ireland with my partner’s family – this was great fun and featured lots of music, tide pools, castles, and sheep
  • Went back to Canada for six days
  • Mastered the art of packing checked luggage and carry-on bags so they are juuust under the weight limit
  • Said a lot of tearful goodbyes
  • Flew to Australia!
  • Discovered Sydney was 11°C and raining
  • Immediately regretted leaving all our warm sweaters behind (“It’s spring in Australia,” we said. “We won’t need these for months yet,” we said)
  • Saw all three animals I had missed the most – bats, lorikeets, and scientists – in the very first day
  • Officially enrolled as a PhD student at UNSW
  • Stumbled into the Sydney real estate market, where rent prices are more than double what we are used to, and only the wealthiest people can afford to buy property
  • Managed to find a great little apartment for rent within our budget
  • Bought out most of IKEA
  • Moved into said apartment (we’re getting good at this moving thing)
  • Helped to finish up 3 papers from the project Katrin, Tim, and I did last year, and 1 paper from the project Steve and I did 3 years ago
  • Read at least a dozen papers on interactions between Antarctic ice shelves and the Southern Ocean – my PhD project will be somewhere in this field
  • Gone out for climate beers (regular beers consumed by climate scientists) and discussed whether the Canadian or the Australian political system is more fundamentally broken
  • Swam in the ocean three times, and discovered that if you put on goggles and look underneath the water you can see FISH swimming around beneath you

Things are finally calming down now, and I should have time to write more frequently. Now that my head is not so full of flight schedules and rental agreements and shopping lists, it has a lot more space for climate science, and for topics to write about here.

I am so, so happy to be back at the CCRC. It is such a friendly, supportive, and enriching place to do research. While I miss my family and the Canadian wildlife and Canadian autumn (definitely not Canadian winter), this is the best time in my life to travel and explore the planet which I spend so much time studying, and hopefully, helping.

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After a long hiatus – much longer than I like to think about or admit to – I am finally back. I just finished the last semester of my undergraduate degree, which was by far the busiest few months I’ve ever experienced.

This was largely due to my honours thesis, on which I spent probably three times more effort than was warranted. I built a (not very good, but still interesting) model of ocean circulation and implemented it in Python. It turns out that (surprise, surprise) it’s really hard to get a numerical solution to the Navier-Stokes equations to converge. I now have an enormous amount of respect for ocean models like MOM, POP, and NEMO, which are extremely realistic as well as extremely stable. I also feel like I know the physics governing ocean circulation inside out, which will definitely be useful going forward.

Convocation is not until early June, so I am spending the month of May back in Toronto working with Steve Easterbrook. We are finally finishing up our project on the software architecture of climate models, and writing it up into a paper which we hope to submit early this summer. It’s great to be back in Toronto, and to have a chance to revisit all of the interesting places I found the first time around.

In August I will be returning to Australia to begin a PhD in Climate Science at the University of New South Wales, with Katrin Meissner and Matthew England as my supervisors. I am so, so excited about this. It was a big decision to make but ultimately I’m confident it was the right one, and I can’t wait to see what adventures Australia will bring.

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During our time in Australia, my partner and I decided on a whim to spend a weekend in the Blue Mountains. This national park, a two-hour train ride west of Sydney, forms part of the Great Dividing Range: a chain of mountains which stretches from north to south across the entire country, separating the vast outback to the west from the narrow strip of coastal rainforest to the east.

For a region so close to Sydney, the Blue Mountains feel surprisingly remote. You can stand at any number of clifftops, gaze out over a seemingly endless stretch of land, and see no sign of civilization whatsoever. Or you can walk down into the valleys between the mountains and explore the rainforest, a vast expanse of ancient gumtrees that’s managed to hide koalas previously thought to have vanished, and possibly even an escaped panther.

Four months later, when we were safely back in Canada, the Blue Mountains bushfires began. It was October, barely even spring in the Southern Hemisphere. To have fires starting so early in the season was virtually unheard of.

The triggers for the fires were decidedly human-caused: arson, a botched army exercise, and sparking power lines. However, unusually hot, dry, and windy conditions allowed the fires to spread far more quickly than they would have in a more normal October.

To get from the clifftops of Echo Point to the walking trails in the valley below, we took the Giant Stairway, which is exactly what it sounds like. Imagine the steepest and narrowest stairway you can manage, cut into the stone cliff and reinforced with metal, and a handrail which you cling to for dear life. Make it 902 stairs long (by my count, so let’s say plus or minus 5) and wind it back and forth around the cliff. After a few minutes walking down the stairway your knees start to buckle, and you require more and longer breaks, but you still can’t see the bottom.

The exhaustion is worth it simply due to the view.

Sometimes we would see swarms of sulfur-crested cockatoos flying over the treetops hundreds of metres below. They looked like tiny white specks at such a distance, but we could still hear them squawking to one another.

The bushfires of 2013 didn’t affect any of the areas we visited in the Blue Mountains – in fact, none of the main tourism regions were damaged. The main losses occurred in residential areas in and around the Blue Mountains. As of October 19th, 208 houses and 40 non-residential buildings had been destroyed.

Despite the huge amount of property loss, there were only two fatalities from the bushfires. This relatively successful outcome was due to mass evacuations organized by the government of New South Wales. At one point a state of emergency was declared, which authorized police to force residents to leave their houses.

As the fires continued to burn out of control, westerly winds blew the smoke and ash right over Sydney. During sunsets the sky over Sydney Harbour turned a bright orange, giving the illusion of a city built on the surface of Mars.

I had heard about lyre birds, widely considered to be among the best mimics of the animal kingdom, many times before. In an elaborate courtship display, the male lyre bird perfectly imitates the songs of nearly every other bird in the forest, one after another like some kind of avian pop-music mashup. Lyre birds blow mockingbirds right out of the water.

Footage from the BBC of a lyre bird imitating camera shutters and chainsaws seemed too good to be true, but its authenticity was bolstered by a similar story from my friend at the climate lab in Sydney. Her neighbours had been doing renovations, and when they were finished the construction equipment went away but the sounds kept going. That’s when they discovered the lyre bird living in the garden.

We saw three or four lyre birds while hiking in the valley that weekend, but for the most part they just wandered around the forest floor, combing through the leaf litter with an outstretched foot and keeping their beaks firmly shut. It was winter in Australia, after all – not courtship season for most birds. On the last day of hiking, we sat by the side of the trail for a rest and a drink of water, while my partner quizzed me on the local bird calls.

“What kind of bird is making that song?”

“An eastern whip-bird, I think.

“Hang on, it just changed into a kookaburra.

“And now it’s a currawong?”

A few minutes later, a male lyre bird strolled out onto the path ahead of us, showing off his fantastic tail feathers and looking extremely pleased with himself.

It is well known among scientists that human-caused climate change increases the risk of severe bushfires. Spells of hot weather will obviously become more common as the planet warms, but so will prolonged droughts, especially in subtropical regions like Australia. Add an initial trigger, like a lightning strike or an abandoned campfire, and you have the perfect recipe for a bushfire.

The current Australian government, which has a history of questionable statements on climate change, really doesn’t want to believe this. Prime Minister Tony Abbott asserted that “these fires are certainly not a function of climate change, they’re a function of life in Australia”, while Environment Minister Greg Hunt cited Wikipedia during a similar statement. I was actually heartened by these events: the ensuing public outcry convinced me that Australians, by and large, do not buy into their government’s indifference on this issue.

It came as a surprise to nobody in the climate science community, and probably nobody in Australia, that 2013 was Australia’s warmest year on record. The previous record, set in 2005, was exceeded by a fairly significant 0.17°C. Even more remarkable was the fact that 2013 was an ENSO-neutral year. For Australia to shatter this temperature record without the help of El Niño indicates that something else (*cough cough climate change*) is at work.

Would the Blue Mountains bushfires have been so devastating without the help of human-caused climate change? In a cooler and wetter October, closer to the historical average, would the initial fire triggers have developed into anything significant? We’ll never know for sure. What we can say, though, is that bushfires like these will only become more common as climate change continues. This is what the future will look like.

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Now that the academic summer is over, I have left Australia and returned home to Canada. It is great to be with my friends and family again, but I really miss the ocean and the giant monster bats. Not to mention the lab: after four months as a proper scientist, it’s very hard to be an undergrad again.

While I continue to settle in, move to a new apartment, and recover from jet lag (which is way worse in this direction!), here are a few pieces of reading to tide you over:

Scott Johnson from Ars Technica wrote a fabulous piece about climate modelling, and the process by which scientists build and test new components. The article is accurate and compelling, and features interviews with two of my former supervisors (Steve Easterbrook and Andrew Weaver) and lots of other great communicators (Gavin Schmidt and Richard Alley, to name a few).

I have just started reading A Short History of Nearly Everything by Bill Bryson. So far, it is one of the best pieces of science writing I have ever read. As well as being funny and easy to understand, it makes me excited about areas of science I haven’t studied since high school.

Finally, my third and final paper from last summer in Victoria was published in the August edition of Journal of Climate. The full text (subscription required) is available here. It is a companion paper to our recent Climate of the Past study, and compares the projections of EMICs (Earth System Models of Intermediate Complexity) when forced with different RCP scenarios. In a nutshell, we found that even after anthropogenic emissions fall to zero, it takes a very long time for CO2 concentrations to recover, even longer for global temperatures to start falling, and longer still for sea level rise (caused by thermal expansion alone, i.e. neglecting the melting of ice sheets) to stabilize, let alone reverse.

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