The Ocean Is Sacrificing Itself To Protect Us

While we gear up for more extreme heat events on land, our oceans are working overtime to keep rising temperatures at bay -- and we don't know how long they'll be able to keep doing it.

The level of carbon dioxide in our atmosphere is unprecedented, with CO2 concentration at a level higher than it's been for at least 800,000 years.

"And we know from our analysis of the air that the cause of the increase in CO2 concentration is human activities, through burning of fossil fuels and through land use change," director of the climate science centre at CSIRO Dr Helen Cleugh said.

The Bureau of Meteorology (BOM) and CSIRO have just released the State of the Climate report, a snapshot of how Australia's climate has changed over the past two years.

And it shows that CO2 isn't just assaulting our atmosphere.

Performing the ultimate environmental favour, Australia's oceans are absorbing a large amount of these emissions, removing them from the atmosphere and essentially slowing down our changes in climate.

The average pH of surface waters around Australia is estimated to have decreased by about 0.1 since the 1880s, corresponding to a more than 30 percent increase in acidity. Image: CSIRO

"If the oceans didn't absorb that carbon dioxide, the changes that we're seeing in terms of temperature and climate would be much more extreme," Dr Emma Camp, a marine bio-geochemist not involved with the study, explained to 10 daily.

But as the oceans absorb more and more CO2, their chemical make-up changes.

Due to dropping pH levels, ocean acidity has increased by around 30 percent since the late 1800s, impacting everything from the tiny living organisms at the base of the food chain to the coral we boast as landmarks.

The Great Barrier Reef has experienced multiple bleaching events due to rising sea temperatures. Image: AAP

"The way we think about ocean acidification is if you think of someone that has a chronic disease and it's always there and it's always affecting them,  then they get the flu or they break their leg," Dr Camp said.

"Their ability to deal with that immediate stressor is compromised because of that long-term stress that they're dealing with."

Consider the large-scale bleaching event the Great Barrier Reef went through in 2016 a broken leg. Acidification has significant implications for any coral's ability to grow back.

Great Barrier Reef coral bleaching risk map shows the risk warming ocean temperatures and marine heatwaves are posing.

The ocean has always absorbed CO2, Dr Camp said, but as the concentration of greenhouse gas emissions continues to climb, scientists are working to determine just when it won't be able to anymore.

"We basically know that at some point the ability of the oceans to buffer that sort of change in climate by absorbing CO2 will reach a tipping point when it won't be able to do its job efficiently."

Fires Igniting Their Own Fires -- Compound Extreme Events

This year's report is an affirmation of what we were told in the one before -- the rising temperatures of the land and sea are making our weather more extreme.

"Australia is already experiencing climate change now," Dr Cleugh said.

"There are impacts being experiences or felt across many communities and across many sectors."

The report's data reveals the country's climate has warmed by more than one degree since 1910.

Though it sounds like only a slight increase, it's resulted in more frequent and severe extreme heat events, compounded by changing rainfall patterns particularly over the southern parts of the country.

There's perhaps a no better example of what this means in the here-and-now than fire weather, as fire season across Australia has become longer -- in some areas by months.

The daily Forest Fire Danger Index is an indicator of the severity of fire weather conditions. Positive trends, shown in the yellow to red colours, are indicative of an increased length and intensity of the fire weather season. Image: BOM

"We saw an example of this with fires in winter earlier this year around NSW," BOM senior research scientist Dr Andrew Dowdy told 10 daily.

It's important to understand these trends, as it helps to determine how fire agencies and authorities plan their resources, Dowdy said.

Fire events are now also more severe, as compound extreme events -- which the report focuses on for the first time -- occur when multiple weather variables coincide together.

“Often the worst fire weather occurs when you’ve had long-term drought, long-term above-average temperatures, maybe a short-term heatwave and then the meteorology that’s consistent with severe fire weather and the ability for fire to spread,” Dr Braganza  said.

“It’s those types of compound events that are going to be most challenging going forward in terms of adapting to climate change in Australia.”

Changing rainfall patterns are attributing to compounding heat events. April to October rainfall deciles for the last 20 years shows where rainfall is above average, average or below average in comparison with the entire rainfall record from 1900. Image: BOM

We saw what these compound events can do in the past during the Black Saturday fires in 2009 and the Canberra fires in 2003.

"These are examples of where the fire plume has been so strong that it's actually burst into the stratosphere and that's because it's made its own thunderstorm connected with the fire," Dr Dowdy said.

"This can sometimes create its own lightning, and that lightning on Black Friday we know ignited a new fire, so that can cause risks of subsequent new fire ignitions."