The Best Australian Science Writing 2014 (8 page)

Since the start of the Industrial Revolution in the late 18th century that introduced coal- and steam-powered manufacturing, we've increased the amount of atmospheric CO
₂
by 40 per cent. As a result of this extra heat-trapping gas in the atmosphere our planet is building up heat. A lot of heat. Over the past few decades, our planet has been absorbing four Hiroshima bombs' worth of heat every second. Only a fraction of this heat warms the atmosphere; over 90 per cent of it goes into the oceans. As the volume of heat-trapping gases in the atmosphere has increased,
so too the rate of heat build-up has increased over the last 50 years.

This build-up of extra heat manifests itself in a number of ways. Our climate is becoming warmer and moister, and this influences extreme weather events such as heatwaves, flooding, bushfires and droughts. By adding extra energy to our climate system, global warming acts like fuel for extreme weather. At this point, it's worth clearing up one of the most common misconceptions about extreme weather and climate change. The question is
not
, as so many people like to ask, did global warming cause a specific extreme weather event?

That's the
wrong
question.

The right question is: is global warming increasing the risk from extreme weather events? Based on the full body of scientific evidence available to us, the answer is a resounding yes.

* * * * *

The most direct result of all the excess heat in the climate system is more intense and frequent heatwaves. Since the 1950s, Australian heatwaves have been lasting longer, getting hotter and occurring more frequently. According to research by Australian climate scientists Sophie Lewis and David Karoly, heatwaves in the last decade are at least five times more likely to occur compared to the 20th century, and this can be attributed to the increase in Australian temperatures due to human activity.

In 2013 Australia experienced the hottest January, the hottest summer and the hottest day ever recorded. The year was on track to be the hottest Australian calendar year on record – and it went on to break the record for the hottest twelve months from November 2012 to October 2013.

Heatwaves have an impact on human health. When temperatures get too high, the body struggles to cool itself, which can
cause damage to the brain or other vital organs. From 1880 to 1990, heatwaves killed more Australians than floods, cyclones, bushfires or lightning strikes. The January 2009 heatwave in Victoria, which culminated in Black Saturday, caused an estimated 374 deaths; Black Saturday alone killed 173 people. Apart from the human tragedy of lost and ruined lives, the economic costs from bushfires can be substantial. Black Saturday was estimated to have cost $4.4 billion in damages.

The most severe impacts from climate change are often felt when several extreme weather events occur in combination. For example, multiple factors are involved in starting bushfires. You need fuel (leaves or wood) that's dry enough to burn, something to ignite the fuel, and weather conditions conducive to fire danger: hot temperatures and windy conditions. These elements are combined to calculate the McArthur Forest Fire Danger Index, which was developed in the 1960s by CSIRO scientist AG McArthur. Measurements of rainfall, wind speed, temperature and humidity are used to calculate the degree of fire danger, from ‘low to moderate' to ‘catastrophic' – this latter category was added in 2009 after the Black Saturday fires.

Climate change raises temperatures and, in some parts of Australia, leads to drier conditions. When it gets hotter or drier, bushfire risk increases. In southern Australia, increases in temperature and a decrease in spring rainfall in recent years have created a perfect storm of bushfire danger conditions.

Severe fire danger conditions, marked by an unusually high Forest Fire Danger Index, have increased particularly in the south-east since the 1970s. Not only is the danger becoming more intense, severe fire danger days are beginning to appear not just in summer but also in spring and autumn. In other words, the fire season is lengthening. The fire season is projected to continue to grow longer in coming decades, with even more days of extreme fire danger each year.

The bushfires that ravaged New South Wales in 2013 were striking, not just because of the magnitude of the blazes, but because they began unusually early, in September. A contributor to the early bushfire season was the fact that the state experienced its hottest September on record along with unusually dry conditions.

Perhaps paradoxically, global warming leads not only to an increased risk of fires but also to more intense rainfall. As heat builds up in our climate system, this accelerates evaporation of water from the ground and from water sources. This leads to more moisture in the atmosphere. But what goes up must come down, and one consequence is more heavy downpours. Since 1990, scientists have been predicting an intensification of the water cycle – both evaporation and rainfall – due to global warming. These predictions have been borne out by subsequent observations.

* * * * *

Over the past four decades, the amount of moisture in the atmosphere has increased by 4 per cent. Globally, that's equivalent to 900 Sydney Harbours' worth of extra water in the air. Consequently, consistent with scientists' expectations, we have experienced an increase in heavy rainfall, particularly in north-western Australia.

Flooding can have a devastating impact on infrastructure and human lives. The Queensland floods in 2011 resulted in the deaths of 35 Queenslanders and cost the state $12 billion. The forces driving the floods were complex, with heavier than normal rainfall conditions accompanying La Niña conditions in the Pacific. At the same time, there were record high sea surface temperatures around Queensland. As with heatwaves and bushfires, global warming is increasing the risk from floods.

But in addition to more floods, we are also experiencing
intensified drought. As it gets warmer and evaporation increases, the ground gives up moisture to the atmosphere. This means that drier regions become even drier, while wet areas are getting wetter. Global warming intensifies the water cycle.

While rainfall has overall increased across Australia, different regions have shown varying responses to global warming. North-western Australia has seen a strong increase in rain but in Australia's south and east, rainfall levels have decreased. The decline in the south has led to severely reduced water supplies in south-western Australia and the Murray Darling basin.

The change in rainfall patterns has several flow-on effects. Key food-growing areas in Australia's south-west and south-east are likely to experience more drought in coming decades, which will have consequences for agriculture. Drier conditions in the south-east, along with increased heatwaves, will combine to increase bushfire danger.

As cyclones travel across the sea surface, they scoop up energy from the ocean water. The warmer the water, the more energy cyclones build up. Ocean heat is fuel for cyclones. Scientists project that as global warming continues and oceans continue to warm, cyclones will grow more intense.

Cyclone Yasi, which struck North Queensland in 2011, was a Category 5 cyclone and caused $1.4 billion damage. In November 2013, Cyclone Haiyan devastated large sections of the Philippines when it recorded the highest ever wind speeds of any tropical cyclone to hit landfall. The stronger winds were fuelled by unusually warm ocean temperatures as the cyclone passed over the west Pacific.

With over 90 per cent of global warming going into the oceans, ocean waters are building up heat. As the oceans warm, the water thermally expands, leading to rising sea levels. In addition, glaciers all over the world are shrinking at an accelerating rate and melting ice sheets are sliding faster into the oceans. The
Greenland ice sheet is currently shedding over 300 billion tonnes of ice each year. The result is that over the last century, global sea levels rose by 21 centimetres. Of even greater concern is the fact that the rate of sea-level rise is accelerating. This means that over the next century, we can expect to see substantially more than a 21-centimetre sea-level rise.

Australia is considered by many climate scientists to be the ‘frontline of climate change' and ‘the canary in the coal-mine', with certain impacts such as rising sea levels more severe here compared to other parts of the world. This is particularly pertinent given that 85 per cent of Australians live near the coast. In northern Australia the rise in sea level is among the highest on the planet, up to 1 centimetre per year – more than three times the global average.

The 2013 United Nation's Intergovernmental Panel on Climate Change (IPCC) report projects that sea levels will rise between 45 and 82 centimetres under a business-as-usual scenario. To put this in perspective, a sea-level rise of 50 centimetres will result in a 75-fold increase in the frequency of coastal flooding; in many regions, the increase is over 1000 times.

Because the world's oceans absorb most of the CO
₂
we emit into the atmosphere, we are starting to pay a very heavy price. Coral reefs, the havens of biodiversity that act as the rainforests of the oceans, are being threatened by the one–two punch of warming and acidification.

When waters get too warm, corals expel the algae that live in their tissues. These algae live symbiotically with the coral, feeding it nutrients and giving the corals their bright colours. After the algae are expelled, the coral dies and is bleached white. In 1998, when the Pacific Ocean experienced an unusually warm El Niño, it is estimated to have bleached 16 per cent of the world's reefs.

Then there is ocean acidification. Ocean waters absorb much of our CO
₂
emissions, converting it to carbonic acid. Since the
Industrial Revolution, the ocean's acidity has increased 30 per cent. This acidity makes it harder for corals to form calcified skeletons. This combination of bleaching and acidification is impacting corals all around the world.

Many Australians do not know that half of the Great Barrier Reef has already lost its coral cover over the last 27 years. It has experienced multiple bleaching events over recent decades, caused by underwater heatwaves. This trend is expected to continue, and Australia is in danger of irrevocably losing one of its national treasures.

* * * * *

In 1908, Dorothea Mackellar characterised our country as a land ‘of droughts and flooding rains'. Australia has always been vulnerable to climate extremes, and global warming is making us more vulnerable. As bushfires, floods and drought intensify, our country is becoming further exposed to extreme weather.

We are handing over to our children a world more dangerous than the world our parents gave us. If our planet warms more than 2° Celsius, we will move beyond the threshold of what is considered ‘safe' global warming. The likelihood of the Greenland ice sheet disintegrating, which would contribute metres of sea-level rise, increases to more than 50 per cent. If we carry on at the present rate, we will see as much as 4° Celsius to 6° Celsius warming. This will take our climate to conditions not seen in millions of years, when sea levels were tens of metres higher than they are now.

But just as we human beings are the cause of the problem, we are also the solution. We are already committed to 1.5° Celsius warming from pre-industrial times: we're currently at 0.8°. We will experience some climate impacts based on our emissions already.

The question is just how intense and dangerous are we willing to let it become. We already possess a range of technologies involving energy efficiency, solar power, biomass, wind power and a range of other options that can reduce the impacts of climate change. What is missing is the will to act, from our political leaders and from the Australian public. The choice to commit our children and grandchildren to a perilous world, or to work to transition our society towards a clean and safe future, is in our hands.

Weathering the storm

Firefront

Weather and mind games

Tom Griffiths

As a teenager I read Charles Darwin's
Voyage of the Beagle
and was intoxicated by the glimpse of a young questing mind wrestling with experience, evidence and argument. In my final year at school we studied Alan Moorehead's
Darwin and the Beagle
and learned how this voyage came to change our understanding of the world. Darwin's insight into the origin of species and the process of natural selection was carefully and anxiously developed over decades in his home at Down House in Kent and then forced into the open by Alfred Russel Wallace's 1858 letter from the feverish jungles of Malaya. Two great and very different offspring of competitive, industrial Britain had arrived at the same idea. It was at heart a beautifully simple concept but its full scientific implications are still unfolding today. As I read Darwin's account of his South American excursions and learned of Thomas Huxley's eloquent defence of
On the Origin of Species
, I yearned to live at a time when a grand and transformative scientific idea burst upon the world.