The Terrible Truth of Climate Change

In June, I delivered a keynote presentation on Australia's vulnerability to climate change and our policy challenges at the annual meeting of the Australian Meteorological and Oceanographic Society, the main conference for those working in the climate science community. I saw it as an opportunity to summarise the post-election political and scientific reality we now face.

As one of the dozen or so Australian lead authors on the United Nations Intergovernmental Panel on Climate Change's (IPCC) sixth assessment report, currently underway, I have a deep appreciation of the speed and severity of climate change unfolding across the planet. Last year I was also appointed as one of the scientific advisers to the Climate Council, Australia's leading independent body providing expert advice to the public on climate science and policy. In short, I am in the confronting position of being one of the few Australians who sees the terrifying reality of the climate crisis.

There is now nowhere to hide from the terrible truth.

Preparing for this talk I experienced something gut-wrenching. It was the realisation that there is now nowhere to hide from the terrible truth.

The last time this happened to me, I was visiting my father in hospital following emergency surgery for a massive brain haemorrhage. As he lay unconscious in intensive care, I examined his CT scan with one of the attending surgeons who gently explained that the dark patch covering nearly a quarter of the image of his brain was a pool of blood. Although they had done their best to drain the area and stem the bleeding, the catastrophic nature of the damage was undeniable. The brutality of the evidence was clear - the full weight of it sent my stomach into freefall.

The results coming out of the climate science community at the moment are, even for experts, similarly alarming.

One common metric used to investigate the effects of global warming is known as "equilibrium climate sensitivity", defined as the full amount of global surface warming that will eventually occur in response to a doubling of atmospheric CO2 concentrations compared to pre-industrial times. It's sometimes referred to as the holy grail of climate science because it helps quantify the specific risks posed to human society as the planet continues to warm.

We know that CO2 concentrations have risen from pre-industrial levels of 280 parts per million (ppm) to approximately 410 ppm today, the highest recorded in at least three million years. Without major mitigation efforts, we are likely to reach 560 ppm by around 2060.

When the IPCC's fifth assessment report was published in 2013, it estimated that such a doubling of CO2 was likely to produce warming within the range of 1.5 to 4.5degC as the Earth reaches a new equilibrium. However, preliminary estimates calculated from the latest global climate models (being used in the current IPCC assessment, due out in 2021) are far higher than with the previous generation of models. Early reports are predicting that a doubling of CO2 may in fact produce between 2.8 and 5.8degC of warming. Incredibly, at least eight of the latest models produced by leading research centres in the United States, the United Kingdom, Canada and France are showing climate sensitivity of 5degC or warmer.

When these results were first released at a climate modelling workshop in March this year, a flurry of panicked emails from my IPCC colleagues flooded my inbox. What if the models are right? Has the Earth already crossed some kind of tipping point? Are we experiencing abrupt climate change right now?

The model runs aren't all available yet, but when many of the most advanced models in the world are independently reproducing the same disturbing results, it's hard not to worry.

When the UN's Paris Agreement was adopted in December 2015, it defined a specific goal: to keep global warming to well below 2degC and as close as possible to 1.5degC above pre-industrial levels (defined as the climate conditions experienced during the 1850-1900 period). While admirable in intent, the agreement did not impose legally binding limits on signatory nations and contained no enforcement mechanisms. Instead, each country committed to publicly disclosed Nationally Determined Contributions (NDCs) to reduce emissions. In essence, it is up to each nation to act in the public interest.

Even achieving the most ambitious goal of 1.5degC will see the further destruction of between 70 and 90 per cent of reef-building corals compared to today, according to the IPCC's "Special Report on Global Warming of 1.5degC", released last October. With 2degC of warming, a staggering 99 per cent of tropical coral reefs disappear. An entire component of the Earth's biosphere - our planetary life support system - would be eliminated. The knock-on effects on the 25 per cent of all marine life that depends on coral reefs would be profound and immeasurable.

So how is the Paris Agreement actually panning out?

In 2017, we reached 1degC of warming above global pre-industrial conditions. According to the UN Environment Programme's "Emissions Gap Report", released in November 2018, current unconditional NDCs will see global average temperature rise by 2.9 to 3.4degC above pre-industrial levels by the end of this century.

To restrict warming to 2degC above pre-industrial levels, the world needs to triple its current emission reduction pledges. If that's not bad enough, to restrict global warming to 1.5degC, global ambition needs to increase fivefold.

Meanwhile, the Australian federal government has a target of reducing emissions by 26 to 28 per cent below 2005 levels by 2030, which experts believe is more aligned with global warming of 3 to 4degC. Despite Prime Minister Scott Morrison's claim that we will meet our Paris Agreement commitments "in a canter", the UNEP report clearly identifies Australia as one of the G20 nations that will fall short of achieving its already inadequate NDCs by 2030.

Even with the 1degC of warming we've already experienced, 50 per cent of the Great Barrier Reef is dead. We are witnessing catastrophic ecosystem collapse of the largest living organism on the planet. As I share this horrifying information with audiences around the country, I often pause to allow people to try and really take that information in.

Increasingly after my speaking events, I catch myself unexpectedly weeping in my hotel room or on flights home. Every now and then, the reality of what the science is saying manages to thaw the emotionally frozen part of myself I need to maintain to do my job. In those moments, what surfaces is pure grief. It's the only feeling that comes close to the pain I felt processing the severity of my dad's brain injury. Being willing to acknowledge the arrival of the point of no return is an act of bravery.

But these days my grief is rapidly being superseded by rage. Volcanically explosive rage. Because in the very same IPCC report that outlines the details of the impending apocalypse, the climate science community clearly stated that limiting warming to 1.5degC is geophysically possible.

Past emissions alone are unlikely to raise global average temperatures to 1.5degC above pre-industrial levels. The IPCC report states that any further warming beyond the 1degC already recorded would likely be less than 0.5degC over the next 20 to 30 years, if all anthropogenic greenhouse gas emissions were reduced to zero immediately. That is, if we act urgently, it is technically feasible to turn things around. The only thing missing is strong global policy.

Although the very foundation of human civilisation is at stake, the world is on track to seriously overshoot our UN targets. Worse still, global carbon emissions are still rising. In response, scientists are prioritising research on how the planet has responded during other warm periods in the Earth's history.

The most comprehensive summary of conditions experienced during past warm periods in the Earth's recent history was published in June 2018 in one of our leading journals, Nature Geoscience, by 59 leading experts from 17 countries. The report concluded that warming of between 1.5 and 2degC in the past was enough to see significant shifts in climate zones, and land and aquatic ecosystems "spatially reorganize".

These changes triggered substantial long-term melting of ice in Greenland and Antarctica, unleashing 6 to 13 metres of global sea-level rise lasting thousands of years.

Examining the Earth's climatic past tells us that even between 1.5 and 2degC of warming sees the world reconfigure in ways that people don't yet appreciate. All bets are off between 3 and 4degC, where we are currently headed. Parts of Australia will become uninhabitable, as other areas of our country become increasingly ravaged by extreme weather events.

This year the Australian Meteorological and Oceanographic Society's annual conference was held in Darwin, where the infamous Cyclone Tracy struck on Christmas Day in 1974, virtually demolishing the entire city. More than 70 per cent of the city's buildings, including 80 per cent of its houses, were destroyed. Seventy-one people were killed and most of the 48,000 residents made homeless. Conditions were so dire that around 36,000 people were evacuated, many by military aircraft. It was a disaster of monumental proportions.

As I collated this information for my presentation, it became clear to me that Cyclone Tracy is a warning. Without major action, we will see tropical cyclones drifting into areas on the southern edge of current cyclone zones, into places such as south-east Queensland and northern New South Wales, where infrastructure is not ready to cope with cyclonic conditions.

These areas currently house more than 3.6 million people; we simply aren't prepared for what is upon us.

There is a very rational reason why Australian schoolkids are now taking to the streets - the immensity of what is at stake is truly staggering. Staying silent about this planetary emergency no longer feels like an option for me either. Given how disconnected policy is from scientific reality in this country, an urgent and pragmatic national conversation is now essential. Other-
wise, living on a destabilised planet is the terrible truth that we will all face.

As a climate scientist at this fraught point in our history, the most helpful thing I can offer is the same professionalism that the doctor displayed late that night in Dad's intensive-care ward. A clear-eyed and compassionate look at the facts.

We still have time to try and avert the scale of the disaster, but we must respond as we would in an emergency. The question is, can we muster the best of our humanity in time?