It is no exaggeration to say that Monday night's release of the latest report from the Intergovernmental Panel on Climate Change (IPCC) is the single biggest moment in the history of climate science.
The report states there is absolutely no doubt that human actions are changing our climate, shows how the impacts of climate change are already being felt by people right across the planet, and lays out a range of possibilities for the future - from optimistic to terrifying - that will be determined by the climate action choices we make.
IPCC reports are an assessment of the latest and best understanding of our climate system. For this report more than 230 climate scientists worked for over three years, drawing together the evidence from more than 14,000 individual studies. Their work was reviewed by other scientists and governments, and the summary document was agreed word-by-word and unanimously by the 195 member governments of the IPCC - including Australia.
The co-operation between scientists and governments in producing IPCC reports means they are owned by governments as much as they are by scientists. All nations have agreed that what is written truly reflects the scientific understanding of our climate, and how we are changing it.
So what are the key messages from this report?
Human activities, mostly from the burning of fossil fuels, have caused our climate to warm by 1.1 degrees on average across the globe. That global warming, and the speed at which the climate is warming, are unprecedented over many thousands of years. It is now inevitable that we will pass 1.5 degrees of global warming within the next decade or two.
But we don't live in the global average. The impacts in Australia of 1.1 degrees of global warming are evident through deadly heatwaves, flooding rains, prolonged droughts, dangerous fire weather and rising seas. All of these climate risks will worsen as we push through 1.5 degrees of global warming. We will need to prepare and adapt.
How far beyond 1.5 degrees of warming we go is still a choice.
Every fraction of a degree of extra warming increases the risks that people and ecosystems will face. Warming of 2 degrees is more dangerous than 1.5 degrees; 3 degrees of warming is worse than 2 degrees. In the worst-case scenarios studied in this report, the world could have warmed by more than 5 degrees at the end of this century.
We will see extreme climate events becoming more intense, happening more often, lasting longer, and affecting places that have never felt these extremes before. This will include climate impacts that haven't been witnessed before. We only need to look back to Australia's Black Summer to see how unprecedented, extreme events stretch our capacity to deal with climate risks.
To help people in all parts of the world prepare for climate change, the latest report also includes an interactive atlas. You can check it out yourself at interactive-atlas.ipcc.ch to see the data on how climate change has affected, and will affect, different parts of the planet.
We have also set in motion climate changes that are irreversible. No matter which future climate pathway we take, the ocean will continue to rise for many centuries to come. By taking urgent action to reduce climate change we can slow the speed of sea-level rise to make the risks to our coasts manageable. But avoiding climate change action would see the oceans rise by up to one metre by the end of this century, potentially causing tens to hundreds of metres of retreat along some of our sandy shorelines. The possibility of two metres of sea-level rise by the end of this century, and five metres by 2150, also can't be ruled out if ice sheets destabilise rapidly.
This latest report from the IPCC also has a very simple message on what needs to be done to avoid the worst-case scenarios.
Since the Industrial Revolution, human activities have emitted 2390 billion tonnes of carbon dioxide into the atmosphere. Almost half of that has been emitted in the 30 years since the first report of the IPCC shone a light on the dangers of human-caused climate change.
If we want a good chance of limiting warming to 1.5 degrees, we have only 300 billion tonnes left to spend. For 2 degrees of warming it is 900 billion tonnes. Currently the world is emitting 43 billion tonnes every year, and we haven't yet started to turn around the trend of year-on-year increases in greenhouse gas emissions. We can literally count on our fingers the number of years of emissions we have left until we breach the budget for limiting warming to 1.5 degrees.
The urgency to reduce greenhouse gas emissions has never been greater. To put the world on a safer climate path, emissions need to be halved by 2030, reach net zero by 2050, and in the second half of this century we need to somehow be pulling more carbon dioxide out of the atmosphere each year than what we put into it.
The political spin in Australia tries to convince Australians that we are doing our fair share to combat climate change. In reality, our current emissions-reduction targets for 2030 are woefully inadequate. Talk of technological solutions delays the immediate and easy actions to reduce fossil fuel use that our government could chose to incentivise. These early actions would buy us time to then develop the technology we will need for the later and harder transitions, including the formidable task of pulling carbon dioxide back out of the atmosphere.
The climate negotiations in Glasgow later this year will be an important marker for whether the Australian government is ready to take the science seriously and step up our commitments to get the world on a safer path for the future.
This is a monumental report on climate change. What needs to follow is monumental global action to avoid the catastrophic future we are currently heading towards.
- Nerilie Abram is a professor of climate science and associate research director at the Australian National University's Research School of Earth Sciences.