At the end of every cycle of work, the Intergovernmental Panel on Climate Change (IPCC) produces a synthesis report, the essence of its entire assessment of the state of knowledge on climate change.
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The synthesis of the sixth assessment cycle was released this week.
The report reiterates findings from the underlying six IPCC reports, written by many hundreds of expert authors. Its currency is neither novelty nor colourful statements. Its power lies in the fact that it is the official document of reference approved by all governments of the world.
Every single statement made in the report has been vetted, debated for its relevance, subjected to many review comments, and probed by hundreds of government delegates in a week-long approval session, with debate on some points raging for hours.
The IPCC reports are perhaps the most comprehensively reviewed documents in the history of humankind.
What is found in its 35-page summary truly counts. It is the bedrock of current understanding about climate change and responses to this that governments use to interact with each other.
The corporate world increasingly also uses it.
The report confirms that humanity is unequivocally causing global warming, with greenhouse gas emissions at record levels. The average global surface temperature is now 1.1 above pre-industrial levels, and likely to reach 1.5 above this level in the early 2030s.
Widespread climatic impacts are already observed and documented. Most are negative. Over 3 billion people are highly vulnerable to climate change.
Climate change has already caused irreversible losses in ecosystems, reduced food and water security, and is getting in the way of sustainable development goals.
"Losses and damages" from climate change are already with us, and often affect those who are least able to cope and who historically have contributed least to the problem.
These impacts will inevitably intensify, and so a sharper focus on adapting to climate change is needed urgently.
In most countries there is some level of awareness that climate change adaptation is necessary, but typically there is no detailed knowledge about what specifically should be done, the means to implement those changes are patchy, and funding is usually lacking to invest in climate-adapted infrastructure, agricultural production systems, urban systems and so forth.
This unfortunately is also the case for Australia, where the considerable momentum on climate adaptation a decade ago has been subsequently lost. Effective adaptation lowers risk and enables opportunities to be realised.
Importantly, the IPCC synthesis shows that climate adaptation is almost always well-aligned with achievement of broader sustainable development goals and can also help address equity issues by reducing the vulnerability of disadvantaged groups.
For the longer term, the world's climate change future depends on greenhouse gas emissions trajectories. The report shows that to limit warming to 2 degrees Celsius with a two-thirds likelihood, greenhouse gas emissions would need to fall in the order of 35 per cent by 2035 compared to 2019, and by around two-thirds by 2050.
The required percentage reductions are higher for carbon dioxide than other greenhouse gases, and they are far higher still if temperature rises were to be limited to 1.5 degrees.
For example, CO2 emissions need to be reduced by 65 per cent by 2035 if we are to have a 50 per cent chance of keeping temperatures to 1.5 degrees.
By contrast, global emissions actually rose by 19 per cent from 2010 to 2019, although this is a slower rate of increase than in previous decades.
So the world needs to cut emissions far more steeply than what governments have to date committed to. Currently policies would likely have temperatures rising by around 3 degrees, with entirely problematic consequences.
If fully implemented, the commitments that countries collectively have made for 2030 emissions would have the world on a pathway below 3 degrees, but still not near 2 degrees.
This means that emissions commitments and action will need to be greatly strengthened.
The good news is that deeper cuts are entirely possible, and on the whole affordable. In the IPCC's assessment, the benefits of acting strongly would clearly outweigh the economic costs of doing so, even without considering the benefits of avoided climate change that cannot easily be economically quantified or the co-benefits such as reduced air pollution.
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The key factor is the dramatic reductions in the cost of zero-emissions technologies, in particular renewable energy, that allows shifting toward low- or zero-carbon energy supply.
Combined with energy efficiency and shift to low-emission industrial processes, electrification of transport, improved housing systems, and importantly actions on the land such as reduced deforestation and higher carbon uptake in agriculture, this allows for deep cuts in net emissions across the board.
The IPCC synthesis report shows that if all technically available options were implemented, cutting global emissions by half would be possible this decade, at manageable costs.
Not every conceivable option will be put into practice, but there is a vast field of low hanging fruit.
The IPCC report points out that government action is already reducing global emissions by a substantial amount compared to what would otherwise be the case.
Policy instruments to cut emissions are also tried and tested. Experience shows that many different policy approaches work in different contexts, and that climate policy can be designed to meet other objectives such as protecting low-income earners and safeguarding energy security.
The situation with climate change is getting rapidly more serious, but we are not helpless bystanders - the means to act are at humankind's disposal.
- Frank Jotzo is a lead author of the IPCC's latest assessment report and a member of the core writing team for the synthesis report. Mark Howden is a vice -chair of the IPCC working group on adaptation and was involved in the synthesis report from its inception. Both are based at the Australian National University.
