IPCC Assessment Report 6: Take Away Messages for Sustainability Leaders

Recent weeks have seen a community wide discussion about the dire need for emissions reduction as COP26 brought the governments of the world together to pledge to do more to address climate change. But it was only a couple of months ago that the world’s leading scientific body on the effects of climate change, the Intergovernmental Panel on Climate Change (IPCC), released its sixth assessment report (AR6). These reports are produced every 5-6 years and provide arguably the most important updates on the latest climate science. In this article, we discuss a selection of key findings from the latest IPCC report that are important for those organisations wanting to take a leadership position on responding to climate change.

Change has already happened 

Until recently, there was regular debate in the media about whether climate change was real. While on the one hand this debate has largely subsided, on the other the evidence of the change that has already occurred is rapidly increasing. The science is clearer than ever that human-induced climate change is already affecting weather and climate extremes in every inhabited region across the globe. For example, AR6 found that human activities are responsible for approximately 1.1°C of warming since 1850-1900, with warming picking up pace in recent decades. The scale of recent changes are considered to be unprecedented over centuries to thousands of years and mean that attention needs to be given to current as well as future climate when undertaking resilience planning. 

Frequency and intensity of extremes is set to increase 

Most physical climate risk is associated with extreme climate events which exceed the coping capacity of our natural, built, social and economic systems. AR6 found that extreme climatic events which are entirely unprecedented in the observational record, will occur with increasing frequency, even if we limit global warming to the now very ambitious target of +1.5°C above the pre-industrial average. Australia’s record hot, dry and charred Black Summer of 2019-20 is a clear reminder of the compound and cascading nature of future climate extremes on the horizon.   

A key driver of the increasing intensity and frequency of extremes is the intensifying water cycle. Additional heating enhances evapotranspiration from the biosphere and with every degree of warming the lower atmosphere is able to hold 7% more water vapour. This combination brings more intense rainfall and associated flooding, as well as more intense drought across many regions. 

Tipping points may be exceeded 

The magnitude of feedbacks between climate change and the carbon cycle becomes larger and more uncertain in high CO2 emissions scenarios. AR6 makes it clear that additional ecosystem responses to warming are not yet fully included in climate models, such as CO2 and methane fluxes from wetlands, permafrost thaw and the giant wildfires we have witnessed around the world since 2000. These feedbacks will further increase concentrations of greenhouse gases in the atmosphere and their combined effects are not yet resolved in the models.  

Up until AR6, there has been a focus on the most likely outcomes of climate change. This is now being tempered with a balanced view across low likelihood, but very high consequence outcomes. Abrupt changes and low-likelihood, high-impact outcomes could occur at global and regional scales even for global warming within a very likely future emissions scenario. The probability of low-likelihood, high impact outcomes does increase with higher global warming levels. Abrupt responses and tipping points of the climate system cannot be ruled out and therefore need to be built into scenario development and planning exercises. 

Urbanisation as an amplifier 

AR6 reminds us that with dark impermeable surfaces our cities act to amplify many aspects of climate change. As the global population continues to rapidly urbanise, our cities become denser and we remove urban canopy cover, parks, cool green zones, floodplains and groundwater infiltration sites. These are the often-undervalued urban natural capital assets which all act to counter the effects of climate change. 

In the Australian context the most deadly impact of climate change is the increasing severity and frequency of heatwaves. The impacts of these events are further amplified by the well known urban heat island effect. Urbanisation also increases mean and heavy precipitation over and downwind of cities which results in increased runoff intensity and impacts from flash flooding. In coastal cities, the combination of more frequent extreme sea level events (due to sea level rise and storm surge) and extreme rainfall/riverflow events will make flooding much more probable. 

People can still make a positive change 

Climate model projections show that the uncertainties in atmospheric CO2 concentrations by 2100 are dominated by the differences between our anthropogenic emissions scenarios. The rate and severity of future climate change is therefore still entirely under our control. The transition to a decarbonised economy is already underway and must be accelerated if we are to avoid the worst impacts of climate change in the coming decades.  

The choice of societal responses to future climate change impacts will act to either increase or decrease community resilience to subsequent extreme events. Smart building design, holistic planning and low cost risk treatments can act together to effectively buffer our communities from climate impacts and markedly increase our resilience. Employing nature based solutions also provides us with an opportunity to sequester carbon while also protecting communities and assets from many climatic hazards. 

The continued need to act 

AR6 provides the strongest evidence yet of the continuing changes being experienced in the Earth’s climate. Given the increasing focus on climate risk disclosure, especially for government agencies and large corporate entities, the results of this new modelling need to be incorporated into current and future risk assessment to provide a better understanding of the challenges we face – and where to invest in building resilience. This is especially the case for organisations wanting to show leadership in how they assess and respond to climate change. AR6 also serves as a strong reminder of the need to rapidly decarbonise the global economy and why global gatherings such as the recent COP26 are essential for coordinated global action to reduce emissions.