The Greenhouse
Unpacking the Latest IPCC Report - What Climate Science is Telling Us
By Sonia Truong
The most comprehensive climate science report to date, this sixth assessment report reveals the reality of climate change and stresses that we need to take action urgently.
Edited by Jessica Nguy & Yen Sim
Issue 1: September 24, 2021
Illustration by Jess Nguyen
On the 9th of August 2021, the United Nations Intergovernmental Panel on Climate Change (IPCC) released its first instalment of the IPCC Sixth Assessment Report from Working Group I, Climate Change 2021 — The Physical Science Basis of Climate Change.
The IPCC is one of the world’s leading authorities on climate change and its reports provide an important scientific framework for governments to develop climate policies. With the collaborative effort of 234 leading climate scientists and more than 1,000 contributors, the latest IPCC report provides the most up-to-date information about the scientific basis of climate change and the effects of human activity on Earth’s systems.
The report can be found online — it features a ‘Summary for Policymakers’ document exploring key findings across four topic areas as well as a comprehensive ‘Full Report’ which assesses and compiles peer-reviewed literature on climate science from across the globe. The report also features the IPCC WGI Interactive Atlas which explores observed and projected regional climate changes across different emissions and warming scenarios.
Three key takeaways from the IPCC report are described below.
#1: Human activity has contributed to climate change
It in unequivocal that human influence has warmed the atmosphere, ocean and land.
Headline statement from the IPCC’s ‘Summary for Policymakers’, AR6 2021
Advancements in attribution studies have allowed scientists to better simulate Earth’s responses to natural and anthropogenic factors and estimate the extent of human influence on observed climate trends. For the first time, the IPCC report has been able to state with a very high level of certainty that anthropogenic factors have been the main driver of increasing temperature extremes since the mid-19th century.
Figure SPM.1 shows that simulated natural factors do not come close to explaining the observed increase in global surface temperature since the mid-19th century.
Figure SPM.1: A powerful comparison of changes in global surface temperature since 1850 with and without human factors. This figure shows that the effects of natural climate drivers on global warming have been negligible compared to human influence on the climate. IPCC AR6, ‘Summary for Policymakers’
Atmospheric greenhouse gas concentrations are higher than what they have been in the last two millennia and have been increasing at an unprecedented rate, mainly due to human activities in greenhouse gas combustion and deforestation. According to the report, greenhouse gas emissions from human activities have caused warming of approximately 1.1°C above pre-industrial average. In fact, human activities have caused enough emissions for even greater warming, but this has been partially counteracted by the cooling effect of aerosols in the atmosphere.
Some recent heat extremes would have been virtually impossible without the influence of human forcing factors. Siberia’s prolonged heatwaves of 2020, for example, would have occurred less than once every 80,000 years without human-induced climate change. Moreover, the onset of Siberia’s wildfire season saw record-high temperatures throughout 2020 and 2021 as well as the burning of over 16 million hectares of land. Even in today’s climate, such extreme weather events are unlikely, but have been predicted to become more frequent by the end of this century.
#2: Every region will experience environmental changes due to climate change
The IPCC report states that the “widespread, rapid and intensifying” effects of climate change will be experienced by every region in a multitude of ways.
Since the release of the last IPCC report in 2018, the world has observed an increase in acute weather events such as widespread flooding, storms, drought, fire weather and heatwaves. These are predicted to increase in frequency and severity as a result of human-induced climate change.
Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.
B.2 from the IPCC’s ‘Summary for Policymakers’, AR6 2021
Several environmental changes due to climate change are already irreversible. Notably, global sea level rise and ocean acidification are set in long-term motion and will proceed at rates which will depend on future emissions. Glacial retreat is occurring synchronously across the world and glaciers will continue to melt for decades or centuries.
All emission scenarios within the 21st century described in the report have revealed that global temperature changes will exceed a 1.5ºC increase, even in the lowest emissions scenario (SSP1-1.9). Thus, warming will reach a critical level regardless of actions that the world takes now. We can, however, prevent further temperature increases with deep reductions in global greenhouse gas emissions (especially carbon dioxide and methane).
Figure SPM.5: All regions of the world (with one exception) will experience warming as a result of climate change, although not at an equal level. IPCC AR6, ‘Summary for policymakers’
Environmental changes at a 2ºC warming will be more pronounced and widespread, and extremes are likely to exceed critical tolerance thresholds in human health, ecological systems and agriculture. Australia, in particular, is vulnerable to experiencing scarce water resources in drought-prone areas and flooding and landslide events due to heavy rainfall events. Australia’s coastlines are also prone to erosion and flooding from rising sea levels and extreme meteorological events.
The IPCC report examines evidence for climate ‘tipping points’ which, due to uncertainty about the Earth’s feedback systems, “cannot be ruled out” in climate projections. These tipping points are key thresholds that will lead to large-scale and irreversible damages to the Earth’s systems if breached.
One of these tipping points is the loss of the Greenland ice sheet which is melting at an unprecedented rate. Surface melt of this major ice sheet involves a number of positive feedback loops which exacerbate the melting as the ice surface gets darker and less reflective of solar radiation. Scientists warn that, while highly unlikely, there is a possibility that we will reach a tipping point with current warming trends.
#3: We need to make drastic reductions in greenhouse gas emissions immediately
The Sixth Assessment Report tells us, with greater certainty than ever before, that human activities over the past six decades have caused global warming trends and affected climate extremes globally. These trends are likely to continue on a long-term scale.
Most importantly, the report stresses that if we want any chance of limiting global temperature rise to 1.5ºC above pre-industrial levels, we must urgently make strong, sustained reductions in global greenhouse gas emissions. The current global carbon budget to remain below 1.5ºC warming is estimated to be at an additional 500 billion tonnes of greenhouse gas. To remain within this budget, we need to achieve net zero carbon dioxide emissions by 2050.
Reductions in greenhouse gas emissions will only be achieved with meaningful climate action. If we can drastically reduce emissions now, we will still have a chance of averting the climate crisis.
The two succeeding instalments of the IPCC Sixth Assessment Report will cover the impacts of climate change and mitigation of climate change and are planned to be released in 2022.
References:
IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [MassonDelmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press.