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Human-induced Climate Change Is Already Affecting Weather And Climate Extremes Across The Globe
Human-induced Climate Change Is Already Affecting Weather And Climate Extremes Across The Globe, According To The Latest Report From Working Group 1 Of The Intergovernmental Panel On Climate Change (IPCC).
Human-induced climate change is already affecting weather and climate extremes across the globe, according to the latest report from Working Group 1 of the Intergovernmental Panel on Climate Change (IPCC).
The evidence has strengthened – not only in the observed changes in heatwaves, heavy rains, and drought extremes – but also in their attribution to human influence, since the last report was published in 2013.
The SMC asked independent experts to comment, as well as the report’s NZ-based authors.
Professor Bronwyn Hayward, Professor of Political Science and International Relations, University of Canterbury, comments:
Note: Professor Hayward is a member of the IPCC core writing team and Co-lead of the Cities & Infrastructure chapter of AR6 Working group 2 report. She was also a lead author on Special Report 1.5°C. These views are her own expert assessment and do not reflect those of the IPCC.
“Climate change is happening, faster than we thought, and humans have caused it.
“That’s the stark message behind the new IPCC physical science climate report.
“In this first of three major research reviews, scientists tell us human activity is ‘unequivocally’ driving the warming of atmosphere, ocean and land. Unequivocal is the strongest term the IPCC can use.
“The report is frank and blunt. It says our climate is changing faster than we anticipated even in 2018. The IPCC says human activity has warmed the climate by 1.1 degrees since the pre-industrial era.
“The report doesn’t put a precise date on when we know we have crossed the dangerous threshold of 1.5 degrees Celsius of warming, but says unless we make far reaching change, this will occur over the next 20 years using average temperatures. This will expose many more people and our natural environment to even more devastating consequences including intense flooding, storms and unprecedented droughts and fires.
“While we need more regional data for New Zealand, cities get a special mention, as hotspots where the experience of localised heat and flooding will be more intense than global averages. This matters because cities in New Zealand are already home to nearly 90 per cent of our population.
“Behind this report are heroic long hours by many climate scientists who have also been working out how to attribute storms and weather events to climate change. This report notes that every additional 0.5°C of global warming ‘causes clearly discernible increases’ in the intensity and frequency of extreme events, including heatwaves, floods and droughts.
“In 2018, I hoped that the Special Report would be the end of magical thinking, that we’d stop thinking somehow climate change wasn’t happening. Opinion polling now shows that New Zealanders do accept climate change is real and all ages are increasingly anxious about its impacts.
“We must now avoid a new kind of magical thinking that relying on technology will save us. Instead, we must take real actions to reduce emissions and protect people, biodiversity and businesses.
“This IPCC report clearly states in the frequently asked questions section that technologies like CO2 removal techniques ‘are not yet ready or unable to achieve the scale of removal to compensate for current levels of emissions and most have undesirable side effects’.
“It’s critical that we stop hoping someone or something else will fix this if we hope to achieve the Paris Agreement of ‘holding the increase in the global average temperature to well below 2°C above pre-industrial levels’ let alone 1.5°C.
“Extreme weather events cannot be the future we leave for our children.
“It will never be easier to act on climate than it is now.
“The next IPCC reports talk about how we can adapt and cut emissions, but we need to start work now. We banned new oil and gas exploration and we know we need a new Paris climate target, let’s just set one. Don’t wait for COP26. Let’s start the real changes in some of the most obvious areas so we can look our children in the eye and report on big actions, not just plans, in Glasgow in November.”
No conflicts of interest.
Professor Iain White, Professor of Environmental Planning, University of Waikato, comments:
“The latest IPCC report lays out a sobering and authoritative assessment of climate change and what the near future might hold. I’ve read all the Assessment Reports on the physical science and implications over the years. I thought I might get desensitized, but I actually felt a little sick at a couple of paragraphs. I feel for the scientists who have to put this together.
“But it’s important to note that while it is new science, it is an old message. The physical science basis of climate change has been largely accepted since I was at school, and each periodic IPCC report only serves to increase the certainty and amplify the risk. To be honest, politicians already know what needs to be done and why. The persistent problem we have failed to grapple with is how and who?
“These difficult conversations about economic and societal transition are decades overdue, but an Emissions Reduction Plan is due by the end of the year. This will be vitally important. We need to change how we live, how we move, and the structure of our economy. We need to use all the levers of government, from incentives and signals to shape markets, to policies and budgets relating to housing, transport, and the wider economy to ensure actions are effective and equitable.
“The hidden challenge is integrating this at scale and pace across government. For example, at the same time as politicians in Wellington react to this report with concern, climate advocacy groups are suing Auckland Transport and Auckland Council over a long-term Land Transport Plan that fails to reduce emissions. It’s a sign that our institutions helped create the current situation, and action may involve new governance structures or fundamental changes to leadership, budgets, or sectors. Otherwise the biggest risk the government has in implementing the plan may be other arms of government.
“We also need to avoid falling into the trap of techno-optimism, which masks that significant changes are required that will be resisted. If anyone is in doubt at the scale of the challenge, reflect on how hard it was to reorient just a few individual streets towards walking and cycling during the Innovating Streets trial. Now do that to a city. Or a sector.
“Science has done its job. It did it decades ago, frankly. Now it’s time for politics and related professions to do their job. Only now they have less time than previous generations of politicians and the implications are ever more certain.”
No conflict of interest
Dr Sara Mikaloff-Fletcher, Principal Scientist – Carbon, Chemistry and Climate, NIWA, comments:
“Climate change is no longer a problem of the future. It has already affected weather and climate extremes in every inhabited region on earth, and these changes will continue for decades to come. The most recent report from the Intergovernmental Panel on Climate Change (IPCC) presents overwhelming evidence that greenhouse gas emissions have already affected every part of the climate system and shows that even with rapid emissions reductions, it will take twenty to thirty years for global temperatures to stabilise. Some other changes, such as melting of ice sheets, are irreversible on human timescales.
“It is still possible to limit the impacts of climate change. Every action we take to reduce our net emissions of carbon dioxide, methane, and other greenhouse gases will help us towards a brighter future. However, the IPCC report shows that the longer we wait to stabilise climate, the harder it will be. Models predict extreme temperatures and droughts brought on by climate change will weaken the ability of forests and other green spaces to absorb carbon dioxide. This is particularly significant for Aotearoa New Zealand, because our forests and land use offsets roughly a third of our total greenhouse gas emissions. We must begin to come to terms with how changes in climate impact our forests and their ability to absorb and store carbon.
“IPCC reports are the climate science community speaking in our most measured collective voice. Each word in this report has been carefully weighed and considered by the authors, and the document has been assessed by nearly eighty thousand experts worldwide. There are no surprises in this report for most climate scientists, only well supported facts. Strong, rapid, sustained reductions in our emissions are the only way to stabilise the earth’s climate.”
No conflicts of interest.
Professor Adrian McDonald, Director of Gateway Antarctica, School of Physical and Chemical Sciences, University of Canterbury, comments:
“The Working Group 1 sixth assessment report from the IPCC represents a vast amount of work from the authors, which must be congratulated. This report summarises the recent work of thousands of climate scientists and represents the most authoritative summary of the current state and possible futures of the Earth’s climate ever created.
“This report continues to confirm that human influences are impacting most aspects of our climate system. Temperatures have continued to increase, precipitation has changed, the oceans have warmed and sea level has continued to rise. The largest leap forward, in my view, is that the attribution of observed changes in the frequency and intensity of heat waves, heavy precipitation and flooding, and droughts to human influences is now much more certain. Basically, we have already changed our climate in dangerous ways based on robust scientific analysis.
“This report also identifies that climate model skill continues to improve. Meaning that the projections of a progressively worse climate state in the future are now even more certain.
“Simply put, this report tells us that the observed impacts of climate change are increasingly worrying. The improved and updated projections of the future in this report also show that efforts to reduce greenhouse gas emissions and prepare our societies for further change must be accelerated to safeguard the climate for future generations.”
No conflicts of interest.
Dr Lauren Vargo, Research Fellow, Antarctic Research Centre, Victoria University of Wellington, comments:
“First, it is striking how different this report is from previous reports. This report reflects a much higher confidence – we know warming is happening and that it is caused by greenhouse gas emissions from humans. That higher confidence comes from the big increases in evidence, including from the atmosphere, cryosphere, ocean, and biosphere, compared to previous reports.
“Reading this report is scary and sobering. For example, climate scientists have recently discussed the benefits of limiting warming to 1.5C compared to 2C. But this report suggests that we’ll pass 1.5C in the next decade. Another example is that we can’t rule out 15 metres of sea level rise by 2300. Finally, changes in climate due to emissions will be irreversible for centuries to millennia.
“Communities and regions will experience different changes in climate. The impacts on New Zealand will likely include: i) sea level rise, which will lead to more frequent and extreme flooding and erosion, ii) increases in extreme rain and flooding in some regions, but increases in drought in other regions, iii) decreases in glacier ice and seasonal snow, leading to impacts on water resources, hydropower, and tourism, and iv) increases in ocean warming, which will impact resources like seafood in New Zealand.
“The report does state that strong and sustained decreases in greenhouse gas emissions will limit the impacts of climate change. Strong and sustained decreases in emissions would require huge changes in our world today. But the costs associated with continuing current rates of emissions and climate change will have far worse consequences.”
No conflicts of interest.
Dr Laura Revell, Senior Lecturer in Environmental Physics, University of Canterbury, comments:
“The IPCC WG1 AR6 assessment is an immense effort, involving the work of hundreds of scientists from around the world volunteering their time over many years to synthesise the state of knowledge on climate change.
“The previous report came out in 2013, and this latest assessment represents a significant advance in our understanding of the climate system and estimating how sensitive it is to emissions of greenhouse gases. The report provides up-to-date information for policymakers, and will be used widely by scientists and science educators for years to come.
“Since 2013, many more field studies have been undertaken to study climate change, and observational time series have become longer. Clear trends are emerging – for example New Zealand, along with most parts of the world, has seen an increase in hot extremes since the 1950s. Climate models have also undergone substantial developments since the 2013 assessment was published. Significant effort has been invested by many countries – including New Zealand – to improve model performance. The climate models used to inform AR6 are more powerful than any previous generation of models, and are better at reproducing real-world observations than models used in the past. This provides confidence in projections of future climate change – noting that while a certain amount of warming is ‘locked in’, how the Earth’s climate evolves over the next century is largely up to us, the humans living in 2021.
“The key outcomes of this report are clear: sea levels are rising and extreme weather events are occurring more frequently. The scale of recent changes are unprecedented over many centuries to millennia. At this point, it is up to governments in every country to steer a course toward a low greenhouse gas emissions future and future-proof infrastructure against climate change. The science will not get much clearer than this.”
Conflict of interest statement: “I receive funding for climate-related research from MBIE, the Deep South National Science Challenge and the Royal Society of New Zealand Marsden fund.”
Dr Luke Harrington, Senior Research Fellow, New Zealand Climate Change Research Institute, Victoria University of Wellington, comments:
“When it comes to the science of climate change, this latest report from the IPCC is now the most up-to-date, authoritative guide as to what is true, what is not yet certain, and what might happen if we fail to immediately slow the rise in global temperatures, which is now driven entirely by human activities.
“Individual scientific papers can sometimes force their way into the news headlines if their results are either ground-breaking or provocative. But this report is different: its strength lies in summarising all the research, including the many pieces of deep-dive, nuanced science that don’t make the news. Some 14,000 papers were reviewed by hundreds of the world’s top climate scientists, and they reached agreement over a core sequence of facts relating to changing climate that were found to be supported by the evidence time and again.
“They then summarised these key points in an easy-to-read language that can understood by non-scientists. Since fixing the problem of a warming world will require buy-in and sacrifices from everyone, it is critical that everyone can understand exactly why dropping carbon dioxide emissions to zero is just so important, and what the consequences of continued inaction will look like.
“A few key points stood out for me in this report.
“In the last report in 2013, the big new idea in the summary for policymakers related to cumulative emissions and carbon budgets. Since then, carbon budget concepts have been both used and misused many times over. The AR6 report does a good job to reiterate that carbon budgets only make sense to use in the context of carbon dioxide and other long-lived greenhouse gas emissions, while all shorter-lived emissions (like methane or aerosols) should be thought about within a separate framework.
“And just as cumulative emissions and carbon budgets were the definitive new science to emerge from the fifth assessment report, one of the biggest improvements in AR6 relates to quantifying changes in extreme events attributable to human activity. The authors have done an excellent job to summarise the state of the science relating to whether and by how much climate change has made recent droughts, flooding and heatwaves worse, and importantly, why no such change has been seen in some regions. One of the clearest summaries is found in Figure SPM.6, which does a particularly good job of showing just how rapidly heat extremes will worsen everywhere in the future.
“That highlights another step change in this report. The IPCC has clearly worked closely with graphic designers and science communicators when designing their summary figures this time round. The clarity of messaging in the visuals, particularly when comparing AR6 with previous reports, is plain to see.
“One final highlight for me was the careful consideration placed on informing and contextualising local climate risks, given the quality of model projections available to us. This is particularly important for New Zealand, since some climate models can struggle with our thin, mountainous wedge of land sticking out of the ocean. The emphasis on never using climate models beyond their limitations, understanding precisely what those limitations are, and always working with local knowledge and contexts when making local decisions, seems to ring true for Aotearoa just as with the rest of the world – particularly as we adapt to an ever-changing climate over the coming decades.”
No conflicts of interest.
Dr Nick Cradock-Henry, Senior Scientist, Manaaki Whenua – Landcare Research, comments:
“The release of the first of three Working Groups’ reports from the IPCC should be a clarion call to civil society of the dangers of widespread and rapid changes in atmospheric conditions. The evidence is unequivocal: human activity has resulted in dramatic shifts in global temperature and precipitation patterns and is driving increased frequency and severity of extreme weather events.
“The physical science is clear and changes in the frequency and severity of extremes have particular relevance for Aotearoa New Zealand. There is evidence for an increase in hot extreme temperatures, and while more difficult to infer, in the seven years between the 5th and 6th Assessment Reports, recurring drought has had a marked impact on primary industries. Drought is now Aotearoa New Zealand’s costliest hazard, with economic and social implications for rural communities. Our agricultural systems – including horticulture, viticulture, arable cropping and livestock – are sensitive to these changes, due to their dependence on stable, long-term climatic conditions in which current land-management and land-use decisions and practices were developed, and through impacts on production, quality and yield.
“Furthermore, primary economic activities such as agriculture are, in many instances, the basis for rural economies, supporting the social, cultural, and economic vitality of our regional rural communities. These changes are expected to continue, with warming to mid-century of 1.5°C to 2.0°C. These changes will have flow on effects for local conditions, increasing the likelihood of drought, flood, and compounding hazard events.
“While an accounting of Aotearoa New Zealand’s vulnerability to climate change is not due until early next year, with the release of the report from Working Group 2, the scale and urgency of problem is clear. Warming will continue unless dramatic reductions in greenhouse gases are made. Mitigation will be insufficient to address the changes in climate presented here. To ensure sustainable long-term futures for Aotearoa New Zealand, the report is a stark reminder of the need for adaptation. Adaptation will require strategic and even radical adjustments to practices, processes, capital, and infrastructure in response to climate change, and must begin now.”
No conflicts of interest. Dr Nick Cradock-Henry is a Contributing Author, Working Group 2 for Australia-New Zealand.
Dr Sam Dean, Principal Scientist – Climate, NIWA, comments:
“The first stage of the IPCC’s 6th Assessment report sets the scene for the full report by providing the latest check-up on the Earth’s climate. It also delivers a prognosis for the future. And it’s nothing but bad news.
“New insights include that global surface temperature has increased a rather scary 0.19 degrees since the last report in 2012, pushing temperatures to the point where they are now the warmest the planet has seen for probably over 100,000 years. Scientific advances in the attribution of extreme weather events have been recognised, allowing the IPCC to make stronger statements about recent extreme weather. Some hot events were found to be ‘extremely unlikely’ to occur without human influence and that climate change is ‘likely’ the main driver of increases in the frequency and intensity of heavy rainfall events observed since the 1950s.
“Time is running out. The IPCC has confirmed that to have a 67 per cent chance of staying below 1.5 degrees of warming, the world can only emit another 400 Giga tonnes of CO2 into the atmosphere. At current global emission rates, that’s about 11 years.
“It is understandable that we may be numbed by such a difficult task. However, the IPCC offer hope with their observation that emissions scenarios with low greenhouse gas emissions can achieve rapid and sustained effects in limiting human-caused climate change. We must keep this urgent message from some of the world’s top scientists at the forefront of our minds as we take our all-important first steps towards a net-zero future.”
No conflicts of interest.
Dr Nathanael Melia, Senior Research Fellow, New Zealand Climate Change Research Institute, Victoria University of Wellington, comments:
“Straight off the bat, I’d like to emphasise that the findings contained in the IPCC Sixth Assessment Report feel significantly more concerning and urgent than the last report eight years ago. As a climate scientist, the updated knowledge presented here is as fascinating as it is impressive, and has enabled a doubling down on the IPCC’s confidence in our now ‘unequivocal’ influence on the climate1.
“However, as a human, with a young family, combined with this understanding, the contents of this report are nothing short of terrifying. In the space of eight years since the last report, the language seems to have changed from a position of a ‘warning, this could happen’, to a position of ‘brace for impact.’
“2 We now expect exponential style increases to the frequency and intensity of extreme heat events with every incremental increase of global warming. For example, a once in 50-year heat event in an 1850-1900 climate is now about five times more likely, and nine to fourteen times more likely at Paris climate agreement levels.
“This latest report shows that, regardless of the most altruistic internationally promised cuts to greenhouse gas emissions, we are committed to increasing global temperatures and associated extreme events for the next few decades. Tragically, however, the future degradation of our oceans and ice sheets is now locked in for centuries to millennia.
“Reading between the lines of the high level summary for policymakers document sea-level-rise section, the inclusion for the potential of a ‘low-likelihood, high-impact storyline’, with ‘ice-sheet processes’ (read instability/collapse) as the protagonist, is, well, alarming.
“Lastly, I would like to highlight the volunteered hard work, excellence, and likely mental health and personal sacrifice of the scientists involved, and the courage and diplomacy required to agree to the necessarily stark and unequivocal statements by the intergovernmental panel.”
No conflicts of interest.
Professor Tim Naish, Antarctic Research Centre, Victoria University of Wellington, comments:
“The sixth assessment report by Working Group 1 of the IPCC further strengthens the scientific evidence and consensus that the consequences of climate change are already being felt, and will continue to be felt for decades to come. It highlights the urgency to mitigate in order to avoid the severest impacts, saying ‘Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades’.
“However, even if the world achieves the target of the Paris Agreement, we are now committed to some pretty serious impacts that can’t be avoided, and adaptation will be paramount. This is certainly the case with rising seas, which will impact at least 800 million people by the end of the century. Although the projected ‘likely’ range (17th-84th percentile) for global sea-level rise by 2100 hasn’t changed significantly from the previous (5th) assessment report (0.44-1.01 m for all emissions scenarios) the new report does state, that ‘mean sea level rise above the likely range – approaching 2 m by 2100 and 5 m by 2150 under a very high GHG emissions scenario (SSP5-8.5) cannot be ruled out due to deep uncertainty in ice sheet processes’. This will continue to challenge local and central government governance and management of infrastructure, assets and communities living on the coast.
“The elephant in the room continues to be our ongoing lack of understanding of how Antarctica’s ice sheets will respond. One of the highest priorities for the international research community, including the Antarctic Science Platform here in New Zealand, is to quantify the rate of future mass loss of Antarctic ice, and to determine when a tipping point may be crossed, that will cause multi-generational ice loss and multi-metre sea-level rise.”
No conflicts of interest. Professor Naish was a Lead Author for IPCC AR5.
Working Group 1 author comments:
Professor James Renwick, School of Geography, Environment and Earth Sciences, Victoria University of Wellington, comments:
NOTE: Professor Renwick is a Coordinating Lead Author for the IPCC AR6 Working Group 1.
“The Working Group 1 Report of the 6th Assessment of the Intergovernmental Report on Climate Change (IPCC) is out, after more than three years of work, writing and revising.
“So what is new? We have more evidence and more certainty about how human activity is driving climate change, including around extreme events and changes in the water cycle. We know that climate change and extreme events are affecting all regions of the globe, and recent news reports make that very clear. We have seen faster changes in climate in recent decades, and faster rates of sea level rise. We know the world has warmed by over one degree Celsius since pre-industrial times. The current rates of global warming, and of sea level rise, are higher than anything that has occurred on earth for at least two thousand years.
“Unless drastic action is taken urgently to reduce emissions, the globe will reach 1.5°C warming shortly after 2030. This is sooner than estimated even in 2018, when the IPCC “1.5 degree report” came out, as the AR6 has taken a more comprehensive approach to assessing both past and future warming. However, even if we miss 1.5°C warming, strong reductions in emissions can still halt the warming at well below 2°C. Rapid reductions in carbon dioxide (and other greenhouse gas) emissions would also lead to improved air quality, something that was demonstrated in 2020 through the Covid-19-related reductions in travel and economic activity. Whatever we do, a changed climate and higher sea levels are locked in for centuries to millennia, as the oceans and the ice sheets take a very long time to respond, and the extra carbon dioxide will be in the atmosphere for centuries.
“Changes in the water cycle are a feature in the new report, with a whole chapter devoted to the topic. Water is vital for life, and changes in water availability have serious implications worldwide. Overall, we see that the water cycle is becoming more intense, that is, precipitation is increasing over land, but so is evaporation. The magnitude and occurrence of both droughts and floods are increasing.
“It is clear that all aspects of the water cycle are being affected, including rain and snowfall, glacier mass, groundwater storage, river flows, and the oceans. One clear signal is that variability and extremes in precipitation are increasing faster than changes in averages. Unless there are rapid reductions in emissions of greenhouse gases, we will see even more substantial changes in the water cycle worldwide, including the loss of glaciers and the river flows they feed, more intense precipitation and more extreme rainfall events and associated river flows, but also more intense droughts and an increase in the danger of wildfires.
“As the climate warms, the tracks of storms are moving towards the poles in many regions, notably across the Southern Hemisphere. At the same time, the high-pressure regions in the subtropics are expanding polewards. The net effects for New Zealand are that the west and south will see increases in precipitation in winter and spring, while the north and east will see reductions. As is seen across the globe, New Zealand glaciers will keep retreating as the climate warms.
“We now have a much better understanding of how aerosols (air pollution) affect the water cycle, especially for the tropical monsoons and tropical rainfall generally. Increased aerosols have generally offset the effect of the warming climate in recent decades. As the world decarbonises and aerosols decrease in the atmosphere, monsoon rainfall will change in different directions in different places.
“Studying both the past and looking to the future, we cannot rule out abrupt human-caused changes to the water cycle. For example, continued Amazon deforestation, combined with a warming climate, means that the Amazon ecosystem could cross a tipping point into a dry state during the 21st century. In addition, should the Atlantic Meridional Overturning Circulation (AMOC) collapse, there would be abrupt shifts in the water cycle worldwide. Such an event is however not considered likely this century.
“One technique for managing climate change is known as “Solar Radiation Modification” (SRM), for example blocking out sunlight by spraying aerosols into the stratosphere. It is clear that such techniques could drive abrupt changes in the water cycle. If such SRM approaches are to be used, recent research shows that that abrupt water cycle changes will occur during a rapid implementation, or termination. The impact of SRM varies spatially and it appears that it could affect different regions in potentially disruptive ways.”
Conflict of interest statement: “I am a New Zealand Climate Change Commissioner, I receive funding from MBIE for climate research.”
Dr Olaf Morgenstern, Principal Scientist – Atmosphere and Climate, NIWA, comments:
NOTE: Dr Morgenstern is the lead author of Chapter 3: “Human influence on the climate system”.
“The latest report by the Intergovernmental Panel on Climate Change (IPCC) is out, assessing the state of climate and the outlook. While human influence on climate had been assessed as ‘clear’ in the previous report in this series, released in 2013, this new assessment in unprecedented detail describes the pervasive reach of human influence into many aspects of climate. Many of these changes are unprecedented in thousands of years; human civilisation has never existed in a climate this hot.
“Restricting global warming to 1.5 degrees by the end of this century – a stated aim of the Paris Accord – will require rapid, deep, and sustained reductions of human-caused greenhouse gas emissions, reaching ‘net-zero’ at a global scale. The report assesses the consequences of warming for climate extremes (several of which have made headlines recently) – every fraction of a degree of additional warming makes most of these events, especially floods, heatwaves, and droughts, more likely and more intense.
“The 2013 report had found that the planet had warmed by 1 degree since preindustrial times. This new report increases this estimate to 1.09 degrees, a result of progressing warming in the intervening years, with several of the warmest years ever occurring since 2013, a re-evaluation of global temperatures during the preindustrial period (1850-1900), and some methodological changes. This increase in realised warming implies reductions in the allowable end-of-century warming while remaining below the targets of the Paris Accord, and also reduces the amounts of future greenhouse gas emissions consistent with these targets.
“The report does not address the practicalities of such reductions of emissions (this is the purview of another IPCC report appearing in 2022). However, it is clear that this latest assessment makes for sobering reading. Its main purpose is to inform policy – we must hope it does so successfully.”
No conflicts of interest.
Professor Nick Golledge, Professor of Glaciology, Antarctic Research Centre, Victoria University of Wellington, comments:
NOTE: Professor Golledge is a Lead Author on Chapter 9: “Ocean, cryosphere and sea level change”.
How rigorous is the new Report?
“The Report has been written by over 200 scientists from all over the world, spanning a substantial cross-section of scientific and cultural backgrounds. Collectively, these experts have assessed approximately 14,000 scientific papers, with a deliberate emphasis on recent publications that haven’t been assessed in previous IPCC reports. The Report has been externally scrutinised at every stage of its evolution during its three years of production, and has attracted nearly 80,000 individual review comments from experts all over the world. Every single submitted review comment has had to be addressed by the author team, with written responses provided and any changes made to the text carefully noted and tracked.”
What’s new?
“AR6 uses a different structure to previous reports and includes new elements such as a chapter on ‘weather and climate extremes’ and a fully-interactive online Atlas. The scientific literature assessed in the new report is as current as possible (publication cut-off was January 2021). Therefore, the scientific evidence presented in the report is largely from newer papers than in previous ARs. However, much of the scientific findings are very much in line with those of previous assessments. And that’s encouraging, because every AR has different authorship, and those authors assess different evidence. So the fact that the scientific conclusions remain consistent reflects the overwhelming agreement within the global scientific community. The thing that changes with every Report, however, is the increasing clarity of the environmental changes taking place and the urgency with which we need to act.”
Was does the new Report say about ice sheets and sea level?
“We have very high confidence that the ice lost from West Antarctica in recent decades has exceeded any gain in mass from snowfall, and we have high confidence that this loss is largely due to increased melting of ice below sea level, driven by warming ocean water. On the other side of the world the Greenland Ice Sheet has also been losing mass over recent decades, but in Greenland this is principally due to warmer air, rather than ocean, temperatures. It is virtually certain that the melting of the two great ice sheets, as well as the many thousands of glaciers around the world, will lead to globally rising sea levels for the rest of the current century. By 2100, global mean sea level is likely to be 0.4 to 0.8 m higher than the 1995–2014 average, depending on greenhouse gas emissions. But there are processes at play that we still cannot fully capture in computer models, mostly because they take place over periods of time longer than we have direct (satellite-based) observations for. In Antarctica some of these uncertain processes could greatly accelerate the loss of ice, and potentially contribute an additional one metre to sea level by 2100.”
No conflicts of interest.
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