Extreme weather caused by climate change has damaged 45% of Australia’s coastal habitat



Bleached staghorn coral on the Great Barrier Reef. Many species are dependent on corals for food and shelter.
Damian Thomson, Author provided

Russ Babcock, CSIRO; Anthony Richardson, The University of Queensland; Beth Fulton, CSIRO; Eva Plaganyi, CSIRO, and Rodrigo Bustamante, CSIRO

If you think climate change is only gradually affecting our natural systems, think again.

Our research, published yesterday in Frontiers in Marine Science, looked at the large-scale impacts of a series of extreme climate events on coastal marine habitats around Australia.

We found more than 45% of the coastline was already affected by extreme weather events caused by climate change. What’s more, these ecosystems are struggling to recover as extreme events are expected to get worse.




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There is growing scientific evidence that heatwaves, floods, droughts and cyclones are increasing in frequency and intensity, and that this is caused by climate change.

Life on the coastline

Corals, seagrass, mangroves and kelp are some of the key habitat-forming species of our coastline, as they all support a host of marine invertebrates, fish, sea turtles and marine mammals.

Our team decided to look at the cumulative impacts of recently reported extreme climate events on marine habitats around Australia. We reviewed the period between 2011 and 2017 and found these events have had devastating impacts on key marine habitats.

Healthy kelp (left) in Western Australia is an important part of the food chain but it is vulnerable to even small changes in temperature and particularly slow to recover from disturbances such as the marine heatwave of 2011. Even small patches or gaps (right) where kelp has died can take many years to recover.
Russ Babcock, Author provided

These include kelp and mangrove forests, seagrass meadows, and coral reefs, some of which have not yet recovered, and may never do so. These findings paint a bleak picture, underscoring the need for urgent action.

During this period, which spanned both El Niño and La Niña conditions, scientists around Australia reported the following events:

2011: The most extreme marine heatwave ever occurred off the west coast of Australia. Temperatures were as much as 2-4℃ above average for extended periods and there was coral bleaching along more than 1,000km of coast and loss of kelp forest along hundreds of kilometres.

Seagrasses in Shark Bay and along the entire east coast of Queensland were also severely affected by extreme flooding and cyclones. The loss of seagrasses in Queensland may have led to a spike in deaths of turtles and dugongs.

2013: Extensive coral bleaching took place along more than 300km of the Pilbara coast of northwestern Australia.

2016: The most extreme coral bleaching ever recorded on the Great Barrier Reef affected more than 1,000km of the northern Great Barrier Reef. Mangrove forests across northern Australia were killed by a combination of drought, heat and abnormally low sea levels along the coast of the Gulf of Carpentaria across the Northern Territory and into Western Australia.

2017: An unprecedented second consecutive summer of coral bleaching on the Great Barrier Reef affects northern Great Barrier Reef again, as well as parts of the reef further to the south.

Heritage areas affected

Many of the impacted areas are globally significant for their size and biodiversity, and because until now they have been relatively undisturbed by climate change. Some of the areas affected are also World Heritage Areas (Great Barrier Reef, Shark Bay, Ningaloo Coast).

Seagrass meadows in Shark Bay are among the world’s most lush and extensive and help lock large amounts of carbon into sediments. The left image shows healthy seagrass but the right image shows damage from extreme climate events in 2011.
Mat Vanderklift, Author provided

The habitats affected are “foundational”: they provide food and shelter to a huge range of species. Many of the animals affected – such as large fish and turtles – support commercial industries such as tourism and fishing, as well as being culturally important to Australians.

Recovery across these impacted habitats has begun, but it’s likely some areas will never return to their previous condition.

We have used ecosystem models to evaluate the likely long-term outcomes from extreme climate events predicted to become more frequent and more intense.

This work suggests that even in places where recovery starts, the average time for full recovery may be around 15 years. Large slow-growing species such as sharks and dugongs could take even longer, up to 60 years.

But extreme climate events are predicted to occur less than 15 years apart. This will result in a step-by-step decline in the condition of these ecosystems, as it leaves too little time between events for full recovery.

This already appears to be happening with the corals of the Great Barrier Reef.

Gradual decline as things get warmer

Damage from extreme climate events occurs on top of more gradual changes driven by increases in average temperature, such as loss of kelp forests on the southeast coasts of Australia due to the spread of sea urchins and tropical grazing fish species.

Ultimately, we need to slow down and stop the heating of our planet due to the release of greenhouse gases. But even with immediate and effective emissions reduction, the planet will remain warmer, and extreme climatic events more prevalent, for decades to come.

Recovery might still be possible, but we need to know more about recovery rates and what factors promote recovery. This information will allow us to give the ecosystems a helping hand through active restoration and rehabilitation efforts.




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We will need new ways to help ecosystems function and to deliver the services that we all depend on. This will likely include decreasing (or ideally, stopping) direct human impacts, and actively assisting recovery and restoring damaged ecosystems.

Several such programs are active around Australia and internationally, attempting to boost the ability of corals, seagrass, mangroves and kelp to recover.

But they will need to be massively scaled up to be effective in the context of the large scale disturbances seen in this decade.The Conversation

Mangroves at the Flinders River near Karumba in the Gulf of Carpentaria. The healthy mangrove forest (left) is near the river while the dead mangroves (right) are at higher levels where they were much more stressed by conditions in 2016. Some small surviving mangroves are seen beginning to recover by 2017.
Robert Kenyon, Author provided

Russ Babcock, Senior Principal Research Scientist, CSIRO; Anthony Richardson, Professor, The University of Queensland; Beth Fulton, CSIRO Research Group Leader Ecosystem Modelling and Risk Assessment, CSIRO; Eva Plaganyi, Senior Principal Research Scientist, CSIRO, and Rodrigo Bustamante, Research Group Leader , CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Increasing tree cover may be like a ‘superfood’ for community mental health



Imagine Hyde Park in Sydney without its tree cover … the impact on this space and the many people who spend time in it would be profound.
EA Given/Shutterstock

Thomas Astell-Burt, University of Wollongong and Xiaoqi Feng, University of Wollongong

Increasing tree canopy and green cover across Greater Sydney and increasing the proportion of homes in urban areas within 10 minutes’ walk of quality green, open and public space are among the New South Wales premier’s new priorities. Cities around Australia have similar goals. In our latest study, we asked if more of any green space will do? Or does the type of green space matter for our mental health?

Our results suggest the type of green space does matter. Adults with 30% or more of their neighbourhood covered in some form of tree canopy had 31% lower odds of developing psychological distress. The same amount of tree cover was linked to 33% lower odds of developing fair to poor general health.

We also found poorer mental and general health among adults in areas with higher percentages of bare grass nearby, but there’s likely more to that than meets the eye.




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Green for wellbeing – science tells us how to design urban spaces that heal us


Treed neighbourhoods have a natural appeal to people.
Tim Gouw/Unsplash

How did we do the research?

Our research involved tracking changes in health over an average of about six years, for around 46,000 adults aged 45 years or older, living in Sydney, Newcastle or Wollongong. We examined health in relation to different types of green space available within a 1.6 kilometre (1 mile) walk from home.

Our method helped to guard against competing explanations for our results, such as differences in income, education, relationship status, sex, and age. We also restricted the sample to adults who did not move home, because it is plausible that people who are already healthier (for instance because they are more physically active) move into areas with more green space.

So is the answer simply more trees and less grass? Not exactly. Let’s get into the weeds.




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Trees make it cool to walk

Imagine you’re walking down a typical street on a summer’s day in the middle of an Australian city. It’s full of right angles, grey or dark hard surfaces, glass structures, and innumerable advertisements competing for your attention. Then you turn a corner and your gaze is drawn upwards to a majestic tree canopy exploding with a vivid array of greens for as far as you can see.

A tree-lined street like Swanston Street in Melbourne is a more walkable street.
kittis/Shutterstock

Let’s get the obvious out of the way. Walking down this green street, you may instantly feel some relief from the summer heat.

Studies are linking high temperatures with heat exhaustion and mental health impacts. Research has suggested trees, rather than other forms of green space, may be best at reducing temperatures in cities. It may also simply be more comfortable to walk outside in cooler temperatures – not to mention going for a run or bike ride, both of which are good for mental health.




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Feeling restored and alert

But as the minutes of walking beneath this natural umbrella of lush foliage accumulate, other things are happening too. The vibrant colours, natural shapes and textures, fresh aromas, and rustling of leaves in the breeze all provide you with effortless distraction and relief from whatever it was you might have been thinking about, or even stressing over.

Trees can provide a soothing sensory distraction from our troubles.
Jake Ingle/Unsplash

Studies back this up. Walks through green space have been shown to reduce blood pressure, improve mental acuity, boost memory recall, and reduce feelings of anxiety. The Japanese have a name for this type of experience: shinrin-yoku.

Friends, old and new

You walk past groups of people on the footpath taking time to catch up over coffee in the shade. Some research has found that tree cover, rather than green space more generally, is a predictor of social capital. Social capital, according to Robert Putnam, refers to the “social networks and the associated norms of reciprocity and trustworthiness” that may have important influences on our life chances and health.

Dogs and trees both contribute to building healthy social relations.
Liubov Ilchuk/Unsplash

You walk further and a chorus of birdsong soars through the neighbourhood noise. Trees provide shelter and food for a variety of animals. Research suggests tree canopy tends to be more biodiverse than low-lying vegetation.

Increased biodiversity may support better mental health by enhancing the restorative experience and also via the immunoregulatory benefits of microbial “Old Friends” – microorganisms that helped shape our immune systems but which have been largely eliminated from our urban environments.

Green spaces with tree canopy are settings where communities can come together to watch birds and other animals, which can also be catalysts for new conversations and developing feelings of community belonging in the neighbourhoods where we live … just ask dog owners.




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So, what about the grass?

Our research did not show a mental health benefit from more bare grassed areas. This does not mean grass is bad for mental health.

Previous research suggests adults are less likely to wander in green spaces that are relatively plain and lacking in a variety of features or amenities.
This may also be partly attributable to preferences for green spaces with more complex vegetation, such as parks that mix grass with tree canopy.

Parks with a variety of vegetation, including trees and grass, may be more attractive for a wider range of outdoor activities than those with few trees.
Author

Furthermore, large areas of bare grass in cities can make built environments more spread-out and less dense. Without tree canopy to shield from the midday sun, this may increase the likelihood of people using cars for short trips instead of walking through a park or along a footpath. The result is missed opportunities for physical activity, mental restoration, and impromptu chats with neighbours. Previous work in the United States suggests this might be why higher death rates were found in greener American cities.

Grassed areas can occupy a large amount of space for surprisingly little mental health benefit.
chuttersnap/Unsplash

Large open areas of grass can be awesome for physical activity and sport, but let’s make sure there is also plenty of tree canopy too, while also thinking about ways to get more people outdoors in green spaces. Here are some suggestions.

Making Australia greener and healthier

As the density of Australian cities continues to increase and more of us live in apartments and/or work in high-rise office blocks, it is great to see strategies to invest in tree cover and urban greening more generally across Australia. Cities with such plans include Sydney, Melbourne, Brisbane, Bendigo, Fremantle, and Wollongong.

You can get involved and have some fun at the same time too. Lots of evidence says gardening is really great for your mental health. So why not grab a mate and spend a couple of hours planting a tree on July 28 for National Tree Day!The Conversation

Both the act of planting a tree and its presence over the decades are good for us.
Amy Fry/flickr, CC BY-NC-SA

Thomas Astell-Burt, Professor of Population Health and Environmental Data Science, NHMRC Boosting Dementia Research Leadership Fellow, University of Wollongong and Xiaoqi Feng, Associate Professor of Epidemiology and NHMRC Career Development Fellow, University of Wollongong

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Budj Bim’s world heritage listing is an Australian first – what other Indigenous cultural sites could be next?



Ranger Trevor Bramwell on the walk up to the Split Rock art galleries in Cape York’s Quinkan Country in 2017.
Rebekah Ison/AAP

Claire Smith, Flinders University; Gary Jackson, Flinders University, and Jordan Ralph, Flinders University

The Budj Bim Cultural Landscape in south-west Victoria is the first Indigenous Australian landscape to be gazetted on the World Heritage List purely for its cultural values.

This listing breaks an invisible barrier: even the most iconic Indigenous Australian cultural sites, such as Uluru-Kata Tjuta and Kakadu National Parks, were listed for both natural and cultural values.




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Could the Budj Bim listing open the door to other Australian Indigenous sites obtaining a World Heritage listing? Here are five that certainly deserve greater attention.

When considering them it’s important to understand how ancestral beings inhabit living Indigenous landscapes, which they created during the era known as the Dreaming.

Today, these beings continue to live in the land. They are seen by Indigenous people as powerful and intelligent, with the capacity to hurt those who don’t act in the right way. They can be in different places at the same time. And they see everything.




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The Dampier Archipelago (including the Burrup Peninsula)

The Dampier Archipelago, 1,550 kilometres north of Perth, has one of the most spectacular rock art landscapes in Australia. The richness and diversity of this art is extraordinary, ranging from small shelters to complexes with thousands of engravings. Some images are similar to those found hundreds of kilometres away in Depuch Island, the Calvert Ranges and Port Hedland, revealing ancient social connections spanning vast distances.

The Ngarda-Ngarlie people believe this area of land was created by the ancestral beings Ngkurr, Bardi and Gardi, who left their marks in its physical features. For instance, the blood of creative beings turned into stains that are now the Marntawarrura, or “black hills”.

Ancient Aboriginal rock art found amongst thousands of drawings and carvings near the Burrup Peninsula in Western Australia.
Robert G. Bednarik/AAP

Baiame’s Ngunnhu (Brewarrina Fishtraps)

The Brewarrina fishtraps, located in the Darling River near Brewarrina in New South Wales, are a clear example of Indigenous science. They offer material evidence of the Ngemba people’s advanced knowledge of dry-stone wall technology, river hydrology and fish ecology.

The Ngemba people believe the ancestral being Baiame revealed the innovative design of the traps by throwing his net over the river. With the help of his two sons, Baiame built the fishtraps in the shape of this net.

Nearly half a kilometre long, the fishtraps’ design and complexity is extraordinary. Dry-stone weirs and ponds were designed to take advantage of the specific configuration of the landscape and seasonal changes in river flows. The pond gates are strategically located to trap fish as they migrate both upstream and downstream. For thousands of years, these distinctive traps have been used to catch fresh water fish.

The fish traps at Brewarrina photographed in 2008.
Dean Lewins/AAP

Ngarrabullgan

Ngarrabullgan, a sacred and dangerous place in north Queensland, is an important example of congruence between Aboriginal traditions and archaeologically recorded changes in behaviours. Excavations show that Aboriginal people began living on Ngarrabullgan more than 37,000 years ago. They stopped camping there about 600 years ago.

There is no evidence of climate or environmental change at this time. Nor is there evidence of depopulation, which could have caused changes in site use. However, the Djungan people believe that a spiritual being called Eekoo lives on Ngarrabullgan (also known as Mt Mulligan). He can cause sickness by throwing stones, hooks or pieces of wood into a person’s body. This does not leave a mark.

Djungan people avoid going near the top of Ngarrabullgan where Eekoo lives to avoid disturbing him. They attribute any sickness when on the mountain to Eekoo.

Ngarrabullgan, also known as Mt Mulligan, in Queensland.
Wikimedia Commons

Quinkan country

The distinctive feature of Quinkan Country in the Cape York Peninsula in North Queensland is the richness, size and density of its Aboriginal paintings and engravings. This country is best known for its depictions of Quinkan spirit beings, tall, slender Timaras and fat-bodied Imjims (or Anurra).

The rock art of Quinkan Country provides insights into Aboriginal occupation of the north-east region of Australia. The cultural traditions, laws, and stories told there were developed over at least 37,000 years.

Ranger Trevor Bramwell points to rock paintings at Split Rock near the Cape York town of Laura in 2017, in the land known as Quinkan Country.
Rebekah Ison/AAP

Western Tasmania Aboriginal Cultural Landscape

The Western Tasmania Aboriginal Cultural Landscape provides evidence of a specialised and more sedentary way of life based on seals, shellfish and land mammals. This unusual Aboriginal way of life began around 2,000 years ago. It continued until the 1830s.

Shell middens in this landscape do not contain the remains of bony fish. However, they do contain “hut depressions”. Sometimes, these are formed into the shape of villages. Circular pits in cobble beaches are near some of these depressions. It is likely that they are hides that were used when hunting seals.

A shell midden in Tasmania.
Candice Marshall/AAP

Other candidates

These places already appear on our national heritage list. There is a plethora of other important ones, both on and off the list, including Mutawintji National Park, Gundabooka National Park and State Conservation area, and Koonalda Cave, on the Nullarbor Plain.

But Aboriginal owners and custodians must be the decision-makers when it comes to proposing a World Heritage listing. They have an inherited right to benefit from a listing – and they hold cultural responsibility for the consequences of it.
Protecting these living landscapes is their responsibility. Increased tourist activity could be a new source of income for them but it could also place cultural landscapes at risk.The Conversation

Claire Smith, Professor of Archaeology, College of Humanities, Arts and Social Sciences, Flinders University; Gary Jackson, Research Associate in Archaeology, Flinders University, and Jordan Ralph, PhD Candidate, Archaeology, Flinders University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

2,000 years of records show it’s getting hotter, faster



European heatwaves are part of a pattern of rapid global warming.
EPA/ABEL ALONSO

Ben Henley, University of Melbourne

New reconstructions of Earth’s temperature over the past 2,000 years, published today in Nature Geoscience, highlight the astonishing rate of the recent widespread warming of our planet.

We also now have a clearer picture of decade-to-decade temperature variations, and what drove those fluctuations before the industrial revolution took hold.

Contrary to previous theories that pre-industrial temperature changes in the last 2,000 years were due to variations in the Sun, our research found volcanoes were largely responsible. However, these effects are now dwarfed by modern, human-driven climate change.




Read more:
40 years ago, scientists predicted climate change. And hey, they were right


Reading the tree rings

Without networks of thermometers, ocean buoys and satellites to record temperature, we need other methods to reconstruct past climates. Luckily, nature has written the answers down for us. We just have to learn how to read them.

Corals, ice cores, tree rings, lake sediments, and ocean sediment cores provide a wealth of information about past conditions – this is called “proxy” data – and can be brought together to tell us about the global climate in the past.

Tree rings, corals and ice cores all provide ‘proxy data’ – information about changing temperatures over the centuries.
Simon Stankowski/Unsplash, CC BY

Teams of scientists around the world have spent many thousands of hours of field and laboratory work to collect and analyse samples, and ultimately publish and make available their data so other scientists can undertake further analysis.

Previously, our team, along with many other proxy experts, meticulously analysed and collated temperature-sensitive proxy data covering the last 2,000 years from around the world, creating the largest database of temperature-sensitive proxy data yet assembled. We then made all of the data publicly available in one place.

Astonishing consistency between reconstruction methods

With this unique dataset in hand, our team set about reconstructing past global temperature.

We scientists are notoriously sceptical of our own analysis. But what makes us more confident about our findings is when different methods applied to the same data yield the same result.

In this paper we applied seven different methods to reconstruct global temperature from our proxy network. We were astounded to find that the methods all gave remarkably similar results for multidecadal fluctuations – a very precise result considering the breadth of the methods used.

This gave us the confidence to delve further into what drove global temperature fluctuations on decadal timescales before the industrial revolution really took hold.

What happened before human-induced climate change?

Our study produces the clearest picture yet of Earth’s average temperature over the past two millennia. We also found that climate models performed very well in comparison, and they succeed in capturing the amount of natural variability in the climate system – the natural ups and downs in temperature from year-to-year and decade-to-decade.

Using climate models and reconstructions of external climate forcing, such as from volcanic eruptions and solar variability, we deduced that before the industrial revolution, global temperature fluctuations from decade to decade in the past 2,000 years were mainly controlled by aerosol forcing from major volcanic eruptions, not variations in the Sun’s output. Volcanic aerosols have a temporary cooling effect on the global climate. Following these temporary cooling periods our reconstructions show there is an increased probability of a temporary warming period due to the recovery from volcanic cooling.

Earlier this year One Nation leader Pauline Hanson suggested that volcanic eruptions may be responsible for the recent rise in atmospheric carbon dioxide levels.

Recent warming is far beyond natural variability

There are, of course, natural changes in Earth’s temperature from decade to decade, from century to century, and also on much longer timescales. With our new reconstructions were also able to quantify the rate of warming and cooling over the past 2,000 years. Comparing our reconstructions to recent worldwide instrumental data, we found that at no time in the last 2,000 years has the rate of warming been so high.

In statistical terms, rates of warming during all 51-year periods from the 1950s onwards exceed the 99th percentile of reconstructed pre-industrial 51 yr trends. If we look at timescales longer than 20 years, the probability that the largest warming trend occurred after 1850 greatly exceeds the values expected from chance alone. And, for trend lengths over 50 years, that probability swiftly approaches 100%. So what do all these stats mean? The strength of the recent warming is extraordinary. It is yet more evidence of human-induced warming of the planet.

But hasn’t there been natural climate change in the past?

Our understanding of past temperature variations of the Earth contributes to understanding such fundamental things as how life evolved, where our species came from, how our planet works and, now that humans have fundamentally altered it, how modern climate change will unfold.

We know that over millions of years, the movement of tectonic plates and interactions between the solid earth, the atmosphere and the ocean, have a slow effect on global temperature. On shorter (but still very long) timescales of tens to hundreds of thousands of years, our planet’s climate is gradually influenced by small variations in the geometry of the Earth and the Sun, for example, small wobbles and variations in the Earth’s tilt and orbit.

From the Last Glacial Maximum, about 26,000 years ago, when huge ice sheets covered large parts of the Northern Hemisphere landmass, Earth transitioned to a 12,000-year warm period, called the Holocene.




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This was a time of relative stability in global temperature, apart from the temporary cooling effect of the odd volcano. With the development of human agriculture, our prosperity and population grew. Before the industrial revolution, Earth had not seen carbon dioxide concentrations above current levels for at least 2 million years.

Following the industrial revolution, warming commenced due to human activity. With a clearer picture of temperature variations over the past two millennia we now have a better understanding of the extraordinary nature of recent warming.

It is up to all of us to decide whether this is the kind of experiment we want to run on our planet.


I would like to gratefully acknowledge the leader of this study, Raphael Neukom, and my fellow co-authors from the PAGES 2k Consortium. We also owe the teams of proxy experts much gratitude. It is their generous contribution to science and to human knowledge that has allowed for this, and other palaeoclimate compilation and synthesis studies.The Conversation

Ben Henley, Research Fellow in Climate and Water Resources, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

40 years ago, scientists predicted climate change. And hey, they were right



It’s been four decades since the first credible, global report on the effect of carbon dioxide on the global climate.
Shutterstock

Neville Nicholls, Monash University

This month the world has been celebrating the 50th anniversary of Neil Armstrong setting foot on the Moon. But this week sees another scientific anniversary, perhaps just as important for the future of civilisation.

Forty years ago, a group of climate scientists sat down at Woods Hole Oceanographic Institution in Massachusetts for the first meeting of the “Ad Hoc Group on Carbon Dioxide and Climate”. It led to the preparation of what became known as the Charney Report – the first comprehensive assessment of global climate change due to carbon dioxide.




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It doesn’t sound as impressive as landing on the Moon, and there certainly weren’t millions waiting with bated breath for the deliberations of the meeting.

But the Charney Report is an exemplar of good science, and the success of its predictions over the past 40 years has firmly established the science of global warming.

What is this ‘greenhouse gas’ you speak of?

Other scientists, starting in the 19th century, had already demonstrated that carbon dioxide was what we now call a “greenhouse gas”. By the 1950s, scientists were predicting warming of several degrees from the burning of fossil fuels. In 1972 John Sawyer, the head of research at the UK Meteorological Office, wrote a four-page paper published in Nature summarising what was known at the time, and predicting warming of about 0.6℃ by the end of the 20th century.

But these predictions were still controversial in the 1970s. The world had, if anything, cooled since the middle of the 20th century, and there was even some speculation in the media that perhaps we were headed for an ice age.

The meeting at Woods Hole gathered together about 10 distinguished climate scientists, who also sought advice from other scientists from across the world. The group was led by Jule Charney from the Massachusetts Institute of Technology, one of the most respected atmospheric scientists of the 20th century.

The Report lays out clearly what was known about the likely effects of increasing carbon dioxide on the climate, as well as the uncertainties. The main conclusion of the Report was direct:

We estimate the most probable warming for a doubling of CO₂ to be near 3℃ with a probable error of 1.5℃.

In the 40 years since their meeting, the annual average CO₂ concentration in the atmosphere, as measured at Mauna Loa in Hawaii, has increased by about 21%. Over the same period, global average surface temperature has increased by about 0.66℃, almost exactly what could have been expected if a doubling of CO₂ produces about 2.5℃ warming – just a bit below their best estimate. A remarkably prescient prediction.


Author provided/The Conversation, CC BY-ND

Reception of the article

Despite the high regard in which the authors of the Charney Report were held by their scientific peers at the time, the report certainly didn’t lead to immediate changes in behaviour, by the public or politicians.

But over time, as the world has continued to warm as they predicted, the report has become accepted as a major milestone in our understanding of the consequences our actions have for the climate. The current crop of climate scientists revere Charney and his co-authors for their insight and clarity.

Strong science

The report exemplifies how good science works: establish an hypothesis after examining the physics and chemistry, then based on your assessment of the science make strong predictions. Here, “strong predictions” means something that would be unlikely to come true if your hypothesis and science were incorrect.

In this case, their very specific prediction was that warming of between 1.5℃ and 4.5℃ would accompany a doubling of atmospheric CO₂. At the time, global temperatures, in the absence of their hypothesis and science, might have been expected to stay pretty much the same over the ensuing 40 years, cooled a bit, possibly even cooled a lot, or warmed a lot (or a little).

In the absence of global warming science any of these outcomes could have been feasible, so their very specific prediction made for a very stringent test of their science.

The Charney Report’s authors didn’t just uncritically summarise the science. They also acted sceptically, trying to find factors that might invalidate their conclusions. They concluded:

We have tried but have been unable to find any overlooked or underestimated physical effects that could reduce the currently estimated global warmings due to a doubling of atmospheric CO₂ to negligible proportions or to reverse them altogether.

The report, and the successful verification of its prediction, provides a firm scientific basis for the discussion of what we should do about global warming.

Over the ensuing 40 years, as the world warmed pretty much as Charney and his colleagues expected, climate change science improved, with better models that included some of the factors missing from their 1979 deliberations.




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This subsequent science has, however, only confirmed the conclusions of the Charney Report, although much more detailed predictions of climate change are now possible.The Conversation

Neville Nicholls, Professor emeritus, School of Earth, Atmosphere and Environment, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.