Climate explained: how the IPCC reaches scientific consensus on climate change


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Rebecca Harris, University of Tasmania


CC BY-ND

Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.

If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz


When we say there’s a scientific consensus that human-produced greenhouse gases are causing climate change, what does that mean? What is the Intergovernmental Panel on Climate Change and what do they do?

The Intergovernmental Panel on Climate Change (IPCC) provides the world’s most authoritative scientific assessments on climate change. It provides policymakers with regular assessments of the scientific basis of climate change, its impacts and risks, and options for cutting emissions and adapting to impacts we can no longer avoid.

The IPCC has already released five assessment reports and is currently completing its Sixth Assessment (AR6), with the release of the first part of the report, on the physical science of climate change, expected on August 9.

Each assessment cycle brings together scientists from around the world and many disciplines. The current cycle involves 721 scientists from 90 countries, in three working groups covering the physical science basis (WGI), impacts, adaptation and vulnerability (WGII) and mitigation of climate change (WGIII).

A group photo showing the diversity of people contributing to the Intergovernmental Panel on Climate Change
People contributing to IPCC reports come from 90 countries and different backgrounds. This image shows the Working Group II team.
Author provided

In each assessment round, the IPCC identifies where the scientific community agrees, where there are differences of opinion and where further research is needed.

IPCC reports are timed to inform international policy developments such as the UN Framework Convention on Climate Change (UNFCCC) (First Assessment, 1990), the Kyoto Protocol (Second Assessment, 1995) and the Paris Agreement (Fifth Assessment, 2013-2014). The first AR6 report (WGI) will be released in August this year, and its approval meeting is set to take place virtually, for the first time in the IPCC’s 30-year history.

This will be followed by WGII and WGIII reports in February and March 2022, and the Synthesis Report in September 2022 — in time for the first UNFCCC Global Stocktake when countries will review progress towards the goal of the Paris Agreement to keep warming below 2℃.

During the AR6 cycle, the IPCC also published three special reports:

Graph of curent warming across the globe.
The IPCC’s special report on global warming at 1.5 showed present-day warming across the globe.
IPCC, CC BY-ND

How the IPCC reaches consensus

IPCC authors come from academia, industry, government and non-governmental organisations. All authors go through a rigorous selection process — they must be leading experts in their fields, with a strong publishing record and international reputation.

Author teams usually meet in person four times throughout the writing cycle. This is essential to enable (sometimes heated) discussion and exchange across cultures to build a truly global perspective. During the AR6 assessment cycle, lead author meetings (LAMs) for Working Group 1 were not disrupted by COVID-19, but the final WGII and WGIII meetings were held remotely, bringing challenges of different time zones, patchy internet access and more difficult communication.




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The IPCC’s reports go through an extensive peer review process. Each chapter undergoes two rounds of scientific review and revision, first by expert reviewers and then by government representatives and experts.

This review process is among the most exhaustive for any scientific document — AR6 WGI alone generated 74,849 review comments from hundreds of reviewers, representing a range of disciplines and scientific perspectives. For comparison, a paper published in a peer-reviewed journal is reviewed by only two or three experts.

The role of governments

The term intergovernmental reflects the fact that IPCC reports are created on behalf of the 193 governments in the United Nations. The processes around the review and the agreement of the wording of the Summary for Policymakers (SPM) make it difficult for governments to dismiss a report they have helped shape and approved during political negotiations.

Importantly, the involvement of governments happens at the review stage, so they are not able to dictate what goes into the reports. But they participate in the line-by-line review and revision of the SPM at a plenary session where every piece of text must be agreed on, word for word.

Acceptance in this context means that governments agree the documents are a comprehensive and balanced scientific review of the subject matter, not whether they like the content.




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The role of government delegates in the plenary is to ensure their respective governments are satisfied with the assessment, and that the assessment is policy relevant without being policy prescriptive. Government representatives can try to influence the SPM wording to support their negotiating positions, but the other government representatives and experts in the session ensure the language adheres to the evidence.

Climate deniers claim IPCC reports are politically motivated and one-sided. But given the many stages at which experts from across the political and scientific spectrum are involved, this is difficult to defend. Authors are required to record all scientifically or technically valid perspectives, even if they cannot be reconciled with a consensus view, to represent each aspect of the scientific debate.

The role of the IPCC is pivotal in bringing the international science community together to assess the science, weighing up whether it is good science and should be considered as part of the body of evidence.The Conversation

Rebecca Harris, Senior Lecturer in Climatology, Director, Climate Futures Program, University of Tasmania

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

This adorable mouse was considered extinct for over 100 years — until we found it hiding in plain sight


Wayne Lawler/Australian Wildlife Conservancy, Author provided

Emily Roycroft, Australian National UniversityAustralia has the world’s worst track record for wiping out mammals, with 34 species declared extinct since European colonisation. Many of these are humble native rodents, who’ve suffered the highest extinction rate of any mammal group.

But today, we bring some good news: one rodent species, Gould’s mouse (Pseudomys gouldii), is set to be crossed off Australia’s extinct species list. This means the number of Australia’s extinct mammals will drop from 34 to 33.

Our new research compared genome sequences across Australia’s rodents, including eight extinct species and their 42 living relatives. In a case of historical mistaken identity, we found the Gould’s mouse was genetically indistinguishable from another living species, the Shark Bay mouse (Pseudomys fieldi), also known by the Indigenous name “Djoongari” from the Pintupi and Luritja languages.

But it’s not all good news. A lack of genetic diversity in remaining populations means Djoongari are less resilient to changing environments, including from climate change. We can’t let this species die out — this time, there’d be no coming back.

Back from the dead

When Europeans colonised Australia, they rapidly and catastrophically changed the environments in which native species thrived. The introduction of feral cats, foxes and other invasive species, agricultural land clearing, inappropriate fire management, and new diseases decimated native rodent populations.

Along with many other native mammals, some rodent species were also intensely hunted for bounty in the late 19th and early 20th centuries.

DNA from this specimen of Gould’s mouse, collected in 1837 from the Hunter Valley of NSW, reveals the species should no longer be considered extinct.
Trustees of the Natural History Museum, London Photographer: C. Ching, Author provided

In 1837, a Gould’s mouse specimen was collected for the Natural History Museum, London, from the Hunter Valley of New South Wales. The last verified time it was seen alive was in 1857, near the border of Victoria and NSW.

After genomic analysis of these specimens, we found the species has been hiding in plain sight for more than 100 years, under a different name, thousands of kilometres away in Western Australia. Djoongari will now be reclassified under the scientific name Pseudomys gouldii.

Djoongari is a shaggy-coated mouse weighing 45 grams on average, making it twice the size of the invasive house mouse. It’s omnivorous, and feeds on a variety of flowers, leaves, fungi, insects and spiders. It also build tunnels and runways to travel at night, and uses above-ground nests as refuges during the day.

Not safe yet

The resurrection of the Gould’s mouse is positive news given Australia’s alarming rate of recent extinctions, but the species remains at risk.

Once occurring across mainland Australia, it now survives only on predator-free islands in Shark Bay, WA. Islands have been an important refuge for the species, protecting them from cats, foxes, diseases and other threats on the mainland.

Feral and pet cats are huge threats to small native animals. If you own a cat, make sure you keep it indoors to protect Australia’s wildlife.
Shutterstock

Conservation efforts are underway to protect the mouse in Shark Bay, with insurance populations established on other nearby islands.

Now we know Djoongari once roamed as far east as the Hunter Valley in NSW, there’s greater scope to reintroduce the species to predator-proof protected areas on the mainland. This would mean more insurance populations, but also contribute towards restoring natural ecosystems on mainland Australia — also known as “rewilding”.

However, remnant populations of this once widespread species contain only a fraction of its original genetic diversity.




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Genetic diversity is often used as a proxy for estimating the resilience of a species to threats and its potential to adapt to changes in its environment. When species have low genetic diversity, or are inbred, they are more susceptible to disease, and more likely to accumulate harmful genetic mutations.

Other eye-opening revelations

Our study also examined the genomes of seven other rodent species lost to extinction: the white-footed rabbit rat, lesser stick-nest rat, Bramble Cay melomys, short-tailed hopping mouse, long-tailed hopping mouse, big-eared hopping mouse and long-eared mouse.

Brown rodent
Bramble cay melomys were declared extinct in 2016.
Ian Bell, EHP, State of Queensland, CC BY-SA

In most cases, we found these now-extinct native rodents had relatively high genetic diversity immediately before they became extinct. High genetic diversity usually means large population sizes, suggesting native rodent populations were stable before European invasion.

This puts an end to any suggestion that these species were already on their way out prior to the arrival of Europeans.

Reports from early naturalists back up our findings. In 1846, John Cotton referred to the now-extinct white-footed rabbit rat as “the common rat of the country”. And in 1866, Gerard Krefft described the now-extinct lesser stick-nest rat as occurring in “great numbers”.




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These species went from common to extinct in less than 150 years. That’s alarmingly fast by any standard.

It shows even though genetic diversity in now-extinct rodents was high prior to colonisation, it wasn’t enough. The environment and threats changed so dramatically and rapidly, these species didn’t have the chance to adapt.

There’s a clear lesson in all this

The threats to native wildlife brought by Europeans — including feral cat predation and land clearing — are ongoing. And under climate change, the environment as we know it is set to change further, dramatically.

It’s not enough to only establish insurance populations to save species. We need to control feral predators, protect and restore habitats, and curb emissions, so more species don’t endure a rapid wipe out.

In total, we’ve lost almost 100 species to extinction since 1788, and that’s just those we know about. In native rodents alone, in less than 150 years, the equivalent of more than 10 million years of unique evolutionary history has been lost forever.

Extinction doesn’t usually offer second chances, but we’ve now got another shot to protect Gould’s mouse. We need to act now, before it’s too late.




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The Conversation


Emily Roycroft, Postdoctoral Research Fellow, Australian National University

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

Breakthrough allows scientists to determine the age of endangered native fish using DNA


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Benjamin Mayne, CSIROIdentifying the age of animals is fundamental to wildlife management. It helps scientists know if a species is at risk of extinction and the rate at which it reproduces, as well as determining what level of fishing is sustainable.

Determining the age of fish has been difficult in the past — primarily involving extracting the inner ear bone, also known as the “otolith”. Layers of growth in the otolith are counted like rings on a tree to reveal an individual’s age. Unless a dead specimen is available, this method requires killing a fish, making it unsuitable for use on endangered populations.

However a non-lethal DNA test developed by the CSIRO enables researchers to determine fish age for three iconic and threatened Australian freshwater species: the Australian lungfish, the Murray cod and the Mary River cod. We outline the technological breakthrough in our research just published.

Our fast, accurate and cost-effective test can be adapted for other fish species. We now hope to share this method to improve the protection of wild fish populations and help promote sustainable fisheries around the world.

gloved hands cut open fish with sciessors
Traditionally, age could only be determined on a dead fish. The new method is non-lethal.
Shutterstock

Iconic species at risk

Human activity has led to the population declines of the three Australian fish species at the centre of our research.

The threatened Australian lungfish is found in rivers and lakes in southeast Queensland. It’s often referred to as a “living fossil” because its extraordinary evolutionary history stretches back more than 100 million years, before all land animals including dinosaurs.

Man-made barriers in rivers reduce the movement of water, which lowers lungfish breeding rates.

Older lungfish do not have hard otolith structures, which makes determining their age difficult. Bomb radiocarbon, which analyses carbon levels in organic matter, has been used to age Australian lungfish, but this method is too expensive to be widely used.

Australian lungfish
In the past, determining the age of Australian lungfish has been challenging.

The threatened Murray cod is Australia’s largest freshwater fish. The Mary River cod is one of Australia’s most endangered fish, found in less than 30% of its former range in Queensland’s Mary River.

Habitat destruction and overfishing are major threats to Murray cod and Mary River cod populations.

Otoliths can be used to determine age for both these cod species, however this has only been done on a population-wide scale for the more prevalent Murray cod.




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Mary River cod
CSIRO estimated the age of Mary River cod.

Our DNA breakthrough

When cells divide to make new cells, DNA is replicated. This can lead to DNA methylation, which involves the addition or the loss of a “methyl group” molecule at places along the DNA strand.

Research has found the level of DNA methylation is a reliable predictor of age, particularly in mammals, including humans.

To develop our test, we first worked with zebrafish. This species is useful when studying fish biology because it has a short lifespan and high reproductive rates. We took zebrafish whose ages were known, then removed a tiny clip of their fin. We then examined DNA methylation levels in the fin sample to identify the fish’s age.

Following this successful step, we transferred the method to Australian lungfish, Murray cod and Mary River cod. Again, we used fish of known ages, as well as bomb radiocarbon dating of scales and ages determined from otoliths.

We found despite the zebrafish and the study fish species being separated by millions of years of evolution, our method worked in all four species. This suggests the test can be used to predict age in many other fish species.




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DNA strand
The test uses co-called DNA methylation to estimate age.
Shutterstock

A conservation management boom?

In the same way human population demographers use census data to understand and model human populations, we now have the tools to do this with animals.

We are looking to expand this DNA-based method to determine the age of the endangered eastern freshwater cod and trout cod. We will also continue to test the method across other species including reptiles and crustaceans.

This work is part of CSIRO’s ongoing efforts to use DNA to measure and monitor the environment. This includes estimating the lifespan of vertebrate species such as long-lived fish and surveying biodiversity in seawater using DNA extracted from the environment.

We envisage that in the not too distant future, these methods may be used by other researchers to better understand and manage wild animal populations.




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The Conversation


Benjamin Mayne, Molecular biologist and bioinformatician, CSIRO

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