The outlook for coral reefs remains grim unless we cut emissions fast — new research


Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Christopher Cornwall, Te Herenga Waka — Victoria University of Wellington and Verena Schoepf, University of AmsterdamThe twin stress factors of ocean warming and acidification increasingly threaten coral reefs worldwide, but relatively little is known about how various climate scenarios will affect coral reef growth rates.

Our research, published today, paints a grim picture. We estimate that even under the most optimistic emissions scenarios, we’ll see dramatic reductions in coral reef growth globally.
The good news is that 63% of all reefs in this emissions scenario will still be able to grow by 2100.

But if emissions continue to rise unabated, we predict 94% of coral reefs globally will be eroding by 2050. Even under an intermediate emissions scenario, we project a worst-case outcome in which coral reefs on average will no longer be able to grow vertically by 2100.

The latter scenarios would have dramatic consequences for marine biodiversity and the millions of people who depend on healthy, actively growing coral reefs for livelihoods and shoreline protection. This highlights the urgency and importance of acting now to drastically reduce carbon dioxide emissions.

Coral reefs are home to more than 830,000 species and provide coastal communities with food and income through fisheries and tourism.

The Great Barrier Reef alone contributes A$6.4 billion to the Australian economy. Critically, coral reefs also protect coastlines from storm surges and create land for many low-lying Indo-Pacific island nations.

Marine heatwaves, caused by ongoing ocean warming, have already had a severe impact on coral reef ecosystems by triggering mass bleaching events. These events are becoming more frequent and intense, and cause mass die-offs across large areas.

Bleaching at the Great Barrier Reef
Marine heatwaves trigger mass bleaching and coral die-offs.
Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Ocean acidification also reduces the growth of corals by limiting their ability to build their skeletons from calcium carbonate. Together, these stressors threaten the ability of coral reefs to grow and keep up with sea level rise.

Complex impacts from ocean warming and acidification

Our understanding of how ocean warming and acidification threaten reef-forming species has improved considerably over the past decade. However, understanding how coral reef growth will be altered by climate change is more complex than simply measuring rates of change from individual taxonomic groups of corals.

Our study of 183 reefs worldwide provides the first quantitative estimate of how most of the processes that control reef growth respond to climate change and affect carbonate accumulation and growth rates.

Coral reef
Coral on the Great Barrier Reef during the 2020 bleaching event.
Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Reefs grow by layering calcium carbonate, produced either by corals and coralline algae. The amount of calcium carbonate built by these reefs depends on many factors.

Cyclones, waves and currents can flush parts of the reef away. Acidifying ocean water means more dissolves chemically. And there is a biological carbonate exchange, known as bio-erosion. Sponges, parrotfish, sea urchins and algae can all eat it, but then return some as defecated sand.

Depending on which of these processes dominates, coral reefs either grow and accrete vertically, or they start to erode. Most of these processes vary for each reef, and almost all are affected by climate change.




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To complicate matters, the frequency and intensity of marine heatwaves will vary geographically, making it difficult to estimate to what degree coral mass bleaching events will reduce coral cover.

In our research, we applied these local and global processes to 233 locations on 183 distinct coral reefs that vary in their species compositions and physical complexity. We found significant variability in responses to ocean acidification and warming.

Geographical and species variability

We predict coral mass bleaching events will have the largest impact on carbonate production across all sites. The world’s coral reefs have already been transformed dramatically by these events over the past few decades.

Coral bleaching at the Maledives
Coral reef in the Maldives, before coral mass bleachign event.
Chris Perry, CC BY-ND



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We just spent two weeks surveying the Great Barrier Reef. What we saw was an utter tragedy


Diver and equipment at a coral reef
Experimental setup used to measure calcification coralline algae on the Great Barrier Reef.
Guillermo Diaz-Pulido, CC BY-ND

We used the documented impacts of the 2016 mass bleaching on the Great Barrier Reef, which affected a large range of reefs with different species compositions, depths and latitudes. During this event, each reef experienced varying heat stress, which manifested in different levels of coral cover loss.

This information helped us to calibrate models to predict heat-stress events globally between now and 2100 and to gauge the future magnitudes of heat stress and their impact on our study sites.

We found currently degraded reefs fared poorly in our model, even under lower emissions scenarios. Reefs whose carbonate production was more robust against the effects of climate change tended to be those with high present-day carbonate production rates, higher contributions from coralline algae (which are also vulnerbable, but comparatively more resistant to warming than corals) and low rates of bio-erosion.

Hope for coral reefs

In higher emissions scenarios, even reefs dominated by coralline algae began to suffer as ocean acidification and warming intensified. It is also important to note that such reefs will provide different, and perhaps reduced, services compared to coral-dominated reefs because they are structurally less complex.

People standing on a coal reef
Team members assess coral health during the 2016 bleaching event in the Kimberley, Western Australia.
Christopher Cornwall, CC BY-ND

We did not explore in depth whether remaining coral reef communities could gain tolerance to rising temperatures over time. This could manifest as an increase in the proportional abundance of heat-tolerant species as more heat-sensitive corals die during mass bleaching events.

Surviving corals could acclimatise or even adapt. But whether these mechanisms could provide hope for the continued growth of coral reefs in the future — and if so, to what extent — is largely unknown. Nor can we say if more heat-tolerant corals could sustain similar rates of reef growth and structural complexity.

Coral reef in Chagos
A coral reef in Chagos before a bleaching event in April 2016.
Chris Perry, CC BY-ND

The best hope to save coral reefs and their ecological, societal and economic benefits is to reduce our carbon emissions dramatically, and quickly. Even under our projected intermediate scenarios we expect mean global erosion of coral reefs.

Under the lowest emissions scenario we examined, we expect profound changes in coral reef growth rates and their ability to provide ecosystem services. In this scenario, only some reefs will be able to keep pace with rising sea levels.

We owe it to our children and grandchildren to reduce emissions now, if we have any hope of them witnessing the majestic nature of coral reef ecosystems.The Conversation

Christopher Cornwall, Rutherford Discovery Fellow, Te Herenga Waka — Victoria University of Wellington and Verena Schoepf, Assistant Professor, University of Amsterdam

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

A great start, but still not enough: why Victoria’s new climate target isn’t as ambitious as it sounds


Anita Foerster, Monash University; Alice Bleby, UNSW, and Anne Kallies, RMIT UniversityIn a great start towards net zero emissions by 2050, the Victorian Government recently released their Climate Change Strategy, committing to halving greenhouse emissions by 2030.

Victoria’s leadership, alongside commitments from other Australian states and territories, stands in stark contrast to the poor climate performance of our federal government.

But is it enough? Climate scientists are urging Australia to do more to reduce emissions and to do it quicker if we’re going to avert dangerous global warming. In fact, a recent Climate Council report claims achieving net zero emissions by 2050 is at least a decade too late.

We think the Victorian government has the legal mandate to do more. But we also recognise that ambitious climate action at the state level is hindered by a lack of commitment at the federal level.

Using law to drive emissions reductions

Victoria’s new strategy was developed under the Climate Change Act 2017, state legislation requiring the government to set interim emissions reduction targets on the way to net zero by 2050.

It spreads the job of achieving these targets across the economy, with different ministers responsible for pledging emissions reductions actions and reporting on progress over time.

Laws like this are emerging around the world to set targets and hold governments accountable for delivering on them. They’re a key tool to deliver on international commitments under the Paris Agreement to limit global warming to well below 2℃.

Although Australia has set a national target for emissions reduction under the Paris Agreement, it’s widely considered to be inadequate, and there’s currently no framework climate law at the national level. Independent Zali Steggall introduced such a bill in 2020, but the Morrison government hasn’t supported it.

Victoria’s new strategy lacks detail

Victoria’s Climate Change Strategy contains many exciting climate policy announcements, including:

  • renewable energy zones and big batteries in the regions
  • all government operations including schools and hospitals powered by 100% renewables by 2025
  • targets and subsidies for electric vehicle uptake
  • commitments to support innovation in hard-to-abate sectors such as agriculture.

It also recognises the need to phase out natural gas and accelerate Victoria’s renewable hydrogen industry.

These policies are designed to reduce emissions while supporting economic growth and job creation. Yet they are scant on detail.

There’s heavy reliance on achieving emissions reductions in the energy sector — arguably, this is the low-hanging fruit. Policies in transport and agriculture are far less developed, with no quantification of targeted emissions reductions to 2030.

Cows in a paddock
Victoria has committed to support innovation in hard-to-abate sectors such as agriculture.
Shutterstock

This makes it difficult to assess whether the sector pledges will drive enough change to achieve the government’s interim targets (ambitious or otherwise) and support a trajectory to net zero.

It has taken several years to develop the Climate Change Strategy. This makes the lack of detail and the undeveloped nature of some pledges a big concern.

There are also few safeguards in the Climate Change Act to ensure pledges add up to achieving targets, or that ministers across sectors deliver on them. Much depends on the political will of the government of the day.

Why Victoria’s targets aren’t enough

The Victorian Government proposes targets to reduce emissions by 28–33% on 2005 levels by 2025, and by 45–50% on 2005 levels by 2030.

The government claims these targets are ambitious. Compared to current federal government targets, this is true.




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However, the target ranges are lower than those recommended in 2019 by the Independent Expert Panel, established under the Climate Change Act to advise the government on target setting.

The panel recommended targets of 32–39% by 2025 and 45–60% by 2030 as Victoria’s “fair share” contribution to limiting warming to well below 2℃ in accordance with Paris Agreement goals. And it acknowledged these recommended ranges still wouldn’t be enough to keep warming to 1.5℃, in the context of global efforts.

Solar panels on a roof
Reducing emissions in the energy sector is low-hanging fruit.
Shutterstock

Ultimately, Victoria’s targets don’t match what scientists are now telling us about the importance of cutting emissions early to avoid the worst impacts of climate change.

A pragmatic approach or a missed opportunity?

In setting the targets, the state government has clearly taken a politically pragmatic approach.

The government claims the targets are achievable and suggests they would’ve set more ambitious targets if the federal government made a stronger commitment to climate action.

Yes, the current lack of climate ambition at the federal level in Australia is a very real constraint on progress in some areas such as energy, where a coordinated approach is crucial. But this shouldn’t outweigh aligning to best available science.

State governments have many regulatory, policy and economic levers at their disposal, with opportunities to drive significant change and innovation. And Victoria has already demonstrated strong progress in emissions reduction and renewables in the energy sector, easily meeting and exceeding previous targets.

Under the Climate Change Act, the Victorian Government will need to set new, more ambitious targets in five years.

But waiting five years goes against Victoria’s aim to lead the nation on climate action and contribute fairly to global efforts to mitigate global warming. More ambitious, science-aligned targets now would’ve been a valuable signal for industry and a sign of real climate leadership.

We need stronger laws

Without doubt, the new Climate Change Strategy is a significant step forward on an issue that’s plagued Australian politics for years. Victoria has showed framework climate laws can drive government action on climate change.




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But there are also opportunities to bolster the Climate Change Act by aligning targets to science, strengthening legal obligations to drive timely progress, and including an ongoing role for independent experts to advise on target setting and oversee progress.

Finally, it’s important to get on with the job at a federal level.

Zali Steggall’s Climate Change Bill 2020 picks up on best practice climate laws from around the world. It’s also supported by industry groups and investors.

Victoria’s experience suggests it’s surely time for Australia to take this important step.The Conversation

Anita Foerster, Senior Lecturer, Monash University; Alice Bleby, PhD Candidate, UNSW, and Anne Kallies, Senior Lecturer, RMIT University

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

Climate explained: when Antarctica melts, will gravity changes lift up land and lower sea levels?


Shutterstock/Nickolya

Robert McLachlan, Massey University


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


I’ve heard the gravity changes when Antarctica melts will lower the seas around New Zealand. Will that save us from sea level rise?

The gravitational changes when Antarctica melts do indeed affect sea levels all over the world — but not enough to save New Zealand from rising seas.

The ice ages and their effects on sea level, geology, flora and fauna were topics of intense scientific and public interest all through the 19th century. Here’s how James Croll explained the “gravity effect” of melting ice in his 1875 book Climate and Time in their Geologic Relations:

Let us now consider the effect that this condition of things would have upon the level of the sea. It would evidently tend to produce an elevation of the sea-level on the northern hemisphere in two ways. First, the addition to the sea occasioned by the melting of the ice from off the Antarctic land would tend to raise the general level of the sea. Secondly, the removal of the ice would also tend to shift the earth’s centre of gravity to the north of its present position – and as the sea must shift along with the centre, a rise of the sea on the northern hemisphere would necessarily take place.

His back-of-the-envelope calculation suggested the effect on sea level from ice melting in Antarctica would be about a third bigger than average in the northern hemisphere and a third smaller in the south.

A more detailed mathematical study by Robert Woodward in 1888 has falling sea level as far as 2000km from Antarctica, but still rising by a third more than average in the north.




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Sea-level fingerprints

Woodward’s method is the basis of determining what is now called the “sea-level fingerprint” of melting ice. Two other factors also come into play.

  1. The elasticity of the earth’s surface means the land will bounce up when it has less ice weighing it down. This pushes water away.
  2. If the ice is not at the pole, its melting shifts the south pole (the axis of rotation), redistributing water.

Combining these effects gives the sea-level fingerprints of one metre of sea-level rise from either the West Antarctic Ice Sheet (WAIS) and Greenland (GIS), as shown here:

Red areas get more than the average sea level rise, blue areas get less.
Fingerprints of sea-level change following melting of ice from West Antartica (WAIS) and Greenland (GIS) equivalent to one metre of sea-level rise on average. Red areas get up to 40% more than the average sea-level rise, blue areas get less.
Author provided, CC BY-SA

Woodward’s method from 1888 holds up pretty well – some locations in the northern hemisphere can get a third more than the average sea level rise. New Zealand gets a little bit below the average effect from Antarctica, and a little more than average from Greenland. Overall, New Zealand can expect slightly higher than average sea level rise.

Combining the sea-level fingerprints of all known sources of melting ice, together with other known changes of local land level such as subsidence and uplift, gives a good fit to the observed pattern of sea level rise around the world. For example, sea level has been falling near West Antarctica, due to the gravity effect.

Changes in sea level around the world, 1993-2019

NOAA

Sea-level rise is accelerating, but the future rate is uncertain

The global average rise in sea level is 110mm for 1900-1993 and 100mm for 1993–2020. The recent acceleration is mostly due to increased thermal expansion of the top two kilometres of the oceans (warm water is less dense and expands) and increased melting of Greenland.

But the Gravity Recovery and Climate Experiment satellite has revealed the melting of Antarctica has accelerated by a factor of five in recent decades. Future changes in Antarctica represent a major source of uncertainty when trying to forecast sea levels.

Much of West Antarctica lies below sea level and is potentially subject to an instability in which warming ocean water melts the ice front from below. This would cause the ice sheet to peel off the ocean floor, accelerating the flow of the glacier towards the sea.

In fact, this has been directly observed, both in the location of glacial “grounding lines”, some of which have retreated by tens of kilometres in recent decades, and most recently by the Icefin submersible robot which visited the grounding line of the Thwaites Glacier, 2000km east of Scott Base, and found the water temperature to be 2℃ above the local freezing point.




Read more:
If warming exceeds 2°C, Antarctica’s melting ice sheets could raise seas 20 metres in coming centuries


The big question is whether this instability has been irreversibly set into motion. Some glaciologists say it has, but the balance of opinion, summarised by the IPCC’s report on the cryosphere, is that:

Observed grounding line retreat … is not definitive proof that Marine Ice Sheet Instability is underway. Whether unstable West Antarctic Ice Sheet retreat has begun or is imminent remains a critical uncertainty.

The IPCC special report on 1.5℃ concluded that “these instabilities could be triggered at around 1.5℃ to 2℃ of global warming”.

What’s in store for New Zealand

Predictions for New Zealand range from a further 0.46 metres of sea-level rise by 2100 (under a low-emission scenario, with warming kept under 2℃) to 1.05 metres (under a high-emission scenario).

A continued rise in sea levels over future centuries may be inevitable — there are 66m of sea level rise locked up in ice at present — but the rate will depend on how fast we can reduce emissions.

A five-year, NZ$7m research project, NZ SeaRise, is now underway, seeking to improve predictions of sea-level rise out to 2100 and beyond and their implications for local planning.The Conversation

Robert McLachlan, Professor in Applied Mathematics, Massey University

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

Paying Australia’s coal-fired power stations to stay open longer is bad for consumers and the planet


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Daniel J Cass, University of Sydney; Joel Gilmore, Griffith University, and Tim Nelson, Griffith UniversityAustralian governments are busy designing the nation’s transition to a clean energy future. Unfortunately, in a misguided effort to ensure electricity supplies remain affordable and reliable, governments are considering a move that would effectively pay Australia’s old, polluting coal-fired power stations to stay open longer.

The measure is one of several options proposed by the Energy Security Board (ESB), the chief energy advisor to Australian governments on electricity market reform. The board on Friday released a vision to redesign the National Electricity Market as it transitions to clean energy.

The key challenges of the transition are ensuring it is smooth (without blackouts) and affordable, as coal and gas generators close and are replaced by renewable energy.

The redesign has been two years in the making. The ESB has done a very good job of identifying key issues, and most of its recommendations are sound. But its option to change the way electricity generators and retailers strike contracts for electricity, if adopted, would be highly counterproductive – bad both for consumers and for climate action.

Electricity lines at sunset
One proposed reform to Australia’s electricity market would be bad for consumers and climate action.
Shutterstock

The energy market dilemma

The National Electricity Market (NEM) covers every Australian jurisdiction except Western Australia and the Northern Territory. It comprises electricity generators, transmission and distribution networks, electricity retailers, customers and a financial market where electricity is traded.

Electricity generators in the NEM comprise older, polluting technology such as gas- and coal-fired power, and newer, clean forms of generation such as wind and solar. Renewable energy, which makes up about 23% of our electricity mix, is now cheaper than energy from coal and gas.

Wind and solar energy is “variable” – only produced when the sun is shining and the wind is blowing. Technology such as battery storage is needed to smooth out renewable energy supplies and make it “dispatchable”, meaning it can be delivered on demand.

Some say coal generators, which supply dispatchable electricity, are the best way to ensure reliable and affordable electricity. But Australia’s coal-fired power stations, some of which are more than 40 years old, are becoming more prone to breakdowns – and so less reliable and more expensive – as they age. This has led to some closing suddenly.

Without a clear national approach to emissions targets, there’s a risk these sudden closures will occur again.




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Wind farm near coast
Wind and solar energy is variable.
Shutterstock

So what’s proposed?

To address reliability concerns, the ESB has proposed an option known as the “physical retailer reliability obligation”.

In a nutshell, the change would require electricity retailers to negotiate contracts for a certain amount of “dispatchable” electricity from specific generators for times of the year when reliability is a concern, such as the peak weeks of summer when lots of people use air conditioning.

Currently, the Australian Energy Market Operator has reserve electricity measures it can deploy when market supply falls short.

But under the new obligation, all retailers would also have to enter contracts for dispatchable supply. This would likely require buying electricity from the coal generators that dominate the market. This provides a revenue source enabling these coal plants to remain open even when cheaper renewable energy makes them unprofitable.

The ESB says without the change, the closure of coal generators will be unpredictable or “disorderly”, creating price shocks and reliability risks.

hand turns off light switch in bedroom
The ESWB says the recommendation would address concerns over electricity reliability.
Shutterstock

A big risk

Even the ESB concedes the recommendation comes with considerable risks. In particular, the board says it may:

  • impose increased barriers to retail competition and product innovation
  • lead to possible overcompensation of existing coal and gas generators.

In short, the policy could potentially lock in increasingly unreliable, ageing coal assets, stall new investment in new renewable energy storage such as batteries and pumped hydro and increase market concentration.

It could also push up electricity prices. Electricity retailers are likely to pass on the cost of these new electricity contracts to consumers, no matter how much energy that household or business actually used.

The existing market already encourages generators to provide reliable supply – and applies strong penalties if they don’t. And in fact, the NEM experiences reliability issues for an average of just one minute per year. It would appear little could be added to the existing market design to make generators more reliable than they are.

Finally, the market is dominated by three large “gentailers” – AGL, Energy Australia and Origin – which own both generators and the retail companies that sell electricity. The proposed change would disadvantage smaller electricity retailers, which in many cases would be forced to buy electricity from generators owned by their competitors.

Australia’s gentailers are heavily invested in coal power stations. The proposed change would further concentrate their market power while propping up coal.




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warning sign on fence
The proposed change brings a raft of risks to the electricity market.
Kelly Barnes/AAP

What governments should do

If coal-fired power stations are protected from competition, it will deter investment in cleaner alternatives. The recommendation, if adopted, would delay decarbonisation and put Australia further at odds with our international peers on climate policy.

The federal and state governments must work together to develop a plan for electricity that facilitates clean energy investment while controlling costs for consumers.

The plan should be coordinated across the states. Without this, we risk creating a sharper shock later, when climate diplomacy requires the planned retirement of coal plants. Other nations have acknowledged the likely demise of coal, and it’s time Australia caught up.




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The Conversation


Daniel J Cass, Research Affiliate, Sydney Business School, University of Sydney; Joel Gilmore, Associate Professor, Griffith University, and Tim Nelson, Associate Professor of Economics, Griffith University

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

The 1.5℃ global warming limit is not impossible – but without political action it soon will be


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Bill Hare, Potsdam Institute for Climate Impact Research; Carl-Friedrich Schleussner, Humboldt University of Berlin; Joeri Rogelj, Imperial College London, and Piers Forster, University of LeedsLimiting global warming to 1.5℃ this century is a central goal of the Paris Agreement. In recent months, climate experts and others, including in Australia, have suggested the target is now impossible.

Whether Earth can stay within 1.5℃ warming involves two distinct questions. First, is it physically, technically and economically feasible, considering the physics of the Earth system and possible rates of societal change? Science indicates the answer is “yes” – although it will be very difficult and the best opportunities for success lie in the past.

The second question is whether governments will take sufficient action to reduce greenhouse gas emissions. This answer depends on the ambition of governments, and the effectiveness of campaigning by non-government organisations and others.

So scientifically speaking, humanity can still limit global warming to 1.5°C this century. But political action will determine whether it actually does. Conflating the two questions amounts to misplaced punditry, and is dangerous.

Women holds sign at climate march
Staying within 1.5℃ is scientifically possible, but requires government ambition.
Erik Anderson/AAP

1.5℃ wasn’t plucked from thin air

The Paris Agreement was adopted by 195 countries in 2015. The inclusion of the 1.5℃ warming limit came after a long push by vulnerable, small-island and least developed countries for whom reaching that goal is their best chance for survival. The were backed by other climate-vulnerable nations and a coalition of high-ambition countries.

The 1.5℃ limit wasn’t plucked from thin air – it was informed by the best available science. Between 2013 and 2015, an extensive United Nations review process determined that limiting warming to 2℃ this century cannot avoid dangerous climate change.

Since Paris, the science on 1.5℃ has expanded rapidly. An Intergovernmental Panel on Climate Change (IPCC) report in 2018 synthesised hundreds of studies and found rapidly escalating risks in global warming between 1.5℃ and 2℃.

The landmark report also changed the climate risk narrative away from a somewhat unimaginable hothouse world in 2100, to a very real threat within most of our lifetimes – one which climate action now could help avoid.

The message was not lost on a world experiencing ever more climate impacts firsthand. It galvanised an unprecedented global youth and activist movement demanding action compatible with the 1.5℃ limit.

The near-term benefits of stringent emissions reduction are becoming ever clearer. It can significantly reduce near-term warming rates and increase the prospects for climate resilient development.

Firefighter battles blaze
The urgency of climate action is not lost on those who’ve experienced its effects firsthand.
Evan Collins/AAP

A matter of probabilities

The IPCC looked extensively at emission reductions required to pursue the 1.5℃ limit. It found getting on a 1.5℃ track is feasible but would require halving global emissions by 2030 compared to 2010 and reaching net-zero emissions by mid-century.

It found no published emission reduction pathways giving the world a likely (more than 66%) chance of limiting peak warming this century to 1.5℃. But it identified a range of pathways with about a one-in-two chance of achieving this, with no or limited overshoot.

Having about a one-in-two chance of limiting warming to 1.5℃ is not ideal. But these pathways typically have a greater than 90% chance of limiting warming to well below 2℃, and so are fully compatible with the overall Paris goal.




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Scott Morrison holding a lump of coal in Parliament
Staying under 1.5℃ warming requires political will.
Lukas Coch/AAP

Don’t rely on carbon budgets

Carbon budgets show the amount of carbon dioxide that can be emitted for a given level of global warming. Some point to carbon budgets to argue the 1.5℃ goal is now impossible.

But carbon budget estimates are nuanced, and not a suitable way to conclude a temperature level is no longer possible.

The carbon budget for 1.5℃ depends on several factors, including:

  • the likelihood with which warming will be be halted at 1.5℃
  • the extent to which non-CO₂ greenhouse emissions such as methane are reduced
  • uncertainties in how the climate responds these emissions.

These uncertainties mean strong conclusions cannot be drawn based on single carbon budget estimate. And, at present, carbon budgets and other estimates do not support any argument that limiting warming to 1.5℃ is impossible.

Keeping temperature rises below 1.5℃ cannot be guaranteed, given the history of action to date, but the goal is certainly not impossible. As any doctor embarking on a critical surgery would say about a one-in-two survival chance is certainly no reason not to do their utmost.

Wind farm
Staying below 1.5°C is a difficult, but not impossible, task.
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Closer than we’ve ever been

It’s important to remember the special role the 1.5℃ goal plays in how governments respond to climate change. Five years on from Paris, and the gains of including that upper ambition in the agreement are showing.

Some 127 countries aim to achieve net-zero emissions by mid-century at the latest – something considered unrealistic just a few years ago. If achieved globally and accompanied by stringent near-term reductions, the actions could be in line with 1.5℃.

If all these countries were to deliver on these targets in line with the best-available science on net zero, we may have a one-in-two chance of limiting warming this century to 2.1℃ (but a meagre one-in-ten that it is kept to 1.5°C). Much more work is needed and more countries need to step up. But for the first time, current ambition brings the 1.5℃ limit within striking distance.

The next ten years are crucial, and the focus now must be on governments’ 2030 targets for emissions reduction. If these are not set close enough to a 1.5℃-compatible emissions pathway, it will be increasingly difficult to reach net-zero by 2050.

The United Kingdom and European Union are getting close to this pathway. The United States’ new climate targets are a major step forward, and China is moving in the right direction. Australia is now under heavy scrutiny as it prepares to update its inadequate 2030 target.

The UN wants a 1.5℃ pathway to be the focus at this year’s COP26 climate summit in Glasgow. The stakes could not be higher.




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The Conversation


Bill Hare, Director, Climate Analytics, Adjunct Professor, Murdoch University (Perth), Visiting scientist, Potsdam Institute for Climate Impact Research; Carl-Friedrich Schleussner, Research Group Leader, Humboldt University of Berlin; Joeri Rogelj, Director of Research and Lecturer – Grantham Institute Climate Change & the Environment, Imperial College London, and Piers Forster, Professor of Physical Climate Change; Director of the Priestley International Centre for Climate, University of Leeds

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

Watching a coral reef die as climate change devastates one of the most pristine tropical island areas on Earth


Sam Purkis, University of MiamiThe Chagos Archipelago is one of the most remote, seemingly idyllic places on Earth. Coconut-covered sandy beaches with incredible bird life rim tropical islands in the Indian Ocean, hundreds of miles from any continent. Just below the waves, coral reefs stretch for miles along an underwater mountain chain.

It’s a paradise. At least it was before the heat wave.

When I first explored the Chagos Archipelago 15 years ago, the underwater view was incredible. Schools of brilliantly colored fish in blues, yellows and oranges darted among the corals of a vast, healthy reef system. Sharks and other large predators swam overhead. Because the archipelago is so remote and sits in one of the largest marine protected areas on the planet, it has been sheltered from industrial fishing fleets and other activities that can harm the coastal environment.

But it can’t be protected from climate change.

A diver carries a plastic pipe for measuring while swimming over a variety of corals
A diver documents the coral reefs in the Chagos Archipelago.
Khaled bin Sultan Living Oceans Foundation

In 2015, a marine heat wave struck, harming coral reefs worldwide. I’m a marine biologist at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, and I was with a team of researchers on a 10-year global expedition to map the world’s reefs, led by the Khaled bin Sultan Living Oceans Foundation. We were wrapping up our work in the Chagos Archipelago at the time. Our report on the state of the reefs there was just published in spring 2021.

As the water temperature rose, the corals began to bleach. To the untrained eye, the scene would have looked fantastic. When the water heats up, corals become stressed and they expel the tiny algae called dinoflagellates that live in their tissue. Bleaching isn’t as simple as going from a living coral to a bleached white one, though. After they expel the algae, the corals turn fluorescent pinks and blues and yellows as they produce chemicals to protect themselves from the Sun’s harmful rays. The entire reef was turning psychedelic colors.

Two bright pink coral mounds
Just before they turned white, the corals turned abnormally bright shades.
Phil Renaud/Khaled bin Sultan Living Oceans Foundation

That explosion of color is rare, and it doesn’t last long. Over the following week, we watched the corals turn white and start to die. It wasn’t just small pieces of the reef that were bleaching – it was happening across hundreds of square miles.

What most people think of as a coral is actually many tiny colonial polyps that build calcium carbonate skeletons. With their algae gone, the coral polyps could still feed by plucking morsels out of the water, but their metabolism slows without the algae, which provide more nutrients through photosynthesis. They were left desperately weakened and more vulnerable to diseases. We could see diseases taking hold, and that’s what finished them off.

We were witnessing the death of a reef.

Rising temperatures increase the heat wave risk

The devastation of the Chagos Reef wasn’t happening in isolation.

Over the past century, sea surface temperatures have risen by an average of about 0.13 degrees Celsius (0.23 F) per decade as the oceans absorb the vast majority of greenhouse gas emissions from human activities, largely from the burning of fossil fuels. The temperature increase and changing ocean chemistry affects sea life of all kinds, from deteriorating the shells of oysters and tiny pteropods, an essential part of the food chain, to causing fish populations to migrate to cooler water.

Corals can become stressed when temperatures around them rise just 1 C (1.8 F) above their tolerance level. With water temperature elevated from global warming, even a minor heat wave can become devastating.

In 2015, the ocean heat from a strong El Niño event triggered the mass bleaching in the Chagos reefs and around the world. It was the third global bleaching on record, following events in 1998 and 2010.

Bleaching doesn’t just affect the corals – entire reef systems and the fish that feed, spawn and live among the coral branches suffer. One study of reefs around Papua New Guinea in the southwest Pacific found that about 75% of the reef fish species declined after the 1998 bleaching, and many of those species declined by more than half.

Research shows marine heat waves are now about 20 times more likely than they were just four decades ago, and they tend to be hotter and last longer. We’re at the point now that some places in the world are anticipating coral bleaching every couple of years.

That increasing frequency of heat waves is a death knell for reefs. They don’t have time to recover before they get hit again.

Where we saw signs of hope

During the Global Reef Expedition, we visited over 1,000 reefs around the world. Our mission was to conduct standardized surveys to assess the state of the reefs and map the reefs in detail so scientists could document and hopefully respond to changes in the future. With that knowledge, countries can plan more effectively to protect the reefs, important national resources, providing hundreds of billions of dollars a year in economic value while also protecting coastlines from waves and storms.

We saw damage almost everywhere, from the Bahamas to the Great Barrier Reef.

Some reefs are able to survive heat waves better than others. Cooler, stronger currents, and even storms and cloudier areas can help prevent heat building up. But the global trend is not promising. The world has already lost 30% to 50% of its reefs in the last 40 years, and scientists have warned that most of the remaining reefs could be gone within decades.

Diver with large sea turtle swimming over corals.
The author, Sam Purkis, dives near a hawksbill turtle in the Chagos Archipelago.
Derek Manzello/Khaled bin Sultan Living Oceans Foundation

While we see some evidence that certain marine species are moving to cooler waters as the planet warms, a reef takes thousands of years to establish and grow, and it is limited by geography.

In the areas where we saw glimmers of hope, it was mostly due to good management. When a region can control other harmful human factors – such as overfishing, extensive coastal development, pollution and runoff – the reefs are healthier and better able to handle the global pressures from climate change.

Establishing large marine protected areas is one of the most effective ways I’ve seen to protect coral reefs because it limits those other harms.

The Chagos marine protected area covers 640,000 square kilometers (250,000 square miles) with only one island currently inhabited – Diego Garcia, which houses a U.S. military base. The British government, which created the marine protected area in 2010, has been under pressure to turn over control of the region to the country of Mauritius, where former Chagos residents now live and which won a challenge over it in the International Court of Justice in 2020. Whatever happens with jurisdiction, the region would benefit from maintaining a high level of marine protection.

A warning for other ecosystems

The Chagos reefs could potentially recover – if they are spared from more heat waves. Even a 10% recovery would make the reefs stronger for when the next bleaching occurs. But recovery of a reef is measured in decades, not years.

So far, research missions that have returned to the Chagos reefs have found only meager recovery, if any at all.

We knew the reefs weren’t doing well under the insidious march of climate change in 2011, when the global reef expedition started. But it’s nothing like the intensity of worry we have now in 2021.

Coral reefs are the canary in the coal mine. Humans have collapsed other ecosystems before through overfishing, overhunting and development, but this is the first unequivocally tied to climate change. It’s a harbinger of what can happen to other ecosystems as they reach their survival thresholds.

This story is part of Oceans 21

Our series on the global ocean opened with five in-depth profiles. Look for new articles on the state of our oceans in the lead-up to the U.N.‘s next climate conference, COP26. The series is brought to you by The Conversation’s international network.The Conversation

Sam Purkis, Professor and Chair of the Department of Marine Sciences, University of Miami

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