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


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.

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.

Earth may temporarily pass dangerous 1.5℃ warming limit by 2024, major new report says

Pep Canadell, CSIRO and Rob Jackson, Stanford University

The Paris climate agreement seeks to limit global warming to 1.5℃ this century. A new report by the World Meteorological Organisation warns this limit may be exceeded by 2024 – and the risk is growing.

This first overshoot beyond 1.5℃ would be temporary, likely aided by a major climate anomaly such as an El Niño weather pattern. However, it casts new doubt on whether Earth’s climate can be permanently stabilised at 1.5℃ warming.

This finding is among those just published in a report titled United in Science. We contributed to the report, which was prepared by six leading science agencies, including the Global Carbon Project.

The report also found while greenhouse gas emissions declined slightly in 2020 due to the COVID-19 pandemic, they remained very high – which meant atmospheric carbon dioxide concentrations have continued to rise.

Woman holds a sign at a climate protest
The world may exceed the 1.5℃ warming threshold sooner than we expected.
Erik Anderson/AAP

Greenhouse gases rise as CO₂ emissions slow

Concentrations of the three main greenhouse gases – carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), have all increased over the past decade. Current concentrations in the atmosphere are, respectively, 147%, 259% and 123% of those present before the industrial era began in 1750.

Concentrations measured at Hawaii’s Mauna Loa Observatory and at Australia’s Cape Grim station in Tasmania show concentrations continued to increase in 2019 and 2020. In particular, CO₂ concentrations reached 414.38 and 410.04 parts per million in July this year, respectively, at each station.

Atmospheric concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂0) from WMO Global Atmosphere Watch.

Growth in CO₂ emissions from fossil fuel use slowed to around 1% per year in the past decade, down from 3% during the 2000s. An unprecedented decline is expected in 2020, due to the COVID-19 economic slowdown. Daily CO₂ fossil fuel emissions declined by 17% in early April at the peak of global confinement policies, compared with the previous year. But by early June they had recovered to a 5% decline.

We estimate a decline for 2020 of about 4-7% compared to 2019 levels, depending on how the pandemic plays out.

Although emissions will fall slightly, atmospheric CO₂ concentrations will still reach another record high this year. This is because we’re still adding large amounts of CO₂ to the atmosphere.

Global daily fossil CO₂ emissions to June 2020. Updated from Le Quéré et al. 2020, Nature Climate Change.

Warmest five years on record

The global average surface temperature from 2016 to 2020 will be among the warmest of any equivalent period on record, and about 0.24℃ warmer than the previous five years.

This five-year period is on the way to creating a new temperature record across much of the world, including Australia, southern Africa, much of Europe, the Middle East and northern Asia, areas of South America and parts of the United States.

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Sea levels rose by 3.2 millimetres per year on average over the past 27 years. The growth is accelerating – sea level rose 4.8 millimetres annually over the past five years, compared to 4.1 millimetres annually for the five years before that.

The past five years have also seen many extreme events. These include record-breaking heatwaves in Europe, Cyclone Idai in Mozambique, major bushfires in Australia and elsewhere, prolonged drought in southern Africa and three North Atlantic hurricanes in 2017.

Left: Global average temperature anomalies (relative to pre-industrial) from 1854 to 2020 for five data sets. UK-MetOffice. Right: Average sea level for the period from 1993 to July 16, 2020. European Space Agency and Copernicus Marine Service.

1 in 4 chance of exceeding 1.5°C warming

Our report predicts a continuing warming trend. There is a high probability that, everywhere on the planet, average temperatures in the next five years will be above the 1981-2010 average. Arctic warming is expected to be more than twice that the global average.

There’s a one-in-four chance the global annual average temperature will exceed 1.5℃ above pre-industrial levels for at least one year over the next five years. The chance is relatively small, but still significant and growing. If a major climate anomaly, such as a strong El Niño, occurs in that period, the 1.5℃ threshold is more likely to be crossed. El Niño events generally bring warmer global temperatures.

Under the Paris Agreement, crossing the 1.5℃ threshold is measured over a 30-year average, not just one year. But every year above 1.5℃ warming would take us closer to exceeding the limit.

Global average model prediction of near surface air temperature relative to 1981–2010. Black line = observations, green = modelled, blue = forecast. Probability of global temperature exceeding 1.5℃ for a single month or year shown in brown insert and right axis. UK Met Office.

Arctic Ocean sea-ice disappearing

Satellite records between 1979 and 2019 show sea ice in the Arctic summer declined at about 13% per decade, and this year reached its lowest July levels on record.

In Antarctica, summer sea ice reached its lowest and second-lowest extent in 2017 and 2018, respectively, and 2018 was also the second-lowest winter extent.

Most simulations show that by 2050, the Arctic Ocean will practically be free of sea ice for the first time. The fate of Antarctic sea ice is less certain.

A polar bear on an ice floe
Summer sea ice in the Arctic is expected to virtually disappear by 2050.
Zaruba Ondrej/AP

Urgent action can change trends

Human activities emitted 42 billion tonnes of CO₂ in 2019 alone. Under the Paris Agreement, nations committed to reducing emissions by 2030.

But our report shows a shortfall of about 15 billion tonnes of CO₂ between these commitments, and pathways consistent with limiting warming to well below 2℃ (the less ambitious end of the Paris target). The gap increases to 32 billion tonnes for the more ambitious 1.5℃ goal.

Our report models a range of climate outcomes based on various socioeconomic and policy scenarios. It shows if emission reductions are large and sustained, we can still meet the Paris goals and avoid the most severe damage to the natural world, the economy and people. But worryingly, we also have time to make it far worse.

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The Conversation

Pep Canadell, Chief research scientist, Climate Science Centre, CSIRO Oceans and Atmosphere; and Executive Director, Global Carbon Project, CSIRO and Rob Jackson, Chair, Department of Earth System Science, and Chair of the Global Carbon Project, Stanford University

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