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'Every fraction of warming matters': Top scientists warn of irreversible climate impacts

Dixie Fire in California

As of Aug. 9, the Dixie fire in Northern California surpassed the Bootleg fire in Oregon to become the largest U.S. wildfire of 2021.

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Climate change is accelerating and intensifying across every region of the planet, bringing with it increases in rainfall, flooding, drought, heatwaves and sea levels that are already having significant implications for economies around the world.

That is the stark consensus of the world's leading climate scientists in a landmark United Nations report Monday, which offers the clearest picture yet of both the scale of global warming already being experienced and the likely impacts of further temperature rises that are set to play out over the coming decades.

The report concludes that the world's average surface land temperature currently stands at around 1.1 degrees Celsius above pre-industrial levels and is likely to reach 1.5 degrees C — the optimal target set out in the Paris Agreement — within the next 20 years regardless of potential actions taken to slash greenhouse gas emissions in the meantime. It also stresses that human actions are "unequivocally" the primary driver of the escalating climate crisis.

Due to human activity — largely the burning of fossil fuels — concentrations of CO2 in the atmosphere are higher than at any time in the last 2 million years, with concentrations continuing to increase in 2020 despite the temporary dip in annual global emissions that resulted from the COVID-19 pandemic, according to the report.

As a result, climate change is already affecting every inhabited region on Earth, and impacts such as sea-level rise, ocean acidification and permafrost melt are inevitable and near-irreversible, leaving only their extent open to question. Some of these impacts are thought to be irreversible within timespans stretching to thousands of years.

Achieving net-zero emissions worldwide by mid-century and then moving to reduce concentrations of CO2 in the atmosphere would likely significantly reduce climate impacts and weather volatility.

The report stresses that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions over the next two decades, then the goals of limiting average temperature increases this century to 1.5 degrees C or even 2 degrees C above pre-industrial levels will be beyond reach, the scientists warn, leading to warming scenarios that could have catastrophic impacts for all ecosystems and societies.

The findings are sure to prompt renewed calls for more urgent action from global governments, businesses and civil society to do everything possible to rapidly reduce emissions and enhance the resilience of critical infrastructure in the face of worsening climate risks. The report comes less than three months before the start of the COP26 United Nations Climate Summit in Glasgow, which is widely seen as critical to global efforts to both unlock a new wave of international climate action and finalize the Paris Agreement following a stalemate at the last major UN talks in Madrid two years ago.

The assessment — drawn up by the UN's Intergovernmental Panel on Climate Change (IPCC) under challenging circumstances due to disruptions wrought by the pandemic over the past year — is the first of its kind in almost eight years. As with previous IPCC analyses, the report effectively brings together the latest climate studies, harnessing improved observational datasets to assess historical warming, as well recent progress in scientific understanding of the response of the climate system to ongoing emissions.

"Climate change is already affecting every region on Earth, in multiple ways," warned Panmao Zhai, co-chair of the IPCC working group, and chief scientist and a research professor at the Chinese Academy of Meteorological Sciences. "The changes we experience will increase with additional warming."

The report reiterates that human actions still have the potential to determine the future course of the planet's climate, detailing how achieving net-zero emissions worldwide by mid-century and then moving to reduce concentrations of CO2 in the atmosphere would likely significantly reduce climate impacts and weather volatility compared to scenarios in which current emissions level remain relatively stable or even rise in the coming decades.

Achieving net zero by mid-century, it states, would have "rapid and sustained effects to limit human-caused climate change."

If global average temperature levels can be limited to 1.5 degrees C, flooding, drought, heatwaves, storms and other impacts would be less severe and frequent, and would affect fewer regions of the world, according to the report. There would also be notable improvements in air quality as a result of the decarbonization of the global economy.

"Stabilizing the climate will require strong, rapid and sustained reductions in greenhouse gas emissions, and reaching net-zero CO2 emissions," Zhai said. "Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate."

However, the report warns that even if the world moves to rapidly reduce emissions — something it is still yet to achieve, with the International Energy Agency (IEA) warning emissions are set to rise over the next two years as the economy recovers from the coronavirus pandemic — a number of significant climate impacts are still set to play out over the coming decades. Even under a scenario where net-zero emissions are achieved worldwide by mid-century and the Paris Agreement's 1.5 degrees C temperature goal is not breached, sea level increases, the melting of ice sheets and glaciers and ocean acidification are on course to continue for hundreds if not thousands of years, making them effectively irreversible within societal timelines.

Due to ongoing melting of glaciers and polar ice sheets, sea levels are likely to rise by an average of 11-22 inches by 2100 and potentially 30 inches by 2150, even under a scenario that sees the world slash emissions to net zero by the middle of the current century, followed by shifts towards net negative emissions thereafter.

The implications for marine ecosystems, such as coral reefs, as well as many coastal regions, cities and small island states are existential with large areas facing more frequent floods and the prospect of them disappearing underwater altogether. "Due to relative sea-level rise, extreme sea-level events that occurred once per century in the recent past are projected to occur at least annually at more than half of all tide gauge locations by 2100," the report states.

However, such an outcome is still very much amongst the best case scenarios contained in the report, with the IPCC warning that if emissions continue to rise as they have been for decades, or even stabilize at current levels by around 2050, then sea level rises of 6.5 feet cannot be ruled out by the end of the current century, with increases of 16 feet possible by 2150, the ramifications of which are near unthinkable for many countries and regions.

For companies with a global footprint, the report provides the most detailed analysis of where and how your operations, supply chains and markets are vulnerable to the impacts of climate change.

The capacity for trees, soils and oceans to naturally soak up human-caused CO2 would also be reduced under higher emissions scenarios, the report warns, further limiting the planet's ability to help regulate the climate. At present land and oceans soak up just over half of human CO2, but the IPCC report warns that unless emissions are curbed natural carbon sinks could be quickly eroded, leading to further increases in atmospheric concentrations of greenhouse gases.

Downing Street was quick to react to the IPCC's findings, which Prime Minister Boris Johnson described as "sobering reading."

"Today's report makes for sobering reading, and it is clear that the next decade is going to be pivotal to securing the future of our planet," he said. "We know what must be done to limit global warming — consign coal to history and shift to clean energy sources, protect nature and provide climate finance for countries on the frontline.

"I hope today's IPCC report will be a wake-up call for the world to take action now before we meet in Glasgow in November for the critical COP26 summit."

Alok Sharma, president-designate of the critical COP26 UN climate summit in November, urged nations signed up to the Paris Agreement to come forward as soon as possible ahead of the Glasgow summit with updated climate strategies with ambitious 2030 targets.

"The science is clear, the impacts of the climate crisis can be seen around the world and if we don't act now, we will continue to see the worst effects impact lives, livelihoods and natural habitats," he said. "Our message to every country, government, business and part of society is simple. The next decade is decisive, follow the science and embrace your responsibility to keep the goal of 1.5C alive. We can do this together, by coming forward with ambitious 2030 emission reduction targets and long-term strategies with a pathway to net zero by the middle of the century, and taking action now to end coal power, accelerate the roll-out of electric vehicles, tackle deforestation and reduce methane emissions."

Green groups were unanimous in their reaction to the IPCC's latest findings, calling for an urgent scaling up of decarbonization efforts from governments, businesses, and society to drive down greenhouse gas emissions in a bid to try to stabilize the climate and avoid the worst warming outcomes.

"With the world on the brink of irreversible harm, every fraction of a degree of warming matters to limit the dangers of climate change," said Stephen Cornelius, chief adviser on climate change and WWF lead on the IPCC. "It is clear that keeping global warming to 1.5C is hugely challenging and can only be done if urgent action is taken globally to reduce greenhouse gas emissions and protect and restore nature."

Katharine Hayhoe, chief scientist for U.S. NGO The Nature Conservancy, said people throughout the world were seeing for themselves the effects of the changing climate on weather and biodiversity, adding that the IPCC's conclusions "couldn't speak any louder."

But she said the Paris Agreement — which commits almost 200 countries worldwide to collectively limiting average temperature rise to 1 degree Celsius or well below 2C — provided governments with the "foundation to act."

"It's clear we're all in the same boat — facing a challenge that will affect every one of us within our lifetimes, not to mention future generations and most other life on Earth," she said. "The need to act collectively and decisively has never been more urgent."

Green business groups were also quick to react to the IPCC's findings. Eliot Whittington, director of the Corporate Leaders Groups on climate change, said the evidence was clear that "climate change is a critical and growing business risk."

"Sensible and forward-looking businesses know they need to act now to change the way they do business and more and more governments are putting in place the plans and actions to deliver a resilient, net-zero economy," he said. "But the sad truth is that too much government commitment fails to live up to its rhetoric, and for every business committed to transformation, many more have yet to understand the significance of this challenge. We need to match our energy for climate action to the fierceness of our burning climate. Ambition needs to turn into action starting now."

Similarly, former Bank of England Governor Mark Carney, now UN Special Envoy for Climate Action and Finance, said the IPCC's assessment was critical to understanding the scale of the climate crisis, and the policy and strategic responses required to address it.

"The ambition of these policy, business and financing decisions must be based on the science, including the reality of the world's rapidly diminishing carbon budget and the fast increasing physical risks to people and planet," he said. "The IPCC report is a must-read for boards, and its implications are an imperative for immediate strategic action."

Emma Cox, global sustainability and climate change leader at consultancy giant PwC, also urged all large businesses to engage with the report. "For companies with a global footprint, the report provides the most detailed analysis of where and how your operations, supply chains and markets are vulnerable to the impacts of climate change," she said. "Climate science should remain the hard basis for all decision making and target setting. In parallel, it must be used to inform and instigate a strong policy response to close the remaining ambition gap to keep the Paris Agreement objectives alive."

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