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The devastating new UN report on climate change, explained

How much has humanity already changed the climate? And how much worse is it going to get?

The answers are now sharper than ever, according to an international team of scientists who say in a new report that far more aggressive measures are needed to contain catastrophic climate change and time is running out.

The Intergovernmental Panel on Climate Change (IPCC), the United Nations' climate science research group, concluded in an important new report that it is “clear” that humans have warmed skies, water and land and that “it is widespread and rapid Changes "" have already occurred in every inhabited region of the world. Many of these changes are irreversible in our lifetime.

This is the first report of its kind in eight years and a lot has changed. Scientists have pulled out of many of the best-case scenarios. They are more confident than ever that human-made climate change is exacerbating already deadly weather events, from floods to heat waves. And they are investigating the culprits of climate change, which are warming the planet even more than carbon dioxide.

The report warns that over the next 20 or 30 years the world is likely to exceed 1.5 degrees Celsius of warming compared to pre-industrial temperatures – one of the target posts of the Paris Agreement – even in scenarios where greenhouse gas emissions drop significantly . It's a strong warning for 1954 Countries will meet later this year in Glasgow, Scotland, to set more ambitious goals to tackle climate change – though many of those countries are not even on track to meet their earlier goals.

"This report tells us that recent climate changes are widespread, rapid and intense, unprecedented in thousands of years," said Ko Barrett, IPCC vice chairman and senior advisor on climate for the National Oceanic and Atmospheric Administration, in a press conference. Climate change "is already affecting every region of the world in a variety of ways," Barrett said. "There is no going back from some changes in the climate system."

Meanwhile, the effects of climate change continue to spread across the planet, compounding catastrophes like the massive forest fires in California, deadly floods in China and record heat in Siberia. Climate change is here, and if drastic action is not taken, it will only get worse.

This first edition of the latest report, known as the Sixth Assessment Report (AR6), delves into the physical sciences of climate change and examines what is driving planetary warming in the atmosphere, oceans and on land. It includes the research that has been done over the eight years since the last report. The next few chapters, which appear in the coming months, will examine the economic and environmental vulnerabilities to climate change, as well as options for mitigating global warming.

The aim of these reports is to compile the best science available and provide a solid foundation for decision-makers to act, whether to invest in clean energy, relocate people from high-risk areas, or to the most vulnerable places in managing unavoidable impacts help . IPCC reports are believed to be the final science behind climate change. Previous IPCC reports have been cited in coastal construction plans, drought risk assessments and even in legal proceedings.

While researchers have better answers on some fronts, they are also blunt about the things they don't yet know, which could have a huge impact on the viability of the planet. Certain tipping points, feedback loops, and currently unappreciated mechanisms could throw the climate further out of balance in ways that are difficult to predict.

The Northern California Dixie Fire burned more than 190,000 acres on July 26th.

Josh Edelson / AFP / Getty Images

Climate science has advanced quickly, but climate protection has not

With the AR6 report, the IPCC is building on assessments of the last few years that dealt with certain topics, such as the shrinking window in which global warming could remain below 1.5 degrees Celsius. The IPCC also examined the effects of climate change on oceans and frozen regions, as well as the impact on global food and water supplies from rising temperatures.

These reports helped spark a global movement, especially among young people, who demanded that world leaders do more to meet their commitments under the Paris Agreement before time runs out.

But in the eight years since the last comprehensive IPCC report and the six years since the Paris Agreement, human emissions of heat-storing gases have only increased. Even with emissions declining due to the Covid-19 pandemic, carbon dioxide levels in the atmosphere hit record highs this year, exceeding 419 parts per million, a level the planet has not seen in at least 2 million years.

This rise in emissions has opened up unprecedented opportunities for scientists to study climate change in real time. In addition to improvements in computer simulations, metrology, laboratory experiments, and historical records, scientists have gained much more insight and confidence in the role of humanity in cranking up the planetary thermostat.

In general, IPCC reports do not contain many new revelations because they are compiled from existing research: AR6 is based on research published before January 31, 2021, and draws on 14,000 research results Items. But paper by paper, these reports illustrate how confident scientists are about the mechanisms of climate change and how their understanding has changed.

Here are some of the most notable sections of the new report:

Scientists are even more confident that climate change is making extreme weather conditions worse

"What is new about this report is that we can now attribute many more global and regional changes to human impact and better predict future changes that we will see due to different levels of emissions," said Barrett.

Since the beginning of the industrial revolution, the world has warmed up by 1.1 degrees Celsius. It is clear that humankind's gigantic greenhouse gas emissions – currently around 2.6 million pounds of carbon dioxide per second – is the culprit. Without the burning of fossil fuels, the planet would very likely be much cooler.

Diagrams with average surface temperatures and a comparison with the expected temperatures without human influence.

The warming observed across the planet since the industrial revolution is unprecedented in its pace and magnitude and would be nearly impossible without human intervention.

IPCC

This deceptively small shift in average temperatures increases the probability and severity of extreme events and is already exacerbating disasters around the world. Now scientists can find out how much human greenhouse gas emissions make them worse.

This is due to advances in an area of ​​climate science called attribution – including better understanding of pre-industrial climate and models of a hypothetical world without human intervention. "The evidence of observed changes in extremes such as heat waves, heavy rainfall, droughts and tropical cyclones, and particularly their attribution to human impact, has increased since (the previous IPCC report)," the report said.

These methods can help scientists determine how much fossil fuel burning has made extreme events like heat waves more likely. The report says it is "almost certain" that human extreme heat events have increased in frequency and intensity. Researchers can also measure how much worse events like coastal flooding have become from sea level rise due to warming.

Climate change is global, but the effects are local

With improved measurements and modeling, scientists have been able to zoom in on parts of the planet and get a better feel for how climate change will develop. While the world is warming on average, certain places are affected by particularly sharp changes. AR6 includes an interactive atlas showing some of these effects around the world.

For example, some warming regions will dry out while others become wetter. In some cases, both can occur in the same place – the averages cannot shift much, but the extremes can increase, resulting in periods of drought followed by floods. This weather whiplash was not so valued until recently and is yet another signal of how humans are changing the climate.

"This whiplash – that increase in both extremely wet and dry events – is expected to increase in the 21st century," said Kim Cobb, lead author of the first chapter of AR6 and director of the Global Change Program at Georgia Tech, during the press conference.

And as temperatures continue to rise, those extremes will "worsen with every step of additional warming," Cobb said. However, with more specific and local information on the effects of climate change, the IPCC authors hope the report will be more useful in making decisions about planning and mitigating warming.

Carbon dioxide isn't the only bad guy

Scientists have long understood that carbon dioxide – the gas that leaks from chimneys, exhaust pipes, and chimneys – is the single biggest factor in global warming and will affect the climate for hundreds of years. However, the report says other greenhouse gases are a growing concern.

Methane, in particular, can store even more heat than carbon in the short term, over 20 years, and countries that have focused on carbon emissions may be less willing to control them. Scientists know that methane pollution from human activities such as agriculture and oil and gas exploration has reached its highest level in 800,000 years, and that other greenhouse gases such as nitrogen dioxide are also increasing.

The upside is that reducing their emissions has huge benefits in curbing climate change because these gases are so effective at trapping heat.

There is no more room for wishful thinking

There are two broad categories of variables that shape climate predictions: what humans will do and what the planet will do in response.

When scientists clear up the physics of climate change, they can better predict how the planet will react to a given concentration of greenhouse gases. This response is known as equilibrium climate sensitivity, and it estimates what would happen if the concentration of carbon dioxide in the atmosphere doubled from pre-industrial levels and reached around 560 ppm.

This year's AR6 report found that doubling the concentration of CO2 would warm the planet by about 3 ° C, with a likely range between 2.5 ° C and 4 ° C. The last major IPCC report was in 2013 a heating range of 1.5 to 4.5 ° C.

In terms of human actions, the IPCC has developed five scenarios for human greenhouse gas emissions known as Shared Socio-Economic Pathways (SSPs). Even in the best case of reducing greenhouse gas emissions, the IPCC authors expect the warming to continue at least until the middle of the century. Of the five scenarios, scientists expect the world to exceed the Paris Agreement warming target of 1.5 ° C in all, but the “Very Low Emissions” SSP expects the temperature of the planet to be before the end of the 20th century.

Diagram showing projections of warming under different common socio-economic paths.

Only two emission scenarios this century will keep warming below 2 degrees Celsius, and only one will stay below 1.5 degrees Celsius.

IPCC

Some of the worst predictions of warming seem less likely in this latest report, but so are many of the more favorable results. According to the report, it now seems impossible for the world to be lucky and for warming to somehow stay within the goals of the Paris Agreement without massive measures to be taken immediately to limit emissions.

The new IPCC report throws up several new secrets of climate change

We know that humans are dangerously warming the planet through human activities like burning fossil fuels and clearing land for agriculture and urban development. The models have become more precise in recent years, but there are still unanswered questions.

Where does all the methane come from?

Methane is increasing, but what exactly are the causes? Scientists generally know that methane comes from a mixture of natural sources like wetlands and melting permafrost and human sources like oil and gas, agriculture and landfills. The report does not identify which of the human sources are the greatest culprit, and it does not consider very carefully the feedback loops that will produce even more of this noxious gas in a warming world. And the world still does not monitor the oil and gas industry closely enough to identify and clog the leaking oil and gas facilities.

Will clouds help heat up or cool down the planet?

Clouds are one of the biggest sources of uncertainty in climate models, as the Vox podcast Unexplainable examined. These clouds of moisture in the atmosphere are complicated, difficult to predict, and can have very different effects depending on the specific conditions at a given point in the sky. Clouds change the distribution of precipitation on the planet, but can also affect temperatures. Low altitude clouds tend to throw sunlight back into space and have a net cooling effect, while high altitude clouds trap heat by absorbing and releasing infrared radiation. Exactly which clouds form when temperatures rise and where they occur will have a major impact on how climate change affects the ground.

Are there tipping points?

One of the most worrying potential outcomes of climate science is passing tipping points where humans cause irreversible, catastrophic effects that accelerate global change. The report believes these events are unlikely to happen this century, but they're terrifying to consider. For example, thawing permafrost could release huge amounts of carbon dioxide and methane, which further increase warming without human intervention. Warming could also reach a point where critical ocean circulation patterns stall, causing global changes in precipitation and sea level. Climate change could also cause critical ecosystems such as tropical rainforests to enter a cycle of collapse.

If any of these potential thresholds are exceeded, the harmful effects of warming will continue even as each country drastically cuts greenhouse gas emissions.

What will people end up doing?

We are still asking the biggest unanswered question for the future: what will humanity actually do to curb climate change? "The main issues are which future directions people on our planet will choose for energy, transport and land use, the main drivers of the changing climate," said Donald Wuebbles, professor of atmospheric science at the University of Illinois and an author on the previous IPCC report in an email.

An abandoned pomegranate orchard seen in Firebaugh, California on July 13th. Drought and heat waves weigh on the state's electricity grid as officials urge residents to reduce their water and electricity use.

David Paul Morris / Bloomberg / Getty Images

It depends what people do with that information

The IPCC's process of producing these reports is lengthy and requires every word to be approved by representatives from 195 countries. AR6 generated more than 70,000 comments. The design of the results therefore tends to be limited by the consensus.

That the group has come to such blatant conclusions shows that humanity has already caused significant damage to the climate and that even worse consequences are imminent without drastic global action. The IPCC authors insist that this report does not prescribe any specific tactics or goals for dealing with climate change, but given the predictions of disasters and faults, anyone reading the report will find it hard to find anything other than a sense of urgency .

"It makes a very compelling case for more aggressive action," said Jane Lubchenco, deputy director of the White House science and technology policy office, in an interview.

For heads of state and government, the report could be an important rationale for doing more to mitigate climate change. The next big test of this will be the Conference of the Parties (COP26) on November 26th, where the signatories of the Paris Agreement are expected to increase their ambitions to curb climate change. "The IPCC report underscores the overwhelming urgency of this moment," said John Kerry, the US special envoy on climate, in a statement. “We can achieve the much-needed low carbon economy, but time is not on our side. This is the crucial decade for action and the COP26 in Glasgow must be a turning point in this crisis. "

For climate activists, this report is a haunting reminder that the world is nowhere near enough to meet its current climate goals – let alone step up to actually keep warming in check.

The upcoming chapters of AR6 will delve into more practical questions about what tactics actually make sense to limit warming, but this first chapter, which focuses on science, leaves no room for wishful thinking. To avoid the worst effects of climate change, according to Maisa Rojas Corradi, IPCC author and director of the Center for Climate and Resilience Research at the University of Chile, far more drastic and urgent measures are needed to reduce greenhouse gas emissions immediately.

“Is it still possible to limit global warming to 1.5 degrees? The answer is yes, but unless there is an immediate, rapid and comprehensive reduction in all greenhouse gases, limiting global warming to 1.5 degrees will be out of reach, ”she said.

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