Global climate change is accelerating and human greenhouse gas emissions are the main cause, according to a landmark report released Monday by the United Nations. There is still time to avoid a catastrophic warming of this century, but only if countries around the world stop burning fossil fuels as quickly as possible, the authors warn.
The message to world leaders is deeper and clearer than ever.
“There is no question that human activities are the root cause of climate change,” said Ko Barrett, vice chair of the Intergovernmental Panel on Climate Change (IPCC) and senior climate advisor at the National United States Oceanic and Atmospheric Administration. “Each of the past four decades has been the hottest on record since pre-industrial times.”
The authors – nearly 200 leading climate scientists – hope the report’s findings will take center stage when world leaders gather for a major climate conference in November.
The effects of this warming are evident and deadly all over the world. Heat waves, droughts and floods are killing people and disrupting lives around the world this summer. Forest fires burn with unprecedented frequency and intensity, including in places that rarely burn. Smoke and smog suffocate people in cities and towns from Asia to the Arctic. Ocean heat waves threaten entire ecosystems and fuel hurricanes and typhoons.
The science is clear: Human emissions of carbon dioxide and other greenhouse gases are the main driver of these changes.
Human greenhouse gas emissions cause extreme weather conditions
One of the biggest recent advances in climate research is in the area of so-called attribution science, which links global warming to individual weather events such as hurricanes or heat waves. Scientists can now say with certainty that humans are the cause of more extreme weather conditions, including heavy rains, prolonged heat waves and droughts.
“This whiplash – this increase in extreme wet and dry events – is expected to increase over the 21st century,” said Kim Cobb, one of the report’s authors and paleoclimate specialist at the Georgia Institute of Technology.
This is the first time that paleoclimate researchers, who study the climate of the past to understand how the Earth will change in the future, have participated in the writing of each chapter of the report. Their work helps to put today’s climate into perspective. “We can now say that global surface temperatures are reaching levels not seen in 100,000 years,” Cobb explains. “The rate of warming since 1970 is higher than any 50-year period in the past 2,000 years.”
The report also confirms that global sea level rise is accelerating. Globally, sea level rose by about 8 inches on average between 1901 and 2018, although water rose much more in some places, including some towns on the east coast and the Gulf Coast of the United States.
The rise in sea level is mainly due to melting glaciers and arctic ice. There is a lag between emissions and melting ice, which means that even if humans stopped emitting all greenhouse gases today, sea level would continue to rise for a few decades, notes the report.
“The sea level change in the middle of this century has been largely blocked,” says Bob Kopp, one of the report’s authors and director of the Institute for Earth, Ocean and Earth Sciences. the atmosphere at Rutgers University. This means that no matter what, people living in coastal areas will have to adapt to the high seas.
Scientists say it’s not too late
Despite the dire descriptions of our warmer Earth, the new report also makes it clear that it is not too late to curb global warming. The more humans reduce their emissions this decade, the more liveable the Earth will be for the rest of this century and for many centuries to come.
One of the big questions posed by world leaders is whether it is still possible to meet the targets set by the 2015 Paris climate agreement. This agreement aims to limit global warming to well below 2 degrees Celsius (3.6 degrees F), and ideally keep it below 1.5 degrees Celsius (2.7 degrees Fahrenheit). The Earth is already about 1 degree Celsius warmer than it was in the late 1800s.
Most of the world’s largest economies are not on track to meet these temperature targets, as they continue to rely too heavily on fossil fuels for electricity, transportation and industry, including the most polluting fuels. such as coal. This includes the United States, which has reduced its emissions very slowly in recent years.
The new report finds that it is still possible to achieve the targets set under the Paris Agreement, but it is becoming more difficult every day. The authors used five theoretical scenarios to predict future global warming. The scenarios include different levels of greenhouse gas emissions, as well as economic and population growth and political collaboration. In all five scenarios, the Earth will reach 1.5 degrees Celsius (2.7 degrees Fahrenheit) over the next two decades.
“Is it still possible to limit global warming to 1.5 degrees [Celsius]? The answer is yes, “says Maisa Rojas Corradi, report author and climatologist at the University of Chile.” But unless there are immediate, rapid and large-scale reductions in all greenhouse gases. greenhouse, limiting global warming to 1.5 degrees will be beyond achieve. “
The authors found that if countries around the world drastically and permanently reduced their emissions immediately, the Earth would begin to cool down around the middle of this century. On the other hand, if countries act slower to reduce emissions or fail to switch to cleaner energy sources, the Earth could warm up by 4 degrees Celsius (7.2 degrees F) or more. ‘by the end of the century.
“I think a key message here is that it’s still possible to prevent most of the most severe impacts, but it really requires unprecedented transformational change,” said Barrett, IPCC vice chair. “But the idea that there is still a way forward, I think, is a point that should give us some hope.”
Climate change is global, but the solutions are local
This is the sixth edition of the IPCC’s climate science report, and the first time scientists have broken down their findings and forecasts by region. This is a big deal because many countries rely on such reports to understand what the future of their citizens will look like and which policies make the most sense.
For example, the rate of sea level rise varies greatly depending on where you live. Governments need regional information to decide where to build new infrastructure and how to protect existing coastal towns. The same goes for drought and flooding from rainstorms, which disrupt agriculture and drinking water supplies. Big cities like Cape Town, South Africa and Chennai, India, have struggled to maintain reservoirs in recent years.
“It is very important that this report gives regional information that will help us make decisions at the regional level,” said Paola Arias, one of the report’s authors and climatologist at the University of Antioquia in Colombia.
When it comes to adaptation, the United States relies less on specific information in this report, as the federal government regularly publishes national climate assessments. However, the UN report provides important global context for the Biden administration’s pledge to reduce US greenhouse gas emissions in the middle of this decade.
“The goal that the Biden-Harris administration articulated earlier this year is the most ambitious ever in US history,” said Jane Lubchenco, deputy director of climate and environment at the Bureau of the science and technology policy of the White House. “This report tells us that we need to be ambitious. We probably need to be even more ambitious.”
It is unclear how the United States will achieve the target it has already set for itself, let alone an accelerated target. The infrastructure package Congress is currently considering includes investments in cleaner electricity, public transport, and electric devices and vehicles. Meanwhile, other major economies, including China and India, are not on track to cut emissions this decade.