People evacuate from wildfire north of Athens, Greece on Friday. A climate-induced heat wave has caused the fire to burn out of control. Scientists warn that people are running out of time to curb greenhouse gas emissions and avoid catastrophic global warming. Thodoris Nikolaou / AP hide caption
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Thodoris Nikolaou / AP
People evacuate from wildfire north of Athens, Greece on Friday. A climate-induced heat wave has caused the fire to burn out of control. Scientists warn that people are running out of time to curb greenhouse gas emissions and avoid catastrophic global warming.
Thodoris Nikolaou / AP
Global climate change is accelerating and human greenhouse gas emissions are the overwhelming cause, according to a landmark United Nations report on Monday. There is still time to avoid catastrophic warming this century, but only if countries around the world stop burning fossil fuels as soon as possible, the authors warn.
The message to world leaders is darker and clearer than ever.
“It is undeniable that human activity is causing climate change,” said Ko Barrett, vice chairman of the United Nations Intergovernmental Panel on Climate Change (IPCC) and chief climate adviser for the US National Oceanic and Atmospheric Administration. “Each of the last four decades has been the warmest since pre-industrial times.”
The authors – nearly 200 leading climate scientists – hope that the report’s findings will be the focus when world leaders meet for a major climate change conference in November.
The effects of this warming are evident and deadly around the world. Heat waves, droughts and floods are killing people and disrupting life around the world this summer. Forest fires burn with unprecedented frequency and intensity, even in places that used to rarely burn. Smoke and smog suffocate people in cities and towns from Asia to the Arctic. The ocean heat waves threaten entire ecosystems and charge hurricanes and typhoons.
The science is clear: human emissions of carbon dioxide and other greenhouse gases are the main reason for such changes.
Human greenhouse gas emissions cause extreme weather
One of the greatest advances in climate research in recent times has been in the field of so-called attribution science, which links global warming to individual weather events such as hurricanes or heat waves. Scientists can now safely say that humans are causing more extreme weather, including heavy downpours and prolonged heat waves and droughts.
“This whiplash – that increase in both extremely wet and dry events – is expected to increase in the 21st century,” said Kim Cobb, one of the authors of the report and a paleoclimate scientist at the Georgia Institute of Technology.
This is the first time paleoclimate researchers studying past climates to understand how the earth will change in the future are writing every chapter of the report. Your work helps to put today’s climate in the right light. “We can now say that global surface temperatures are reaching levels not seen in 100,000 years,” says Cobb. “The rate of warming since 1970 is greater than any 50-year period in the past 2,000 years.”
The report also confirms that global sea level rise is accelerating. Globally, sea levels rose an average of about 8 inches between 1901 and 2018, although the water rose much more sharply in some locations, including some cities on the east coast and the Gulf Coast of the United States
Sea level rise is mainly driven by melting glaciers and arctic ice. There is a lag between emissions and the melting of the ice, which means that even if people stopped emitting all greenhouse gases today, sea levels would continue to rise for a few decades, the report said.
“The change in sea level by the middle of this century has largely been recorded,” says Bob Kopp, one of the authors of the report and director of the Institute for Earth, Ocean and Atmospheric Sciences at Rutgers University. This means that people in coastal areas definitely have to adapt to the higher seas.
Heavy rain in July caused severe flooding in Henan Province, China. Scientists say human greenhouse gas emissions are causing more extreme rainfall in many parts of the world. Dake Kang / AP Hide caption
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Dake Kang / AP
Heavy rain in July caused severe flooding in Henan Province, China. Scientists say human greenhouse gas emissions are causing more extreme rainfall in many parts of the world.
Dake Kang / AP
Scientists say it’s not too late
Despite the disastrous descriptions of our hotter earth, the new report also makes it clear that it is not too late to contain global warming. The more people reduce emissions in this decade, the more livable the earth will be for the rest of this century and for many centuries to come.
One of the big questions facing world politicians is whether it is still possible to achieve the goals of the 2015 Paris Agreement. This agreement aims to limit global warming to well below 2 degrees Celsius (3.6 degrees F) and ideally to keep it below 1.5 degrees Celsius (2.7 degrees Fahrenheit). The earth is already around 1 degree Celsius hotter than it was at the end of the 19th century.
Most of the world’s largest economies are not on track to meet these temperature goals because they continue to rely too heavily on fossil fuels for power, transportation and industry – including most polluting fuels like coal. This also includes the USA, which has only very slowly reduced emissions in recent years.
The new report notes that it is still possible to achieve the goals set in the Paris Agreement, but it is getting more difficult every day. The authors used five theoretical scenarios to predict future global warming. The scenarios include different greenhouse gas emissions as well as economic and population growth and political cooperation. Under all five scenarios, the earth will reach 1.5 degrees Celsius (2.7 degrees Fahrenheit) in 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, author of the report and a climate scientist at the University of Chile.”
The authors found that if countries around the world immediately dramatically and permanently reduce emissions, the earth will be cooler around the middle of this century. On the other hand, the earth could warm 4 degrees Celsius (7.2 degrees F) or more by the end of the century if countries act slower to curb emissions or fail to switch to cleaner energy sources.
“I think a key message here is that it is still possible to prevent most of the worst effects, but what is needed is truly unprecedented, transformative change,” said Barrett, vice chairman of the IPCC. “But the idea that there is still a way forward is something I think should give us some hope.”
Eastman Lake in Madera County’s California was only one-fifth its usual water volume in June. An extreme drought is spreading in the western United States this summer and is being exacerbated by climate change. Noah Berger / AP Hide caption
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Noah Berger / AP
Eastman Lake in Madera County’s California was only one-fifth its usual water volume in June. An extreme drought is spreading in the western United States this summer and is being exacerbated by climate change.
Noah Berger / AP
Climate change is global, but solutions are local
This is the sixth edition of the IPCC’s climate science report, and it is the first time scientists have broken down their findings and predictions by region. This is a big deal because many countries rely on reports like this to understand what the future will be for their citizens and which policies make the most sense.
For example, the rate of sea level rise varies dramatically depending on where you live. Governments need regional information to decide where to build new infrastructure and how to protect existing coastal cities. The same applies to droughts and floods caused by rainstorms, which disrupt agriculture and the drinking water supply. Large cities like Cape Town, South Africa and Chennai, India have struggled to maintain reservoirs in recent years.
“It is very important that this report contains regional information that will help us make decisions at the regional level,” says Paola Arias, one of the report authors and climate scientist at the University of Antioquia in Colombia.
When it comes to adaptation, the US relies less on the specific information in this report, as the federal government regularly publishes national climate assessments. However, the UN report provides an important global context for the Biden government’s promise to cut US greenhouse gas emissions in half this decade.
“The goal set by the Biden Harris administration earlier this year is the most ambitious of all time in US history,” said Jane Lubchenco, assistant director of climate and environment for the White House science and technology policy. “This report tells us we have to be ambitious. We probably have to be more.”
It is unclear how the US will achieve the target that has already been set, let alone an accelerated target. The infrastructure package currently under consideration by Congress includes some investments in cleaner electricity, public transportation, and electrical appliances and vehicles. Meanwhile, other major economies, including China and India, are not on track to reduce their emissions this decade.
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