“Global warming is real, it is dangerous, and it’s unequivocally caused by humans,” was the theme of the United Nations Intergovernmental Panel on Climate Change (IPCC) in a report published 9 August.
Approved by 195 governments and based on more than 14,000 studies, it is the most comprehensive summary to date of the physical science of climate change.
The challenge, according to the report, is that preventing further warming and resulting perils would require a coordinated effort among countries to stop adding carbon dioxide (CO2) to the atmosphere by around 2050, which would entail a rapid shift away from fossil fuels starting immediately, and potentially removing vast amounts of carbon and other greenhouse gases from the air.
If that happened, global warming likely would stop and level off at around 1.5°C. But if that effort fails, global average temperatures will keep rising—potentially passing 2, 3, or 4°C above preindustrial levels. Every additional degree of warming will cause more vicious floods, longer and more intense heat waves and droughts, and greater risk of crossing dangerous tipping points such as the irreversible collapse of the immense ice sheets in Greenland and West Antarctica. This, in turn, could accelerate the rise in sea levels, which could threaten the existence of some island nations.
“There’s no going back from some changes in the climate system,” said Ko Barrett, a vice chair of the IPCC panel and a senior adviser for climate at the National Oceanic and Atmospheric Administration. “But,” she added, “immediate and sustained emissions cuts could really make a difference in the climate future we have ahead of us.”
Why Is This Time Different?
The IPCC has released six assessments on climate change since it was created in 1988. One thing that has changed over the course of those assessments is the assuredness of the language, as evidenced by the following examples from the Bloomberg Green newsletter:
1990—“Human activities have increased greenhouse-gas concentrations, and rising concentration will result in greater warming of the Earth’s surface.”
1995—“The balance of evidence suggests a discernible human influence on the global climate.”
2001—“There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.”
2007—“Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse-gas concentrations.” This report also said for the first time, “Warming of the climate system is unequivocal.”
2013—“It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”
2021—“It is unequivocal that human influence has warmed the atmosphere, ocean, and land.”
The implications of the IPCC authors’ use of “unequivocal” to describe the connection between human activity and global warming are huge. “There is no uncertainty about the language in this sentence because there is no uncertainty that global warming is caused by human activity and the burning of fossil fuels,” said IPCC report coauthor Friederike Otto, a climatologist at the University of Oxford.
What We Can’t Change
According to the IPCC report, nations have delayed curbing their fossil-fuel emissions and addressing climate change for so long that they can no longer stop global warming from intensifying over the next 30 years, and it is too late to avoid some of the perils of climate change, such as the following:
- A hotter future because, even if nations start slashing emissions today, total global warming is likely to rise around 1.5°C within the next 2 decades, essentially locking in a hotter future
- Extreme weather such as severe heat waves, droughts, winter temperatures, snowfall, rain, and hurricanes becoming more common and often lasting longer
- A doubling in frequency since the 1980s of bursts of extreme heat in the ocean that can kill fish, seabirds, and coral reefs
- Ocean levels that have risen 8 in. on average over the past century, with the rate of increase doubling since 2006
- The 2010s, likely the hottest the planet has seen in 125,000 years
- Glaciers that are melting and receding at a rate “unprecedented in at least the last 2,000 years
- Atmospheric levels of CO2 at their highest in at least 2 million years
“Things are unfortunately likely to get worse than they are today,” according to Piers Forster, a climate scientist at the University of Leeds and one of hundreds of international experts who helped write the report.
If warming increases, nearly 1 billion people worldwide could face more frequent life-threatening heat waves. Hundreds of millions more would struggle for water because of severe droughts. Some animal and plant species alive today would disappear. Coral reefs, which sustain fisheries for large swaths of the globe, could suffer more frequent mass die-offs. And, even at 1.5°C of warming, ocean levels are projected to rise another 1 to 2 ft this century, regularly inundating many coastal cities with floods that in the past would have occurred just once in a century.
A Narrow Window of Opportunity
With 2.4 trillion tons of climate-warming CO2 having been emitted to the atmosphere since the mid-1800s, the average global temperature has risen by 1.1°C. Meeting the Paris Agreement goal of 1.5°C will require sticking to a “carbon budget,” a term that describes how much additional carbon can be pumped into the atmosphere before that goal is likely out of reach.
The current carbon budget is 400 billion tons that can be added before the carbon budget is blown. Global emissions currently total a little more than 40 billion tons a year. The world is now on track to deplete that budget in about a decade.
Not all is lost, however, and humanity can still prevent the planet from getting even hotter, say the IPCC authors. A growing number of world leaders, including US President Biden, have endorsed the Paris Agreement goal of limiting global warming to 1.5°C.
The 10 biggest emitters of greenhouse gases are China, the US, the European Union, India, Russia, Japan, Brazil, Indonesia, Iran, and Canada. Current policies in some of the major polluting countries are still far off-track from achieving the Paris target. It—and the IPCC report and its repercussions—are certain to be a focal point when diplomats gather in November for the 26th UN Climate Change Conference of the Parties (COP26) in Glasgow to discuss how to move forward.
