Monday's report from the United Nations' Intergovernmental Panel on Climate Change (IPCC) represents the most comprehensive and conclusive "state of the science" on the climate crisis: why it is happening, how it is impacting every region of the planet, how much worse things are set to get and what must be done to avoid the worst consequences.
UN Secretary-General António Guterres called the report "a code red for humanity," noting that "global heating is affecting every region on Earth, with many of the changes becoming irreversible."
The report is about 3,500 pages, represents years of research on the topic, was authored by more than 200 scientists from over 60 countries and cites more than 14,000 individual studies.
Humans are unequivocally warming the planet
This report goes farther than any previous IPCC climate report in placing the blame for global warming squarely on human greenhouse gas emissions. It is no longer a question of "natural versus human-caused" climate change.
Society's reliance on fossil fuels is the reason the planet has already warmed 1.2 degrees — every bit of it through the emission of greenhouse gases such as carbon dioxide and methane.
The warming is happening even faster than scientists previously thought, and the latest projections have us reaching or exceeding 1.5 degrees — a key threshold scientists say is critical to stay below — within the next decade or two.
The only way to stop the warming is to end greenhouse gas emissions: The longer it takes, the hotter it gets
Just as the report clearly blames carbon pollution for the rising temperatures, it is also clear that the only way to slow down and eventually reverse the warming is to reduce greenhouse gas emissions to zero.
Avoiding 1.5 degrees of warming is all but impossible, but we can still keep warming around that critical threshold and avoid the worsening impacts that come from approaching and passing 2 degrees of warming.
Avoiding those impacts will take significant cuts to greenhouse gas emissions starting immediately. If emissions continue to increase, the world will top 2 degrees of warming — possibly before 2050 — and reach 3 degrees before the end of the century.
Climate impacts are severe in every region of the planet, and will worsen with every fraction of a degree of warming
Here are some specific impacts and what the report has to say about them.
Heat waves — Extreme heat waves, such as the deadly one that occurred in the Pacific Northwest and Canada earlier this summer, are already about five times more likely to occur with our current warming of just over 1 degree. At 2 degrees warming, this frequency increases to 14 times as likely to occur. Heat waves are getting hotter, and with 2 degrees of warming, the hottest temperatures would reach nearly 3 degrees higher than previous heat waves.
Droughts — Climate change is increasing the frequency and severity of droughts — such as the current drought plaguing the Western United States. Severe droughts that used to occur an average of once per decade are now occurring about 70 per cent more frequently. If warming continues to 2 degrees, these droughts will occur between two and three times as often.
Flooding — Climate change is intensifying the water cycle on both sides. While more intense evaporation will lead to more droughts, warmer air can hold more water vapour to produce extreme rainfall (as we have seen play out dramatically in Western Europe and China this summer). On average, the frequency of heavy downpours has already increased by about 30 per cent and they contain about 7 per cent more water.
Cyclones — Cyclones are growing stronger and producing more rain as global temperatures increase. It has already been observed that, globally, a higher percentage of storms are reaching the highest categories (categories 3, 4 and 5) in recent decades. This is expected to continue as temperatures climb.
Sea level rise — The sea level is rising around the world, and the rate is increasing. This is worsening high-tide flooding and storm surge. By 2100, once-in-a-century coastal flood events will occur at least once per year at more than half of coastlines across the world, the report said.
Weather whiplash — Climate change is not just increasing the severity of extreme weather, it is interrupting the natural patterns, leading to "weather whiplash" — wild swings between dry and wet extremes. This has been experienced recently in California, with "atmospheric rivers" causing destructive floods one year and extreme drought causing water shortages the next.
Some changes are irreversible, even under the lowest emissions scenarios
Warming that has already occurred has triggered changes that will persist even if the emissions stop and temperatures stabilize.
Ice sheets will continue melting for hundreds to thousands of years, according to the report, which will cause sea levels to rise well beyond 2100 and stay higher for millennia.
Sea levels are expected to rise 2–3m by 2300 even if warming is kept below 2 degrees, but could reach 5–7m or higher if warming continues unabated.
Atmospheric methane is skyrocketing
This report points to another villain in the climate crisis — methane — an invisible gas that contains more than 80 times the planet-warming power of carbon dioxide in the short term.
Newer data shows that methane in the atmosphere is skyrocketing and is currently the highest it's been in 800,000 years, largely because of a combination of natural gas leaks and unsustainable agriculture and cattle farming.
Considering its massive warming potential and its shorter lifetime in the atmosphere compared to carbon dioxide, controlling methane could significantly lessen global warming in the coming decades.
IPCC reports, while long on science and exhaustive in scope and detail, contain precious little in suggesting policy to remedy the climate crisis. This report, for example, is purely the scientific facts and forecasts for the future.
Major IPCC reports coming next year will go into more detail on specific impacts and ways to mitigate them, but before then global leaders will meet at a UN-led climate conference in November, in what is being billed as the most consequential climate policy meeting since the Paris Agreement was signed in 2015.
"As today's report makes clear, there is no time for delay and no room for excuses," the UN Secretary-General declared on Monday, as he implored government leaders to ensure COP26 was a success in order to "avert climate catastrophe."