Drawing on more than 14,000 scientific studies, the report gives the most comprehensive and detailed picture yet of how climate change is altering the natural world – and what still could be ahead.
Unless immediate, rapid and large-scale action is taken to reduce emissions, the report says, the average global temperature will likely cross the 1.5 degrees Celsius warming threshold within the next 20 years.
So far, nations’ pledges to cut emissions have been inadequate for bringing down the level of greenhouse gases accumulated in the atmosphere.
Reacting to the findings, governments and campaigners expressed alarm.
“The IPCC report underscores the overwhelming urgency of this moment,” United States climate envoy John Kerry said in a statement. “The world must come together before the ability to limit global warming to 1.5 degrees Celsius is out of reach.”
IRREVERSIBLE CHANGE
Emissions “unequivocally caused by human activities” have pushed today’s average global temperature 1.1 degrees Celsius higher than the pre-industrial average – and would have pushed it 0.5 degrees Celsius further if not for the tempering effect of pollution in the atmosphere, the report says.
That means that, as societies transition away from fossil fuels, much of the aerosols in the air would vanish – and temperatures could spike.
Scientists warn that warming more than 1.5 degrees Celsius above the pre-industrial average could trigger runaway climate change with catastrophic impacts, such as heat so intense that crops fail or people die just from being outdoors.
Every additional 0.5 degrees Celsius of warming will also boost the intensity and frequency of heat extremes and heavy rainfall, as well as droughts in some regions. Because temperatures fluctuate from year to year, scientists measure climate warming in terms of 20-year averages.
“We have all the evidence we need to show we are in a climate crisis,” said three-time IPCC co-author Sonia Seneviratne, a climate scientist at ETH Zurich who doubts she will sign up for a fourth report. “Policymakers have enough information. You can ask: Is it a meaningful use of scientists’ time, if nothing is being done?”
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