A new study by Scripps Institution of Oceanography finds a 5 percent chance that rapid global warming will be “catastrophic” or worse for the human race.
The study led by Veerabhadran “Ram” Ramanathan, a distinguished professor of climate and atmospheric sciences and adviser to Pope Francis, found that an average global temperature increase greater than 3 degrees centigrade could result in “catastrophic” — and over 5 degrees “existential” — threat to humanity.
These categories describe two low-probability but statistically significant scenarios that could play out by the century’s end according to an analysis of different models of global warming by Ramanathan and Yangyang Xu of Texas A&M University.
“When we say 5 percent-probability high-impact event, people may dismiss it as small but it is equivalent to a one-in-20 chance the plane you are about to board will crash,” said Ramanathan. “We would never get on that plane with a one-in-20 chance of it coming down but we are willing to send our children and grandchildren on that plane.”
The 2015 Paris Agreement, which President Trump rejected earlier this year, calls for keeping the rise in global average temperatures below 2 degrees centigrade (3.6 degrees fahrenheit), well below the level that would cause catastrophe but still potentially dangerous.
Planetary warming between 3 degrees centigrade (5.4 degrees fahrenheit) and 5 degrees centigrade (9 degrees fahrenheit) could trigger what scientists term “tipping points” such as the collapse of the West Antarctic Ice Sheet and subsequent global sea-level rise and the dieback of the Amazon rain forest.
Warming beyond 5 degrees centigrade has not been experienced on the earth for at least the past 20 million years and would likely be an existential threat to humanity.
“This report shines a bright light on the existential threat that climate change presents to all humanity,” said Gov. Jerry Brown, who has collaborated with Ramanathan on carbon neutrality measures in the state. “Scientists have many ideas about how to reduce emissions, but they all agree on the urgency of strong and decisive action to remove carbon from the economy.”
The release of the study coincides with the start of Climate Week NYC, a summit of business and government leaders to highlight global climate action.