By Ethan Brown and Iliana Garner
Climate Central’s daily temperature attribution system, the Climate Shift Index (CSI), allows scientists to determine the degree to which human greenhouse gas emissions influenced a given temperature.
Studies conducted using CSI reveal over 80% of the world population experienced at least one day in July whose extreme heat was made at least three times likelier due to human-caused climate change, with around 870 cities notching at least 25 such days.
These findings come amidst a trend of high temperatures. July 2023 was the hottest month on record according to the World Meteorological Organization.
Climate Central’s team created CSI to allow people to view attribution science models in real time, displaying maps of geographic areas whose temperatures are impacted the most by human-caused climate change.
“[CSI] not just highlights the events that get people’s attention, but really screens the data every day to try to identify where climate change is having its strongest effect on any given day,” says Andrew Pershing, Vice President for Science at Climate Central.
Pershing says that they found developing countries in the tropical zone are disproportionately affected by greenhouse gas emissions. These areas have more consistent temperatures, so it is easier to see the impact of human-caused climate change.
“This is not the new normal. There’s nothing about this that is normal,” Pershing says. “These are conditions that are going to become more common, more severe as we continue to put more CO2 in the atmosphere.”
While CSI focuses on heat, a newly emerging field called attribution science can link climate change to other extreme weather events as well.
“We are now seeing heat waves that would have been impossible a few years ago,” says Friederike Otto, Senior Lecturer at the Grantham Institute for Climate Change and the Environment at Imperial College London.
Greenhouse gasses such as carbon dioxide and methane have three or more atoms, allowing them to twist and vibrate unlike other atmospheric gasses such as nitrogen and oxygen. This vibration leads to more collisions among energized particles, which trap infrared radiation in the atmosphere and ultimately raise temperatures.
Armed with that knowledge, climate scientists can now develop computer models that allow them to change the concentration of greenhouse gasses in the atmosphere and play out hypothetical climate scenarios. They can then compare how often a given event happens with human greenhouse gas emissions or without them.
“It is chaos and it is complex, but it is defined by the laws of physics,” says Otto.
One of the early attribution science studies, co-authored by Otto, showed climate change made the extreme rainfall during Hurricane Harvey about three times more likely, or about 15% more intense, than it would have been without human greenhouse gas emissions.
Since then, a 2019 Earth’s Future study found human-caused climate change has increased the frequency of large fires in California by a factor of five, and a 2020 paper in Science revealed human-caused climate change accounted for 47% of 2000-2018 drought severity in the American Southwest.
How attribution science tools such as CSI could influence the public’s understanding of climate change remains unclear. While CSI can rapidly evaluate climate change fingerprints on extreme heat, climate impacts on more complex weather events such as tornadoes remain far more difficult to calculate.
Furthermore, national news outlets are already hesitant to cover climate change during extreme weather events — a recent Media Matters analysis found from June 15-29, only 5% of the 310 segments and weathercasts about the Texas heat wave across national TV news mentioned climate change.
But according to a Covering Climate Now (CCNow) “Climate Beat” newsletter on June 15, attribution science could help reporters tangibly incorporate climate change into their breaking news coverage of extreme weather events, offering the public new opportunities to engage with the latest climate science.
“Scientists are not always the most plainspoken people, but a skillful reporter can still make the climate connection clear by briskly summarizing the prevailing science.”
Offering guidance to journalists, CCNow says scientists often hedge their comments to the media to be as precise as possible, but wider use of attribution science could enable them to share data-driven climate connections in real time.
They reference a testy exchange during the aftermath of Hurricane Ian in 2022 where then National Hurricane Center Acting Director Jamie Rhome told then CNN anchor Don Lemon, “On the whole…climate change may be making storms worse, but to link it to any one event, I would caution against that.” Several prolific climate scientists criticized Rhome at the time for making what they deemed an inaccurate and outdated statement, noting that attribution science can now accurately measure links between individual storms and climate change.
But CCNow hopes that exchange during Hurricane Ian, coupled with the development of attribution science, can be a learning opportunity for the future.
“The 2023 hurricane season is an opportunity to do better, and journalists have a powerful new tool at their disposal.”