Pennsylvania faces unprecedented, deadly heatwaves in the coming decades unless aggressive action is taken to combat climate change, according to a new report published Tuesday by the Union of Concerned Scientists.
Historically, Pennsylvania has experienced an average of eight days per year where the heat index (the temperature it feels like, with humidity taken into account) surpassed 90 degrees Fahrenheit, according to the report. Under a "slow action" scenario for addressing climate change, the UCS analysis finds that number would increase to 40 days per year on average by midcentury. "Slow action" assumes carbon emissions start declining at midcentury and the global average temperature rises 4.3 degrees Fahrenheit by century's end.
On current emission pathways, with no action taken, Pennsylvania would see 71 such days by the century's end.
The analysis covers the lower 48 states and includes interactive maps showing projections by county and state. It finds large swaths of the country could become dangerously hot. The report authors examined temperature and humidity projections, based on scenarios of little to no action on climate change, versus aggressive climate action. Then they ran those projections through the National Weather Forecast heat index equation and looked at how conditions are likely to change for different communities.
For example, with no action taken to curb climate change, parts of Florida and Texas would experience the equivalent of five months per year on average when the heat index is greater than 100 degrees Fahrenheit by the end of the century.
"If we wish to spare people in the United States and around the world the mortal dangers of extreme and relentless heat, there is little time to do so and little room for half measures," the report's authors write. "We need to employ our most ambitious actions to prevent the rise of extreme heat — to save lives and safeguard the quality of life for today's children, who will live out their days in the future we're currently creating."
The 2015 Paris climate agreement seeks to strengthen the global response and avoid the worst effects of climate change, by limiting a global temperature rise in this century well below 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels. A stark United Nations report issued late last year calls on governments to do even more — and try to keep the warming below 1.5 Celsius (2.7 degrees Fahrenheit). The scientists who authored it concede that there is "no documented historic precedent" for such a rapid transformation of the global economy.
The Union of Concerned Scientists' analysis examines four levels of heat index thresholds: above 90 degrees Fahrenheit, above 100, above 105, and "off the charts" — an extreme scenario in which the heat index reaches 127 degrees Fahrenheit or greater — effectively limiting the body's ability to cool itself.
With no action taken on climate change, parts of south-central and southeastern Pennsylvania would experience an average of at least one day per year with an "off the charts" heat index by mid-century, the report finds.
Rachel Licker, a senior climate scientist with the Union of Concerned Scientists, said the analysis is meant to deliver very fine resolution information to communities across the country about how extreme heat is likely to play out.
"These kinds of dangerous temperatures can exacerbate pre-existing health conditions, like cardiovascular disease and respiratory disease. It can affect children," she said. "It can affect the mentally ill, who may not be able to protect themselves. Heat is one of the top weather-related causes of death across the United States. As we see more extreme temperatures, that's just going to make matters worse."