According to Stanford University scientists, the tropics and much of the Northern Hemisphere are likely to undergo an irreversible temperature shift during summers over the next 20 to 60 years if greenhouse gas emissions are not curtailed immediately.
In the study, the Stanford team concluded that many tropical regions in Africa, Asia and South America could see “the permanent emergence of unprecedented summer heat” in the next two decades. Middle latitudes of Europe, China and North America – including the United States – are likely to undergo extreme summer temperature shifts within 60 years, the researchers found.
“According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years,” said the study’s lead author, Noah Diffenbaugh, an assistant professor of environmental Earth system science and fellow at the Woods Institute for the Environment at Stanford. The study is co-authored by Stanford research assistant Martin Scherer.
“When scientists talk about global warming causing more heat waves, people often ask if that means that the hottest temperatures will become ‘the new normal,'” Diffenbaugh said. “That got us thinking – at what point can we expect the coolest seasonal temperatures to always be hotter than the historically highest temperatures for that season?”
Diffenbaugh and Scherer analyzed more than 50 climate model experiment and found that large areas of Earth could experience a permanent increase in seasonal temperatures within only 60 years. Their analysis included computer simulations of the 21st century when global greenhouse gas concentrations are expected to increase, and simulations of the 20th century that accurately “predicted” the Earth’s climate during the last 50 years.
“We also analyzed historical data from weather stations around the world to see if the projected emergence of unprecedented heat had already begun,” Diffenbaugh said. “It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well.”
“We find that the most immediate increase in extreme seasonal heat occurs in the tropics, with up to 70 percent of seasons in the early 21st century (2010-2039) exceeding the late-20th century maximum,” the authors wrote in their paper, which will be published later this month in the journal Climate Change Letters.
Based on the climate model analysis and historical weather data, the tropics are heating the fastest, and will thus likely see the most dramatic climatic changes first. However, large areas of North America, China and Mediterranean Europe will likely enter into a new series of temperatures by the time 2070 rolls around.
“The fact that we’re already seeing these changes in historical weather observations, and that they match climate model simulations so closely, increases our confidence that our projections of permanent escalations in seasonal temperatures within the next few decades are well founded,” Diffenbaugh said.