A week of highs: See where climate change made heat worse in America
Overnight low temperature Difference from 1991-2020 average Cooler Warmer Friday June 17 Thursday June 16 Wednesday June 15 Tuesday June 14 Monday June 13 Sunday June 12 Saturday June 18 Last week, 96 percent of people in the contiguous United States experienced nighttime temperatures more likely to occur due to human-caused warming. The findings come from a Washington Post analysis of data provided by the nonprofit Climate Central, which released the worlds first tool to show how climate change is affecting daily temperatures in real time. Overnight temperatures, as opposed to daytime temperatures, were boosted the most by climate change. While more and more people are increasingly exposed to warmer nighttime temperatures , which are potentially more dangerous to the body, last weeks number stands out. June 13 Overnight low temperature Difference from 1991-2020 average Cooler Warmer 0 -10oC +10oC -18oF +18oF Phoenix experienced a record overnight temperature of 90F (32C) Dodge City, Kan., had its warmest minimum temperature ever observed in any month of the year of 83F (28C) June 13 Overnight low temperature Difference from 1991-2020 average Warmer Cooler 0 -10oC +10oC -18oF +18oF Phoenix experienced a record overnight temperature of 90F (32C) Dodge City, Kan., had its warmest minimum temperature ever observed in any month of the year of 83F (28C) June 13 Overnight low temperature Difference from 1991-2020 average Cooler Warmer 0 -10oC +10oC -18oF +18oF Phoenix experienced a record overnight temperature of 90F (32C) Dodge City, Kan., had its warmest minimum temperature ever observed in any month of the year of 83F (28C) June 13 Overnight low temperature Difference from 1991-2020 average Cooler Warmer 0 -10oC +10oC -18oF +18oF Phoenix experienced a record overnight temperature of 90F (32C) Dodge City, Kan., had its warmest minimum temperature ever observed in any month of the year of 83F (28C) More than 3,000 new daily high temperatures were reached in the Lower 48 states that week with nearly twice as many unprecedented warm temperatures reached at night than during daytime. Climate change is impacting us every day somewhere. Thats a big part of the world that were living in right now, said Andrew Pershing, director of climate science at Climate Central. Our goal is really to be able to talk about everyday conditions. Over the past decade, climate scientists have sharpened the ability to link how climate change has influenced extreme weather events across the world. The field, known as climate attribution science, has traditionally been reserved for notable, damaging events on society, but Climate Centrals new endeavor shows how everyday weather that may not make news headlines is altered as well. June 13 Cooler Warmer 0 -10oC +10oC -18oF +18oF Where overnight low temperatures were more likely due to climate change Where overnight low temperatures were less likely due to climate change Where overnight low temperatures did not have a detectable climate signal June 13 Warmer Cooler 0 -10oC +10oC -18oF +18oF Where overnight low temperatures were more likely due to climate change Where overnight low temperatures were less likely due to climate change Where overnight low temperatures did not have a detectable climate signal June 13 Cooler Warmer 0 -10oC +10oC -18oF +18oF Where overnight low temperatures were more likely due to climate change Where overnight low temperatures were less likely due to climate change Where overnight low temperatures did not have a detectable climate signal June 13 Cooler Warmer 0 -10oC +10oC -18oF +18oF Where overnight low temperatures were more likely due to climate change Where overnight low temperatures were less likely due to climate change Where overnight low temperatures did not have a detectable climate signal The new tool called the Climate Shift Index (CSI) calculates how much more likely daytime high and overnight low temperatures are to occur because of climate change. An index score, or CSI, of 2, for example, means climate change made the days temperature twice as probable. On June 13 alone, Phoenix, Memphis, Nashville, Atlanta, St. Louis, Tampa and Santa Fe, N.M., all experienced warm overnight temperatures that were made at least five times more likely because of climate change earning a CSI of 5. The Climate Shift Index shows where human-caused warming made the temperature in a region more or less likely to occur Less likely More likely -5x -4 -3 -2 -1.5 1.5 2 4 5x 3 June 13 Overnight low temperatures Nashville experienced an overnight low temperature made at least 5 times more likely by climate change Dodge City, Kan. 3x Santa Fe, N.M. 5x Memphis 5x Phoenix 5x Atlanta 5x Tampa 5x The Climate Shift Index shows where human-caused warming made the temperature in a region more or less likely to occur Less likely More likely -5x -4 -3 -2 -1.5 1.5 2 4 5x 3 June 13 Overnight low temperatures Nashville experienced an overnight low temperature made at least 5 times more likely by climate change Dodge City, Kan. 3x Santa Fe, N.M. 5x Memphis 5x Phoenix 5x Atlanta 5x Tampa 5x The Climate Shift Index shows where human-caused warming made the temperature in a region more or less likely to occur Less likely More likely -5x -4 -3 -2 -1.5 1.5 2 4 5x 3 June 13 Overnight low temperatures Nashville experienced an overnight low temperature made at least 5 times more likely by climate change Dodge City, Kan. 3x Phoenix 5x Santa Fe, N.M. 5x Memphis 5x Atlanta 5x Tampa 5x In contrast, climate change played little to no influence in the daytime temperatures in those cities. Theres just really strong evidence that our nighttime climate is altered. ... It seems to be especially in this early summer period , Pershing said. Thats just really an important way that people in the United States are experiencing climate changes. Warm nighttime temperatures are potentially more dangerous than daytime highs. Typically, temperatures dip at night and allow our bodies to cool down from the daytime heat. If temperatures remain elevated, the prolonged heat increases the risk of heat exhaustion, cramps, strokes and even death. The Climate Central tool employs well-established methodologies previously used in attribution studies of extreme weather events. The team uses data and computer models to create simulations of a world with and without carbon emissions to determine the effect of climate change on daily temperatures. Friederike Otto, an expert in climate attribution science and co-lead of the World Weather Attribution initiative, said one really good feature of the tool is that it shows how different the natural variability is across the United States what is and isnt climate-change-related. Locations with the largest temperature anomalies in the country may not present the strongest fingerprint of climate change. For instance, temperature anomalies were the highest in the central United States on June 13, yet the climate change fingerprint was relatively small, as seen in Dodge City. Meanwhile, nighttime temperatures in Atlanta hit 74 degrees on Monday. While the temperature anomaly was lower than in other locations on the same day, climate change made the overnight warmth at least five times more likely to occur. In the central regions, you see large anomalies, but the influence of climate change is relatively small, said Otto, who helped develop the framework for the tool but is not involved in the operation. She said the tool takes the natural variability out of the climate change signal ... [and] makes climate change visible in a way that just [temperature] anomalies cant. Where climate change made temperatures more likely Sunday, June 12 Overnight low temperature Daytime high temperature Difference from 1991-2020 avg. Climate Shift Index Monday, June 13 Tuesday, June 14 Wednesday, June 15 Thursday, June 16 Friday, June 17 Saturday, June 18 Where climate change made temperatures more likely Sunday, June 12 Overnight low temperature Daytime high temperature Difference from 1991-2020 avg. Climate Shift Index Monday, June 13 Tuesday, June 14 Wednesday, June 15 Thursday, June 16 Friday, June 17 Saturday, June 18 Where climate change made temperatures more likely Overnight low temperature Daytime high temperature Sunday, June 12 Difference from 1991-2020 avg. Difference from 1991-2020 avg. Climate Shift Index Climate Shift Index Monday, June 13 Tuesday, June 14 Wednesday, June 15 Thursday, June 16 Friday, June 17 Saturday, June 18 Where climate change made temperatures more likely Overnight low temperature Sunday, June 12 Monday, June 13 Tuesday, June 14 Wednesday, June 15 Thursday, June 16 Friday, June 17 Saturday, June 18 Difference from 1991-2020 avg. Climate Shift Index Daytime high temperature Difference from 1991-2020 avg. Climate Shift Index Climate scientist Sonia Seneviratne, who was not involved in the project, said the tool is important for communication and could be useful for daily weather bulletins. It helps make climate change more tangible, said Seneviratne, who coordinated the chapter on weather and climate extremes of the recent report by the United Nations Intergovernmental Panel on Climate Change (IPCC). While attribution of extreme events is probably of higher interest to the general public, it is also important to show that climate change is affecting everyday weather. People who experienced overnight temperatures that were ... ... were more likely due to climate change 300 million 200 ... did not have a detectable climate signal 100 ... were less likely due to climate change 0 June 12 June 18 South West 120 million 80 40 0 June 12 June 18 June 12 June 18 Midwest Northeast 120 million 80 40 0 June 12 June 18 June 12 June 18 People who experienced overnight low temperatures that ... 300 million ... were more likely due to climate change 200 ... did not have a detectable climate signal 100 ... were less likely due to climate change 0 June 12 June 14 June 16 June 18 South West 120 million 80 40 0 June 12 June 18 June 12 June 18 Midwest Northeast 120 million 80 40 0 June 12 June 18 June 12 June 18 People who experienced overnight low temperatures that ... 300 million ... were more likely due to climate change 200 ... did not have a detectable climate signal 100 ... were less likely due to climate change 0 June 18 June 12 June 14 June 16 Midwest Northeast South West 120 million 80 40 0 June 12 June 18 June 12 June 18 June 12 June 18 June 12 June 18 Some estimates say more than 1,300 people die each year in the United States because of extreme heat, but numbers are higher elsewhere in the world. Between 1980 and 2017, the worlds 150 most-populated cities experienced a 500 percent increase in exposure to extreme heat, according to a February report from the IPCC. The problem will become even worse as the planet continues to warm, according to the IPCC. If global average temperatures rise to 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels, 16 times as many people will be exposed to heat waves each year, with people in low-income countries most affected. Under the worst-case warming scenarios, people in tropical regions of Africa could suffer from year-round deadly heat. [ The science of heat domes and how climate change makes them worse ] The Climate Central team plans to roll out real-time daily weather attribution across the globe later this year. I think there is still a huge underestimation of just how much climate change already influences our daily life, Otto said. Theres still not really an appreciation of just how much the impacts today are costing us. Every time we go outside, its different because of climate change. Sarah Kaplan contributed to this report.