Climate science at a glance
- Extreme heat and heat waves are some of the clearest impacts of climate change on extreme weather.
- Four out of five record-hot days globally are now amplified by global warming.
- Hot nights are particularly characteristic of climate change on a warming planet.
- Hot nighttime temperatures reduce the number of critically important relief windows during heat waves.
- The hottest summers since 1500 AD in Europe were: 2018, 2010, 2003, 2016, 2002.
- Attribution studies have found climate change had a direct hand in the severity of European heat waves during the following summers: 2018, 2017, 2015, 2010, and 2003.
Climate signals breakdown
Climate signal #1: extreme heat and heat waves
Record-breaking temperatures are a classic signal of climate change. As the average global temperature rises and the climate shifts, hot temperatures that were extreme under the old climate are closer to the middle of the new temperature range.
Many urban areas across the globe have witnessed a significant increase in the number of heat waves, with the largest number of heat waves occurring in the most recent decade studied, 2003-2012. In Europe, the five hottest summers since 1500 AD have all occurred since 2000 and include the years 2018, 2010, 2003, 2016, 2002.
Observations consistent with climate signal #1
- Germany recorded its highest-ever June temperature on June 26. The mercury hit 38.6°C (101.5°F) at 2:50 p.m. local time in Coschen, on the country's border with Poland.
- Record highs for June were also set on June 26 in the Czech Republic and Poland, where temperatures also topped 100 degrees.
Climate signal #2: humidity and heat stress increase
As air warms, its capacity to hold water vapor increases, and measurements show that atmospheric humidity is increasing around the globe, consistent with a warming climate. The Northern Hemisphere has had increasingly warmer and more humid summers, and the global area covered by extreme water vapor is increasing significantly.
Exposure to extreme heat is already a significant public health problem and the primary cause of weather-related mortality. A 2016 study finds there has been a detectable human-caused increase in mean summertime heat stress since 1973, both globally and in most land regions analyzed.
Observations consistent with climate signal #2
- The warm air has been linked to the deaths of three swimmers at beaches in France. One man, aged 70, suffered a cardiac arrest and is believed to have experienced “thermic shock” as a result of the temperature difference between the hot air and cool water. Two other people are believe to have died in similar circumstances: a 62-year-old woman and 75-year-old man died at beaches near Montpellier as the nation recorded temperatures above 40°C (104°F).
Climate signal #3: atmospheric blocking increase
In addition to shifting the distribution of local temperatures, global warming is also altering the pattern of atmospheric circulation (e.g. the jet stream). And some of these global changes are dramatically amplifying local heat extremes. Waves in the jet stream are stalling in place (as opposed to moving eastward), leading to persistent weather patterns. This kind of weather pattern is often referred to as a “blocking” pattern because it slows the flow of weather systems circulating around the Northern Hemisphere.
A high-pressure zone over Greenland set the stage for the persistent, extreme heat in Europe during June 2019. When present, this kind of persistent weather extreme can affect the same areas for extended periods and fuel the intensity and duration of heat waves.