Northern and Southern hemisphere summers differ in three main ways, according to climate experts interviewed by Live Science.
The hemispheres experience summer at opposite times of the year because Earth's axis tilts 23.4 degrees relative to its orbital plane. Northern summers run from late June to late September, while Southern summers span late December to late March, six months apart.
Northern hemisphere summers last 4.5 days longer than Southern ones. Georg Feulner, a senior researcher at the Potsdam Institute for Climate Impact Research in Germany, explained that Earth's slightly elliptical orbit causes this difference. Earth travels at 18.2 miles per second when farthest from the sun during Northern summer, but accelerates to 18.82 miles per second when nearest to the sun during Southern summer. This means Earth's path covers 53,686 miles less ground in a 24-hour interval at aphelion compared to perihelion.
Northern summers are also hotter. A 2015 study in Climate Dynamics found Northern summers average 7.83 degrees Fahrenheit (4.35 degrees Celsius) warmer than Southern ones when temperatures are averaged across all latitudes and domains.
Richard Seager, a professor at Columbia University's Lamont-Doherty Earth Observatory, attributed this to the Northern Hemisphere's greater fraction of land. "Land has a lower heat capacity than water and so increases temperature more for a given heating than water does," Seager said. Solar heat warms only the first few feet of atmosphere above land, while heat absorbed by water distributes throughout its depths, keeping ocean regions cooler.
Georg Feulner added that the Atlantic Meridional Overturning Current transports heat from the Southern Hemisphere to the Northern one, warming Northern oceans and adjacent land masses.