Global surface temperatures in 2015 were the warmest since modern record-keeping began in 1880. That’s according to independent analyses done by NASA and NOAA. Compared to 2014, average globally-averaged temperatures rose by 0.23 degrees Fahrenheit (0.13 Celsius). Only one other year has seen the new record be that much higher than the old record, and that was in 1998.
Since 1880, Earth’s average surface temperature is up about 1.8 degrees Fahrenheit (1.0 Celsius). According to NASA and NOAA scientists (plus many others), this increase is caused by increased carbon dioxide and other human-made emissions into the atmosphere.
Did You Know:Carbon dioxide and other gases are often referred to as ‘greenhouse’ gases. Light from the sun passes through our atmosphere and heats the Earth’s surface. The heat radiated from the Earth’s surface is absorbed by these greenhouse gases and then re-emitted in all directions. Some of the heat goes into space, some of it comes back to the surface. Light comes in – but not all the heat comes out. Like a greenhouse.
But not all of the increase comes from us. Seasonal weather phenomena such as El Niño (warming) or La Niña (cooling) can cause short-term swings in the global average temperature.
Gavin Schmidt touches on this in a press release. “Last year’s temperatures had an assist from El Niño, but it is the cumulative effect of the long-term trend that has resulted in the record warming that we are seeing.”
Plus, not every place on Earth saw record heat. Take a look at the map below.
Large parts of Europe and Asia saw record warmth while other areas saw smaller increases. For instance, 2015 was the second warmest on record for the contiguous 48 U.S.
How NASA and NOAA track temperatures
6,300 weather stations, ship and buoy-based measurements play a part in coming up with how warm 2015 was compared to previous years. Each surface temperature measurement from these stations is analyzed using a sophisticated algorithm. This algorithm takes into account where the stations are in relation to each other and urban heating effects that may affect individual measurements.
Urban heating effects are better known as an ‘urban heat island.’ Temperatures can be as much as 10 degrees warmer in metropolitan areas compared to surrounding areas. That’s because of all the buildings, asphalt and people packed into a smaller area. Climate scientists have to take this into account when looking at temperature measurements.
Also, where weather locations are changes over time. Because of this, NASA’s analysis can’t say with 100% certainty that 2015 was the warmest year on record. Instead, we get a 94% certainty. So yeah, NASA is pretty sure 2015 was the hottest.
Head on over to NASA’s News Audio page to listen to Gavin Schmidt and Thomas R. Karl dive into more detail about 2015’s data.