Surface temperature data from NOAA show 2014 on track to be the warmest year ever measured on Earth. But satellite temperatures of the lower atmosphere show it not quite as warm.
John Christy, an atmospheric scientist at the University of Alabama-Huntsville (UAH), maintains a record of temperatures over the lowest 40,000 feet of the atmosphere (disproportionately below 10,000 feet) estimated from weather satellites, the layer known as the lower troposphere. The record spans 1979 to present.
Through November, 2014 is tied with 2005 as the third warmest on record. Christy emailed me the chart below which shows how the different years in the satellite record stack up and compare with 2014, dating back to 1979:
Christy told me in an email he “guesses” 2014 will end up in third place when it comes to a close. “However, the error bars on this value will show 2014 will be 3rd to 8th place (using +/- 0.1 C as error bar),” Christy wrote.
In Christy’s satellite-based dataset, both 1998 and 2010 – the two warmest years – are substantially warmer than 2014.
You can compare Christy’s chart of satellite-estimated temperatures with a similar chart of surface-based temperature measurements of Earth (both land and ocean) prepared by NOAA, dating all the way back to 1880, below:
In the NOAA chart, you see 2014 edging out several other recent years at the top. A zoomed in version of this same chart (also from NOAA), below, shows more clearly 2014 just a bit ahead of the three previous warmest years: 2010, 2005, and 1998.
So NOAA’s surface temperature record shows 2014 likely to be the warmest year by a hair, while the UAH satellite record shows 2014 trailing 1998 and 2010 by a healthy margin. Why the differences? It’s important to remember that these datasets are measuring different things (surface versus lower troposphere temperatures) using different methods (read more here) – so we shouldn’t expect an exact match.
Nevertheless, both temperature datasets clearly show the concentration of the warmest years occurring after 2000 (see the dotted lines in the UAH satellite record chart and the red lines in the NOAA surface record chart).
Furthermore, despite differences in which year is “warmest”, the trends computed in these two datasets since 1979 are very similar. NOAA shows the Earth warming at a rate of about 0.27F per decade, while the UAH satellite record shows a warming rate of about 0.25F per decade.
What these charts collectively show is that the warmest years on record are fairly tightly packed together and that different analyses give different results – all of which are also sensitive to measurement error. Thus, when looking at temperature charts, it’s a lot more meaningful to look at tendencies and trends rather than to focus on individual years.