2015 was the hottest year worldwide since record-keeping began. The previous hottest year was 2014.
2015 was the hottest year worldwide since record-keeping began in 1900, according to the State of the Climate in 2015 report by the American Meteorological Society. This is a report that came out in August, 2016, and I’m just catching up to it now. I will summarize a few of the many findings.
Figure 1 shows how much 2015 temperatures around the globe varied from the average temperature for that location (reference years 1981-2010). The yellow and red areas were warmer than average, the blue areas cooler. White represents areas for which there is not enough data to make a characterization. You can see that the map has many more yellow and red areas than blue. The previous record was set the year before, and 2015 was 0.13 – 0.18°C warmer. That is a large jump.
Figure 2 shows the trend in global temperatures from 1880 to 2015. The top two graphs represent different analyses of temperature over both land and ocean, the middle two graphs represent different analyses of temperature over land only, and the bottom two represent different analyses of temperature over ocean only. An inspection of the charts shows considerable year-to-year variation, but all of them show a continuing trend towards warmer temperature. Climate change deniers have been making much of a multi-year pause in the increase in surface temperature at the beginning of the 21st Century. Climate scientist have pointed out that this pause was illusory, as it represented a period during which heat was being shunted from the surface to the depths of the ocean faster than usual, not an actual pause in warming. It now seems that surface temperature has resumed its upward march: 2014 and 2015 show up on the charts as a quite large spike upward.
One of the ways global warming has its effect is by increasing the number of warm days, defined as “number of days above the seasonal 90th percentile of daily maximum temperatures over the 1961-1990 base period.” (Blunden and Arndt, 2016, p. S19) Figure 3 shows the map. You can see that there are large blobs of red over Australia, Southeast Asia, China, Siberia, Europe, South Africa, eastern Greenland, and most of North America. That means that all these regions had an above average number of warm days, in most cases by a lot (+30 days or more).
Extreme days are important. In the summer a “warm” day might indicate that it was extremely hot, which is hazardous. During the winter, on the other hand, it might indicate that the day was above freezing.
The map of warm days for 2015 looks quite similar to the map for 2014 (here): many of the same areas were involved.
There is a great deal more information in the report that is beyond the scope of this blog. For those interested in meteorology and climatology, it would make interesting reading.
I’m writing this post in early January, 2017. United States climate data for 2016 should post-up on Climate at a Glance during January, so hopefully by the time this post goes live, I’ll be able to follow up with information about the USA and Missouri.
Blunden, Jessica and Derek Arndt (eds.) 2016. “State of the Climate in 2015.” Bulletin of the American Meteorological Society, 97 (8) Special Supplement. Downloaded 1/8/17 from https://www.ametsoc.org/ams/index.cfm/publications/bulletin-of-the-american-meteorological-society-bams/state-of-the-climate.