2015 Was the Hottest Year on Record; the Odds of Recent String of Hot Years Due to Natural Variation Alone is .01%

According to a January 20 article on Grist and another on Jan. 25, 2015 the hottest year ever recorded and the statistical probability of the recent string of hot years—i.e. 13 of the 15 hottest years on record occurring from 2000 to 2014 (as really happened)—due solely to natural variations is only .01%. The 2015 news was announced jointly by NASA and the NOAA, who conducted separate analyses of the same data (which comes from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures and Antarctica-based stations) and reached the same conclusion that global surface temperatures in 2015 were the hottest ever recorded. The global average temperature was 0.13 degrees Celsius (0.23 °F) hotter than the previous hottest year (2014), whereas this record is typically only broken by a few hundredths of a degree Celsius. The second piece of information–that there is only a .01% chance of 13 of the 15 hottest years on record (now 14 of the 16 hottest years due to 2015’s record-breaking heat) occurring from 2000 to 2014 (see graph below for a visualization) due to natural variation alone is also interesting because it comes from a study in Scientific Reports that uses statistical analysis, real-world data and climate models to come up with a scientifically-determined probability of the recent string of hot years occurring due to natural climatic variations. The study acknowledges, unlike others, that the probability of a record-setting hot year is not independent of the previous year’s temperature, but that in fact one record-setting hot year increases the chances of the next year being especially hot. According to the study’s author,”natural climate variation causes temperatures to wax and wane over a period of several years, rather than varying erratically from one year to the next” [emphasis added]. The study says it corrects some media reports that the odds of the recent string of hot years is 1 in 650 million (which assumes incorrectly that each year’s temperature is independent of the last’s), but it still pegs this probability very low at .01%, or 1 in 10,000. Of course the only culprit that can explain the extraordinarily high concentration of record-setting hot years is—you guessed it—human-caused climate change. The studies’ authors also re-ran the models and found the string of record-hot years is “quite likely to have occurred in the presence of anthropogenic climate forcing” (emphasis original). And for all those people out there (mostly in the U.S.) who still deny the existence of climate change, here is NASA’s updated chart of global average temperature from 1951 to present (y=0 is the 1951-1980 average, which allows us to compress the y axis to +1 to -0.2 °C compared to 1951-1980 and enables us to see smaller changes more easily):

annual temp 1950 to 1980

It even has three nifty trend lines for those who don’t seem to understand trends (i.e. the entire Republican leadership)-orange is for El Niño years, the dashed line is for all years and blue is for La Niña years. The graph can be found from a NASA news release here. Overall I think it’s pretty unambiguous which way the trend is going-and especially when you consider the UK’s Met Office is already predicting 2016 will break 2015’s record (due to climate change and El Nino both being in effect). Things are definitely heating up with the planet’s climate. I hope our political leaders take notice.

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