Warmest year (probably) on record, globally.
It was another important year for what is perhaps the most overused climate change indicator out there: globally-averaged surface temperature. This metric is very good for one thing: tracking climate change in a broad-brush sense. Beyond that relatively important function, it’s not particularly relevant. The data aren’t final, but it appears very likely that 2016 will go down as nominally warmer than 2015, which blew away 2014, which was nominally warmer than the rest of the years in modern history.
Why it matters:
Taken individually, especially in a warming world, the “warmest year on record” is not much more than a curiosity item—a headline atop a much broader story. If the world is warming, and it is, a new “warmest year on record” is inevitable every few years. However, one thing makes this year more notable than the other four "warmest years on record" we've had since 2000. 2016 will make a hat trick for 2014-16: three years in a row setting a new record. That’s rare. With the exception of 1939-41, when the NOAA time series was barely in statistical adulthood, this is only time the modern record yields three straight "warmest years on record."
Beyond the Data:
Of course, those 1939-41 years aren’t even in the top 30 any more. The world has warmed—a lot—since then. For some perspective of how much, consider this: 1940 was the first year of the record to be warmer than the 20th-century average.
I like to think of long-term change, the kind that has been going on since the early-to-mid 20th century, as riding up an escalator. Transitory bumps from factors like El Nino, are like jumping up and down while you’re on the escalator. Yes, a big jump will help you reach new highs, and make a difference between nearby years on the time series. But it’s that escalator ride that makes the next record inevitable: even if it’s not likely in 2017, it’s inevitable.
At times this year, Alaska’s temperatures were literally off the charts. No, seriously. They broke our map legends. Alaska skated to its warmest year on record, by 1.6 degrees Fahrenheit. That's a lot.
Why it matters:
Alaska is America’s crucible of change. Much of Alaska sits in the Arctic, which, not coincidentally, is the globe’s crucible of change. The Northern Hemisphere’s high latitudes are changing more rapidly than any other major geographic region on the planet, and taking Alaska with them.
Like most things climate, temperature is only one indicator of change. In the Arctic, moreso than just about anywhere else on the planet, we see different climate elements mutually reinforcing the changes set in motion by global-scale warming. Climate scientists, perhaps ironically, call this “positive feedback,” and it goes something like this: warmer temperatures lead to smaller sea ice cover, which leads to more warming of the waters, which lead to smaller sea ice cover. Or, alternatively, warming leads to less snow, which leads to warming, which also leads to shrubbier and darker vegetation, which reinforces warming. And so on.
Beyond the Data:
There might not be a clearer example of this feedback than September and October in Alaska’s North Slope. These are the months surrounding the time when Arctic sea ice retreats to its annual minimum—it’s smallest footprint of the year. In the past, on average, the retreat didn’t make it very far from Alaska’s Arctic coast, and the sea ice, on average, ad returned during October. Now, it retreats well offshore and October returns are largely a thing of the past.
All of that open water during these two months brought profound changes to the climate of the North Slope since just 2000. The result is striking: look at the September-October temperatures there. It’s not that the place is hitting new records, which it is, it’s that a new normal, much different from the previous one, has taken root.