July 2016 was the hottest month ever recorded. That record lasted for all of one month as global temperatures remained at record-high levels through August, resulting in a tie with July during a period when the Earth typically cools.
Given natural variability, we might expect August to remain hot if an El Nino were forming in the Pacific, but at that time, with a weak La Nina struggling to fire off, the exact opposite was the case. In other words, the El Nino/La Nina cycle, which typically helps to drive global warm and cool periods, was pointed in the direction of ‘cool’, but the world remained near record-hot levels.
(2016 Climate Year continues to redefine global temperature boundaries as August ties July for hottest month ever recorded. Image source: NASA GISS.)
So what the heck was going on?
Rising Greenhouse Gasses are Steadily Rearranging How the Earth Balances Heat
We can’t answer this question without looking at the amazing overburden of greenhouse gasses that are trapping an enormous amount of heat in the Earth’s atmosphere and ocean. Due to decades of rampant fossil-fuel burning, 2016 will likely average around 404 parts per million CO2, which is the Earth’s primary heat-trapping gas that drives global climate. The last time levels of this gas were so high, more than 3 million years ago, the Earth was 2 to 3 degrees Celsius hotter than 1880s averages, seas were 25 to 75 feet higher, and the Earth was a remarkably different place.
CO2 isn’t the only gas adding heat-forcing to the Earth’s atmosphere. Human-emitted methane and other chemical compounds now add together with CO2 to produce a total CO2-equivalent forcing near 490 ppm. If this measure in any way remotely correlates to past climate forcings, then the Earth could well be on a path toward Middle Miocene climates that were around 4 C hotter than 1880s values.
Greenhouse Gas Accumulation Causes the Poles to Warm Faster than the Rest of the World
The way this extra heat — due to greenhouse gas forcing — emerges in the atmosphere is not even. In fact, science has long indicated that the poles warm faster than the rest of the world as the greenhouse gas overburden increases due to global burning of fossil fuels. Ever since the 1990s (and probably before), global climate models have shown that adding CO2 and other greenhouse gasses to the Earth’s climate system preferentially warms the far north and the far south.
This effect is due to the fact that greenhouse gasses more effectively trap and re-radiate the sun’s heat during periods of darkness. The long dark of polar night, lasting for the many months of polar winter, presents a period in which greenhouse gas warming has the opportunity to go into overdrive. In addition, oceans preferentially transfer heat toward the poles. Meanwhile, the melting of heat-reflecting ice coverage traps more heat in the local polar oceans (primarily in the Arctic) even as local carbon stores are increasingly vulnerable to release due to thaw. The result is that the polar regions of the world generate various amplifying feedbacks to the preferential heat forcing already in play. This can drive some big changes in atmospheric circulation patterns, which pull heat up from tropical regions and dump it over the frozen parts of our world.
Ridiculous Antarctic Warmth during Southern Hemisphere Winter
Coming back to El Nino and La Nina, it goes to reason that if the poles warm enough relative to the rest of the climate system, then such a global warming-related polar warm-up might eventually start to warp natural variability to the point that peak warming periods push a bit beyond the typical cycling.
(Polar amplification hit high gear during August as Southern Hemisphere winter saw extreme Antarctic warming. Image source: NASA GISS.)
This appears to have been the case during August 2016. As the Equator cooled, Antarctica warmed to a rather extreme degree. Though most of the globe saw above-average temperatures, the highest extreme anomalies were centered over Antarctica. There, the entire region above 75° South Latitude experienced temperatures greater than 3 C above average and a large region saw temperatures striking between 4 to 5.9 C above average for the entire month.
This heat came on the back of numerous high amplitude Jet Stream waves that delivered heat to the polar region during the Southern Hemisphere winter month of August. These waves, which have become a signature feature of Northern Hemisphere winter during recent years, bear with them the trappings of equator-to-pole energy transfer, a new climate effect playing havoc with traditional seasonal variability and possibly messing with some of the most well-established seasonal climate markers (such as the equatorially emerging quasi-biennial oscillation).
(No latitudinal zones saw below-average temperatures in August of 2016, another rather disturbing feature of this record-hot month. Image source: NASA GISS.)
As the South Pole saw repeated warm-air deliveries from the tropics, the Equatorial Pacific experienced only moderate negative departures below normal, a sign that the emerging La Nina was starting to splutter.
Overall, no latitudinal zone experienced below-average temperatures — another odd marker as the Southern Ocean (which pulls in an enormous amount of the Earth’s rising heat) tends to show below-normal departures in the region of 50° to 60° South Latitude.
We Appear to be on Track to Hit Above 1.5 C Within 15-25 Years
In total, global temperatures, according to NASA, hit 1.2 C above 1880s averages in the NASA measure (or about 0.98 C above NASA’s 20th-century baseline average). As a result, the first nine months of the December-to-November climate year are now averaging around 1.28 C above 1880s levels. And since the last three months of the year are unlikely to average below 1.05 C above 1880s, it appears that a 1.2 C departure or higher is now a lock for 2016.
With so much polar heat in place (this time shifting to the Arctic during September), it appears at least somewhat likely that the final three months for this climate year will tend to average closer to 1.05 to 1.20 C above 1880s averages. Consecutive months in this range or higher would push end-2016 values closer to 1.21 to 1.24 C above 1880s values. Notably, this is a range about 0.4 C higher than 1998 average temperatures. A similar period of warming occurring over the next 18 years would result in a year in which global temperatures exceeded 1.6 C above 1880s levels before 2035.
With global civilization continuing to burn massive volumes of fossil fuels and spewing greenhouse gasses into the atmosphere at a record rate, and with global temperatures so high, we are nearing a time when the first major climate threshold of 1.5 C (dangerous warming) is likely to be breached. Under current rates of fossil-fuel burning, this crossing will likely occur within the next 15 to 25 years. We know this because the Earth is now experiencing a rapid warming (0.15 to 0.2 C per decade), the likes of which has never been seen in human reckoning, and may have never been seen at all during any time of its deep past. It really all is, quite frankly, terrifying.
Scientific hat tip to Gavin Schmidt