The year that just finished, 2015, was the warmest year recorded in the instrumental record. The actual data for December is not officially available yet, but my friend and colleague John Abraham keeps track of the global surface temperature daily and has done an amazing job at estimating the final temperature anomaly value that is eventually reported in each of several databases. He has provided a graph using his estimated value, above.
There are two major contributing factors, maybe three depending on how you count everything, to 2015 being the warmest year. The main factor is, of course, global warming. The Earth’s surface temperature is going up because of the Greenhouse Effect, and along with that, we are seeing remarkable climate disruption, including floods, other inclement weather, and a host of problems. On top of this, the last part of 2015 saw a strong El Niño, the strongest recorded in historic documents. This weather event, which involves the departure of ocean-stored heat in the Pacific into the atmosphere, is continuing, though it will likely peak soon and begin to decline (but see below). That is all we need, really, to explain 2015, but there may be a third factor that overlaps with those two worth singling out. Some areas of the world’s oceans, including parts of the Atlantic and the Pacific (outside the usual Pacific El Niño warming effect), have been exceptionally warm on the surface. This is really just part of the whole anthropogenic global warming thing, but seems more extreme this year. In other words, it seems as though the ocean is putting more stored heat into the atmosphere than just that part that El Niño contributes, and the surface temperature measurements include sea surface temperature.
How warm will 2016 be? Playing the odds, it would always be a good bet that the next year will be warmer than the current year, on average, because global warming continues. However, even as the surface temperature trends upwards over time, the actual measurements from year to year wiggle up and down a fair amount owing to a number of factors. So, on average, if you bet on warming for each subsequent year you would overall win, but you might lose that bet during some years. (In fact, you could lose your shirt if warming happens to occur with infrequent large spikes interspersed among years that see modest cooling, so be careful!)
However, 2016 is actually more than 50-something percent likely to be warm compared to 2015. One reason is that El Nino will continue for the first part of 2016, and the effect that El Niño has on surface temperature is delayed. The peak effect occurs several months after the peak of the El Niño itself. So, if El Niño peaks in February, for example, we will have global warming + El Niño enhancement through early summer. So at least half of the months of 2016 will be very warm. There is a very good chance, then, that 2016 will be warmer even than 2015.
Mark Boslough, a physicist who writes quite a bit about Global Warming, has made a bet along these lines. He is not betting that 2016 will be warmer than 2015, but he is betting on the long term upward trend of the Earth’s surface temperatures. He’s really putting his money where his mouth is, by the way, to the tune of 25,000 US dollars. The details of his bet are here. So far, as far as I know, none of those in the climate science denial world have taken him up.