Scientists have found that the year 2015 is the hottest on record since the late 1880s began reliable worldwide record keeping. Relative to the 20th average, the month of December was registered as the hottest month on record in the past 136 years.
The globally-averaged temperature across ocean and land surfaces in December 2015 was 1.11°C (2.00°F). This value is surpassing the previous all-time record set two months ago in October by 0.12°C (0.21°F) and it is the highest for any month of December since records began in 1880. This also sets another record, being the first time when the global monthly departure from average has surpassed 1°C.
According to Extreme Tech, some of this rise in global temperatures was driven by the strong 2015 El Niño cycle, however not all of it can be explained by this reason. Depending on geographical location, El Niño cycles are in general wetter and warmer than average. The 2015 El Niño can be compared in strength to the 1997 El Niño, but has produced a much stronger total impact on warming. According to NOAA's data, the temperatures in December 1997 were 0.49C lower than in December 2015.
The year 2015 was setting record temperatures in general. For instance, the global land surface temperature in 2015 reached 0.9C above the historical average for the 20th century. Scientists came to the conclusion that, even without El Niño phenomenon, global temperatures are steadily increasing.
A study published in the journal Nature by lead author Lawrence Livermore has shown that the global ocean's heat content (OHC) suggests that only within the last few decades have occurred almost half of the temperature increases since the beginning of the industrial age. Over a third of the heat is dissipated at high ocean depths. Even if Earth's oceans can absorb great amounts of heat, increasing temperatures at the bottom of the ocean are a dangerous phenomenon that can lead to sea level rise.
