The Earth is getting hot. A 1⁰C temperature rise has been recorded on almost every monitoring site on the globe. With the Paris Climate Summit ongoing how has this 1⁰C, half of the proposed 2⁰C warming limit, gone under the radar?
In the light of the Paris Climate Summit I think it’s important to make note of an article written in the New Scientist back in August. This article “Earth Now Halfway to Warming Limit” reported that the Earth is already halfway towards the warming limit of 2⁰C that was outlined in the Intergovernmental Panel on Climate Change’s (IPCC) climate assessments. According to the New Scientist article all but one surface monitoring station is recording a one degree Celsius rise relative to the second half of the 19th Century. The first half of the 19th century isn’t used as a baseline temperature set because of an abnormally cold climate period known as the Little Ice Age but also because of significant gaps in climate records in this period. The latter half of the 19th century isn’t a perfect start for the record either because of the Krakatoa eruption in 1883 which led to generally cooler temperatures in the following years due to the large amounts of aerosols released into the atmosphere. This aside, the latter half of the 19th century is probably the best example of a complete climate record as close to the start of the industrial revolution as possible.
This year’s El Nino event could lead to a warming of 0.1⁰C in 2015, a record amount of warming in just one year. Yet, let’s not get too jumpy just yet. The general trend in warming has been a slowing from 0.26⁰C a decade between 1984 and 1998 to 0.4⁰C a decade between 1998 and 2012. This slowing in warming has been accounted for by an increase in aerosol production from volcanic activity and Asian factories but also due to a less active sun. Less solar flares, coronal mass ejections and other activity has led some scientists to believe that the sun may be shifting into a less active state (known as solar minima) after reaching peak activity in 2012-2013. The Ocean too has contributed to this slowdown in warming thanks to a phenomenon known as the Pacific Decadal Oscillation in which the northern Pacific switches between a warm and cold phase. The Northern Pacific has been in its cold state allowing it to absorb more thermal energy from the atmosphere but this is now expected to flip back into a warm state and therefore become less efficient at absorbing heat energy. This could lead to an acceleration of warming in the next few years similar to that, or perhaps larger than that, of the 1980s.