Is Global Warming Taking a Break?

The average temperature on Earth has barely risen over the past 16 years, indicating that global warming is currently taking a break - though that doesn't mean it's over yet.

According to new research published in the journal Nature Geoscience, both natural climate fluctuations and solar irradiance - or the power of electromagnetic radiation per unit area - are responsible for this seemingly contradictory conclusion.

Global temperatures rose drastically into the late 1990s, and since 1998 have only risen slightly - which is surprising considering scientific climate models predicted considerable warming due to rising greenhouse gas emissions. While climate skeptics cite this discrepancy as evidence that climate change is not a current reality, researchers from ETH Zurich attempt to explain the factors behind this "warming hiatus."

After looking into all possible explanations for this global warming break over the last few years, the researchers landed on two important factors equally responsible for the phenomenon.

Natural climate fluctuations like El Niño and La Niña in the Pacific, for instance, important influences.

"1998 was a strong El Niño year, which is why it was so warm that year," lead study author Reto Knutti, a professor of Climate Physics at ETH Zurich, said in a statement. In contrast, La Niña has made the past few years cooler than they would otherwise have been.

Normal climate models typically take such phenomena into account, but it is impossible to determine when they will occur.

According to the study, the second important reason for the warming hiatus is that solar irradiance has been weaker than predicted in the past few years. In the past, this weaker cycle lasted 11 years, whereas now it's lasted for 13 years. Also, volcanic eruptions such as Iceland's Eyjafjallajökull in 2010 have increased the concentration of floating particles (aerosol) in the atmosphere, which has further weakened the solar irradiance arriving at Earth's surface.

The research teams reached these conclusions after looking for periods in which the El Niño/La Niña patterns corresponded to the measured data from the years 1997 to 2012. The ETH researchers suspect that the discrepancy between theirs and other climate models is due to incomplete measured data.

While it's good news that global warming is taking a break, Knutti does believe that it will resume as soon as solar activity, aerosol concentrations in the atmosphere and weather phenomena such as El Niño naturally start returning to the values of previous decades.