Ocean Cycles, Not Humans, Likely Behind Climate Change.

• Author: Tsonis, Anastasios
• Position: EYE ON ECOLOGY

RESEARCH INTO NATURAL climatic cycles, including the well-known El Nino cycle and the less familiar North Atlantic Oscillation and Pacific Decadal Oscillation, demonstrates how interactions between these ocean cycles have been shown to drive changes in the global climate on time scales of several decades.

We can show that, at the start of the 20th century, the North Atlantic Oscillation pushed the global climate into a warming phase and, in 1940, it pushed it back into cooling mode. The famous "pause" in global warming at the start of the 21st century seems to have been instigated by the North Atlantic Oscillation as well.

In fact, most of the changes in the global climate over the period of the instrumental record seem to have their origins in the North Atlantic. This has profound implications for the way we view calls for climate alarm. It may be that another shift in the North Atlantic could bring about still more phase shifts in the global climate, leading to renewed cooling or warming for several decades to come.

These climatic cycles are entirely natural, and can tell us nothing about the effect of carbon dioxide emissions, but they should inspire caution over the slowing trajectory of global warming we have seen in recent decades. While humans may play a role in climate change, other natural forces may play important roles, too.

The El Nino Southern Oscillation cycle (ENSO) was discovered in the 1970s when satellite images of the Earth were first routinely collected. Since then, it has been recognized as a major driver of the dynamics of the climate system. Its connection to climate change is discussed frequently--for instance, its role in global warming and whether there wiU be more El Nino events in a warmer climate.

El Nino, Spanish for "the little boy," is a recurring phenomenon in the tropical Pacific Ocean and is considered one of the most-influential occurrences in our climate system. Its name comes from the "Christ child" because it usually starts some time in December. It was coined in the late 1880s by Peruvian fishermen, who noticed that the cold north-flowing current in which they fished would change every few years into a warm southflowing one. They understood that this change meant trouble for their business. What they did not know is that many other areas of the world, one way or another, also suffer the consequences of El Nino.

To explain how El Nino occurs, we have to start with the fact that, in the subtropics, the...