We all know that the weather is variable. One year it may be a warm winter and the next a cool winter. The same goes for all of the seasons. It may be more wet and rainy one year and the next it will be dry.
Of course, a lot of these changes are bound to be blamed on climate change, but they really shouldn't all be. Yes, the climate is warming, even with the annual variations. Yes, the last 12 years have been among the 14 warmest years on record. These things are true, but the annual variations are nothing new. Global climate change may enhance some of these variations but not create them.
That leads us to one of the most important drivers of weather the oceans. Here on land, we often forget about the impact that these large bodies of water have on weather. Even very large lakes can have an impact, as anyone in Buffalo can attest to. They see snow totals that we can't even fathom in this region.
So it should be no surprise that if a lake can affect local weather, that an ocean can affect global weather. One need to look no farther than the warmest years on record to see how important the oceans are to our weather.
If you look at the warmest two years on record (2010 and 1998), they both occurred during what is referred to as the positive phase of the El Nino Southern Oscillation. A positive phase of the ENSO is often called El Nino conditions and a negative phase is often called La Nina conditions.
Of course, the overall general trend is toward warming, the coolest years of the 2000s (which were still for the most part warmer than the 1900s temperatures) occurred during La Nina years. So this Pacific Ocean event has shaped world weather, causing cooler years worldwide during La Nina and warmer years during El Nino and moderate years during what is called the neutral phase.
This doesn't tell the whole story either, the oceans have more tricks for us than ENSO. The ENSO occurs near the equator in the Pacific Ocean, but the entire Pacific Ocean goes through what is called the Pacific Decadal Oscillation. The ENSO goes through an oscillation over roughly a 2-to-7-year period. The PDO oscillates on closer to a 20- year time scale.
If you look at the El Nino years, some years seem to be much warmer El Nino years than others, so what is going on here? Well that is thanks to the PDO. If El Nino happens during a positive PDO phase then the El Nino conditions are strengthened and we end up with years like 1998, which held the record for being the warmest year on record until 2010, even though there was an El Nino year in between those two scorchers.
There are other ocean oscillations that have an effect on weather. For instance, the North Atlantic Oscillation, which has its largest effect on regions in the North Atlantic such as Western Europe and the Eastern United States.
During positive phases of the NAO, there are warmer winters in Western Europe and the eastern U.S. and Greenland is colder. The opposite is true in the negative phase. During a negative phase the polar jet stream migrates south allowing for a strong blast of polar air to migrate as far south as Florida. This allows for winter temperatures to drop well below normal in the U.S (Sound a little familiar?) Several forecasts have predicted a strong negative phase of the NAO this winter and it appears that they were correct.
I have only mentioned two oceans, because these are the two that most effect our weather in the U.S. but of course the other oceans contribute as well. The oceans make it extremely difficult to predict our weather and they have even provided difficulty in predicting overall climate change.
The oceans are able to absorb additional heat and also large amounts of CO2 (which raises the acidity of the ocean because CO2 is then turned into carbonic acid). Predicting what the oceans will do with that additional heat is difficult, and knowing how much CO2 can be absorbed is also proving difficult (the oceans are absorbing less and less CO2 as more and more is emitted).
As I mentioned before, the overall trend is toward a warming planet, but the oceans may have a few surprises for us in yearly temperature variations. Don't be surprised to see a very cold winter every now and then.
Jeremie is a Wilmington resident and Clarkson University graduate student. He can be contacted at firstname.lastname@example.org.