This week, we explore the Earth’s oceans and natural ocean-atmosphere interactions.

Chapter 3: Natural Climate Change: The Oceans and Internal Variability
When the air temperature starts to warm and it’s time to open up the backyard pool and go for a swim, it’s important to remember one thing: that water has a very high specific heat capacity. If you were to jump into the water, you’d probably jump right back out! High heat capacity means it takes a LONG time to warm up (but also a long time to cool off once warmed up). Hurricane season in the Northern hemisphere is particularly bad between the end of August and into October because the ocean waters have had enough time to warm up sufficiently by then, providing “fuel”, in the form of heat energy, to the storms.
So, if the air temperatures are getting warmer and the ocean eventually takes up that heat (~80% of the heat in the planet is stored in the ocean), can’t the warming of the planet then be due to heat being released from the ocean into the atmosphere? The laws of physics can answer this one: unless more heat was being poured into the oceans somehow, they would have to cool off when the heat got transferred to the atmosphere. But the ocean is getting overall consistently WARMER over time (there’s variability on a year-to-year basis, but we’ll get to that below).
Changes that have no external trigger – caused instead by interactions within the climate system itself – often involve what’s called “positive feedbacks,” processes in which the end product of an action causes more of that action to occur. One example is the El Niño/La Niña cycle, which can cause temporary warming and cooling in the Pacific Ocean. Both phenomena affect oceanic and atmospheric circulation patterns and influence global climate. While El Niño increases global temperature, La Niña decreases it. When El Niño occurs, it impacts the west coast of South America. Normally, cold water comes up along the coast, bringing with it nutrients and ample fishing opportunities. During an El Niño year, warm water pools instead (due to weakening trade winds), thus suppressing the cold upwelling. These effects are felt globally. If you ever hear “it’s an El Niño year” during a weather report, now you know why – it will affect temperature and precipitation (e.g., devastating rains and flooding can occur in South America, while Indonesia and Australia can experience droughts). In a La Niña year, colder than usual water appears off the west coast of South America instead due to stronger blowing trade winds, also affecting global temperature and precipitation patterns. Have a look at the images from NOAA Climate to see these global ‘teleconnections’ in El Niño and La Niña years. This cycle repeats itself on a timescale of about five years, but the changes are short-term. El Niño cannot explain the long-term warming trend of the last few decades.
Another example of internal variability is the Arctic Oscillation (AO), which is associated with changing patterns of air pressure in the Northern hemisphere. This phenomenon brings warmer weather to parts of Europe and North America, leaving the Arctic colder than usual when it’s in its “positive” phase. The “negative” phase of the AO brings the opposite conditions, resulting in a warmer-than-usual Arctic and colder weather in the sub-polar regions. Because of this seesaw effect, the AO has little effect on global temperatures, but can significantly influence local and regional weather, still impacting species and habitats on a large-scale.
The oceans and internal variabilities within our climate system are not driving the overall warmer temperatures on our planet. So, what’s the cause? Tune in next week to learn more about the human touch. For small creatures such as we, we are certainly having a large impact.