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the human influence on global warming.

The “Long” and “Short” of Temperature Trends

When one hears the words “global warming,” the image that comes to mind is one of a globe where temperatures are going up constantly, like the water in a kettle on the burner of a stove that steadily rises in temperature. But when it comes to climate the process is not quite the same.

While global temperatures have been going up overall, the rate of warming varies. As a result, some years are warmer than others. That is because there are factors, like air and ocean circulation patterns, that affect both the rate and the intensity of the global warming. For example, every few years an ocean cycle appears in the Pacific ocean either as an El Niño and La Niña with global temperature and regional precipitation pattern changes.

Imagine that you add a few external factors to that imaginary warming kettle (a fan or air conditioning vent blowing directly at the stove; adding more water (hot or cold) to the kettle; a bucket of ice cubes sitting by its side; etc.) and what we have is a heating system that is affected by those other factors – but the water will still eventually boil unless the burner is turned off or turned down significantly.

The “burner” in global warming is represented by the heat-trapping emissions released to the atmosphere from the burning of coal, oil, and natural gas – and since that burner has not (yet!) been reduced significantly (enough for the heating to slow down and prevent boiling), what we have is a warming planet. Relatively short-term natural phenomena that cause global temperatures to fluctuate are also occurring throughout the seasons, which we experience as a result of the Earth’s tilted axis as it revolves around the sun.

Short-term effects and external factors make it possible to have “cooler” periods in regions even as the general trend of warming continues. For example, during late 2007 and early 2008, the tropical Pacific Ocean was much cooler than normal due to a strong La Niña episode that kept temperatures across much of the globe lower than usual. Nevertheless, both years were still among the warmest years on record and would have been even hotter without this short-term cooling effect. Conversely, in 2015, a very strong El Niño episode, which made the tropical Pacific Ocean warmer than normal, combined with human-induced global warming to make that year the hottest on record to date (Nov 2016). And needless to say, winters continue to be colder than summers, even though some are more or less cold.