We all know that many things affect global temperature. Some, like greenhouse gases, cause long-term changes and can create significant trends. Others fluctuate but don’t really go anywhere over the long term, so they cause temperature fluctuations but don’t create long-term trends.
At least two such fluctuating influences have been identified. One is solar variation. The energy output of the sun is variable, especially showing a cyclic variation with the roughly 11-year solar cycle. Another is the el Nino Southern Oscillation (ENSO), which when high warms the planet and when low cools it. It too fluctuates up and down, but hasn’t exhibited long-term trends which could account for the trend we observe in global temperature. You might wonder, what has been the short-term impact of these two influences recently? Let’s look at their temperature influence over a recent 10-year period, from January 2002 through December 2011.