Short-term vs. Long-term Trends

From Walsh, J., et al. – Walsh, J., et al. (11 January 2013), “Figure 6: Short-term Variations Versus Long-term Trend

One often hears that the Earth stopped warming 15 years ago. This is based on the erroneous notion that one can just look at a decade or so and conclude what is happening. As can be seen in the chart, if one just looks at decade-long temperature trends, one might conclude that the temperature is going up, down, or sideways. If one looks at the longer trend, though it is clear that the globe is warming.

As we all know, the weather is constantly changing. It is a chaotic phenomena meaning that a small change can create a large result. This variability can dominate the long term trend over short intervals of time, and it is this variability in the weather that is mostly responsible for the short-term temperature trends.

However, other influences such as the oceanic circulation both along the surface, like the Gulf Stream or ENSO (El Niño – Southern Oscillation), and circulation between the deep and surface waters can affect temperatures measured at the surface. Based on measurements made in the Southern oceans, it appears that the energy has been transferred to the deep ocean, causing it to warm by about 0.005°F per year for the past decade. Although this seems like a small number, because of the high specific heat capacity of water and the large volume of water involved, this may account for the apparent plateau in the temperature rise the past 15 years.

But even the assumption that temperatures haven’t changed for 15 years is wrong. 2010 surpassed 1998 as the warmest year on record and the first decade of the twenty-first century was also the warmest decade on record. Beginning with the decade of the 1960s, which was warmer than the 1950s, every decade has been warmer than the previous decade.

NOAA – NOAA (July 2010), State of the Climate in 2009, as appearing in the July 2010 issue (Vol. 91) of the Bulletin of the American Meteorological Society (BAMS)

 

10 warmest years on record
(°C anomaly from 1901–2000 mean)
Year Global[66] Land[67] Ocean[68]
2010 0.6590 1.0748 0.5027
2005 0.6523 1.0505 0.5007
1998 0.6325 0.9351 0.5160
2003 0.6219 0.8859 0.5207
2002 0.6130 0.9351 0.4902
2006 0.5978 0.9091 0.4792
2009 0.5957 0.8621 0.4953
2007 0.5914 1.0886 0.3900
2004 0.5779 0.8132 0.4885
2012 0.5728 0.8968 0.4509

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