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Mission of the York Energy Efficiency Committee

Our mission is to respond to the global warming crisis by promoting energy efficiency, alternative energy, and environmental initiatives throughout the town of York, Maine.
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[Source: The US Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE)]

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2011: Earth’s 11th warmest year, Part 2

As detailed in a previous post, 2011 was tied for the 11th warmest year on record globally. But there are number of natural climate forces that appear to be holding the temperature down lower than it might be.

How much of the warming in recent decades is due to natural causes?
The El Niño/La Niña cycle causes cyclical changes in global temperatures that average out to zero over the course of several decades. La Niña events bring a large amount of cold water to the surface in the equatorial Eastern Pacific, which cools global temperatures by up to 0.2°C. El Niño events have the opposite effect. The year 2011 was the warmest year on record when a La Niña event was present. Global temperatures were 0.12°C (0.2°F) cooler than the record warmest year for the planet (2010), and would very likely have been the warmest on record had an El Niño event been present instead . . .

Correcting for natural causes to find the human contribution
We know that natural episodes of global warming or cooling in the distant past have been caused by changes in sunlight and volcanic dust. So, it is good to remove these natural causes of global temperature change over the past 33 years we have satellite data, to see what the human influence might have been during that time span.

. . . A 2011 paper published by Grant Foster and Stefan Rahmstorf, Global temperature evolution 1979 – 2010, took the five major global temperature data sets and adjusted them to remove the influences of natural variations in sunlight, volcanic dust, and the El Niño/La Niña cycle. The researchers found that adjusting for these natural effects did not change the observed trend in global temperatures, which remained between 0.14 – 0.17°C (0.25 – 0.31°F) per decade in all five data sets. The warmest years since 1979 were 2010 and 2009 in all five adjusted data sets. Since the known natural causes of global warming have little to do with the observed increase in global temperatures over the past 33 years, either human activity or some unknown natural source is responsible for the global warming during that time period.

Figure 3. Departure from average of annual global temperatures between 1979 – 2010, adjusted to remove natural variations due to fluctuations in the El Niño-Southern Oscillation (ENSO) cycle, dust from volcanic eruptions, and changes in sunlight.

In Part 3, we’ll see what climate scientists are predicting based on the the trends measured to date. Or you can read the rest of the analysis at Dr. Jeff Masters’ blog.

 

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