Most of manmade global warming is ending up in the ocean, just as scientists had predicted (see “Global Warming Has Accelerated In Past 15 Years“). And while recent “observations support predictions of extreme warming” this century, even sophisticated media outlets, like “The Economist,” get the story wrong (see “Memo To Media: ‘Climate Sensitivity’ Is NOT The Same As Projected Future Warming, World Faces 10°F Rise“). Former Hurricane Hunter Jeff Masters has a good chart-filled piece reviewing the latest temperature observations.
By Dr. Jeff Masters, via Weather Underground
One often hears the statement in the media that global warming stopped in 1998, or that there has been no global warming for the past 16 years. Why pick 16 years? Why not some nice round number like 20 years? Or better yet, 30 years, since the climate is generally defined as the average weather experienced over a period of 30 years or longer?
Temperatures at Earth’s surface undergo natural, decades-long warming and cooling trends, related to the La Niña/El Niño cycle and the 11-year sunspot cycle. The reason one often hears the year 1998 used as a base year to measure global temperature trends is that this is a cherry-picked year.
An extraordinarily powerful El Niño event that was the strongest on record brought about a temporary increase in surface ocean temperatures over a vast area of the tropical Pacific that year, helping boost global surface temperatures to the highest levels on record (global temperatures were warmer in both 2005 and 2010, but not by much.) But in the years from 2005 – 2012, La Niña events have been present for at least a portion of every single year, helping keep Earth’s surface relatively cool.
Thus, if one draws a straight-line fit of global surface temperatures from 1998 to 2012, a climate trend showing little global warming results. If one picks any year prior to 1998, or almost any year after 1998, a global warming trend does result. The choice of 1998 is a deliberate abuse of statistics in an attempt to manipulate people into drawing a false conclusion on global temperature trends. One of my favorite examples of this manipulation of statistics is shown an animated graph called “The Escalator”, created by skepticalscience.com (Figure 1).
Figure 1. Average of NASA’s GISS, NOAA”s NCDC, and the UK Met Office’s HadCRUT4 monthly global surface temperature departures from average, from January 1970 through November 2012 (blue), with linear trends applied to the time frames Jan ’70 – Oct ’77, Apr ’77 – Dec ’86, Sep ’87 – Nov ’96, Jun ’97 – Dec ’02, Nov ’02 – Nov ’12. Climate change skeptics like to emphasize the shorter term fluctuations in global temperatures (blue lines) and ignore the long-term climate trend (red line.) The global surface temperature trend from January 1970 through November 2012 (red line) is +0.16°C (+0.29°F) per decade. Image credit: skepticalscience.com.
Correcting for natural causes to find the human contribution to global temperature changes
We know that natural global warming or cooling on time scales of 1-11 years can be caused by changes in the El Niño-Southern Oscillation (ENSO) cycle, dust from volcanic eruptions, and changes in solar energy. For example, a study published in March 2013 in Geophysical Research Letters found that dust in the stratosphere has increased by 4-10 percent since 2000 due to volcanic eruptions, keeping the level of global warming up to 25 percent lower than might be expected. So, it is good to remove these natural causes of global temperature change over the past 34 years for which we have satellite data, to see what the human influence might have been during that time span.