Tuesday, December 06, 2016

Climate Change Won’t Stop in 2016, Despite Misleading Reports - By Bob Henson and Jeff Masters

With just three years left to go, it’s virtually certain that the 2010s will be warmer than any decade on record, barring a massive volcanic eruption.  As greenhouse gases produced by human activity continue to build up in the atmosphere, it’s also a very good bet--again barring a volcanic or geopolitical cataclysm--that the 2020s will be warmer than the 2010s.  You wouldn’t know about these perfectly reasonable, science-based inferences if all you had to go by was this article published by Breitbart.com on November 30:  “Global Temperatures Plunge. Icy Silence from Climate Alarmists.”  The article includes this statement:  “The last three years may eventually come to be seen as the final death rattle of the global warming scare.” 

Along with its presence on the high-profile Breitbart site, this article drew even more attention after a link to it was retweeted by the U.S. House Committee on Science, Space, and Technology.  Fortunately, the article has been effectively rebutted by several excellent bloggers (see links below).  Though we’d prefer to focus on our usual coverage of weather and climate science, in this case we felt it was important to add our two cents—especially because a video clip from weather.com (“La Niña in Pacific Affects Weather in New England”) was prominently featured at the top of the Breitbart article.  Breitbart had the legal right to use this clip as part of a content-sharing agreement, but there should be no assumption that The Weather Company endorses the article associated with it.

A plump cherry, carefully picked
The Breitbart article is a prime example of cherry picking:  pulling a single item out of context in order to build a misleading case.  The article draws heavily on a (U.K.) Daily Mail article from November 26 by David Rose titled “Stunning new data indicates El Niño drove record highs in global temperatures suggesting rise may not be down to man-made emissions.”  (In the U.K., the phrase “down to” is a synonym for “attributable to”.)  The plucked cherry, in this case, is the fact that satellite-based estimates of temperature in the lower several kilometers of the atmosphere over Earth’s land areas have decreased from early 2016 to late 2016 (a graphic in the Daily Mail attributed only to “NASA satellites” shows this drop as being more than 1.0°C).  The article implies that global temperatures may soon return to levels seen in the late 1990s.

Here are a few points crucial for putting this isolated factoid into proper context:

--On time scales of a few months, temperatures rise and fall more quickly over land than over the ocean (as acknowledged by Rose).  The ocean takes up about 70% of Earth’s surface, so land-only temperatures are an incomplete measure of global climate change.  The land-plus-ocean data for the lower atmosphere published by Dr. Roy Spencer (University of Alabama in Huntsville, UAH) shows a cooling of about 0.5°C earlier this year, or only about half of the 1.0°C claimed for the land-only dataset.  Despite this, the year 2016 is on pace to be the warmest year on record in the UAH lower atmosphere dataset.

--Satellite-based temperature estimates for the lower atmosphere are not the same as temperature trends measured at Earth’s surface, where people live.  Satellite-derived estimates of the lower atmosphere air temperatures are much more sensitive to El Niño, the large-scale natural warming that occurs in Eastern Pacific waters every 2 - 7 years.  When a strong El Niño event ends, as occurred earlier this year, we expect to see a substantial drop in satellite-based temperature estimates for the lower atmosphere—and just a slight drop in temperatures measured by weather stations on Earth’s surface, as was observed.

Figure 1: Global surface temperature (including both ocean and land areas) for the 12-month-long November-to-October periods from 1880 to present. (Image credit: NOAA/NCEI) Click to Enlarge.
--Three different groups publish satellite-based temperature estimates for the lower atmosphere:  UAH, RSS, and NOAA’s STAR.  The Breitbart and Daily News articles picked the one with the largest drop, from RSS.  The other two data sets show no similar dramatic drop, just the sort of normal decline one would expect to see after the end of a strong El Niño event.  Recently, RSS found an error in their lower tropospheric temperature estimates which has yet to be corrected. They state on their website that the data suffers problems “with the adjustment for drifting measurement times” and “should be used with caution”.  Ironically, the RSS data for the month of November, which was released on Friday after the Breitbart and Daily News articles were published, shows a substantial uptick in satellite-based temperature estimates for the lower atmosphere over land.  Notably, the combined land plus ocean numbers from both RSS and UAH for November showed Earth’s warmest November on record!

A pointless argument:  Was it El Niño or climate change that led to the record warmth in 2015-16?
Much of the Breitbart and Daily News articles focused on the idea that the two-year El Niño event that ended this year may have been entirely responsible for the record-warm global readings of 2015 and 2016.  It is well established that El Niño and La Niña produce spikes and dips in global temperature, typically lasting a year or two, atop the long-term trend of warming from increasing human-produced greenhouse gases.  It’s apparent from Figure 2 below (featured at the indispensable website skepticalscience.com) that the spikes and dips from typical El Niño and La Niña events average about 0.1°C each, and roughly 0.2°C to 0.3°C for the very biggest events.  In comparison, global surface temperatures have risen more than 0.6°C since the mid-20th century, and close to 1.0°C over the last 100 years.  Thus, the bulk of the unusual warmth of a year like 2016, compared to readings a century ago, is the result of long-term warming.  Put another way, the spikes that set record global highs are typically related to El Niño, but these spikes couldn’t set global highs without resting atop the rock-solid foundation of long-term warming.  Otherwise, we’d see strong La Niña events setting global record lows--and this clearly isn’t happening.  If we remove the El Niño spike, 2016 (to date) is still the hottest year on record and 2015 is the second hottest year on record (see the excellent analysis on this by Zeke Hausfather, a climate scientist and energy systems analyst at Berkeley Earth.)

Figure 2: Global surface temperature trends for the period 1966 - 2015 analyzed for El Niño years (red boxes), La Niña years (blue boxes), and neutral years (black boxes), along with volcanic years (gold triangles). The three trend lines show that global temperature has been rising at a fairly consistent rate of about 0.15 - 0.17°C (0.27 - 0.31°F) once La Niña and El Niño departures are factored out. (Image credit: skepticalscience.com; data from Berkeley Earth) Click to Enlarge.
Assuming that 2016 sets a new global surface temperature record (a virtual certainty), it will actually be the third record-warm year in a row.  The most recent El Niño event did not begin until the last quarter of 2014, so most of the record warmth of that year cannot be attributed to El Niño at all.  It’s also important not to confuse the multi-decadal ups and downs evident in Figure 1 with the longer-term warming trend caused by greenhouse gases.  During periods when El Niño events are more common than La Nina events, more heat is being sent from ocean to atmosphere and global temperatures can rise dramatically, as was the case during most of the 1980s and 1990s.  Similarly, when La Niña is more common than El Niño, more heat is being stored in the oceans and the global atmosphere may warm a bit more slowly, as was the case from about 1998 to 2013.  (See our 2015 post on the Pacific Decadal Oscillation for more background.)  These shifts play out atop the human-produced warming trend, which is forced by greenhouse gases accumulating in our atmosphere at greater and greater concentrations every year. 

Read more at Climate Change Won’t Stop in 2016, Despite Misleading Reports

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