Monday, July 17, 2017

+Myth: El Niño Caused Post-1997 Global Warming

The outline for this post is as follows:
  1. The Myth and Its Flaw
  2. Context and Analysis
  3. Posts Providing Further Information and Analysis
  4. References

This is the "+References" version of this post, which means that this post contains my full list of references and citations. If you would like an abbreviated and easier to read version, then please go to the "main version" of this post.

References are cited as follows: "[#]", with "#" corresponding to the reference number given in the References section at the end of this post.

1.  The Myth and Its Flaw

El Niño caused post-1997 global warming. Thus the recent warming is natural, as opposed to anthropogenic or caused by humans.

Purveyors of this myth include Roy Spencer [1], the Daily Caller [2], The Competitive Enterprise Institute [3], Leo Goldstein [4], Marc Morano [5], and David Wojick [25]. Spencer seems to be the primary purveyor of this myth, since other myth proponents typically cite Spencer [2 - 5].

The myth's flaw: Post-1997 global warming remains, even after one corrects for El Niño [11 - 17; 24].

2. Context and Analysis

During El Niño (also known as the El Niño phase of ENSO, the El Niño Southern Oscillation) the oceans' surface warms, as does a region of the lower atmosphere known as the troposphere [6; 7]. The strength of El Niño can be measured using the multivariate ENSO index, or MEI [8; 9]. Spencer should be aware of this, since Spencer employed the MEI in his published research [10, page 231].

MEI-corrected temperatures still show post-1997 global warming, as shown in published research [11 - 17; 24] and unpublished analyses [18 - 21]. Thus El Niño did not cause the post-1997 global warming. Even Spencer's colleague John Christy admits that ENSO did not cause the post-1997 tropospheric warming trend [23] (though Christy gets little else right when it comes to climate science). Another source makes a similar point regarding long-term tropospheric and ocean warming: ENSO, and other ocean cycles, do not account for most of this warming [51].

Figure 1 depicts some MEI-corrected temperature trends, illustrating that ENSO does not explain most of the multi-decadal warming:

Figure 1: Relative temperature from 1979 - 2010 for three surface temperature records (GISS, NCDC and CRU) and two lower tropospheric temperature records (RSS and UAH), after correction for ENSO (using MEI), volcanic effects, and changes in solar irradiance [12].

In fact, the 2015/2016 El Niño was weaker than [8] (or about as strong as, in some regions [7]) the 1997/1998 El Niño, even though 2015/2016 was warmer than 1997/1998, as shown in "Myth: No Global Warming for Two Decades". Figure 2 below depicts this warming using the mid- to upper tropospheric warming that Spencer commented on [1], while figure 3 displays the MEI and figure 4 depicts one regional component of the MEI:

Figure 2: Near global mid- to upper tropospheric temperature averaged for the UAH, NOAA, and RSS satellite-based analyses [22].  

Figure 3: Multivariate ENSO index (MEI). The red peaks represent El Niño events and the blue troughs represent La Niña events. The relative magnitudes of the peaks and troughs are proportional to the strength of corresponding El Niño and La Niña events [8]. See figure 4 for a representation of some of the uncertainties involved in calculating the magnitude El Niño and La Niña events.

Figure 4: Non-cumulative ENSO index (Niño3.4) based on ocean temperature in the east central equatorial Pacific, up to the year 2016. Niño3.4 is one of several non-cumulative indexes used in generating the non-cumulative MEI shown in figure 5. Red lines indicate the Niño3.4 index values, while the black region represents uncertainty at the 95% confidence level [7].

So given this evidence, why do Spencer and his followers defend their myth? Well, they may be (intentionally or unintentionally) conflating the following two claims:
  • El Niño contributed to 2015/2016 being warmer than 2014
  • El Niño contributed to 2015/2016 being warmer than 1997/1998

The first claim is true, since El Niño conditions were stronger in 2015/2016 than 2014 [8]. However, since the 2015/2016 El Niño was weaker than the 1997/1998 El Niño (see figure 3) [8], then the second claim is false. It is this second claim that Spencer defends when he claims that the past two decades of warming was natural [1]. So Spencer is defending a false myth.

To put this another way [26, from 5:22 - 14:25], the distinction between the above two bullet points is analogous to the distinction between:
  • Earth's 24-hour rotation cycle contributed to late afternoon in summer being warmer than midnight in summer in Canada
  • Earth's 24-hour rotation cycle contributed to late afternoon in summer being warmer than noon (with the Sun at its zenith) in winter in Canada

The first claim is true, since Earth's shorter-term, 24-hour rotation cycle causes Canada to receive more solar energy at during late afternoon than during midnight. However, the second point fails, since Earth's 24-hour rotation cycle would cause a late afternoon day to be cooler than noon. Instead Earth's axial tilt relative to the Sun, not Earth's 24-hour rotation cycle, explains the longer-term, multi-month warming from the winter to summer. 

Analogously, El Niño contributes to shorter-term warming on an inter-annual time scale, while other factors contribute to longer-term warming on a multi-decadal time-scale. If you're curious about what those "other factors" are, then see section 3.7 of "John Christy Fails to Show that Climate Models Exaggerate CO2-induced Warming" and "Myth: The Sun Caused Recent Global Warming and the Tropical Stratosphere Warmed".

In response to what I've said, a critic might claim that the energy from El Niño accumulates over the long-term [27 - 32]. So, for instance, the 1997/1998 El Niño expelled a large amount of energy that persisted for 10+ years, explaining why the post-1998 period was warmer than the pre-1998 period. According to a such a critic, I would need to use a cumulative MEI to account for this accumulated energy, instead of the non-cumulative MEI I used above [27 - 30]. Figure 5 below presents John Christy's cumulative MEI, in contrast to the non-cumulative MEI I presented above in figure 3:

Figure 5: Cumulative TSI (total solar irradiance) and cumulative MEI used by Christy et al. [34, page 18].

But scientists rarely (if ever) use a cumulative MEI. In fact, I know of no peer-reviewed scientific paper that uses a cumulative MEI. Instead the cumulative MEI remains relegated to non-peer-reviewed sources [27 - 31] (or fake, predatory "journals" [32] not listed on a reputable citation index [39]) which are more amenable to unfounded claims than are peer-reviewed sources [36, page 712; 37; 38]. Scientists instead use a non-cumulative MEI in their peer-reviewed work [11 - 17; 23; 24; 33]. Even Spencer [10, page 231] and Christy [23, page 512; 56], two critics of mainstream climate science, use a non-cumulative MEI in their peer-reviewed research. Christy even cites [34, page 18; 35, page 10] peer-reviewed sources that use a non-cumulative MEI [8; 9; 10, page 231], including work from his research colleague Roy Spencer [10, page 231].

There are at least three reasons why scientists employ a non-cumulative MEI instead of a cumulative MEI:
  • A cumulative MEI is arbitrary, since it involves arbitrarily selecting a period over which the MEI accumulates.
  • A cumulative MEI compromises the relationship between the MEI and the temperature trends one uses the MEI to predict.
  • A cumulative MEI violates basic physics.

Christy, as a climate scientist, makes a version of the first two points in his peer-reviewed work [23, page 514]. Yet he previously used a cumulative MEI in his non-peer-reviewed blog articles [34, pages 16 and 18; 40] to argue that solar-induced changes in ENSO caused most of the post-1970s global warming [34; 40; 41]; I discuss Christy's double standard on this in section 2.3 of "Myth: The Sun Caused Recent Global Warming and the Tropical Stratosphere Warmed". Timothy Osborn, another climate scientist, argues for [41] the first and third points in response to Christy's use of a cumulative MEI [34, pages 16 and 18; 40; 41].

Osborn points out [41] that a warmer Earth would radiate more energy into space (as per the Stefan-Boltzmann law [52 - 55]), instead of all the energy just accumulating [42 - 44]. Scientists can observe this increased radiation during a warm El Niño [45 - 47]; the radiation increase occurs largely because El Niño increases cloud cover and these clouds then reflect the solar radiation Earth would otherwise absorb [45; 48]. This cloud-based mechanism compensates [45; 47] for less emission of radiation by clouds during El Niño [49; 50]. 

So increased radiation during warm El Niño events means that energy from a two-year El Niño event does not simply accumulate for 10+ years, contrary to the cumulative MEI. Thus a cumulative MEI violates basic physics, making a non-cumulative MEI more appropriate than a cumulative MEI. And a non-cumulative MEI reveals that El Niño did not cause the post-1997 warming trend [11 - 17; 24], as I explained above and as Christy himself showed [23].

3. Posts Providing Further Information and Analysis

4. References

  4. (and the comments section there)
  6. "Comparing tropospheric warming in climate models and satellite data"
  7. "Ranking the strongest ENSO events while incorporating SST uncertainty"
  8. (accessed June 12, 2017)
  9. "El Niño/Southern Oscillation behaviour since 1871 as diagnosed in an extended multivariate ENSO index (MEI.ext)"
  10. "The role of ENSO in global ocean temperature changes during 1955-2011 simulated with a 1D climate model"
  11. "Deducing multidecadal anthropogenic global warming trends using multiple regression analysis"
  12. "Global temperature evolution 1979–2010"
  13. "Volcanic contribution to decadal changes in tropospheric temperature"
  14. "Spectrally dependent CLARREO infrared spectrometer calibration requirement for climate change detection"
  15. "Natural variability, radiative forcing and climate response in the recent hiatus reconciled"
  16. "Equilibrium climate sensitivity in light of observations over the warming hiatus"
  17. Foster et al.: "Comment on “Influence of the Southern Oscillation on tropospheric temperature” by J. D. McLean,C. R. de Freitas, and R. M. Carter"
  22. "Tropospheric warming over the past two decades"
  23. "Satellite bulk tropospheric temperatures as a metric for climate sensitivity"
  24. "Lower tropospheric temperatures 1978-2016: The role played by anthropogenic global warming"
  26. potholer54's 2015 video: "Why global temperatures never go up in straight lines"
  30. Comment #16.2:
  31. Stockwell and Cox: "Comment on ”Influence of the Southern Oscillation on tropospheric temperature” by J. D. McLean, C. R. de Freitas, and R. M. Carter"
  32. "The Southern Oscillation Index as a random walk"
  33. "Clarifying the roles of greenhouse gases and ENSO in recent global warming through their prediction performance"
  34. "On the Existence of a “Tropical Hot Spot" & The Validity of EPA’s CO2 Endangerment Finding"
  35. "U.S. House Committee on Science, Space & Technology, 29 Mar 2017, Testimony of John R. Christy"
  36. "Climate change denial books and conservative think tanks: Exploring the connection"
  37. "Science and the public: Debate, denial, and skepticism"
  38. "Internet blogs, polar bears, and climate-change denial by proxy"
  40. "On the Existence of a “Tropical Hot Spot” & The Validity of EPA’s CO2 Endangerment Finding, Abridged Research Report, Second Edition"
  42. "Global monthly precipitation estimates from satellite-observed outgoing longwave radiation"
  43. "An observationally based energy balance for the Earth since 1950"
  44. "An analysis of the dependence of clear-sky top-of-atmosphere outgoing longwave radiation on atmospheric temperature and water vapor"
  45. "ENSO-driven energy budget perturbations in observations and CMIP models"
  46. "Advances in understanding top-of-atmosphere radiation variability from satellite observations"
  47. "Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty"
  48. "The ENSO effects on tropical clouds and top-of-atmosphere cloud radiative effects in CMIP5 models"
  50. "Does vertical temperature gradient of the atmosphere matter for El Niño development?"
  51. "Evidence for external forcing on 20th-century climate from combined ocean-atmosphere warming patterns"
  52. "Positive feedback in climate: stabilization or runaway, illustrated by a simple experiment"
  53. "Spatial patterns of modeled climate feedback and contributions to temperature response and polar amplification"
  54. "How well do we understand and evaluate climate change feedback processes?"
  55. "Four perspectives on climate feedbacks"
  56. "The carbon cycle response to two El Nino types: an observational study"