NOAA’s Climate Prediction Center issued an “El Niño Watch“ today. This chart from NOAA makes clear why that is a big deal:
Global average surface temperatures during El Niño and La Niña years.
An El Niño in the second half of 2012 would make it quite likely that 2013 would be the hottest year on record. NASA had a long discussion of this very point in a January analysis, “Global Temperature in 2011, Trends, and Prospects.”
NASA explains that the apparent recent slowdown in global surface temperature rise is likely to prove “illusory”:
The cool La Niña phase of the cyclically variable Southern Oscillation of tropical temperatures has been dominant in the past three years, and the deepest solar minimum in the period of satellite data occurred over the past half dozen years. We conclude that the slowdown of warming is likely to prove illusory, with more rapid warming appearing over the next few years.
Of course, the warming never slowed down in the place where climate science predicted 90% of the heat would go in the first place — the oceans (as discussed here).
The El Niño Southern Oscillation (ENSO) doesn’t change the overall warming trend, but it is a short-term modulation, what NASA labels the largest contributor to the “natural dynamical variability” of the climate system. El Niño and La Niña are typically defined as sustained sea surface temperature anomalies (positive and negative respectively) greater than 0.5°C across the central tropical Pacific Ocean. You can read the basics about ENSO here.
NASA has some great charts to explain the impact of the solar minimum and ENSO on the recent warming trend:
Figure 9 reveals that solar irradiance is beginning to emerge from a protracted minimum, at least two years longer than prior minima of the satellite era, making the sun a significant source for cooling during the past several years. The magnitude of the solar forcing, which varies about 0.25 W/m2 from solar minimum to solar maximum, is much smaller than the forcing by human-made greenhouse gases. However, the most relevant comparison of the solar forcing is with Earth’s energy imbalance, 0.58±0.15 W/m2 (Hansen et al., 2011), because the combined effect of all forcings is less than that of greenhouse gases alone, and much of the greenhouse gas forcing has been “used up” in causing the warming of the past century. It is apparent that the solar forcing is not negligible in comparison with the net climate forcing.
Figure 9. Solar irradiance from composite satellite-based time series
Because of the ocean’s thermal inertia, global temperature change caused by solar variability lags solar irradiance by about 18 months. Thus the influence of the sun in 2011 continued to be a cooling effect. However, the sun’s influence will change rapidly to a warming effect over the next 3-5 years.
What would an El Niño do in combination with this return to (almost) normalcy in total solar irradiance? NASA explained back in January:
Figure 7 helps us examine the issue of whether global warming has “stopped” in the past decade or at least slowed down from the rate of the prior two decades. Global temperature in 2011 was lower than in 1998. However, global temperature has a strong interannual variability tied to the Southern Oscillation (El Niño-La Niña cycle), as is apparent in Fig. 7.
Figure 7. Global monthly and 12-month running mean surface temperature anomalies relative to 1951-1980 base period, and 12-month running mean of the Niño 3.4 index.
Hansen et al. (2010) showed that the correlation of 12-month running-mean global temperature and Niño 3.4 index is maximum with global temperature lagging the Niño index by 4 months. Thus the 1997-1998 “El Niño of the century” had a timing that maximized 1998 global temperature. In contrast, the 2011 global temperature was dragged down by a strong La Niña. Indeed, the strength of the current double-bottomed La Niña, being based on ocean surface temperature relative to base period 1951-1980, is under-emphasized by the long-term trend toward higher temperature.
… there is a good chance of moving into El Niño conditions in the latter half of 2012, and in any case within the next 2-3 years. Because of the 6-month lag between tropical ocean heat content and global temperature, and the relatively cool state of global climate at the beginning of 2012, the next maximum global temperature is more likely to be in 2013 or 2014, rather than 2012.
So if there is an El Niño in the second half of the year, then a very warm 2013 seems the likely outcome. What are the chances of that?
The monthly ENSO diagnostic discussion from NOAA’s Climate Prediction Center (CPC) and the International Research Institute for Climate and Society (IRI), which included the “El Niño Watch,” explains:
The extensive volume of above-average sub-surface water temperatures indicates that the tropical Pacific SST anomalies will likely warm further in the coming months. A majority of models predict ENSO-neutral to continue through the June-August (JJA) season (Fig. 6). Thereafter, most of the dynamical models predict El Niño to develop during JAS, while the statistical models tend to favor the continuation of ENSO-neutral. Thus, there remains uncertainty as to whether ENSO-neutral or El Niño will prevail during the second half of the year. The evolving conditions, combined with model forecasts (Fig. 6), suggest that ENSO-neutral and El Niño are roughly equally likely during the late northern summer and fall.
Finally, the ENSO discussion concludes:
The CPC/IRI forecast calls for ENSO-neutral conditions through JAS, followed by an approximately 50% likelihood for El Niño during the remainder of the year (see CPC/IRI consensus forecast).
Stay tuned. The heat is on.
- Hottest Decade on Record Would Have Been Even Hotter But for Deep Oceans — Accelerated Warming May Be On Its Way