According to data released by NASA and NOAA this week, July 2012 was the 12th and 4th warmest July (respectively) globally on record.  NASA’s analysis produced the 12th warmest July in its dataset; NOAA recorded the 4th warmest July in its dataset.  The two agencies have slightly different analysis techniques, which in this case resulted in not only different temperature anomaly values but rather different rankings as well.

The details:

July’s global average temperatures were 0.47°C (0.85°F) above normal (1951-1980), according to NASA, as the following graphic shows.  The warmest regions on Earth coincide with the locations where climate models have been projecting the most warmth to occur for years: high latitudes (especially within the Arctic Circle in July 2012).  The past three months have a +0.56°C temperature anomaly.  And the latest 12-month period (Aug 2011 – Jul 2012) had a +0.50°C temperature anomaly.  The time series graph in the lower-right quadrant shows NASA’s 12-month running mean temperature index.  The recent downturn (post-2010) is largely due to the latest La Niña event (see below for more) that recently ended.  As ENSO conditions return to neutral or even El Niño-like, the temperature trace should track upward again.

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Figure 1. Global mean surface temperature anomaly maps and 12-month running mean time series through July 2012 from NASA.

According to NOAA, July’s global average temperatures were 0.63°C (1.13°F) above the 20th century mean of 15.2°C (1.12°F).  NOAA’s global temperature anomaly map for July (duplicated below) reinforces the message: high latitudes continue to warm at a faster rate than the mid- or low-latitudes.  Unfortunately in July 2012, almost the entire Northern Hemisphere was warmer than normal.

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Figure 2. Global temperature anomaly map for July 2012 from NOAA.

These figures show just how extreme (intensity & spatial extent) the heat wave over most of the US was during July 2012.  As many people saw during the preceding two-and-a-half weeks, England was cooler than usual.  The same was true for northwestern Europe, most of Australia, and a good portion of South America (Argentina, Bolivia, etc.)  Additional anomalous warmth occurred over Greenland, Russia, eastern Europe, and into central Asia and the Middle East.  The two different analyses’ importance is also shown by these figures.  Despite differences in specific global temperature anomalies, both analyses picked up on the same temperature patterns and their relative strength.

The continued anomalous warmth over Siberia is especially worrisome due to the vast methane reserves locked into the tundra and under the seabed near the region.  Methane is a stronger greenhouse gas than carbon dioxide over short time-frames (<100y),which is the leading cause of the warmth we’re now witnessing. As I discussed in the comments in a recent post, the warming signal from methane likely hasn’t been captured yet since the yearly natural variability and the CO2-caused warming signals are much stronger.  It is likely that we will not detect the methane signal for many more years.  Of additional concern are the very warm conditions found over Greenland.  Indeed, record warmth was observed at a 3200m altitude station in early July.  3.6°C may not sound that warm in July, but the station’s location at 10,500ft altitude is of interest.  I want to post more on this later, but the early July melt occurred over a very short time period, which did not result in a great deal of runoff.  In contrast, continued warmth over portions of Greenland that have not witnessed such warmth did result in rapid melting during 2012 (note: the melt season isn’t over yet either).

These observations are also worrisome for the following reason: the globe is still returning to ENSO-neutral conditions:

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Figure 3. Time series of weekly SST data from NCEP (NOAA).  The highest interest region for El Niño/La Niña is NINO 3.4 (2nd time series from top).

As the second time series graph (labeled NINO3.4) shows, the last La Niña event hit its highest (most negative) magnitude more than once between November 2011 and February 2012.  Since then, SSTs have slowly warmed back above a +0.5°C-1.0°C anomaly (y-axis).  La Niña is a cooling event of the tropical Pacific Ocean that has time-delayed effects across the globe.  It is therefore significant that the past handful of months’ global temperatures continued to rank in or near the top-5 warmest in the modern era.  You can see the effect on global temperatures that the last La Niña had via this NASA time series.  Both the sea surface temperature and land surface temperature time series decreased from 2009 to 2011.  Note that the darker lines (running means) started to increase at the end of 2011, following the higher frequency monthly data.

As the globe returns to ENSO-neutral conditions this summer and early fall, how will global temperatures respond?  Remember that global temperatures typically trail ENSO conditions by 3-6 months: the recent tropical Pacific warming trend should therefore help boost global temperatures back to their most natural state (i.e., without an ENSO signal on top of it, although other important signals might also occur at any particular point in time).  Looking further into the future, what will next year’s temperatures be as the next El Niño develops, as predicted by a number of methods (see figure below)?

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Figure 5. Set of mid-July predictions of ENSO conditions by various models (dynamical and statistical).  To be considered an El Niño event, 3-month average temperature anomalies must be measured above +0.5°C for 5 consecutive months (so the earliest an El Niño event is likely to be announced is sometime this fall).  Approximately 1/2 of the models are predicting a new El Niño event by the end of this year.  The other models predict ENSO-neutral conditions through next spring.

From the above, I hope it is clear that the US’s recent record heat wave and historic drought are associated with the most recent La Niña event.  This is typical for the US, given dominant wind patterns that La Niña establishes.  While El Niño would add additional anomalous warmth on top of the slowly evolving climate change signal, it usually also heralds above-average precipitation over most of the US.  That would be a welcome event, given the reach and severity of the drought currently underway.

Cross-posted at WeatherDem – the blog.