July 2015 temperature anomalies, relative to the 1951-1980 average. Graphic: NASA

By Jason Samenow
17 August 2015

(Washington Post) – For planet Earth, no other month was likely as hot as this past July in records that date back to the late 1800s. And the global is well on its way to having its hottest year on record.

Both NASA and the Japan Meteorological Agency (JMA) have published data that show it was the hottest July on record. Since July is on average the planet’s warmest time of year, it’s fair to say temperatures this past month were at or very close to their highest point in the history of instrumental records.

NASA’s map of July temperatures shows large areas of much warmer than normal temperatures in the Pacific Northwest, western Europe, central Asia and Africa. It also reveals the telltale signature of the powerful El Nino event, portrayed by the much warmer than normal sea surface temperatures in the eastern and central tropical Pacific.

The heat from El Nino not only manifested itself over the tropical Pacific, but also likely boosted temperatures in other areas due to its ripple effects on global weather patterns. In sum, NASA data reveal July 2015’s average temperature edged July 2011 as the warmest on record(by 0.02 degrees), making back-to-back months of record-setting temperatures after a toasty June. Every month this year has ranked among the top four warmest in NASA’s analysis. [more]

July was likely Earth’s hottest month in what’s destined to be Earth’s hottest year

By Tamino
15 August 2015

(Open Mind) – Now that NASA has released their data updated through July, we know that in that data set, this July was the hottest July on record with a temperature anomaly of 0.75 deg.C, i.e. it was 0.75 deg.C above “climatology” (which is what’s usual for the given month). It’s not the hottest temperature anomaly in the data set, however; that record still belongs to January 2007, at 0.96 deg.C above climatology.

Yet it does seem that this July, while not the hottest temperature anomaly on record, is the hottest month on record.

Every year, the global average temperature goes through an annual cycle — not just the temperature at a given location. In the northern hemisphere we tend to be hottest in July and coldest in January, but in the southern hemisphere the seasons are reversed, hottest in January and coldest in July. The seasons are definitely hemisphere-dependent.

But what about the global average? My first instinct, many years ago, was that earth would, overall, be hottest in January simply because we’re closer to the sun (at the perihelion of our orbit). But it turns out (as was quickly pointed out by a blog commenter) earth is actually hottest in July. That’s because when the southern hemisphere is tilted toward the sun in January, all that solar heat mainly strikes ocean, which dominates the southern hemisphere rather than land. The thermal inertia of the oceans is much greater than that of the land masses, so it heats up more slowly, and just doesn’t get that hot even at the peak of summer.

But in July, it’s the northern hemisphere that’s tilted toward the sun. The lower thermal inertia of land (mostly in the northern hemisphere rather than the southern) means it can heat up quickly, so the northern hemisphere reaches higher temperatures at its summer peak than the southern hemisphere does at its summer peak.

Why not translate those temperature anomalies into actual temperature estimates? [more]

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