This past June was the warmest ever recorded by scientists since record keeping began in the 19th century. The average surface temperature of the earth was 61.2 degrees Fahrenheit, up 1.3 degrees from the 20th century's typical June.

May 2014 set a comparable new record. That month, too, the planet's average surface temperature was about 1.3 degrees above the normal warmth of May.

It's reasonable to expect that the whole year may end up with the warmest surface temperatures ever recorded—especially if El Niño, the periodic shifting of warm waters in the Pacific now thought to be incipient, develops robustly.

On the face of it, data like this, reported Monday by National Oceanic and Atmospheric Administration, might seem powerful enough evidence that climate change has indeed arrived, as is widely accepted by mainstream scientists.

But lately, climate scientists have felt the need to explore the emerging evidence in more sophisticated ways.

One of these methods is to examine the temperature records not just in terms of global seasonal averages, but with an eye to the patterns of temperature extremes.

How frequent are the unusually warm days, and how often do the uncommonly cool nights occur?

Another new report, State of the Climate in 2013, issued by the American Meteorological Society on July 17, introduces an analysis of temperature extremes since 1950.

Like the vast majority of climate measurements explored in this report, the data on temperature extremes confirm the general trend of a warming planet.

Extremes in recorded temperatures can be a more significant measurement than averages, the annual checkup explains, since "societal impacts are more often related to extreme events than changes in the mean climate."

"While monthly and annual means...are fundamental to monitoring climate change, it is more often the climate extremes that noticeably impact society, infrastructure, and ecosystems," the report said.

On its cover was an illustration of the devastating typhoon that hit the Philippines last year with the greatest force ever recorded in such a storm, doing damage that the meteorological society said will last for generations.

Globally, 2013 was again one of the 10 warmest years on record, both at the surface and in the troposphere, according to the large range of estimates cited in the report. It was compiled by 425 scientists from 57 nations.

Following the Extremes

Scientists are now paying more attention to the percentage of days when the mercury soars into the top-tenth of the annual temperature range, and conversely to the percentage of nights when the mercury falls into the bottom-tenth of the year's range.

"The year 2013 ranked within the top 10 years for the frequency of warm days and bottom 10 years for the frequency of cool days," the meteorological society reports. "The global average maximum temperature index which tracks extreme daytime heat was also within the top 10 highest years."

The overall warming was vividly on display in what is called the TXx, which tracks the highest temperature reached on a single day during each each year. It hit a record value in 2013, just as it did in 2012. As a global average, the hottest day of 2013 reached 96.3 degrees Fahrenheit, up from 95.9 degrees in 2012. (Its value varies from region to region, of course; in Australia, TXx hit an astonishing 111.2 degrees in 2013.)

Credit: State of the Climate in 2013

"Globally, 2013 had the sixth-highest number of warm days on record, and the eighth-lowest number of cool nights," the society reported.

Examining warm days and nights and cool days and nights on global and regional scales exposes more starkly "a general long-term tendency towards warmer conditions, as indicated by increasing numbers of warm extremes...and decreasing numbers of cool extremes."

"This is consistent with the general observed warming trends. As global temperatures increase, more warm extremes and fewer cold extremes are expected to occur."