This year is on track to be the second-hottest on record, surprising climate scientists who thought natural weather patterns could break a multiyear trend of record-breaking temperature increases.

Global temperatures this year have been 1.64 degrees Fahrenheit above the 20th-century average of 56.3 F, according to NOAA. That's second only to last year, by a difference of about 0.29 F. Last year is the warmest on record.

Each of the last three years have broken global high temperatures records. But temperatures since January have caught some researchers off guard, because they expected that the tapering off of an El Niño period, which typically raises temperatures, would hold down global heat levels. Instead, this year is on pace to top every record except the one set in 2016, researchers found. At this point in the year, 2015 was the third-hottest on record. It ended up breaking every heat record — until being topped by 2016.

There is a greater than 57 percent chance that 2017 will turn out to be the second-hottest year on record, according to Gavin Schmidt, director of NASA's Goddard Institute for Space Studies. There are greater odds that 2017 will be one of the top three hottest years ever recorded.

Global carbon emissions have slowed recently, but they continue to build in the atmosphere at a record pace, because the gas can be present for centuries. That drives warming. Researchers released the latest measurement of atmospheric CO2 yesterday; it reached 406.56 parts per million in June at the Mauna Loa Observatory in Hawaii.

High temperatures, like those occurring now, are linked to rising CO2 levels, said Pieter Tans, lead scientist at NOAA's Global Greenhouse Gas Reference Network. However, he cautioned against attributing a single year's temperatures to CO2 growth.

"The annual increase is still above 2 ppm per year. I think that is directly linked to the fact that CO2 emissions from fossil fuel burning and cement production are also at a record high. That is directly linked," he said. "Now, the temperature increase is also directly linked to high CO2, but maybe not on a year-to-year basis."

The observatory in Hawaii has recorded five consecutive years of CO2 increases of at least 2 ppm, an unprecedented rate of growth, according to NOAA. Since 1960, CO2 has increased more than 30 percent, or 100 ppm. About 150 years ago, before the age of industrialization, atmospheric CO2 was 280 ppm. It had been at that level for about 10,000 years.

Sea ice in both the Arctic and Antarctic are also near record lows. Sea ice cover in Antarctica is now 6.3 percent below average from 1981 to 2010. That's the second-lowest ever observed for this time of year over 40 years of record-keeping. In the Arctic, sea ice cover is 7.5 percent below average, the sixth-smallest ever recorded.

Heat spiked in spots across the globe. Africa saw its hottest June ever recorded. Europe and South America were much warmer than average. The American Southwest saw a heat wave break multiple temperature records, as well. Eastern Russia was an anomaly, with cooler-than-average conditions, even as the rest of the country was much warmer than average.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.