Today the National Oceanic and Atmospheric Administration (NOAA) announced that 2016 was the second-hottest year on record in the U.S. And worldwide, 2016 is poised to go down as the hottest year on record.
I asked one of the world's leading climate scientists put the numbers in perspective.
Dr. Kevin Trenberth shared the Nobel Peace Prize in 2007 for his work explaining climate change; he was a lead author of that year's IPCC assessment of climate change. So when he, and others, say the periodic warming of the Pacific Ocean – known as El Niño – is the smoking gun that accounts for the last two years being the warmest on record, it's important.
"There's some new work of ours coming out very soon which shows the oceans have been warming more than thought, and so this is the memory of past global warming."
"The 2015-16 El Niño certainly went well into 2016 [and] certainly played a role. The warmest 12 months on record was from about September 2015 to August of 2016," he told me. We all know, from experience, that air and large bodies of water interact with and influence each other; wind creates waves on the water, and an icy lake breeze in the spring can make an otherwise mild day feel chilly. Well, in much the same way, the oceans can interact with, and change, the climate.
Dr. Trenberth went on to explain that "in the second half of the El Niño heat comes out of the ocean into the atmosphere, and that contributes, especially, to the global warming." In fact, the oceans will continue to emanate heat for at least 3 months after the El Niño ends, like a radiator that stays warm for a few minutes even after the heat has turned off.
That, Trenberth says, is what accounts for making 2015, and then 2016, consecutive warmest years on record. But that's not all that's at work.
"There's some new work of ours coming out very soon which shows the oceans have been warming more than thought, and so this is the memory of past global warming," he said. "[Even] without the El Niño, more than 1° Fahrenheit above values prior to 1970, or thereabouts."
El Niño tends to simply add to the warming that's already occurring. The opposite pattern, called La Niña, can temporarily subtract, meaning global average temperatures tend to change like, according to Trenberth, "a staircase rather than a steady rise. And, at the moment, we've sort of taken a step up. [In the past] we've stalled a little bit, and may go down a little bit, but we won't go back down to the previous levels that we've seen earlier, back in say the 1990s or earlier."
"There are other indicators – like sea level rise, and the heat content in the oceans – that are much more steadily increasing that show that global warming is clearly occurring, and we better watch out because it has consequences," he continued.
He also told WCCO's Mike Augustyniak that climate change is "very likely" a factor in it being the Twin Cities' wettest year on record.
"The atmosphere can hold 4 percent more moisture for 1° Fahrenheit increase in temperature. And, so, if the atmosphere is running warmer, there tends to be more moisture in it, and it rains harder," he said.
Trenberth says 2017 will likely be a cooler year for the earth, compared to 2016, because the El Nino pattern has ended. Nevertheless, he said, the weak La Niña that's going on in the tropical Pacific is "having some quite distinctive influences on the weather patterns across the United States; the heavy rains that are coming into northern California, for instance."
The World Meteorological Organization is expected to release worldwide figures on 2016 in mid-to-late January 2017.