Long-term, cyclical patterns in both the Atlantic and Pacific will have a major influence on our weather.
When the graybeards said the drought that Texas and the Southwest suffered this year and last was the worst they’d seen since the ’50s, they knew what they were talking about after all.
“Welcome to the new normal,” says Evelyn Browning Garriss, an historical climatologist in Albuquerque, NM. Or, she says, welcome to conditions that your grandfather might call the old normal. “We are looking at some of the same conditions that Texas weathered in the 1950s.”
However, while you’re digesting that bit of news, consider this: while the U.S. is looking at some long-term weather shifts for the next 20 years or so, Garriss says the abnormal summers of 2011 and 2012 were just that – abnormal.
This summer’s unusual weather was influenced by several things. First, two volcanoes erupted last year, one in Iceland and another in Russia, and blew ash and chemicals high enough to affect the stratosphere and alter air pressure. “And air pressure controls wind.”
The phenomena caused arctic winds to strengthen to the point that they trapped cold air and didn’t allow it to come south. “That’s why it was so warm last winter,” she says. “None of the cold air could get to us.”
The last time two volcanoes erupted in the same year was back in the 1700s. “(Last year’s eruptions) were a once in a two or three-century occurrence. Don’t expect it this year,” she says.
What is happening, however, is changing water temperature in both the Atlantic and Pacific. The Pacific Decadal Oscillation (PDO) is a 50-year cycle in water temperature. Through the ’70s, ’80s and most of the ’90s, most of the hot water in the Pacific was off the coasts of North and South America, Garriss says. Hot water combined with a hot wind pulls a lot of moisture and the westerly winds blew it inland.
“Starting in 1998, however, the Pacific started to change back to the pattern it had in the 1950s. It is colder air off the Pacific coastlines, and the air being blown into the U.S. is drier. We started seeing it in 1998; in 2006, it tipped. When it changed, it changed global weather patterns. It changed the rules,” Garriss says. “This is now the new normal and you can expect it for another 20-30 years.”
Then there’s the Atlantic Multidecadal Oscillation (AMO), a 70-year water temperature cycle. “What it means is sometimes the Gulf Stream is fast, sometimes it’s slow,” Garriss says. “When it’s fast, it carries a lot of tropical water north and it gets hot. When it’s slow, it doesn’t carry as much tropical water north and the Atlantic gets cold.” It’s not a new or manmade phenomena, she says. Using meticulous records from Scandinavian fishing fleets, the cycle has been documented for at least 500 years.
Buckle up, though, because the AMO has the pedal down.
The U.S. has been in a general warming trend since the mid to late 90s, she says, due to the PDO and the AMO. The AMO began its work in 1995 and the North Atlantic has been warming ever since. “And when you have hot Atlantic water, you have hotter temperatures. We are going to be seeing more extreme summers than we have since 1995, more hurricanes. And this trend of hotter summers is going to continue for the next 20 years.”
However, all is not bleak because, finally, there’s El Niño to consider. The cold La Niña conditions that brought drought to Texas last year are gone and a hot El Niño is taking its place. Typically, an El Niño warps the jet stream south, bringing rain to parts of the southern U.S.
“I don’t know if it’s going to be enough to restock everything we’ve lost in two years of drought,” Garriss says. “But if history repeats itself, and it normally does, Texas can expect a wet winter. And the longer El Niño lasts, the wetter it’s going to be.”
That’s very good news because, should El Niño last into next spring, it should bring some relief to the parched Midwest.
Long term, however, don’t expect weather patterns to go back to the way they were a decade or two ago. “We’re facing a new pattern,” she says. “I compare it with riding a horse. Mankind better cope with the movements or we’ll get thrown off.”