A curious local meteorologist’s dive into century-old regional weather data has yielded a disconcerting finding — a notable increase in average minimum weather temperatures consistent with the expectations of climate-change researchers.
National Weather Service forecaster Joe Ramey has analyzed records from 11 western Colorado and eastern Utah sites all dating back to at least 1911, including both valley and higher-elevation communities. He found that while average maximum temperatures per decade haven’t changed much over the last century, average minimum temperatures showed a notable increase. The increase has largely occurred since the 1970s, rising from 28.7 degrees that decade to 31.8 degrees for 2011-15, when that half-decade is included in the comparison.
Ramey said while he was surprised to see average minimum temperatures rise noticeably, but not average maximums, in fact that’s in keeping with what the National Oceanic and Atmospheric Administration and the Intergovernmental Panel on Climate Change have been saying to expect with a changing climate.
The IPCC has said to expect faster increases in daily minimum temperatures than daily maximum ones almost everywhere, leading to a decrease in 24-hour temperature ranges. In 2011, when NOAA reported a half-degree overall U.S. increase in temperatures between 1981-2010, compared to 1971-2000, it showed higher jumps in nighttime maximum temperatures than daytime maximums in many states.
“That’s what NOAA has been saying for awhile, that we would see larger changes in the minimum temperature, and indeed that’s what I found occurring here,” Ramey said of his local findings.
“It’s data, right. It’s not wisdom, and it’s no projection for the future. … But what I’m seeing at local specific sites in our forecast areas is what seems to fit for what NOAA says for the nation and what IPCC is saying for the planet.”
‘A very simple study’
Ramey said he undertook what is “really a very simple study” involving crunching historical weather records in the region and seeing what trends they might reveal. It was driven in part by personal curiosity, and also by a side climate assignment of his job, outside his forecasting work. He became interested in going beyond what NOAA was saying, and trying to better determine what was going on specific to the region.
He first began looking at 30-year averages that are updated once a decade, most recently in 2011, to look for changes over time. He compared data from 21 sites, but as he went further back in time he got to the point where just 11 remained that date back to at least 1911, and he focused on them.
While detecting the temperature trend, he worried that some of those long-term monitoring sites may have been affected over time by things such as changes in specific measurement locations, changes in the instrumentation used to make measurements, and increasing urbanization that can have effects like warming as pavement and rooftops increase. Grand Junction’s measurement location was originally downtown, for example, before moving twice, most recently to the Grand Junction Regional Airport.
But then Ramey considered the fact that there are weather stations in the region that aren’t subject to these influences — at national parks, monuments and recreation areas. He looked at data from nine of them, including at Colorado and Dinosaur national monuments, and Canyonlands and Mesa Verde national parks. Their one drawback is that their data generally dated back only to the 1960s. But Ramey saw the same distinct pattern of sizable increases in average minimum temperatures per decade and little noticeable change in average maximum temperatures. That similarity in trends gave him confidence that the older data was pretty reliable despite the concerns he’d had about it.
Ramey then looked farther to compare historical records, to places like Salt Lake City, Denver, Fort Collins, Rocky Ford, Taos, N.M., and Lander, Wyo.
“They too showed the same trend as the data that I’d seen here,” he said.
Ramey analyzed precipitation trends as well, and saw a lot of variation over the last century. The wettest decade was the 1980s, with more than 16 inches of annual precipitation on average, but there’s been a drying trend since then.
Ramey said precipitation is a complicated thing to forecast, for seven days much less over the longer term. He said that generally speaking, a warmer atmosphere can hold more moisture, and experts predict that with warming will come wetter wet periods and drier dry periods.
He was careful to note that individual sites he has studied have seen differing trends, and his findings apply to the region as a whole. For example, Grand Junction actually has seen a cooling trend over the last five years, which Ramey suspects may be the result of strong wintertime temperature inversions. The warming trend has been stronger at higher-elevation sites over the last five years than across the region as whole.
Ironically, too, Ramey has noted an actual shortening recently of local growing seasons as determined by first and last frosts, something he thinks might be the result of stronger shoulder-season storms that bring in cold fronts.
Just the facts
Ramey has given some public presentation on his findings, but said he’s not trying to jump to conclusions or forecast the future based on them.
“I’m just trying to show people what we’ve seen since we’ve had a fairly robust hundred years of climate information now — what that information says.”
Asked if he’s concerned about climate change, he said, “Personally, yes it concerns me. But that’s just personally.”
“… I’m trying to avoid any kind of political whatever. My point is, here’s my methodology, here’s what I was curious about … here’s the results, here’s what we’re seeing.”
He said while a lot of people have opinions about climate change, he wanted to see what the facts — the numbers — say in the region. “I think it’s an important, a hugely important topic, and I wanted to say that I actually looked into it and this is what I found.”
He said for him personally, climate change is enough of a concern “that three or four years ago we put solar panels on our house.”
He said that wasn’t an economic decision, as it will take a long time to recover that investment, but it was just something he felt a need to do.
Colorado as a whole has seen an increase in overall average temperatures in recent decades. Nolan Doesken, state climatologist at Colorado State University’s Colorado Climate Center, said those who have tracked such data have tried to normalize comparisons despite changes over the decades such as a decrease in weather stations in the mountains.
“It’s hard to perfectly adjust for major changes in the locations and numbers of weather stations,” he said.
He said there are few individual weather stations with what he considers a perfect long-term weather record, but the stations in Grand Junction and Montrose are two of the better ones on the Western Slope.
He said it’s generally been consistent statewide and nationwide that nighttime minimum temperatures have shown a bit more warming than daytime maximums have. He said one line of thinking is that during the wet 1980s there was increased nighttime cloud cover that trapped heat at night. With the drier period of the last 10 or 15 years, some people believe the discrepancy between average temperature increases between night and day may be diminishing, he said.
Doesken said he’s been in Grand Junction a number of times, and knows a lot of people locally think the climate is changing and a lot don’t. Scientists are on the side of thinking it is changing, he said, adding, “Every year there’s more evidence on that side of the argument, that’s for sure.
“Fifteen years we said, well, give us another 15 years and we’ll know for sure, and we know a lot more now with 15 more years of information. But now I’ll say for sure we’ll know in 15 years.”
He said if current projections are even halfway close to correct, by 2030 or so it will be distinctly warmer almost everywhere, with what are now considered to be really hot years being pretty much the norm by 2030-40.
Rising temperatures, and the expectation of more to come, concern everyone from Colorado ski resort operators, to forest officials who fear more insect infestations and fires, to water managers.
Hannah Holm, coordinator of the Ruth Powell Hutchins Water Center at Colorado Mesa University, said increasing temperatures are expected to pinch water supplies.
“I think the main thing is that it’s becoming more and more apparent that even in the absence of much change in precipitation, higher temperatures make drought worse because they increase water use by plants, whether that’s native vegetation or agriculture,” she said.
She said Ramey’s findings are in keeping with other data she’s seen experts present. “It’s a pretty consistent story,” she said.
And despite the uncertainty over what may happen precipitation-wise in coming years, “the temperature projections are all pretty consistent and they pretty much all say we’re getting hotter.”
Streamflows also likely will go down, Holm said Tuesday from St. George, Utah, where she was headed into a climate-change presentation at the Utah Water Users Workshop.