If the world is warming, why am I so cold?

Icicles in Basalt, CO 2013. Credit: ECO

This year in particular, December seems to have gotten off to a cold start in the Valley.

The thermometer on our monitoring station at Sky Mountain recorded a low of -15 degrees Fahrenheit in the first week of the month. The thermometer at my own house, mid-valley, reads in the low teens each morning. So why, if global atmospheric warming is really happening, do these bitterly cold days still occur? To answer this question, you first have to take a look at the difference between weather and climate.

Humans tend to think in terms of weather. Might it be cold today? Is there enough snow for good skiing this week? Will there be water for my crops this summer? All of these weather conditions--measured as temperature, inches of rain, or wind speed--vary widely, sometimes even within the same day.

Climate is more stodgy than weather. It is slower to change and describes the average conditions found in a region over an extended period of time: decades or more. So climate describes what conditions generally existed in the past and allows us to project what conditions are generally likely occur in the future.

Weather, by contrast, describes what is happening at a single given moment. Ben Kirtman, a meteorologist who spoke on this topic at a public lecture in Aspen in 2011, described weather as being "the statistics of climate."

>20"-long icicles, Dec. 2013. Credit: ECO

Think for a moment about baseball. To a certain degree, baseball players, like climate, are rated in terms of their averages. You might have an excellent player experience an off-day and not hit a single ball thrown at him. Conversely, you might have a player who usually strikes out hit a home run one game. People trying to predict the outcomes of future games are not likely to base their predictions on the single off-day or a lucky home run. They want to know what the players' averages are. Climate, likewise, is not determined by an outlier; it is determined by overall trends.

For example, let's take a look at an indicator of weather conditions in Aspen for 2011 vs. 2012. The indicator we will use is frost free days, or the number of days between the last frost in Spring and the first frost in Fall. The more frost free days in a year, the longer the warm season. For more about the significance of frost free days in the valley, visit iRON's "Temperature and Frost" page.

In 2011, Aspen had 128 frost free days. In 2012, that number dropped to 106. If you looked only at these two years, it would seem as though frost free days in Aspen are decreasing, in other words, it is getting colder, and the growing season is not lasting as long. Looking only at these two years, however, would be like watching your baseball player for just two innings. When you place these two years in perspective with 70 years worth of data, frost free days tell a very different story. Below is a graph showing the average number of frost free days for each decade since 1940 in Aspen, Colorado.
Looking at average frost free days over this longer period of time, you see an upward trend. Compared to the 1940's and 1950's, this decade has an average of 30 more frost free days--an entire additional month that did not have frost.

Frost Free Days from the Aspen Weather Station. Note that the station moved to a higher elevation in 1980. Data available through NCDC.  For further information on ecology and frost free days, visit the FHI website

Looking at extreme low temperatures over the same time period tells a similar story. Some individual years have a large number of days below 0 degrees Fahrenheit, while others have very few. Looking at the number of days per year below 0 over the long term reveals a sharp downward trend from 1940 to 1980 and a less steep slope from 1980 to 2012. In other words, very cold days are becoming less common.

Days below 0 Deg F. Data is from the Aspen weather station, which moved to a higher elevation in 1980. Data is available through NCDC. For further information on ecological importance of very cold days, visit the FHI website

Trends matter in nature. As was discussed in November's post, living things have a range of flexibility for conditions in which they can survive. If that range is exceeded or the change persists for too long, then the living thing must adapt or perish. For example, the bark beetle that wreaked havoc on Colorado's Ponderosa pines a few years ago was able to proliferate so successfully because several years followed one another where the temperature did not remain below 20 degrees F for long enough to disrupt the beetle's life cycle. As a result, the beetles thrived, placing pressure on pines. The spruce bark beetle, has a similar life cycle, where overwinter survival is determined by temperature. If the warmer winters continue, then the pines and spruce of the Rocky Mountains will be increasingly forced to adapt or may may dies off, leading to a shift in which trees dominate this regions.

Frosty days and icy nights have been a part of Colorado's climate for 100's of years before today, and the ecosystems and native species that make the Roaring Fork Valley unique are present because of their ability to succeed in those previous conditions. Changes in weather can determine the survival of an individual, but changes in climate can determine the survival of an entire species.

You don't know where you're going until you know where you've been...

Hiking through a powdery layer of snow on a crisp day in early November, moisture for the valley was looking promising for this fall. It was not even Thanksgiving, and the snow was already deep enough to over-top our boots when we went off trail. There were other clues as well, hinting this was a wet late summer/early fall. Many service berry bushes were still loaded with fruit. The fruits were dry and wizened by then, but the fact they still clung to the brown branches suggests that berries were so plentiful this summer that the bears and birds found more than they could eat. But is this really a wet year or a normal year? What is normal? These are questions that observations of just a day or even just a season can't answer.  These are the types of questions that require gathering information long before you know you'll need it.

This monitoring station measures air temperature, 
soil moisture, relative humidity, and precipitation.
Credit: Marci Krivonen

Monitoring is not a glamorous business, routine rarely is. Yet it is consistency and long-term commitment that makes data from monitoring valuable. Monitoring is type of scientific practice whereby a single or a few variables are measured on a regular basis for an extended period of time--the longer the period of time the better. Once data on these variables has been gathered, it can be analyzed to show changes (or lack thereof) in the variables, to find natural patterns, or to compare current conditions with conditions of the past.

Human activities--where we live, what crops we grow, where we vacation--are based on assumptions about the conditions of certain areas, and if conditions in those areas change, they may no longer be able to support the our activities. Natural systems likewise require specific conditions to function and survive. By looking at conditions in the past and comparing them to the success of human or natural systems, we are able to gain understanding about what conditions are conducive to a system thriving and what conditions may threaten it.

With the widespread use of human fossil fuels that skyrocketed in  the 20th century, changes have begun occurring on our planet at a rapid rate and on a large scale. Monitoring provides a lens through which we can study those changes. Looking at a past dataset, the last 100 years of temperature for example, gives us an idea of what we may need to prepare for in the future. If we saw that the average temperatures for each year went up and down a little bit over the past century but that the cold periods and warm periods alternated pretty regularly, then we could speculate that the climate in the valley is likely to continue to be similar to conditions in the past and can plan our growing season accordingly. If the average yearly temperatures vary from year to year, but in general show that each decade is on average warmer than the last, then we can speculate that our future climate is likely to be warmer than our past one has been. Warmer temperatures on a regular basis translate into local concerns such as higher risk of fire and the possibility of drier soil during the growing season.

The famous Keeling curve shows a clear trend in atmospheric CO2. Credit: NOAA

Mundane though gathering data (by instruments or by hand) on a regular, extended basis may be, monitoring data have been the trigger for important discoveries and even political and social debate. Perhaps the most well-known example of a revolutionary monitoring application is the CO2 monitoring station on Mona Loa. Founded by Charles David Keeling in the late 1950's, the instruments on this Hawaiian volcano provided scientists with evidence that atmospheric CO2 levels were rising at an unprecedented rate. Because of CO2's role as a greenhouse gas, this data provided warning of a potential global warming trend.

Service berries in November. Credit: AGCI

By giving us a window into the past, monitoring helps us to better understand what present conditions mean for our ecosystems and what we might expect from the future. So to return to the snowy November day when we hiked to our own, young monitoring station: what did the snow on the ground mean for the aspens, sage, scrub oak, and service berries that depend upon it?  It's all a matter of context. This fall (the portion that has already passed at least) received considerably more rain than the previous fall (see iRON's data page comparing 2012 and 2013). That being said, the late rains came on the heels of a dry summer preceded by a "drought condition" spring. Whether or not the trees and shrubs in this sub-alpine ecosystem survive depends on more than just a season--it depends on the cumulative conditions of a number of years. In other words, only time will tell. In the meantime, we'll be keeping tabs.