Friday, July 1, 2011

"New Normals" are released publicly today

It's out with the old, and in with the new for weather data across the U.S. to determine what is considered "statistically normal" at about 8000 weather measurement sites. For example, whenever I tell you that our high temperature today is "warmer than average" for a specific date, or that a first freeze is occurring "much earlier than the average first freeze" for Richmond, I'm using 30-year-averaged weather data that is compiled at The National Climatic Data Center (NCDC), the world's largest active archive of weather data. For the past decade, we've been providing you with information ranging from 1971-2000. But every ten years, the NCDC sifts through, verifies, and releases a new 30-year data set that will serve as the "new normals" for which we can relate each day's weather to what the trend has been over the most recent 30 year period. The new range is 1981-2010, dropping the "old" decade of the 1970's.

(Image: NOAA)
Recently at my trip to the American Meteorological Society's 39th Conference on Broadcast Meteorology, I was able to talk with NCDC climate expert Deke Arndt about what these "new normals" mean for the Mid-Atlantic. (Interview on 6-22-11.) Here are his results:

Deke's data shows that the Mid-Atlantic has experienced a warmer shift of "baseline averages" during the time period 1981-2010. Thanks to Deke for taking time to chat with me!

For you pinpoint data junkies, here's the July difference between the newly added decade (2001-2010) and the old decade (1971-1980) that's being dropped, where you can clearly see that the Mid-Atlantic is taking on a warmer data-set than previously used.

NCDC Figure 1

And here's the same thing, but for January mins:

NCDC Figure 2.

Now let's make this a little smoother graphically. Here's a smoothed image of the same information:

(Image Credit: NOAA)

The decade that has been dropped, the 1970's, is considered by most climatologists to be an unusually cold decade for the U.S., whereas we know from data measurements taken globally that 2001-2010 was the warmest decade on record. From the maps above, we can see it's not necessarily the afternoon high temperatures that are warmer, it's the overnight low temperatures that are warmer, and the map above shows a Winter month!

So now let's look at the comparison of individual states' changes in annual "normal" or "average" temperatures. The annual average minimum temperatures are the image on the left, and the annual average maximum temperatures are the image on the right. You can see that with this most recent decade's data included, those temperatures are warmer in the 1981-2010 Climate Normals than in the 1971-2000 version.

(Maps by NOAA.)

Virginia's overnight temperatures are warmer by about 0.5-0.6 degrees Fahrenheit, and our afternoon highs are warmer by about 0.4-0.5 degrees Fahrenheit. That may not sound like much...but if this "new baseline" continues to climb higher over each decade, then we will have seen a significant warming trend in a relatively short time, by Earth's standards. Here's what the temperature trend has looked like since the Industrial Revolution, including an older 30-year-time-frame of 1961-1990 as the 0-line "mean" from which the average temperature deviates above or below the "baseline":

So this shows you that the past decade's data is consistent with a gradual warming trend, especially over the last several decades.

The latest climate data the scientific community as a whole knows of is that as greenhouse gas concentrations have increased (things like methane, water vapor, and carbon dioxide), so has the average global temperature increased about 0.8 degrees Celsius (the international temperature unit) over the past 100 years. Changes in the Earth's energy balance can produce changes in the Earth's climate over time (we've seen this before with volcanic eruptions, for example). But there are uncertainties as we move forward over the next century for potential further rises in that "baseline average," such as expected continued population growth globally, future greenhouse gas emissions (how much and where), and future technology that may change the way the energy business works worldwide. Just as the Industrial Revolution sent a ripple effect of changes in the Earth's energy balance, so may new technology over the next 100 years similarly impact climate, but how? The types of changes that may be seen in the future, both cool and warm variations, will really only be noticeable on a 50-100 year time scale. This isn't something where if we have a major snowstorm one winter or one super hot summer that we can immediately blame the "rising baseline." We're talking about longer-term average changes right now, not weekly forecast time-scales upon which the weather occurs. Weather extremes aren't going anywhere, I assure you. They've been around for ages, and will continue to be.

Back to the "new normals" data...

Here's what the NCDC says about the exact data it's releasing today and soon:
"We currently plan to release NOAA’s official 1981-2010 climate normals in two waves. The main set of normals (station-based monthly and daily normals of temperature, precipitation, snowfall, and degree days) are scheduled to be made available to the public by October 2011, followed by a release of all other climate normal products by April 2012. All the information contained herein is preliminary and subject to change. Final documentation will be made available as NCDC technical reports and/or manuscripts published in peer-reviewed journals."

So in coming months, when you hear me tell you that we are warmer than average on a morning low temperature, I'll be using the "new baseline" data.
--Meteorologist Carrie Rose
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