What’s “Normal”? A Confusing But Important Concept in Climate Change

One thing I notice with human uncertainty and understanding of climate change is our memories are quite short. We don’t always remember how things have changed in the places we have lived in our relatively short lifetimes on this Earth.

Sometimes perspectives from the past help us out.

You might remember in my previous post I discussed a rather random exchange I witnessed between a Mom and adult daughter in a coffee shop where I live, effectively about how the winter climate has changed in Nebraska over the decades. The daughter says “these wild swings (in temperature) are normal”. And the Mom basically says “Not so fast!”…”I remember when it used to be more consistently cold and snowy all winter long”. Basically back in the day there wouldn’t be low 70s in February.

So what’s “normal?”

It’s a strange concept, if you think about it, but an important one. As a meteorologist (who aren’t climatologists), we use “normal” as a moving target. The previous 30 calendar years as the standard for “normal”. So it’s 2018, so we compare what’s happening today or this week or this month thus far to the previous average for the 1981-2010 time period. During the previous decade, we used 1971-2000, the previous decade before that, 1961-1990, etc. But when your “normal” is shifting with time, it’s under the assumption that the climate of your region is relatively stable with natural variability. But it is not any longer. Anthropogenic climate change being produced by industrial civilization is strongly dominating our planet in timescales of years to decades, which means, moving the “target” to some degree actually masks just show significant global warming is changing the climate of a given area (and of course the planet as a whole).

Without data or communication across generations, the current pace climate change (which is still nearly 170 times faster the past 50 years than the previous 10,000 years) can still go unnoticed by the current living generations of people who haven’t noticed or experienced the weather of the “past climate”. Here are some rather stark examples-

I decided to take a look at climate data from the National Climate Data Center for the city of San Diego. I gathered temperature data from San Diego International Airport for the period 1998-2017 and from the San Diego Weather Bureau (the ancestor to the modern National Weather Service) for the period 1890-1909. The most significant symptom of climate change is the shift of the weather to more extreme conditions.  Extremes which never occurred previously, but also known extremes which become much higher in occurrence. In this case I looked at the occurrence of low temperatures at or below 41 degrees F (5 C) and the occurrence of high temperatures at or above 86 degrees F (30 C). The results were…stunning.


High temperatures at/above 86 F: 62 (Highest temperature in period: 100 in 1909).

Low temperatures at/below 41 F: 206 


High temperatures at/above 86 F: 158 (highest temperature in period: 101 in 2012/2016).

Low temperatures at/below 41 F: 28

So what’s normal? If you account for the fact that climate change has been underway since the late 19th century (and before that), occurrences of high temperatures at/above 86 F are running 96 days above normal, while occurrences of low temperatures at/below 41 F are running 178 days below normal. If you were born in the 80s or 90s in San Diego might not even realize your city used to be a lot cooler place. And I do mean A LOT cooler, even if you have actually notice it has warmed more abruptly since you were younger.

I did this same “instant study” for my home city of Seattle some months ago. I don’t have the numbers on me any longer, but it was for shorter time frames (1896-1905) and (2008-2017) looking at high temperatures at or above 90 degrees F. Less than a dozen 90 degree days during the early era vs. nearly *60* in the most recent era, as well as the all-time record high for Seattle of 103 in 2009. Nearly 60 days at or above 90 degrees in just one decade! I don’t remember the exact values for the low temperatures (at or below 32) but there was a notable drop in the number of below freezing temperatures compared to the past. But even going back to my childhood…born in 1984 and a “child of the 90s”. I remember significantly cool, wet periods in the summers, 90 degree temperatures being possible, but rare. When Seattle had its first 100 degree temperature on record in 1994, it was my first experience with triple digit heat in my life and it was absolutely awful. The 2009 heat wave (my last full summer living in the city) was equally roasting with no air conditioning in my parents apartment. In a climate where such heat is rare, many buildings don’t have air conditioning. You use fans and block your (open) windows from the relentless sun with whatever you can. Builders didn’t plan for the summer heat of climate change. And now I look at the 2010s and see more roasting hot summers in the Northwest, raging fires in Western Canada, ashfall in Seattle from those fires. Changing times for my home region.

Photo of a Canadian fire smoke filled Seattle sky from summer 2017. (National Weather Service – Seattle, WA).

Continuing beyond the data, stories from the past can give us a glimpse into previous climate regimes. Yesterday, I was discussing with my friend and Florida author Vanessa Blakeslee about how climate has changed via a humanities perspective. She discussed with me the mid-1930s novel “Cross Creek” by author Marjorie Kinnan Rawlings. She lived in rural north-central Florida and in the novel, the timing of the summer rains are mentioned and “long, cool winters” are reminisced…temperature and precipitation patterns which Vanessa told me are typically very much different today compared to more than 80 years ago.

So what’s normal? What allows humanity the resources (fertile soil, water availability) to sustain agriculture and feed a population, from which towns and cities and economies can grow and develop. The past 10,000 years of a Holocene epoch has witnessed climate stability which has allowed humanity to know when the rains will come, when the rivers will flood, when the dry seasons happen, when to expect the snows, etc. Variability, yes, the occasional extreme sure. But you KNEW the pattern.

Projected rise in global temperature of at least 4 degrees C/8 degrees F (relative to mid-20th century) during the 21st century relative to the past 10,000 years.

But now we’re leaving that behind. There’s no “new normal” in the “Anthropocene”, there’s only a continuous and accelerating shift to more extreme conditions until climate change stops. It only stops when the planet is back in energy balance given the amount of energy its greenhouse gasses are forcing it to retain. And given what humanity has already done to the atmosphere and the continuous acceleration of changes in the climate system, our planet still has much more to go through to get to that actual “new normal”. But it will be likely full of catastrophic impacts for humanity and already so for many species.


Author: Meteorologist Nick Humphrey

Meteorologist and geoscientist in Lincoln, NE. Seattle, WA native. Love weather, storm chasing/photography and planetary science.

3 thoughts on “What’s “Normal”? A Confusing But Important Concept in Climate Change”

  1. Great post Nick. The trend is most definitely not our friend, and the consequences of inaction are hard to imagine. My hope is that we’ll reach a tipping point soon, by whatever means, that pushes through all of the ignorance and denial so we can get some kind of plan going for abrupt climate change, that gains general acceptance.


  2. For someone forecasting the weather it becomes an impossible task as abrupt heat gain sets in. The trend is even before massive methane releases. There is the possibility of an aerosol event like nuclear war or lifts of materials, or super volcanic eruption. Human population must and will plummet probably in less than a decade, either way. It is a question of a bottleneck or a Permian end style event. I am not looking forward to any of it.

    Liked by 1 person

    1. Well impacts from abrupt climate change will likely “get us” long before any super volcano given the return period for those type of eruptions and how long they take to build up even as the volcano wakes up for eruption. As for nuclear war…well, so few would survive that for other reasons, the climate impacts of that wouldn’t matter for humanity or much of the rest of the biosphere anyways. Interestingly our computer models are doing better at forecasting the weather than ever before simply because the science has advanced. But of course, forecasting increasingly more frequent extreme weather events of an increasing magnitude won’t do us much good once those events cross thresholds where they become impossible to defend against (too violent and devastating or happening too often to recover before the next one). And of course, along with habitat destruction and resource abuse, there’s your 6th mass extinction we concern ourselves with.


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