CRS InFocus Report: 'Weather and Climate Change: What’s the Difference?'

Jane A. Leggett wrote this CRS InFocus two-pager (uodated 25 February): Weather and Climate Change: What’s the Difference? 

Download CRS_Report_Weather_Climate_Change_Difference_25February2021

Let's hope Congress reads this.

Okay - here we go. Click on the graphics to display/enlarge them.

With much discussion of climate change in Congress, in the news, and among constituents, some commonly used words may be misunderstood or misused. Below are explanations of several key terms: weather, climate, climate variability, and climate change, as well as some associated concepts.

Weather is the state of the atmosphere at a specific place and time, described by such conditions as temperature, precipitation, humidity, cloudiness, and wind speed. Weather can include conditions of the Earth’s water and land surfaces as well, with such variables as wave heightand snow cover. Weather conditions can vary rapidly or last up to a few days in the mid-latitudes. NOAA compiles observations from weather stations around the United States, in the oceans, from international sources, and from other federal agencies. NOAA analyzes historical weather data and provides multiday forecasts or seasonal outlooks.

Climate is defined by the long-term statistics of weather compiled for a specified place (Figure 1), including the globe. For example, climate would include the maximum hourly precipitation in July in a particular county over 30 years or the global mean surface temperature from 1981 to 2010. The availability of long-term data varies by location, making climate analysis for some locations challenging.

NOAA’s National Centers for Environmental Information defines U.S. climate normals as “three-decade averages of climatological variables including temperature and precipitation” for defined locations. The most recent climate normal for a defined location uses weather observations for 1991-2020. People use climate normals for a wide array of purposes, such as placing daily weather into a historical context or determining technical specifications for the resilience of buildings and infrastructure against extreme weather.

Climate variability can include several different concepts. Generally, it means the differences from the long-term averages (or other statistics) of climate-related variables, such as precipitation, over longer time or wider areas than individual weather events. Climate variability may describe how a season is above or below the climate normal average for, say, temperature or snowfall. Climate variability may also describe longer, multiyear patterns that are not average, such as when certain large-scale weather patterns occur. An example is the so-called El Niño/La Niña (ENSO) cycle, with cycles of warm and cool periods in the Pacific Ocean and the atmosphere. ENSO phases typically last from nine to 12 months and on average occur every two to seven years. With only climate variability, scientists would expect the climate to reflect historically average conditions.

When the climate continues to change over longer times, climatologists discern climate change. In effect, this means that what was “normal” has shifted. See Figure 2.

Cutting to the chase...

Global Change Is Broader Than Climate Change 
Another concept, broader than climate change, is that of global change. The Global Change Research Act of 1990 (P.L. 101-606) defined it as “changes in the global environment (including alterations in climate, land productivity, oceans or other water resources, atmospheric chemistry, and ecological systems) that may alter the capacity of the Earth to sustain life.” 

Good stuff, indeed! You can watch a two-minute NASA video here.

"Nature abhors a moron." -- H.L. Mencken

Comments

[Elaine Hanford]

We humans tend to subdivide time into units that are scaled to our lifetimes: days, weeks, months and years. The media encourages us to think that any deviation for the 30-year weather averages represents climate change. Modern technology has refocused our attention to still smaller units of time as it is not uncommon that we become impatient when it takes more than a few seconds for our computers or cell phones to connect or download information. And NOAA promotes this approach.
Yet the time scale of climate which is better measured in geologic time. geologic time is culturally relevant. While not easily grasped, the varied temporal spans of geologic time (e.g., the period since the last glacial maximum, rates of evolution, or the length of time it takes to wear down a mountain or replace a lost species) offer perspectives of practical use to our everyday lives (Cervato and Frodeman 2012), who note:

“Nor can we begin to adequately understand our economic and environmental challenges—the end of the age of oil; the prospect of future climate change; the loss of biodiversity; the fatality of current rates of consumption— without the perspectives of deep time. Finally, geologic time presents a fundamental challenge to many in terms of its implications concerning the place of humanity in the greater scheme of things.”

The Holocene (our current geologic epoch) is defined by the end of the long-term drying and warming trend that marked the end of the last major ice age. Since about 9,000 years ago, the average northern hemisphere temperature has fluctuated over periods measured in hundreds or thousands of years. The warmest interval persisted between about 6,000 and 8,000 years BP. Following the Medieval Warm Period, the Little Ice Age dropped the average northern hemisphere temperature about 2 degrees Celsius. Average northern hemisphere temperatures have been warming, bringing us out of the Little Ice Age in the 1800s and into our current warm period that is not as warm as previous Holocene warm intervals.
Weather is the shorter-term fluctuations that occur within a climatic regime on a daily, monthly, seasonal, decadal, or century-long intervals, perhaps even a longer time interval. For weather, the mean or average conditions are calculated, by convention, as a 30-year average updated every 10 years, with the most recent installment covering the period from 1981 to 2010.
The media conflates variations in weather with climate change. The media further emphasizes that statistically derived weather averages are “normal.” But “normal” has societal connotations (and denotations) and can vary according to perception, experience, culture, politics and period of history.
Our weather records in the United States date to Colonial time in the East, but in the Western States, a network of weather (typically temperature and precipitation) observers linked by telegraph began to be established in the 1850s. The US Weather Service was not established until 1870 when President Ulysses S. Grand signed the Joint Congressional Resolution into law under the U.S. Army Signal Service’s Division of Telegrams and Reports for the Benefit of Commerce. Our systematic recorded history of weather began 150 years ago and weather records in the Western States represent an even shorter time interval.
If for example, we look at eastern Oregon, then recent "global warming" temperatures of 2014-2015 are the same as the average annual high temperature of 1934, with 5 degree Fahrenheit temperature fluctuations over the intervening interval (including from 1981-2010).
So, let's hope Congress DOES NOT read this CRS In Focus report....they make enough stupid decisions without the sort of misinformation put forth by NOAA on what constitutes weather vs climate.

Cervato, C. and R. Frodeman. 2012. The significance of geologic time: cultural, educational and economic frameworks. Geological Society of America Special Papers 486, 16 p.