Pam Knox, The University of Georgia INITIAL PUBLICATION MAY 2014

Is It Weather or Is It Climate? What’s the Difference?

KEY POINTS• WEATHER represents short-term and small-scale

changes in the atmosphere.

• CLIMATE describes the distribution of weather over

longer periods.

• Humans have adapted to deal with the day-to-day

changes of weather.

• Changes in climate can impact every aspect of life

on Earth, especially if they happen rapidly or are

large changes.

WEATHER AND CLIMATE

Both weather and climate rely on observations of

temperature, pressure, sunlight, clouds, rain, and

snow. The main difference between the two is the time

scale over which the conditions are described. Weather

is generally a snapshot of the atmosphere at a single

time or over a few days. Climate generally refers to

conditions spanning months, years, and even decades.

One way to remember the difference between weather

and climate is: Weather tells you what to wear on any

given day; climate tells you what wardrobe to own.

MEASURING THE ATMOSPHEREFor most of us, weather and climate are two different

ways of looking at measurements of atmospheric

conditions. These measurements are taken at

surface weather stations and at higher levels of the

atmosphere with weather balloons. For consistency,

those measurements should be taken from standard

instruments at locations that are stable over long

periods. In that respect, weather is easier to measure

consistently. Climate scientists have to be mindful of

changes in the record caused by relocation of observa-

tions sites, changes in times of observations, changes

in the instruments used to collect the measurements,

or changes at the sites due to construction, growth of

trees, or expansion of cities over time.

Animal Agriculture &Climate Change

Livestock and Poultry Environmental Learning Center

This project was supported by Agricultural and Food Research

Initiative Competitive Grant No. 2011-67003-30206 from the

USDA National Institute of Food and Agriculture.

CONTENTS

Key Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Weather and Climate . . . . . . . . . . . . . . . . . . . . . . . . . .1

Measuring the Atmosphere . . . . . . . . . . . . . . . . . . .1

Describing the Atmosphere . . . . . . . . . . . . . . . . . . .2

Modeling Weather

vs . Modeling Climate . . . . . . . . . . . . . . . . . . . . . . . . . .2

2IS IT WEATHER OR IS IT CLIMATE? WHAT’S THE DIFFERENCE?Visit www.animalagclimatechange.org for more information and a full list of available fact sheets.

DESCRIBING THE ATMOSPHEREAtmospheric scientists use both time and space to

describe weather and climate. Some of the methods

they use in their descriptions are weather maps,

timelines, and climate maps. A series of weather maps

shows the variability of weather across a location over

a day, week, or year. A weather timeline shows how

the weather at one location has changed over time.

A climate map shows the spatial variations of

atmospheric conditions from one location to another

that are caused by elevation, presence of lakes and

oceans, and latitude. A climate timeline or trend line

would show changes in temperature, for example

over many years.

Most people can adjust to changes in weather by

choosing different clothes from their closets. But,

adapting to climate change can be more difficult.

Not only might people need different clothing, they

might also need to transform houses, roads, and

business practices to adapt to the new conditions.

MODELING WEATHER VS. MODELING CLIMATESkeptics sometimes say that if we can’t even predict

the weather, how can we predict the future climate?

Weather and climate models are used to predict future

conditions. The models are created using the same

physical laws of motion and energy, but they are

applied over different time and space scales.

A weather model responds to changing initial condi-

tions, or weather observations taken around the world

(at least twice daily), and must excel at getting the

details of fronts and storms correct for the next week,

but it is not designed to model the long-term state of

the atmosphere.

Atlanta GA - 2013

Record High Temperatures

Observed High and Low Temperatures

Record Low Temperatures

BelowAverage

NearAverage

AboveAverage

Average High and Low Temperatures

Total Observed PrecipitationBelow

AverageAbove

Average

Average Precipitation

Daily High

Daily Low

Jan Feb Mar Apr May Jun AugJul Sep Oct Nov Dec

Jan Feb Mar Apr May Jun AugJul Sep Oct Nov Dec

110

100

90

80

70

60

50

40

30

20

10

0

65

Prec

ipita

tion

(inch

es)

Tem

pera

ture

(deg

F)

6055504540353025201510

50

Weather timeline. Source: NOAA.

3IS IT WEATHER OR IS IT CLIMATE? WHAT’S THE DIFFERENCE?Visit www.animalagclimatechange.org for more information and a full list of available fact sheets.

A climate model needs to predict expected

patterns of temperature and rainfall over

wide areas but it is not focused on the

effects of individual storms. Climate models

are more sensitive to changes in forcing,

like sea surface temperatures, land and ice

surfaces and greenhouse gas concentrations,

rather than initial conditions.

Both weather and climate models have

improved greatly over time, and each type

performs well at the task for which it was

designed; neither model is good at tasks

for which it was not created.

WEATHER MODEL CLIMATE MODELUses physical equations of motion & energy

Yes Yes

Grid size Very small, on the order of miles . Large, on the order of 100 miles .

Time step Very short, on the order of minutes . At most a few per day .

Length of run Most models up to 72 hours; longer range models up to 15 days .

Models run for up to 100 years after an initial stabilization period .

Assumptions Climatic factors like atmospheric composition, incoming solar radiation are held constant; precipitation processes parameterized because they happen on sub-grid scale .

Precipitation processes parameterized due to large grid spacing; oceans are usually simplified or held constant

although new models include interactive oceans .

Number of models used

Approximately ten well-documented ones . Approximately 100 models with different assumptions .

Strengths Can provide detailed, small-scale descriptions of a specific weather event for up to five days

ahead (no skill for more than 10 days) .

Can provide realistic representations of average weather conditions across the globe on long time scales .

WeaknessesDo not provide good climatological simulations when

run for long time periods due to design for getting short-term correct which magnifies errors over time .

Do not predict individual storms well due to grid and time spacing; simplify spatial patterns in mountains and

along coasts where spatial detail is high; tend to drift over time; do not always capture current climate well .

Weather map. Source: NOAA.

4IS IT WEATHER OR IS IT CLIMATE? WHAT’S THE DIFFERENCE?Visit www.animalagclimatechange.org for more information and a full list of available fact sheets.

Extension programs and employment are available to all without discrimination. Evidence of noncompliance may be reported through your local Extension office.

This project was supported by Agricultural and Food Research Initiative Competitive Grant No. 2011-67003-30206 from the USDA National Institute of Food and Agriculture.

www.animalagclimatechange.org

PARTICIPATING UNIVERSITIESCornell University

Texas A&M University

University of Georgia

University of Minnesota

University of Nebraska-Lincoln

Washington State University

Animal Agriculture &Climate Change

Climate trend graph. Source: NOAA.