Climate Series Introduction

Science Notes

Educators may be unfamiliar with some of the more advanced concepts discussed in the climate modules. In the segments below, you will find short introductions to these concepts as well as links to further information and resources.

Weather vs. Climate

In a nutshell, the difference between weather and climate is time scale.

Weather is the set of short-term conditions that exist in the atmosphere over periods of minutes, hours, or days, or possibly across weeks. Weather includes atmospheric conditions such as air temperature, precipitation, wind speed, humidity, and fog.

Climate, on the other hand, is a statistic: it is defined by the average weather for a date and location across much longer time scales. How long? Organizations such as the National Climatic Data Center (NCDC) define climate statistically by averaging the previous 30 years of weather, but longer time periods can also be used.

Natural Climate Variability vs. Climate Change

Like weather vs. climate, the biggest difference between climate variability and climate change is timescale. Climate does vary on scales of years to decades, for instance in the event of an El Niño year, the climate may warm for that one year, and then settle back to a more "normal" pattern the next year. While a true change is more "permanent" or entrenched. Climate change has a definite directional trend.

Considering All the Data

Selecting specific bits of data to support a particular viewpoint is not uncommon. People often do that when arguing a point of view. To understand what is actually happening, in order to make effective decisions, it's important to take into account all of the data available. Consider the three graphs below. The first shows all of the data regarding the average extent of Arctic sea ice for the month of May between 1979 and 2015. The second graph highlights just two years of data from the 37 year long history1990 and 2009and the third graph suggests that average sea ice extent for May is increasing. While it is true that sea ice extent in May 2009 was greater than that in May of 1990, it is obvious how misleading it can be to not consider all of the data. Note: Click on images for a larger view.

Natural Climate Change and the Milankovitch Cycles

We know that Earth's climate has been highly variable over time, but what processes are behind these climatic swings?

Serbian astrophysicist Milutin Milankovitch is credited for developing one of the most significant theories relating changes in Earth's orbit to long-term changes in climate, including ice ages. Milankovitch's theory is based on cyclical variations in three aspects of Earth's orbit that result in changes to the seasonality and location of solar radiation reaching Earth. The three aspects are:

  • Changes in the obliquity (tilt) of Earth's axis
  • Variations in the shape of Earth's orbit (eccentricity)
  • Changes in Earth's "Wobble" (Precession)

Greenhouse Gases, Electromagnetic Radiation, and Climate

Every object that has a temperature above absolute zero (-273 C or -459 F) emits electromagnetic radiation. Really hot objects emit more of the shorter, higher energy wavelengths (such as visible light, ultraviolet light, x-rays, and gamma rays) and cooler objects emit more of the longer, lower energy wavelengths (such as infrared radiation, microwaves, and radio waves). If you heat up a metal rod it will first emit or radiate the longer wavelengths, such as infrared radiation, which we can sense as heat but that is not visible to our eyes. Heat up that rod enough and it will start to glow because it is emitting shorter wavelength radiation (visible light) that our eyes can detect, in addition to the infrared radiation that we can feel but not see.

Climate and Feedback Loops

Throughout the EarthLabs modules you'll find references to the Earth system, the interconnected set of sub-systems or spheres (atmosphere, hydrosphere, biosphere, geosphere, cryosphere) that exchange energy and matter and that interact to form our planet's environment. Some examples of these interactions are: 1) volcanic eruptions move matter and energy from the geosphere into the atmosphere and the hydrosphere; 2) decaying plants and animals (biosphere) result in chemical changes to the atmosphere and to the geosphere. The resource Earth System: The Basics (Microsoft Word 2007 (.docx) 151kB Jun6 12) provides a simple overview of this very complex Earth system with its interacting elements.

Anomaly Maps and Graphs

Anomaly Maps and Graphs don't show actual measurements for weather variables. Instead they show the difference, or anomaly, between a recent average and the long-term average for a selected period of time, referred to as a base period. These types of maps and graphs help us to see change in an absolute value. In other words, they allow us to answer the question: how much above or below average are the given values?

Anomaly maps most often use dot size or a color gradient to represent the difference between a given period and the base period. That base period is typically 30 years on maps. Notice that in the anomaly map, shown right, most places on Earth had a warmer average temperature in 2011 than they had during the 1971-2000 base period. In this example map, the temperature anomalies (difference from average) in 2011 were greatest in northern Asia.

Interactive maps of climate, including temperature and precipitation anomalies, for the United States can be viewed online at Climate at a Glance.