The state of Earth’s climate system is receiving huge attention because Earth’s temperature is rising, causing drought, wildfires, floods, rising sea levels and loss of habitats. According to 97 percent of climate scientists, this global warming now threatens the planet’s entire biosphere and everything in it. 1 In this article, we examine the difference between climate and weather and how climate is calculated.
What’s The Difference Between Climate And Weather?
Weather and climate involve the same atmospheric or meteorological components – namely, temperature, sunshine, rain, air-pressure and wind – but viewed over a different time scale. In other words, the difference between weather and climate is simply a matter of duration. 2 3
For example, our interest in the weather is typically limited to short-term questions like: “How long is this shower going to last?” “Is it going to rain tomorrow?” “Will tomorrow be as hot as today?” “Are we going to get snow this week?” When we talk about the weather we are mostly interested in conditions at a specific location or locality, over a short-term period: a matter of hours, days or weeks. The longest period we would be interested in would be a season: as in, “This summer has been so much hotter than last summer.”
In a similar way, meteorologists look at weather patterns to understand relatively short-term developments. They study air pressure to check for rain, cloud patterns to predict types of precipitation or overnight temperatures, and wind speed/direction for temperature and chill factor. 4
Some weather scientists combine their interest in meteorology with oceanography, by studying the influence of the El Niño-Southern Oscillation cycle – on weather patterns at either ends of the equatorial Pacific. Even so, this is at most a 2-3-year development cycle, with Nino/Nina episodes typically lasting no more than 9-12 months.
Other weather cycles that can have a longer term impact on meteorological conditions within a particular region, include: the Indian Ocean Dipole (active between Africa and SE Asia), the travelling Madden-Julian Oscillation (MJO) in the Indo-Pacific, and the Southern Annular Mode (active in the Southern Ocean).
Climate Is Weather Averaged Over Decades
By comparison, climate is the average weather in a given area over a period of decades. As a result, unlike weather, which can change completely in a matter of minutes, climate takes hundreds, thousands, even millions of years to change. Determining the climate of a region or larger area requires the accumulation of long-term average data on climate components including temperatures, sunshine, humidity, precipitation, air pressure and wind. In addition, climate data usually includes observed weather extremes for the area in question, as well as the normal weather data. 5
According to an international meteorological convention, introduced by the World Meteorological Organization (WMO), in 1900, a “normal climate” is calculated for each 30-year period, based upon the average weather statistics for the period. The first normal period ran from 1901 to 1930. The next periods lasted from 1931 to 1960, from 1961 to 1990 and from 1990 to 2020. Climate scientists also produce an extended 100-year normal climate, but this is unusual.
With these normal climate scenarios worked out and filed away, it is possible to ascertain what the normal temperature, sunshine, wind and rainfall are for (say) New York, Geneva, Sydney and Rio de Janeiro, on 1st June.
Weather Tends To Be More Local Than Climate
As we know, weather conditions can change markedly in a matter of hours if not minutes. This is because weather systems typically tend to be geographically limited in size. The main focus of interest therefore tends to be more local – or at most, regional – rather than countrywide. In contrast, climate is measured over decades, and is therefore ideally suited for the study of larger-scale national or global weather patterns. For example, despite their regularity, tornadoes are regarded as a local weather event, due to their reliance on local weather elements like temperature, supercell thunderstorms and wind shear.
Climate Is Relatively Unaffected By Short-Term Events
The reason why climate is measured by averaging weather conditions over a period of 30 years or more, is because there are many factors that can affect weather conditions or extreme weather events over shorter timescales.
For example, an underwater earthquake or volcanic eruption can trigger a tsunami with significant adverse effects on coastal weather conditions; a severe El Nino episode can lead to severe floods in the southern United States and drought in Indonesia; a severe Indian Ocean Dipole episode can produce floods in East Africa and droughts in Australia.
At the very least, these factors can lead to unusually hot, cold, wet, or dry years in several parts of the globe. But none of this means that the overall climate is changing. Furthermore, when averaged out over 30 years, the effect of these unusual factors is hardly noticeable.
But sometimes abnormal weather patters persist in a region for longer than 30 years, and so become part of the climate of that region.
For example, since the 1970s, the average temperature of the Arctic has risen by 2.3°C, according to World Wildlife Fund for Nature. So we can now speak of a definite climate change in the Arctic. For more on this, see: Why Are Arctic Fires So Dangerous? Also: Why is Permafrost a Climate Danger? and Arctic Sea Ice: How Fast is it Melting?
What Are The 5 Different Climate Types?
There are five main types of climate on Earth: tropical, dry, temperate, continental and polar. They vary according to temperature, precipitation and their distance from the equator. Our understanding of climate types owes a great deal to Wladimir Koppen (1846-1940), a Russian-German geographer, meteorologist and botanist who was active in the late 1800s and early 1900s. Today, some climate types are beginning to change as a result of global warming. The main trend is the migration of climate patterns away from the equator towards the poles, destabilizing animal habitats in the process.
If meteorologists generally analyze weather patterns to make short-term forecasts, climatologists study weather data to search for long-term trends and changes. Geoscientists studying the carbon reservoir of the Amazon Rainforest, for hints as to the effects of deforestation, take a long-term view several decades into the future. 6 Scientific stations in Antarctica keep a constant watch on the thickness of the continent’s ice sheets, in order to predict the extent of polar ice at the end of the century and beyond.
Paleoclimatologists who study ancient climates take an even longer view of the weather as they analyze data from tree rings, ice cores and layers of sedimentary rock. For example, in 2009, research teams examining stone cores from the Southern Ocean, discovered that Antarctica’s ice sheet was born 14 million years ago, during a period when global temperatures dropped by up to 8°C. 7 Yet the Arctic remained largely ice-free for another 10 million years, until about 4 million years BC. 8 The point is, while meteorologists usually focus on a time-span of (at most) a few years, climate science involves tracing patterns that sometimes take millions of years to unravel.
Right now, climate change is beginning to affect weather patterns across the world. This has triggered the development of highly complex climate models, to determine issues such as future rate of ice melt or sea level rise, or how much deforestation of the Amazon Rainforest is needed before the whole biome is affected by savannization. Fortunately, after 50 years of development, climate models are getting better at predicting the future. 9
What Is Global Climate?
Earth’s climate is determined by the impact of sunlight on the planet and its five major subsystems:
(1) The atmosphere (air), the quick-reacting medium which envelopes us and has an immediate impact on our condition.
(2) The lithosphere (the rigid outer layer of the Earth), the largest store of carbon and the source of all volcanic and tectonic activity, whose climate impact used to be measured over millions of years, but is now measured in decades due to its accessible stores of fossil fuels.
(3) The hydrosphere (liquid water) which controls precipitation and operates an interchange of carbon dioxide with the atmosphere.
(4) The cryosphere (frozen water), which plays an important role in climate regulation through its ability to reflect sunlight back into space (albedo effect) and its storage of water which would otherwise inundate coastlines around the world.
Other systems that influence Earth’s climate include the carbon cycle and water cycle, as well as wind patterns and ocean currents. These global subsystems and cycles act to regulate the impact of solar energy by distributing it to all areas of the planet.
Over the past 10,000 years, thanks to this regulatory system, Earth’s climate has been amazingly stable. Since the end of the last ice age, over a period of some 400 generations, we have taken advantage of this stability to build our civilization. Unfortunately, this period of stability is about to be replaced by an unpredictable period of climate change. 11
What Is Climate Change?
The term “climate change” ordinarily describes systematic changes in climate components (chiefly temperature) which continue for 30 years or longer. These changes usually take many millennia if not millions of years to develop, though on rare occasions – think asteroid collision – it can happen suddenly, as the dinosaurs discovered.
Up until the late 18th century, the factors that had a direct impact on global temperature and the radiative forcing of the planet were limited to (1) variations in solar energy (2) volcanic eruptions (3) tectonic up-thrusts of rock, and (4) changes in the “albedo effect” – the reflection of sunlight back into space.
Since the late 18th century, we humans have created another, much more powerful climate forcing, which now threatens to destroy the planet. It stems from our use of fossil fuels (coal, oil, natural gas) to power the engines and factory processes upon which our civilization is based. The combustion of these fossil fuels releases huge amounts of greenhouse gases into the lower atmosphere, where they amplify the greenhouse effect, raising the temperature of the Earth in the process.
It is these greenhouse gas emissions that now threaten our planet.
Is Climate Change The Same As Global Warming?
No. Strictly speaking, the term “climate change” refers only to a long term “differences” in weather patterns. Thus, it includes climate cooling as well as warming.
However, the United Nations – through the UN Framework Convention on Climate Change (UNFCCC) and the prestigious Intergovernmental Panel on Climate Change (IPCC) – has appropriated the term to headline its campaign of climate action – although climate crisis is probably a more accurate description. As a result, climate change has become synonymous with global warming and rising temperatures.
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- “All About Arctic Climatology and Meteorology.” National Snow and Ice Data Center.
- “American Geosciences Institute – FAQs”
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- “What Is Climate Change?” NASA. May 14, 2014. (5)
- “Amazon forest response to CO2 fertilization dependent on plant phosphorus acquisition.” Katrin Fleischer, et al; Nature Geoscience. August 5, 2019. (7)
- “Driller thriller: Antarctica’s tumultuous past revealed.” Douglas Fox. New Scientist. 7 April, 2009. (8)
- “Final closure of Panama and the onset of northern hemisphere glaciation.” G.Bartolia, M.Sarnthein, M.Weinelt, H.Erlenkeuser, D.Garbe-Schonberg, D.W.Lea. Earth and Planetary Science Letters. Volume 237, Issues 1–2, 30 August 2005, Pages 33-44. (9)
- “Evaluating the Performance of Past Climate Model Projections.” Zeke Hausfather, Henri F. Drake, Tristan Abbott, Gavin A. Schmidt. Geophysical Research Letters. Published: Dec 4, 2019. (10)
- “Annex III: Glossary.” Planton, S. (2013). In Stocker, T.F. et al; Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. (11)
- “Copenhagen: The era of climate stability is coming to an end.” Fred Pearce. The Guardian. Nov 30, 2009. (12)