WEATHER AND CLIMATE: WHAT’S THE DIFFERENCE
Weather is a specific event or condition that happens over a period of hours or days. For
example, a thunderstorm, a snowstorm, and today’s temperature all describe the weather.
Weather is highly variable day to day, and from one year to the next. For example, Minneapolis
might have a warm winter one year and a much colder winter the next. This kind of change is
normal. But when the average pattern over many years changes, it could be a sign of climate
change.
Climate refers to the average weather conditions in a place over many years (usually at least 30
years, to account for the range of natural variations from one year to the next). For example, the
climate in Minneapolis is cold and snowy in the winter, while Miami’s climate is hot and humid.
The climate in one area, like the Midwest or Hawaii, is called a regional climate. The average
climate around the world is called global climate. When scientists talk about global climate
change, they’re talking a pattern of changes happening around the world over many years. One
of the most important trends that scientists look at is the average temperature of the Earth, which
has been increasing for many years.
Rising global temperatures are leading to other changes around the world, such as stronger
hurricanes, melting glaciers, and the loss of wildlife habitats. That's because the Earth’s air,
water, and land are all related to one another and to the climate. By examining trends in weather
and temperature data, along with the changes occurring in all of these systems, scientists can get
a good understanding of today’s climate change.
GETTING TO THE CORE: THE LINK BETWEEN
TEMPERATURE AND CARBON DIOXIDE
Since the start of the Industrial Revolution around 1750, people have burned large amounts of
coal, oil, and natural gas to power their homes, factories, and vehicles. Today, most of the world
relies on these fossil fuels for their energy needs. Burning fossil fuels releases CO2, a heattrapping gas, into the atmosphere, which is the main reason why the Earth’s climate is getting
warmer.
Heat-trapping gases are also called greenhouse gases. They exist naturally in the atmosphere,
where they help keep the Earth warm enough for plants and animals to live—a phenomenon
called the greenhouse effect. By adding more greenhouse gases to the atmosphere, however,
people are contributing to an enhanced greenhouse effect and causing the atmosphere to trap
more heat than it otherwise would.
The Earth’s climate has changed many times before. There have been times when most of the
planet was covered in ice, and there have also been much warmer periods. Over at least the last
650,000 years, temperatures and CO2 levels in the atmosphere have increased and decreased in a
cyclical pattern. The Earth’s temperature has also experienced a similar cyclical pattern
characterized by glacial and interglacial periods. During glacial periods (more commonly called
ice ages), the Earth has experienced a widespread expansion of ice sheets on land. Intervals
between ice ages, called interglacial periods, have brought higher temperatures. The Earth has
been in an interglacial period for more than 11,000 years. Historically, temperature and CO2
have followed similar patterns because the heating or cooling of Earth’s surface can lead to
changes in the concentrations of greenhouse gases in the atmosphere, which can then cause
additional warming or cooling.
For hundreds of thousands of years, the concentration of CO2 in the atmosphere stayed between
200 and 300 parts per million (ppm). Today, it’s up to nearly 400 ppm, and the amount is still
rising. Along with other greenhouse gases, this extra CO2 is trapping heat and causing the
climate to change.
Before people had thermometers, indeed before any temperatures were recorded, the Earth itself
recorded clues about temperature, precipitation, atmospheric gases, and other aspects of the
environment in the thick layers of ice that have accumulated in places like Greenland and
Antarctica. To reveal these clues to the past, researchers drill into glaciers and ice sheets and
remove cylinder-shaped samples of ice called ice cores. Back in the laboratory, scientists can use
chemical sampling techniques to determine the age of each layer of ice and the concentrations of
different gases trapped in tiny air bubbles within the ice, which reveals the composition of the
atmosphere in the past. They can also examine the water molecules in the ice itself to get
information about historical temperatures. Trapped pollen and dust provide additional clues
about the climate. Ice core records can go back hundreds of thousands of years, and they help
scientists find out whether the rapid increase in CO2 levels and temperature we are currently
observing fits a natural pattern or not.
Investigating the Earth’s air temperature and the amount of CO2 in the atmosphere over a long
time period helps us to better understand the Earth’s carbon cycle, its relationship to the
greenhouse effect, and its role in regulating the Earth’s climate.
El Niño and La Nina:
The El Niño-Southern Oscillation (ENSO) is a global coupled ocean-atmosphere phenomenon.
El Niño and La Nina are important temperature fluctuations in surface waters of the tropical
Pacific Ocean. ENSO is associated with floods, droughts and other disturbances in a range of
locations around the world. ENSO is the most prominent known source of inter-annual
variability in weather and climate around the world. ENSO conditions seem to have occurred at
two to seven year intervals for the past three hundred years. The mechanisms which might cause
an ENSO are still being investigated. As the phenomenon is located near the Equator, it may
affect both hemispheres.
The first signs of ENSO are:
1. A rise in air pressure over the Indian Ocean, Indonesia and Australia.
2. A fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean.
3. Trade Winds in the South Pacific weaken or head east.
4. Warm air rises near Peru, causing rain in the Peruvian deserts.
5. Warm water spreads from the West Pacific and the Indian Ocean to the East Pacific and it
takes the rain with it, causing extensive drought in the Western Pacific and rainfall in the
normally dry Eastern Pacific.
During the 1997-98 El Niño, sea surface temperatures in the central and eastern equatorial
Pacific were higher than normal. The sea surface temperature for September 1997 was the
highest in the last 50 years. Also, in late September easterly winds over the equatorial Pacific
between 150E and 120W decreased the most in the last 30 years.
Recent years in which El Niño events have occurred are 1951, 1953, 1957-1958, 1965, 1969,
1972-1973, 1976, 1982-1983, 1986-1987, 1991-1992, 1994 and 1997. The high sea surface
temperatures and the magnitude of the westerly wind anomalies over the Pacific are very high.
These conditions suggest that the strength of 1997 El Niño event could equal or surpass that in
1982-1983, making it the strongest El Niño this century.
The El Niño of 1982-83 was responsible for the loss of nearly 2,000 lives and displacement of
hundreds of thousands from their homes. The losses were caused by droughts and fires in
Australia, Southern Africa, Central America, Indonesia, the Philippines, South America and
India. There were floods in the USA, Gulf of Mexico, Peru, Ecuador, Bolivia and Cuba. More
hurricanes than usual affected Hawaii and Tahiti.
La Niña is the name of the cold phase of ENSO, during which the cold pool in the eastern Pacific
intensifies and the trade winds strengthen. La Niña causes the opposite effects of El Niño. For
example, El Niño would cause a wet period in the Midwestern United States, while La Niña
would cause a dry period. At higher latitudes, El Niño and La Niña are among a number of
factors that influence climate. However, the impacts of El Niño and La Niña at these latitudes are
most clearly seen in wintertime. In the continental US, during El Niño years, temperatures in the
winter are warmer than normal in the North Central States, and cooler than normal in the
Southeast and the Southwest. During a La Niña year, winter temperatures are warmer than
normal in the Southeast and cooler than normal in the Northwest.