# Presentation: 359830

## Climate Variability and Change: An Overview 

- Climate Variability and Change: An Overview

- Leigh Welling
- Crown of the Continent Research Learning Center
- Glacier National Park

## What is Climate?

**Notes:**
Introduction
The earth's climate is generally defined as the average weather over a long period of time. A place or region's climate is determined by both natural and anthropogenic (human-made) factors. 
The natural elements include the radiation from the sun, composition of gases and particles in the atmosphere, geologic processes such as plate tectonics that cause volcanoes to erupt and land masses to change location and shape, changes in the water cycle and where water is held (in ocean, atmosphere, glaciers), and biology. 
Human factors can include land and resource uses. 
Changes in any of these factors can cause local, regional, or even global changes in the climate.

## How does climate differ from weather? 

- Climate is what you expect,
- weather is what you get.
- OR...
- Climate tells you what clothes to buy,
- weather tells you what clothes to wear.

**Notes:**
How does climate differ from weather? 
Weather is the current atmospheric conditions, including temperature, rainfall, wind, and humidity at a given place. If you stand outside, you can see that it's raining or windy, or sunny or cloudy. Weather is the day to day conditions that we experience directly. 
Climate, on the other hand, is the general weather conditions over a long period of time. For example, on any given day in January, we expect it to be rainy in Portland, Oregon and sunny and mild in Phoenix, Arizona. And in Buffalo, New York, we're not surprised to see January newscasts about sub-zero temperatures and huge snow drifts. 
Climate is sometimes referred to as "average" weather for a given area. The National Weather Service uses data such as temperature highs and lows and precipitation rates for the past thirty years to compile an area's "average" weather. However, to accurately portray an area's climatic character - variations, patterns, and extremes must also be included. 
Thus, climate is more than “average” weather but is the sum of all statistical weather information that helps describe a place or region.
The term also applies to large-scale weather patterns in time or space such as an 'Ice Age' climate or a 'tropical' climate.

## Slide 4

**Notes:**
A fundamental forcing that cause climate in one area to be different from another is latitude because only in the equatorial region do the sun’s rays strike the earth’s surface directly.
And this varies with season – causing changes in temperature between summer and winter.
This picture shows the orientation of the earth toward the sun during northern hemisphere winter, when the most direct rays strike the earth north of the equator, with the maximum being at 23.5 degrees north on the summer solstice in mid-June.

## Net transfer of heat from tropics to higher latitudes

- Is the fundamental driving force for weather and climate

**Notes:**
Because the most direct rays are always in the equatorial region, most of the heat from the sun is taken up here. Turns out the majority of the region is covered by water – and most of it is in the Pacific. 
Many of you probably know that water has a higher specific heat than air – what this means is that it takes longer for water to heat up and cool down. It also means that water holds heat – which is energy. 
The oceans are the capacitor for the planet’s heat engine – holding heat and moving it around. The redistribution of heat from the tropics to higher latitudes is the fundamental driver for weather and climate.

- Intertropical  Convergence Zone (ITCZ)

- GOES Satellite

**Notes:**
The redistribution of heat on the planet happens in a couple of different ways.
Much of the heat that builds up in the tropical oceans is radiated back into the atmosphere.
This is a satellite image of the eastern equatorial Pacific and what you see is a recurring feature called the Intertropical Convergence Zone (ITCZ).
This huge line of clouds can be found along the equator because the heat from the sun causes water to evaporate and form clouds. Similar features are found in the Atlantic and Indian Oceans.
The heated water is then carried north or south through the atmosphere – toward higher latitudes. That’s how tropical storms are made and is a fundamental mechanism for moving excess heat out of the tropics. 

## Gulf Stream Temperature

- warm, tropical water travels north
- heat is released to atmosphere
- affects weather and climate on East Coast and in Europe

**Notes:**
Another way for excess heat to move out of the tropics is through ocean currents. 
This is a satellite image of the Gulf Stream that carries warm water north along the east coast, heating the atmosphere as is moves. The water cools by releasing heat to the atmosphere and this provides a certain maritime climate for the region – all the way over to Europe.

## What is Climate Variability?

- Earth’s climate varies across latitudes, seasons, and over multi-year, multi-decade and even multi-century time scales.

**Notes:**
What is climate variability?So different parts of the world have different climates according to latitude, altitude, proximity to water.... and most change with season. This is all part of our “normal” climate. 
But there are also periodic (and now predictable) differences between years, decades, and even centuries. When we talk about climate variability we are usually talking about cycles, patterns that shift over time from one set of conditions to another. 
Climate variability that goes beyond seasonal cycles will be associated with modification in the location and intensity of wind and pressure cell patterns, meaning shifts in storm tracks, rains, drought etc. 
An example is the coupled ocean-atmosphere phenomenon known as El Niño/Southern Oscillation. El Nino refers to the oceanic manifestation – it is a warm water current that occurs periodically off the coast of S. America during December so they named it after the Christ Child. The southern oscillation refers to what is going on in the atmosphere at this time, which is one part of a cycle or an oscillation in pressure cells across the equatorial Pacific.
Notice that the ITCZ is normally located a bit to the north of the equator. The northward displacement of the ITCZ is because the water right on the equator in the eastern part of the basin is not warm. 

## Equatorial Cold Tongue:

- red = warm water
- blue = cold water

**Notes:**
This is a satellite image of the eastern equatorial Pacific showing sea surface temperature, red is warm and blue is cold. What you see is a strip of cold water right along the equator. The ITCZ sits north of the cold tongue over the warmest water. 
This is recurring feature called the Equatorial Cold Tongue. It looks like a tongue sticking out from the coast of S. America, and in fact, it is. 
Because of the earth’s rotation, water tends to flow from east to west along the equator. So where you have warm water currents bringing tropical water toward the poles on the east coasts of continents (like with the Gulf Stream), you have cold water currents returning water back toward the equator on the west coasts of continents (like the Peru current). 

## ENSO is an example of natural climate variability

**Notes:**
the equatorial current is generally cold in the east
the western Pacific warm pool is the warmest water on the planet
During an El Nino the cold tongue is suppressed and there is a greater build up of warm water over on the east side of the Pacific. 
This is a process that we call interannual variability because it normally happens on a time scale that is longer than a year. 
The counterpart to El Nino is often referred to as La Nina – and is a colder than normal condition in the equatorial Pacific.

## Typical US winter patterns during El Niño and La Niña

- Persistent, extended Pacific Jet Stream & amplified storm track

- El Niño

- La Niña

- Polar Jet Stream

- Variable Polar Jet Stream

- Variable Pacific Jet Stream

- warm

- dry

- dry

- wet

- cool

- cold

- wet

- wet

- warm

**Notes:**
Specific weather, temperature and rainfall patterns are associated with the warm and cold phases of ENSO. Because El Niño brings warmer water eastward in the topics, warmer and wetter than normal conditions tend to be observed along much of the western coasts of N. America, and extending inland. Areas of the world that normally receive monsoons in winter, however, are generally drier. Because the winds shift, the Gulf Coast, is cooler during an El Nino.   
During La Niña rainfall is enhanced across the western equatorial Pacific, Indonesia and the Philippines and is nearly absent across the eastern equatorial Pacific. This makes the SW even drier than usual. 

## Pacific Decadal Oscillation (PDO)

*warm phase*

*cool     phase*

*PDO index*

**Notes:**
The "Pacific Decadal Oscillation" (PDO) is a long-lived El Niño-like pattern of Pacific climate variability. While the two climate oscillations have similar spatial climate fingerprints, they have very different behavior in time. 
Two main characteristics distinguish PDO from El Niño/Southern Oscillation (ENSO): first, 20th century PDO "events" persisted for 20-to-30 years, while typical ENSO events persisted for 6 to 18 months; 
second, the climatic fingerprints of the PDO are most visible in the North Pacific/North American sector, while secondary signatures exist in the tropics - the opposite is true for ENSO. 
Major changes in northeast Pacific marine ecosystems have been correlated with phase changes in the PDO; warm eras have seen enhanced coastal ocean biological productivity in Alaska and inhibited productivity off the west coast of the contiguous United States, while cold PDO eras have seen the opposite north-south pattern of marine ecosystem productivity. 
From a societal impacts perspective, recognition of PDO is important because it shows that "normal" climate conditions can vary over time periods comparable to the length of a human's lifetime . 

## positive phase

- North Atlantic Oscillation (NAO)

-  *negative phase*

*positive phase*

**Notes:**
North Atlantic Oscillation 
The NAO is the dominant mode of winter climate variability in the North Atlantic region ranging from central North America to Europe and much into Northern Asia. The NAO is a large scale seesaw in atmospheric mass between the subtropical high and the polar low. The corresponding index varies from year to year, but also exhibits a tendency to remain in one phase for intervals lasting several years.

Positive NAO Index 
The Positive NAO index phase shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low. The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track. This results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland The eastern US experiences mild and wet winter conditions

Negative NAO Index
The negative NAO index phase shows a weak subtropical high and a weak Icelandic low. The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east pathway. They bring moist air into the Mediterranean and cold air to northern Europe The US east coast experiences more cold air outbreaks and hence snowy weather conditions. Greenland, however, will have milder winter temperatures 

## Slide 14

**Notes:**
The greenhouse effect: certain “greenhouse” gases in the atmosphere permit sunlight to pass through the atmosphere, but absorb much of the  infrared (heat) radiation from Earth’s surface.  The atmosphere warms, and radiates additional heat to the surface. The planet’s temperature is therefore higher than it would be without greenhouse gases, and it stands to reason that adding more greenhouse gases to the atmosphere is likely to warm the planet.

## Carbon dioxide: up 32% 

- Carbon dioxide: up 32%

**Notes:**
Air bubbles trapped in ice have been analyzed.  Until the industrial revolution, carbon dioxide was relatively stable in the atmosphere - the inputs and outputs were closely balanced.  However, by burning coal, oil, and natural gas, we have disturbed that balance and led to accelerating increases in the amount of atmospheric CO2 in the atmosphere.  Note that the present amount is less than 0.04% of the atmosphere.

## Slide 16

## Slide 17

## Gulf Stream Temperature

- warm, tropical water travels north
- heat transfer affects weather and climate
- surface water becomes dense and sinks

**Notes:**
Abrupt changes can occur by disturbing parts of the system – that can cause shifts in regional climate that are opposite what we might expect.
Deep water formation in NA

- GREAT OCEAN CONVEYOR BELT

**Notes:**
Warm, Gulf Stream water moves north
It cools by releasing heat to the atmosphere
It also gets more saline
Cold, salty water sinks in the North Atlantic

## Natural Climate Influence

- Human Climate Influence

- All Climate Influences

**Notes:**
Various groups of researchers have attempted to simulate the 20th century climate using “climate models”, sophisticated computer programs that represent the laws of physics as they apply to the Earth’s atmosphere, ocean, land, and ice.  This figure shows one such study in which a climate model was run several times with natural climate influences (solar variations, volcanic eruptions), human climate influences (greenhouse gases and sulfate aerosols), and both kinds of influences.  The best simulation of the 20th century climate uses all climate influences.  In particular, the warming of the last 30 years (when human climate influence is expected to have grown strongest) 

## Slide 21

**Notes:**
Global Carbon Dioxide Emissions, per country and per capita

This graphic from Time magazine (4/9/01 edition on global warming) illustrates global carbon dioxide emissions both by total tons emitted per country and total tons emitted per capita.
- The black smoke plumes show total CO2 emissions since 1950 in billions of tons: US/186.1 billion tons; Canada/14.9; Mexico/7.8; European Union/127.8; Russia/68.4; Ukraine/21.7; Poland/14.4; Kazakhstan/10.1; China/57.6; Japan/ 31.2; India/15.5; South Africa/8.5; and Australia/7.6
- The 3-D map shows yearly per capita carbon dioxide emissions in tons: red/16 to 36 tons per person; orange/7 to 6 tons; yellow/2.5 to 7 tons; dark green/0.8 to 2.5 tons; light green/0.1 to 0.8 tons; and light blue/0 to 0.1 tons.
 Although the United States makes up only 4% of the world's total population, we produce nearly 25% of the world's greenhouse gases. In comparison, India, with over 1 billion people (~17% of the world’s  population), is responsible for just over 2% of carbon dioxide emissions currently in the atmosphere, while China, the world’s most populous country, accounts for about 8.5% of emissions.

Data: World Resources Institute

## Slide 22

## Generalized Atmospheric Circulation

**Notes:**
This process of equatorial heating sets up recurring patterns in our climate – the low equatorial pressure cells that move heat poleward to the midlatitudes, where the air cools enough to descend, causing subtropical high pressure systems. 
The spinning of the earth interacts with the rising and descending air to cause more or less predictable circulation patterns so that we have predominant trade winds in the tropics, westerlies in the midlatitudes, and polar easterlies at high latitudes. The gradients between these regions provide our storm tracks.