GEO011 Midterm 1

Define Climate

Average of many years worth of weather.

Weather

Actual state of the atmosphere at a particular time.

How is Climate different from Weather?

The actual state of the atmosphere at a particular time; highly variable and unpredictable.

Climate is what you expect, weather is what you get.

Why is Climate predictable?

It depends relatively fixed features of the earth including its spherical shape, shape of orbit around the sun, and tilted axis of rotation.

Oceans, Continents, Multi-layered atmosphere composed of greenhouse gases (GHGs)

Climate Change

Significant and lasting changes in climate, such as increased global average temperatures and sea-level rise due to human activities.

Sunlight related to latitude

Amount of sunlight depends on latitude. Reasons why tropics are hot, and poles are cold.

Near the poles (high latitudes), the sun's rays are more spread out, resulting in cooler temperatures.)

Feature of seasonal contrast with latitude

The temperature are more pronounced at higher latitudes due to the tilt of the Earth's axis, leading to varying angles of sunlight throughout the year. How hot (cold) the summer (winters) are. Tropics (mid-to-high latitudes) have low (high) seasonality.

What happens to season when you are farther from the equator?

More extreme seasons become.

Cause of Seasons

Tilt of Earth's spin axis and its orbit around the sun cause varying angles and durations of sunlight.

Causes of warm seasons and cold winters?

As earth orbits the sun, different parts of tilt towards or away from the sun, changing how much sunlight they get

Oceans influence on seasonal contrast

Oceans warm (cool) slowly during summer (winter) coastal regions benefit from ocean’s moderating influence. Continental interiors respond quickly to seasonal changes why central plains have warm summers and cold winters compared to coastal locations. 

Ocean Influence on Climate

Water has a high capacity for storing heat much greater than that for land. Oceans warm (cool) slowly during summer (winter) coastal regions benefit from ocean’s moderating influence. Continental interiors respond quickly to seasonal changes why central plains have warm summers and cold winters compared to coastal locations.

Gulf Stream

A warm Atlantic Ocean current originating in the Gulf of Mexico, flowing up the eastern coast of North America.

Kuroshio

A warm current flowing northward off the eastern coast of Japan.

California Current

A cold current flowing southward along the western coast of North America.

Climate in South California

“Mediterranean Climate”: Hot, dry summers & mild, relatively wet winters; Importance of latitude (~32^oN) and ocean, including the cold California Current. Inland Temperatures (Riverside) similar, but larger seasonal cycle warmer summer temperatures by about 20^oF.

Atmosphere layers and vertical temperature distribution in each layer

Thermosphere (640 km), Mesosphere (50 to 80 km), Stratosphere (50 km), Troposphere (8 to 17 km)

What happens to temperature in each layer?

1. troposphere: temperature decreases with altitude
2. stratosphere: temp increases due to ozone
3. mesosphere: temp decreases again
4. thermosphere: temp increases due to absorption of solar radiation

Where does weather occur?

Troposphere

Where is the ozone layer?

Stratosphere

Where is the ozone hole?

Antarctica (Stratosphere)

CFCs related to ozone hole

Chlorofluorocarbons (CFCs) accelerate destruction of ozone, reducing its abundance and ability to protect the planet from UV radiation.

General circulation of atmosphere

3 cells, Hadley, ferrel and polar

Large-scale movement of air that redistributes heat from the equator to the poles. driven by sunlight and earth's rotation

Hadley Cell

A key component of the general circulation of the atmosphere, it helps transport heat from the equatorial region to higher latitudes.

InterTropical Convergence Zone (ITCZ)

A belt of low surface pressure that is centered near the equator but migrates north and south within the tropics as the seasons change.

Why are tropics rainy?

Cold air holds less water vapor, so as rising tropical air cools, water condenses out as droplets that congeal and form towering cumulus clouds and rainfall-producing thunderstorms. 

Where do most of the world’s deserts exist?

Subtropical latitudes

Why do deserts occur at the Subtropical latitudes?

The air sinking in the subtropics is now quite dry because most of the water vapor was precipitated out of it when the air was rising. Furthermore, as air descends it gets compressed and warms. 

Where are the jet streams?

Fast-flowing air currents found in the upper atmosphere, influencing weather patterns. The subtropical jet is located above near the convergence of the Hadley and Ferrel cells, and the polar jet is located above the Polar Front

How will climate change affect the location of the polar jet stream and the subtropical dry zones?

Altering precipitation patterns and increasing drought risks. Shift Poleward

What is the implication of migration with climate change affecting the location of the polar jet stream and the subtropical dry zones?

Allows the dry subtropical zones (drought) to penetrate farther into mid-latitude regions such as Europe and the U.S. during the summer season.

Greenhouse gases (GHGs)

Gases caused by human and natural causes, they absorb heat and warm the atmosphere around them.

Are GHGs abundant gases in our atmosphere?

The most abundant gases in the atmosphere—aren’t greenhouse gases.

List of GHGs

Water vapor, CO2, CH4 (Methane), N2O (Nitrous Oxide)

Lifetime periods of GHGs (CO2, CH4 and N2O)

CH4:10 years, N2O: 100 years, CO2: 100s to 1000s of years

Primary sources of anthropogenic GHGs

Human activities: fossil fuel combustion, agriculture, deforestation and industrial processes.

Global Warming Potential (GWP)

A measure of how much a given mass of greenhouse gas is estimated to contribute to global warming relative to the same amount of carbon dioxide.

Evidence of world warming

Independent temperature data from the atmosphere, the ground, and the ocean subsurface, combined with evidence such as melting snow, ice and permafrost, rising sea levels, and observed changes in plant and animal behavior make it clear that Earth is warming noticeably.

How much has global average surface temperature increased over the 20th century? Global average surface temperatures have risen over the 20th century, with significant warming observed since the mid-20th century

Global temperature has increased by nearly 1.0°C (1.8°F) since 1880. The rate of warming in recent decades has increased by 50% relative to the longer-term trend. This is ~25% of the estimated change in global temperature during the last Ice Age, when NYC was covered by an ice sheet 0.5 km thick. Rate of warming accelerating: 0.10°C/decade over the 20th century; 0.15°C/decade in past few decades.

Pre Industrial atmospheric CO2 level and how much has atmospheric CO2 increased since preindustrial times?

Has increased 1 degree celsius, pre industrial CO2 level was 280 ppm (now 400 ppm) 40% increase

Are the changes of CO2 and temperature large relative to past CO2 and temperature variations over the geologic record? If not, then what’s the big deal?

Global CO2 records have been higher, but the rapidity of CO2 increase from anthropogenic factors makes Anthropocene dangerous

IPCC (Intergovernmental Panel on Climate)

Established in 1988 to evaluate the risk of human-induced climate change, and its periodic assessment reports are the authoritative source for accurate information.

What are some of their climate projections for the late 21st century?

Cold days and nights will be warmer and less frequent. Hot days and nights will be more frequent. Extent of permafrost will decline. Ocean acidification will increase as the atmosphere accumulates CO2. ocean acidification will increase with CO2. Global sea levels will rise and continue for centuries.

How does the IPCC account for uncertainty?

AR5 presents conclusions in terms of the likelihood of particular outcomes, expressed as a probability based on the quality, volume and consistency of the evidence of extent of expert agreement.

Water Vapor Feedback

Adding CO2 to the atmosphere tends to warm the atmosphere. The initial warming causes more surface water to evaporate, increasing the atmospheric water vapor content. Since water vapor is a greenhouse gas, the atmosphere will then tend to warm even more.

Positive feedback loop

Ice albedo feedback

Melting ice reduces Earth's albedo (reflectivity), leading to more solar absorption and further warming

Positive feedback

Positive Feedback

Amplifies initial change. Clouds (Fewer low clouds, more high clouds), Permafrost Carbon, Ocean Circulation, Wildfire, Soil Respiration, Stress of Vegetation, Methane Clathrate, Glacier Melt.

Negative Feedback

Decreases initial change. Low Cloud (Increased Clouds), Vegetation, Planck (Radiative), Lapse Rate (Temperature), Ocean Heat Uptake, Aerosol (from natural sources), Ice - Albedo (cooling). Carbon cycle (some parts).

Net impact of feedback on Earth

Doubles the magnitude of the expected warming or cooling response to imposed changes and outweighs negative.

Positive feedbacks outweight the negative ones, so warming is stronger that it would be from GHGs alone

Albedo

Reflectivity of solar radiation back to space; the planetary albedo is about 1/3.

A measure of reflectivity -> how much sunlighta. surface reflects. high albedo = more reflection (like ice), low albedo = more absorption (like ocean or soil)

Natural factors that influence climate

The Sun. Volcanic Eruptions. Earth’s orbit.

Anthropogenic factors that influence climate

GHGs, Nitrogen fertilizers, tropical deforestation, Industrial Aerosols

Industrial aerosols affect climate

The impact of aerosols (mostly sulfate and nitrate) are regionally limited and variable than well-mixed GHGs. Aerosols generally reflect solar radiation back to space, creating a regional cooling effect.

Volcanoes affect climate (Short time scale)

Volcanic eruptions modify composition of the atmosphere by injecting small particles (aerosols) into the stratosphere. These particles reflect/absorb incoming sunlight that would otherwise warm Earth’s surface.

Difference in climate impacts between aerosols and GHGs

Aerosols reflect solar radiation back to space, creating a regional cooling effect. GHGs have a surface warming effect.

How do we know the increase in CO2 since preindustrial times is caused by human activity?

Because fossil-fuel consumption is such an integral part of the global economy, utilization rates are reasonably well known. 

How are carbon isotopes involved? What are the carbon isotopes?

Carbon 12 (C-12): common in plants (photosynthesis) and fossil fuels. Carbon 13 (C-13): heavier, less common. Carbon 14 (C-14): radioactive, found in living things (but absent in fossil fuels)

Carbon Cycle

The sum of the processes, including photosynthesis, decomposition, respiration, weathering, and sedimentation, by which carbon cycles between its major reservoirs

Importance of Carbon Cycle

It regulates the Earth's temperature, makes up the food that sustains us, and provides energy that fuels our global economy. 

Reservoirs of carbon in a carbon cycle

Atmosphere, ocean, and vegetation, soils, and fossil fuel. 

How have humans perturbed the carbon cycle?

Added burning coal to the carbon cycle increasing atmospheric carbon dioxide so more carbon dioxide produced than natural ratios. 

Do all of our CO2 emissions stay in the atmosphere? If not, where do they go?

No, 50% into oceans and forests, double the Co2 emitted

What do all of our CO2 emissions that stay in the atmosphere imply in terms of the magnitude of global warming/climate change?

Even though not all CO2 stays in the atmosphere, there's still enough to cause long term warming, because CO2 lasts a long time and builds up

Greenhouse effect

When gases have a warming influence on Earth’s surface because they absorb terrestrial radiation, trap heat in atmosphere to warm life.

Greenhouse effect on atmospheric temperature (troposphere)?

Warms it

Greenhouse effect on atmospheric temperatures (Stratosphere)?

Cools it

Does the greenhouse effect occur naturally? How have humans perturbed it?

Yes, but humans driven up atmospheric CO2 concentration with fossil fuel burning, deforestation, agricultural practices

Where is most of the GHG-induced heat going?

Much of the warming due to increased greenhouse gas concentrations has gone into heating the oceans

How does GHG-induced heat affect sea level?

Cause sit to rise, warmer water expand, melting glacier adds water

Ocean Acidification

A decrease in ocean pH levels caused mainly by the uptake of carbon dioxide from the atmosphere.

How does climate change affect O2 levels in the ocean?

Warmer water holds less oxygen -> leads to lower oxygen levels in oceans. Less O2. Dissolves into oceans, including the cold, dense polar oceans that sink to the deep sea and provide essential oxygen to organisms living at depth

Why does climate change affect O2 levels in the ocean?

Warming reduces the tendency for water to sink by making it less dense, further isolating the oxygen-depleted deep waters from oxygen-rich surface waters. 

Climate “proxies”

Tree rings, ice cores, corals, cave deposits, lake and ocean sediments, tree pollen, and historical records

Why are proxies useful? What do they tell us?

Can be used to reconstruct climate for times prior to the establishment of a widespread instrumental atmospheric and oceanic data set

Has Earth’s climate been very stable over geologic time intervals?

No, earth has gone through many cold (glacial) and warm (interglacial) periods. climate has naturally varied over time

How are ice cores used to infer past climates?

Scientists extract the gas from tiny bubbles in the ice core to measure the concentration of ancient air

What do paleoclimate data indicate about long-term temperature and CO2 variations?

Three GHGs have been rising at dramatic rates for the last two centuries. CO2 increased by 40%; CH4 by 150%; N2O by 20%.

Driven by fossil-fuel burning, deforestation and agriculture, the recent skyrocketing trends greatly exceed the natural fluctuations of the preceding hundreds of thousands of years

From ice cores, the last interglacial had atmospheric CO2, CH4 and N2O levels close to pre-industrial.

Pleistocene Epoch

2 million years ago until 10,000 years ago; Ice Age, fluctuations in sea level are the result of 40,000 and 100,000-year "glacial-interglacial" cycles of the last 2 million years

Last Glacial Maximum

About 21,000 years ago

Holocene

Last 10,000 years-most recent interglacial period

Eocene Optimum

50 (53-49) million year ago alligators and sequoia forests were thriving above the Arctic circle

Pliocene

5.3 to 2.6 million years ago, was a time of global cooling

Anthropocene

Industrial Revolution to Present, unprecedented GHGs, human alteration of the atmosphere

Little Ice Age

15th-19th centuries (1400-1800s)

Medieval Warm period

10th - 13th centuries (900-1300)

Last Interglacial

125,000 years ago

Milankovitch Cycles

Changes in the shape earth's orbit and tilt that cause glacial and interglacial periods.

What orbital cycles are important for climate?

Orbital ellipticity, Precession (Wobble), Tilt

What are the orbital cycle periods?

Orbital ellipticity (100,000 year cycle), Precession: Wobble (19,000 and 23,000 year cycles), Tilt (41,000 year cycle) 

Are the orbital cycle periods fast or slow processes (on human timescales)?

Slow

Why is the last interglacial warm enough to melt the Greenland ice sheet?

Northern Hemisphere received 10% more solar radiation than it does today (not because the sun is brighter, but because Earth's orbit around the Sun was different than it is today).

How will climate change affect drought?

The combination of decreased summer precipitation and increased evaporation due to warming surface temperatures sill cause more in dry regions

For the western U.S., how is drought related to tropical Pacific sea surface temperatures (SSTs)?

These SST changes are associated with the enhanced North American drought (based on a calculation for the 1998–2002 period). The concentration of warming in the western tropical Pacific and Indian oceans is reminiscent of the east–west temperature contrast typical of La Niña events.

El Niño

An event where trade winds weaken, causing warmer ocean water in the tropical Pacific, influencing global weather patterns.

La Niña

An event where trade winds strengthen, resulting in cooler ocean water in the tropical Pacific.

How will climate change affect record high temperatures/heat waves?

More record highs and heat waves

Record low temperatures/cold snaps?

Does not affect overall climate change; more record highs less record lows

How will extreme warm/cold events change with global warming?

Hot days increasing, cold days decreasing

How will climate change likely affect hurricanes?

Stronger hurricanes, more stronger hurricanes, less hurricanes in general

A warmer ocean surface, all other things being equal, is likely to fuel intense tropical cyclones, with stronger sustained winds. The combination of sea level rise and strong tropical storms could pose a “double whammy” when it comes to damaging storm surges.

Why is Hurricane Sandy so powerful?

Merged with an extra-tropical, wintertime cyclone. Climate change raised sea surface temperatures (SSTs) along the eastern coast of the U.S contributed to the unusual strength and flooding potential of the storm, and global sea level rise added roughly 30 cm (1 ft) to the coastal surge, leading to an estimated extra 65 square kilometres (25 square miles) of flooded area.