Climate

Seasons

The Earth’s Axial Tilt and the Seasons The Earth’s axis of rotation is tilted 23.5 from perpendicular It is this tilt that explains the different seasons on Earth

The Earth’s Axial Tilt and the Seasons During the course of the Earth’s orbits around the Sun, certain areas of the Earth are tilted toward the sun and experience summer while others are tilted away from the Sun and experience winter. That is why when it is summer in Colorado (the Northern Hemisphere) it is winter in Australia (the Southern Hemisphere).

Summer in the Northern Hemisphere

Winter in the Northern Hemisphere

The Change of Seasons

Other Factors that affect the Earth’s climate Over periods of thousands of years, changes in the following three areas affect the Earth’s climate: Eccentricity Obliquity Precession Together these things are called the Earth’s orbital parameters

Eccentricity Remember, the Earth’s eccentricity is very low, almost zero, which means the Earth’s orbit is nearly a perfect circle. The distance between the Earth and the Sun varies very little throughout the course of a year (3.3%) The Earth is closest to the Sun on January 5 th - perihelion. It is furthest from the Sun on July 5 th - aphelion

Obliquity The tilt of the Earth axis relative to the plane of it’s orbit is called the Obliquity. A smaller obliquity would mean warmer winters and cooler summers in the Northern Hemisphere. The Earth’s obliquity changes over a period of about 40,000 years.

Precession The gravitational pull of the Sun, Moon, and other planets on the Earth causes the Earth to have a slight wobble.

Milankovitch Cycles Makes long term predictions about the Earth’s climate based upon the combined affects of Eccentricity, Obliquity, and Precession.

Influences on Climate

Climate Climate – The average weather conditions for a region over a long period of time. Weather and climate are not the same thing!

Factors that influence climate: Latitude Elevation Geographic features

Latitude Latitude tells us the distance of a location from the Equator. Latitude determines the amount of incoming solar radiation. High latitudes get much less solar radiation. For every 1 degree further we move away from the equator, temperature decreases by approximately 3 o F

Elevation Higher elevations have colder temperatures (3.6°F/1000ft.) and greater precipitation.

Geographic Features The windward side of a mountain range receives more precipitation than the leeward side. The leeward side is in a rain shadow.

Oceans The ocean moderates the climate of nearby cities. Winters are warmer, and Summers are cooler. Water has a higher heat capacity than rock and soil. This means water does not heat or cool as quickly as land.

Lake Effect Snow Large lakes can create lake effect snow in the winter. This can dramatically change a climate!

Climate- looking into the past

Paleoclimate - a climate that existed sometime in the past, as recently as a few centuries or as long as billions of years ago. For example, the world was warmer in the Mesozoic Era.

Continental Ice Sheets Presently, Earth is in an interglacial interval: a period of warmer climate following a colder, glacial period. Earth today has two continental ice sheets, one covering most of Greenland and one covering most of Antarctica.

Continental Glaciers The last retreat of continental glaciers occurred between about 20,000 and 8000 years ago. Without written records, Paleoclimatologists must use a variety of methods to infer past climate.

Glacial Retreat

Inferring Paleoclimate Many kinds of evidence give us an indirect record of past temperature. These are called climate proxies. Something that represents something indirectly is called a proxy (none are perfect).

Proxy - Fossil Pollen Pollen - tiny particles produced in flowers to make seeds. Blown into lakes or bogs and preserved in sediments. Pollen from spruce trees infers cold climates.

Ah-chooo! Pollen

Proxy - Ice Cores Scientists study ice cores drilled deep into glaciers for inferring paleoclimates.

Proxy - Air bubbles Bubbles of air trapped in ice contain samples of the atmosphere from the time when the snow fell. Oxygen in the atmosphere is in two forms of isotopes. They are 18 O (heavier and in higher proportion from warmer climate), and 16 O. Paleoclimatologists can also measure 1 H and 2 H.

Air Bubbles in Ice CO 2 in the glacier depends on the amount in the air at that time, which can be correlated to global temperature. Warmer times show higher levels of CO 2 than in colder times. This can give a more accurate proxy because CO 2 is uniformly distributed in the global atmosphere.

Using Ice Cores to understand paleoclimates:

Proxy - Dust In colder climates the wind is stronger, eroding more dust, and deposits it in small quantities over larger areas of the Earth.

Proxy - Deep Sea Sediments Sand sized shells of a kind of single celled animal called Foraminifera accumulate in layers of ocean bottom sediment. During warm climates, the shells spiral in one direction, and in cold climates, the opposite direction. Also, the shells contain calcium carbonate, which contains oxygen that can be studied. foraminifera

Proxy - Glacial Land Forms and Sediments Glaciers leave recognizable evidence in the geological record. Glacial land forms are common in North America. Glaciers erode the rock beneath and carry the sediment and deposit it to form distinctive landforms. (Here in Colorado) Glacial till

Glacial Sediment Fine glacial sediment is picked up by the wind and deposited over large areas as a sediment called loess. These layers reveal several intervals of glaciation during the Pleistocene Epoch. Glaciers also leave evidence in the ocean. When they break off into ice bergs which melt, the glacial sediment rains down to the ocean bottom, where it is easily recognized. Loess blowing off Glacial sediment from ocean floor

Proxy - Tree Rings Paleoclimate is also recorded in the annual growth rings in trees. Trees grow more in warm years than in cold years. A drawback is that few tree species live long enough to provide a very far look. Bristlecone pines and Sequoias which are both long lived, are most often used.

Ranger Rick Dating Sequoia Tree Rings for two fashionable attractive young ladies from the past

Climate Change

Using ice core data to see previous climate There is a positive correlation between CO2 levels in the atmosphere and temperature Ice sheet

Greenhouses Gasses… Greenhouse gasses absorb some of the energy that is radiated back to space from Earth’s surface. With out these gasses Earth would be frozen. Example of greenhouse gasses are: -water vapor (H 2 O) - most important contributor to the green house effect -carbon dioxide (CO 2 ) -methane (CH 4 ) -nitrous oxide (N 2 O) -chlorofluorocarbons (CF x Cl x ) -ozone (O 3 )

How we contribute to Greenhouse Gasses: Carbon Dioxide: Burning fossil fuels, deforestation Methane: increasing cattle ranches, landfills and water treatment plants CFCs: found in aerosols, coolants, and fire retardants Nitrogen Oxides: burning fossil fuels

How Can We Remove Carbon from the Atmosphere? The oceans absorb a large amount of CO 2. Some people want to pump CO 2 into the ocean but the oceans can only hold so much Reforestation is the replanting of trees on depleted farmland. The trees would absorb CO 2 for photosynthesis. What are some ways that you think we could help reduce CO 2 emissions?

Effects of Global Warming Depending on how hot the Earth gets, we may see: Melting of ice caps and glaciers Rising ocean levels Less coast land More severe storms More forest fires More droughts Changes in animal and plant life Decreased salinity of the ocean Changes in ocean currents