Global Warming

Our planet has been through many cycles of climate change in the past. At the present time, we are undergoing a period of global warming. There is almost no disagreement on this point in the scientific community.

Global Warming It is also widely agreed upon that the cause of this warming trend is the increase in greenhouse gases in the Earth’s atmosphere. Is this increase part of a natural cyclical process, such as has occurred in the geologic past? Or, is human activity responsible for the rise in greenhouse gases?

Most solar energy is in the form of shortwave radiation (e.g. visible light, UV rays). Our atmosphere allows most of these energy waves to pass through it. Earth absorbs this energy and re-emits as longwave radiation (infrared or “heat”). This heat radiates away from the planet at night. If all of it escaped, the average temperature of Earth would be about C (0 0 F).

Greenhouse Gases Greenhouse gases in the atmosphere do not allow infrared radiation to pass through them like shortwave radiation. Instead they absorb this energy, keeping it close to the Earth. This natural process allows the Earth to maintain an average yearly temperature of about 15 0 C (60 0 F). This is necessary for life on the planet. The most important greenhouse gases are water vapor (H 2 O), and carbon dioxide (CO 2 ). Other include: methane (CH 4 ) ozone (O 3 ) and chlorofluorocarbons (CFCs).

Until the 19 th century, ice core data show atmospheric CO 2 levels at less than 300 parts per million (ppm) By the middle of the 19 th century, levels were at about 300 ppm (0.03%).

In 1958, Roger Revelle and Charles David Keeling started direct monitoring of atmospheric CO 2 from the Mauna Loa Observatory. Levels have increased to as high as 380 ppm.

Can scientists correlate temperature change with atmospheric concentrations of CO 2 ? Red line is atmospheric CO 2 : ice core data Blue is temperature: isotope analysis

A more recent comparison, using thermometers for temperature data and direct sampling of atmospheric CO 2

Does this mean that human activity is responsible for global warming?

Those who say Yes would argue the following: The Earth’s yearly average temperature has increased in the last century. Atmospheric concentration of CO 2, a principal greenhouse gas, has increased since the mid- 19 th century (the Industrial Revolution). Rise has been especially rapid since the 1950s. It is a known fact that humans emit carbon dioxide into the atmosphere due to transportation and industrial processes. Loss of forested land exacerbates this process, since photosynthesis is a process that removes CO 2 from the atmosphere.

And those who would say No? Is it possible that Global Warming is occurring naturally? It is only through the reconstruction of past climates that we can truly evaluate the magnitude of this present warming trend.

Paleoclimatology – Study of ancient climates What can paleoclimatology tell us about climate change that is relevant to society in the future?

Is the last century of climate change unprecedented relative to the last 500, 2000, and 20,000 years? Do recent global temperatures represent new highs, or just part of a longer cycle of natural variability? Is the recent rate of climate change unique or commonplace in the past? What does it mean if the last century is unprecedented in terms of warming? Can we find evidence in the paleoclimate record for mechanisms or climate forcings that could be causing recent climate change?

Climate change in the geologic past How can scientists create a graph like this when thermometers, rain gauges and other instrumentation did not come into use until the late 19 th century? By using proxy climate data! What are proxy climate data? What are some examples of proxy climate data indicators?

Proxy Climate Data Proxy climate data are obtained from natural recorders or indicators of climate variability These proxy climate indicators cannot directly measure temperature, rainfall, etc. as do modern instruments. Scientists must analyze and interpret the results. What are some examples of proxy climate data indicators?

Proxy Climate Data The chart shows sources of climate information and the time frame over which they are useful. All except the instrument records are examples of proxy climate indicators.

Measuring recent climate change Instrument records - measure only about the last hundred years Historical records – accounts recorded as records, or in stories –Vikings’ tales of the Little Ice Age ( ) and the retreat from Vineland –Wine harvest records –Landscape paintings, other historical & archeological accountings chronicle changes over the span of human history

Climate Data from Historical Records

Measuring climate change Tree rings – growth rings of trees hold climate information (thinner rings mean less growth due to lower temperatures or less rainfall Plant pollen – the pollen record records what was able to grow, which is linked to temperature and precipitation –e.g.10,500 years ago pines replaced spruce in some areas of northern U.S., indicating warmer temperatures

Oxygen Isotope Analysis How does oxygen isotope analysis enable us to study climate changes in the past?

Oxygen Isotope Analysis Oxygen isotopes in glacial ice – 18 O & 16 O (common isotope) both occur, although 16 O is more common. – 18 O is heavier, needs warmer air/water temperatures to evaporate. –Glacial ice is made up of precipitation from ocean evaporation. –Therefore glacial ice with a higher 18/16 ratio was deposited when the earth’s average temperature was greater. –Ice from Greenland and Antarctica show a record back >100,000 yrs.

Fig. 21-6, p.505

Measuring climate change Oxygen isotopes in marine fossils –When earth’s average temperatures are lower, more 18 O remains in the water. –Coral take in seawater to make their exoskeleton. –Therefore in coral and plankton a higher 18/16 ratio indicates lower average temperatures.

Using δ O18 ratios in coral to measure ocean temperatures Oxygen isotopes in coral –When earth’s average temperatures are lower, more 18 O remains in the water –Coral take in seawater to make their exoskeleton –Therefore in coral and plankton a higher 18/16 ratio indicates lower average temperatures

Measuring climate change Plankton and isotopes in ocean sediment –Shells and other “hard parts” preserved in marine rocks / muds give two lines of information What was alive at the time gives climate information 16/18 O ratios in biogenic carbonate Rock and fossil record –fossils give much information, what lived when –Rock records formative environment

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Tectonics and climate change Position of the continents –200 mya, the single continent Pangea was near the south pole Continental interiors tend to have more severe winters. For a single large landmass, even more so. Influences winds and ocean currents

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Does Data from the Vostok ice core support those who claim that humans are responsible for global warming? Why or Why not

Human contribution to the Greenhouse Effect Humans release, fossil fuels,CFCs and other greenhouse gases into the environment. –Concentrations of these gases has increased in the recent past –The atmosphere has warmed 0.8 o C during the last century

Thermohaline circulation – how global warming could cause global cooling –Warmer sea surface temperature could slow or stop vertical currents –This would stop, or re-route the Gulf Stream, which would cool the Earth –Thermohaline currents have decreased 30% from

If the Labrador Current (Cold) is too fresh to sink, it may block passage of the N. Atlantic Drift (warm) which moderates the climate of Great Britain and Scandinavia

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The Kyoto treaty on greenhouse warming Dec. 1997, 160 nations met to discuss global warming –By Feb a treaty was ratified by many of them –Creates a global trading market for CO 2 emissions –Sets limits and goals –Caps and goals tied to nations’ economies –Developing nations, eg China, India excluded from CO 2 caps

21.9 The Kyoto treaty on greenhouse warming –The U.S. has never ratified the treaty –Treaty supporters argue: Wealth not necessarily tied to fuel consumption Curbing consumption and emissions could help the economy Models show the longer we wait, the worse it will get Consider the alternatives: runaway temperature changes, famine, global unrest. The treaty expires in 2012 – the sequel is looking less than inspired.

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Possible Consequences of Global Warming Sea-level changes – sea-level has risen markedly from 1900 to 2000 –water expands when warm –Glacial (ice on land) melting is increasing Effects on people –Tropical diseases flaring up in new areas –Population stress on food and water supplies as well as other global systems

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The Kyoto treaty on greenhouse warming Dec. 1997, 160 nations met to discuss global warming –By Feb a treaty was ratified by many of them –Creates a global trading market for CO 2 emissions –Sets limits and goals –Caps and goals tied to nations’ economies –Developing nations, eg China, India excluded from CO 2 caps

21.9 The Kyoto treaty on greenhouse warming –The U.S. has never ratified the treaty –Treaty supporters argue: Wealth not necessarily tied to fuel consumption Curbing consumption and emissions could help the economy Models show the longer we wait, the worse it will get Consider the alternatives: runaway temperature changes, famine, global unrest. The treaty expires in 2012 – the sequel is looking less than inspired.

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Climate change in the geologic past Early Precambrian Time (4-2.7 bya) –Sun was 20-30% fainter, delivered less energy –Effect offset by large greenhouse effect of Earth’s early atmosphere, largely composed of CO 2, and H 2 O. Late Precambrian to Permian (2.7 bya to 250 mya) –Severe ice ages occurred at least five times in this period

Climate change in the geologic past Mesozoic to Present –Climate mostly warmer than today. –Most recent ice ages occurred over the last 2 million years. –Some scientists think the last 10,000 years represent an interglacial warming episode and the ice will return. –Recent records show mean temperature increase from the late 1800s.