Climate Change Part 1

Is the World Getting Warmer?

What’s Wrong with The Weather?

Past 10 Years:• Hotter Summers • Warmer Winters• Increased Flooding• Severe Droughts• More Intense Storms and Rainfall

Bad weather in one place at one time does not prove the climate is changing.

Two Questions

• In order to address the issue of global warming we have to answer to questions:

1. Is the world getting warmer?

2. What forcing mechanism is causing the warming?

Is the World Getting

Warmer?• During the

past 50 years, the global surface temperature has risen by 0.6 °C

• Sea level has risen and snow cover has decreased

Global Temperature Trends

Global Temperature Trends

• Two Warming periods: 1900-1945 (by 0.5°C), the mid-1970s to present. – The decade of the 2000s (2000-2009) was

warmer than the decade spanning the 1990s (1990-1999), which in turn was warmer than the 1980s (1980-1989).

• Cooling period: 1945-1975.– 1960’s: A few scientists warned that an ice

age was fast approaching.

U.S. Temperature Trends

• Since 1901, temperatures have risen across the lower 48 states at an average rate of 0.13°F (0.18°C) per decade (1.3°F / 0.74°C) per century).

• Average temperatures have risen more quickly since the late 1970s

• Seven of the top 10 warmest years on record for the lower 48 states have occurred since 1990, and the last 10 five-year periods have been the 10 warmest five-year periods on record.

Temperatures in the Lower 48 States, 1901–2009

U.S. Temperature Trends

• Some parts of the United States have experienced more warming than others (see next slide)

• The North, the West, and Alaska have seen temperatures increase the most, while some parts of the South have experienced little change.

U.S. Temperature Trends

Is The Recent Climate Change Significant?

• Records show that in the Middle Ages, some parts of the world, like Greenland, were warmer than today. The Vikings built settlements there and farmed the land.

• This is called the Medieval Warm Period

Is The Recent Climate Change Significant?

• Following the Medieval Warm Period, Europe went through a period of cooling known as the Little Ice Age.

Is The Recent Climate Change Significant?

• But records of one place, like Greenland or Europe, during one time, may not prove anything.

• Only by understanding past climates on a global scale can scientists know whether the recent warming is significant or just a return to warm conditions like the Medieval Warm Period.

Measuring Past Climates

• Direct Measurements– Weather Instruments– Historical records

• Proxy (Indirect) Measurements– Tree Rings– Coral Growth– Lake Sediments– Ocean Sediments– Ice Cores– Pollen

Measuring Past Climates

Direct Data:Weather Instrument Measurements

• Thermometer data available for Europe and United States for past 200 years

• Data indicates a slight warming trend since the mid-19th century

• Problem: Data is limited only to only two continents for a short period of time.

Direct Data: Historical Records

• Historical data can be grouped into three major categories.

1. observations of weather phenomena per se, for example the frequency and timing of frosts, or the occurrence of snowfall.

2. records of weather-dependent environmental phenomena such as droughts and floods.

3. records of weather-dependent biological phenomena, such as the flowering of trees, or the migration of birds.

Historical Records• Example: Monks in Switzerland.

– 100’s of years of documents.– Recorded the time the cherry blossom appeared, the

freezing and thawing of lakes, the state of the wine harvest.

• By combining historical data from many sites, climate of central Europe can be assembled going back more than 1,000 years.

• European Climate: Periods of warm temperatures but none compares to the past 10 years.

• Problem: Data is limited only to select geographic areas where records were kept.

What is Proxy Data?

• Instrumental measurements only go back a couple hundred years at most

• More data is needed to determine past climates

• “Proxy” data is used to infer conditions beyond several hundred years– Many things change with changing climate– Relate changes (in organisms, plants, etc..) to

climate changes

• Indirect measure of climate change

Tree Rings

• Tree rings have useful information of the last tens to hundreds (occasionally up to thousands) of years.

• Tree growth responds to annual weather fluctuations

• Tree rings are “clocks”• One ring = one year• Carbon in tree can be age-

dated.

Tree Rings

• When the growing season is extremely short, cold and dry, trees put most of their limited resources into the leaves that feed them and the roots that store their food. – Very little new wood is added to the trunk

each year. – Thin annual ring of Growth

• When the growing season is favorable (warm and humid) the more wood is added to the truck and a wider growth is produced.

Tree Rings

• Disadvantages– Annual layers are best

developed in mid-latitude and high-latitude regions that experience large seasonal climate changes.

– Can’t be used in tropical areas – lack of rings due to year-round growth

Ice Cores• Annual deposition of

snow can pile up continuous sequences of ice.

• Ice core records can date back over 800,000 years in Antarctica and 100,000 years in Greenland.

• Many mountain glaciers have records of the last 10,000 years.

Ice Cores• The wind in Greenland blows most strongly in the

late winter and early spring, and at those times more dust is deposited over the snow.

• So one year of snow deposition is equal to one high dust and one low dust pair. The ice core below contains 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers.

Ice Cores and Oxygen Isotopes

• Both O18 and O16 are isotopes of oxygen found in the glacial ice.

• Since O18 has two more neutrons than O16 water (H2O) containing O18 is heavier, harder to evaporate.

• O18 in ice constitutes a proxy thermometer.

• Low O18 levels indicate the ice was deposited during cold conditions worldwide.

• High O18 levels indicate a warmer climate.

Ice Cores and Oxygen Isotopes

Coral Growth • Like trees, corals add a

layer of growth annually, can live for hundreds of years and grow at different rates, depending on the temperature at the sea surface.

• Coral will grow more when -sea surface temperatures are warmer, thus thicker layers indicate a warmer climate.

Coral Data and Oxygen Isotopes

• Corals secrete a hard CaCO3 surface made from sea water and dissolved ions.

• As global temperature decreases, less evaporation of O18 occurs, therefore, there will be a higher concentration of

O18 in the shell.• As global temperature

increases, more evaporation of O18 occurs, therefore, there will be a lower concentration of O18

in the shell

Oxygen Isotope Data Corals near Galapagos Islands

Coverage of Proxy Data So Far….

Artic Lake Sediments

• Lakes frozen over for most of the winter• Very brief period during the summer when the

snow melts and the sediments are carried into the lake.

• These year-by-year variations in thickness will be used to estimate past temperatures

• A thicker layer (varve) means there was a warm spring which melted more snow and produced more mud.

Pollen and Lake Sediment

• Pollen in the lake sediment provides details of past climate. Different plant species live in different climate ranges

• In Minnesota lake - 11,000 year old sediment contains spruce pollen– Spruce trees grows today only in northern Canada– indicates colder climate

• Sediment about 10,500 years old begins to contain pine pollen– Pine trees grow today in Minnesota – indicates warming climate

Isotopes and Lake Sediments

• Isotopes can be used to determines wet and dry periods in tropical lakes.

• During dry periods of strong evaporation, the lake water becomes enriched in 18O. These isotopic values are incorporated into the growing shells of organisms that live in the lake.

• During dry periods evaporation concentrates sulfur in the lake water. If the sulfur concentration becomes high enough, salts such as gypsum (CaSO4) will start to precipitate from the lake water and add sulfur to the lake sediments.

Isotopes and Lake Sediments

• 18O and S isotopic analysis from the a lake on the Yucatan Peninsula

• Note that an increase in 18O and S indicates a draught and corresponds to the collapse of Mayan Classic Civilization

Increased Continental Coverage

Ocean Sediments• Oceans occupy more than

70% of Earth’s surface• Sediments (dead organisms,

runoff from land) accumulate in ocean basins

• Collection of these sediments has taken place over hundreds of thousands of years on ocean floor.

• Most reliable source on long-term climate change

Ocean Sediments• Biological sediments are

formed from the shells of dead organisms (calcium carbonate: CaCO3 )

• Analysis of Oxygen isotopes in CaCO3: low O18 in marine deposits indicates warm period.

• Carbon in CaCO3 can be used to get a age-date the sediment.

Increased Ocean Coverage

Is The Recent Climate Change Significant?

• Combining all historical and proxy data, scientists have been reliably able to extend back the temperature record for the northern hemisphere about 2,000 years.

• The graph on the next slide shows the data from 10 different proxy data studies (each a different color)

• According to this graph, the 0.6°C warming over the past 100 years stands out dramatically.

2009

Is The Recent Climate Change Significant?

Yes!But, what forcing mechanism is causing the warming (is this a natural trend or

is it due to human activity)?

Based on the peer reviewed scientific evidence……..