Current Climate Change

Ch. 17, Bush

Outline

v Evidence for recent climate change

v Are humans the cause?

v Potential ecological effects of climate change

Outline

v Evidence for recent climate change

v Are humans the cause?

v Potential effects of climate change

Evidence of Temperature Changes

v Three main sources of data:

– Direct measurements of temperature

– Location of ice caps and tropical glaciers

– Thickness of ice caps

Temperature records

v We have accurate records only for the past 120 years

v Most temperature readings taken at cities which are “heat islands”

Whaling and Polar Ice caps

Changes in extent of sea ice Thickness of Ice Caps

v Submarines make careful measurements of the distance between the ice and the bottom of the sea

v Have estimated that the thickness of the ice caps have decreased from 3.1m to 1.8m

Tropical Glaciers are melting

v All tropical glaciers are above 4800 m

v At the current rate of temperature change, it is estimated that all will be gone in 50 yearsKilimanjaro

The effect of melting ice caps

v There is not enough water trapped in the ice caps to create “Waterworld”

v The biggest effect of ice caps melting comes from the decrease in ALBEDO

Albedo = brightness Ice caps have high albedo

Outline

v Evidence for recent climate change

v Are humans the cause?

v Potential effects of climate change

Last glacial period ended 11,000 years ago

v 90% of last 2 million years has been glacial

v For the last 10,000 years, plants and animals have been living in an unusually warm environment

Temperature changes over the years

v The rate of climate change we are currently experiencing is only matched by the rapid warming at the end of the last ice age

Temperature changes in history

v Between 1400-1700 the earth was a few degrees colder

v Called “The Little Ice Age”

v Influenced history:– Outcome of battles– Crops failing causing

famine

Greenhouse effect

v Light energy enters the atmosphere

v Changes to heat energy

v Light energy exits atmosphere but heat energy is trapped

The Greenhouse effect

v The greenhouse effect is not all bad

v Without the greenhouse effect, the earth would be, on average, -18 οC

Creation of greenhouse gases

v The burning of fossil fuels is increasing the greenhouse effect

v Important greenhouse gases:– HCF’s, CFC’s– Methane– CO2

– Water vapour

Relative contribution of greenhouse gases

v Other chemicals are actually better at trapping heat but CO2 contributes more to the greenhouse effect due to the fact that it is way more abundant

CO2 and water vapour

v CO2 causes minor increase in temperature

v Increase in temperature causes more water vapour via evaporation

v Water vapour leads to further greenhouse effect and higher temperature

Carbon cycle

v In the natural carbon cycle, respiration and decomposition increase CO2

v Photosynthesis decreases CO2

v Burning fossil fuels now contributes to CO2 gain

Fossil fuels

Fossil fuels are ancient organisms that did not decompose

The major culprits…

Carbon sinks

v Each year humanity dumps roughly 8 billion metric tons of carbon into the atmosphere– 6.5 billion tons from fossil fuels and 1.5 billion

from deforestation

v But less than half that total, 3.2 billion tons, remains in the atmosphere to warm the planet

v Forests, grasslands, and the waters of the oceans are acting as carbon sinks

Outline

v Evidence for recent climate change

v Are humans the cause?

v Potential effects of climate change

Potential effects of CO2 increase

v Predicted changes in temperature

v Changes to the natural world

v Changes to human life

Recent increases in CO2

v Jagged line is caused by seasonal changes in photosynthesis; in summer N. Hemisphere plants use up more CO2

Pollution can mitigate increases in temperature

v Pollutants such as those from car exhaust are causing increases in cloud cover

v Cloud cover increases albedo

Air pollution increases albedo

CO2 and temperature changes

v Simulations of temperature changes are becoming increasingly accurate

Predicted temperature change

v Five principal research groups all produce climate models

v Differences arise in the predictions made about social and political change

v Medium estimate is that the average temperature on Earth will rise ~3.5 οC

Increased photosynthesis Planting trees to decrease temp

v Deforestation causes decreases in CO2 absorption

v Planting trees will have the opposite effect ->decreases CO2

C4 evolution changing atmospheres

v C4 photosynthesis appears to have evolved at a time when O2 was high and CO2 was low and temperatures were high

The global distribution of C4 plants in today's world

v C4 grasslands (orange) have evolved in the tropics and warm temperate regions where C3 forests (green) are excluded by seasonal drought and fire.

v C3 grasses (yellow) remain dominant in cool temperate grasslands because C4 grasses are less productive at low temperatures.

Temperature and precipitation Climate affects ecology

Deserts will spread N. Hemi. plants will migrate north

Predicted migration of beech and maple trees

Migration of species

v Industrialization may impede the migration of many species

v Temperate species (and island species) may have nowhere to migrate to

v If migration can not occur then extinction will likely take place

Cold-adapted species

Implications to Conservation Extinction and global warming

v One study indicated that, by 2050, current warming trends could bring about extinction of 15 to 37 percent of the 1,103 species they studied

v A mere 6 degrees of global warming was enough to wipe out up to 95 per cent of the species which were alive on earth at the end of the Permian period, 250 million years ago

Arable land will have new locations

v Best conditions for farming will move towards poles

v Will be at the latitude of the Canadian Shield

v More irrigation needed as crop land will be drier

v Expected 20% decrease in cultivatable land

Other reasons why global warming a threat to life on Earth?

v Incidences of heat attacks, respiratory disease and stroke will increase

v Disease and pests are more likely to spread

v Tropical storms, tornadoes, landslides, heatwaves and droughts will both increase in number and intensity

v Air quality will become poorer

v coastal cities like Miami, New Orleans, Los Angeles and Bangkok will be flooded as ocean level rises due to melting glaciers

v ocean levels rise, some inland drinking water sources will become contaminated by saltwater

Summary

v The Earth is becoming increasingly warm

v Recently, humans have contributed to this phenomenon

v Temperature increases will have severe effects to the natural world