PROSPERIDAD J. ABONETEJULY 3, 2003

Understanding Climate Change

Outline

Climate Change and Global Warming Definition Causes

The Greenhouse EffectEvidence of Climate ChangeEffects of Global Warming

Climate change

Long-term change in the average weather patterns over a specific period, over a significant period of time

The Earth's climate has always varied, so the term climate change is now generally used to describe the changes caused by human activity - specifically, greenhouse emissions which build up in the atmosphere and trap heat.

Global Warming, increase in the average temperature of the atmosphere, oceans, and landmasses of Earth

Causes of Climate Change

Solar variationOrbital variationPlate tectonicsVolcanic actionThermohaline circulationHuman influences

Measurements at the Earth's surface show that average temperatures have risen by some 0.4C since the 1970s. Scientists are confident this change can be blamed on human emissions because the increase is too big to be explained by natural causes.

Although natural factors such as changes in the sun and large volcanic eruptions are known to have warmed and cooled the planet in the past, these effects are not powerful enough to explain the rapid warming seen recently. Only an increased greenhouse effect caused by higher amounts of heat-trapping gases in the atmosphere can explain it.

The Greenhouse Effect

Greenhouse Gases

Occur naturallyConcentrations determined by natural factorsNaturally-occurring GHGs:

Water vapor Methane (CH4) Nitrous oxide (N20) Carbon dioxide (CO2)

Not naturally occurring: Halocarbons – e.g CFCs Artificial/human-made; products from chemical

industry

Enhanced Greenhouse Effect

Today, concentrations of naturally occurring GHGs, e.g. CO2, are enhanced by human action

Summary of Principal Greenhouse Gases

GHG CO2 CH4 CFC-11 CFC-12 N2O

Atmospheric concentration

Late 18th century

280 ppm 0.7 ppm 0 0 288 ppb

2001 371 ppm 1.75 ppm 252 ppt 480 ppt 315 ppb

Atmospheric lifetime (yrs)

50-200 12 45 130 114

Carbon Cycle

The current concentrations of greenhouse gases

IPCC WG1 SPM, 2007

13

Carbon dioxide and temperature last 420, 000 years

100

150

200

250

300

350

0100,000200,000300,000400,000years before present

CO

2 (p

pm)

-10

0

10

20

tem

pera

ture

(oC

)

Source: Jones, 2002

Global Surface Temperature (IPCC, 2007)

Intergovernmental Panel on Climate Change (IPCC)

International scientific guidanceEstablished in 1988 by WMO & UNEPTasks:

Assess the scientific information related to the various components of the CC issue, such as…, as well as the science needed to assess environmental and socio-economic consequences

Formulate realistic response strategies for the management of CC issues

IPCC 2007 Report

The understanding of anthropogenic warming and cooling influences on climate has improved …, leading to very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming….

Warming of the climate system is unequivocal…. Increases in global average air and ocean temperatures Widespread melting of snow and ice Rising global mean sea level

Anthropogenic warming and sea level rise would continue for centuries due to timescales associated with climate processes and feedbacks, even if GHG concentrations were to be stabilized.

Effects of Global Warming

Weather Sea levelsAgricultureAnimals &

PlantsHuman Health

Forests

Climate interrelated with biology/ecologyRising CO2 levels – increased global temperatureCarbon sequestration by forestsforest vegetation accounts for 80% of above-

ground C; forest soils capture 40% C of soil Cforests both C source and sinkeven 1oC change in air T sustained over time is

likely to affect growth and regeneration patterns of many forest species

1/3 of global forests will experience major changes