The Science of Climate Change:The Global Picture

Adam Monahanmonahana@uvic.ca

School of Earth and Ocean SciencesUniversity of Victoria

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OutlineWhy do we think the climate is changing?

How can we predict future climate changes?Where do we think the climate is going?

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OutlineWhy do we think the climate is changing?How can we predict future climate changes?

Where do we think the climate is going?

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OutlineWhy do we think the climate is changing?How can we predict future climate changes?Where do we think the climate is going?

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The Greenhouse Effect

Figure source: UCAR

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Past Climate Changes

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The Last Millennium: Temperature

Source: IPCC Third Assessment ReportThe Science of Climate Change:The Global Picture – p. 5/24

The Last Millennium: CO2

Source: IPCC Third Assessment Report

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The Recent Past: Temperature

Source: IPCC Third Assessment Report

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The Recent Past: CO2

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Recent Wintertime Temperature Trends

Source: IPCC Third Assessment Report

Warmest Yearson Record

1. 19982. 20033. 20024. 20015. 19976. 19957. 19908. 19999. 2000

10. 1991

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What Causes Sea Level Changes?

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Past Sea Level Changes

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What is the “Climate System”?

Source: IPCC Third Assessment ReportThe Science of Climate Change:The Global Picture – p. 12/24

Modelling the Climate System: What is a GCM?

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Modelling the Climate System: Model Evolution

Source: IPCC Third Assessment ReportThe Science of Climate Change:The Global Picture – p. 14/24

Modelling the Climate System: Past Changes

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Radiative Forcing: Estimates and Uncertainties

Source: IPCC Third Assessment Report

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The Scientific Consensus

“There is new and stronger evidencethat most of the warming observedover the last 50 years is attributableto human activities”

The Intergovernmental Panel on Climate Change, 2001

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Climate Change Scenarios

Source: IPCC Third Assessment Report

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Temperature Changes: Today vs. 2075

Source: IPCC Third Assessment Report

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Climate Change: Precipitation

Source: IPCC Third Assessment Report

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Climate Change: Sea Level

Source: IPCC Third Assessment Report

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Climate Change: Extreme Events

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Climate Change: Extreme Events

72

projected to occur over nearly all land areas and are generally

larger where snow and ice retreat. Frost days and cold waves

are very likely to become fewer. The changes in surface air

temperature and surface absolute humidity are projected to

result in increases in the heat index (which is a measure of the

combined effects of temperature and moisture). The increases

in surface air temperature are also projected to result in an

increase in the “cooling degree days” (which is a measure of

the amount of cooling required on a given day once the

temperature exceeds a given threshold) and a decrease in

“heating degree days”. Precipitation extremes are projected to

increase more than the mean and the intensity of precipitation

events are projected to increase. The frequency of extreme

interannual variability and mean precipitation. Future

increases in mean precipitation will likely lead to increases

in variability. Conversely, precipitation variability will likely

decrease only in areas of reduced mean precipitation.

F.5 Project ions of Future Changes in

Extreme Events

It is only recently that changes in extremes of weather and

climate observed to date have been compared to changes

projected by models (Table 4). More hot days and heat waves

are very likely over nearly all land areas. These increases are

projected to be largest mainly in areas where soil moisture

decreases occur. Increases in daily minimum temperature are

Confidence in observedchanges (latter half of the 20th

century)Changes in Phenomenon

Confidence in projected changes(during the 21st century)

Likely Higher maximum temperaturesand more hot days over nearly allland areas

Very likely

Very likely Higher minimum temperatures,fewer cold days and frost daysover nearly all land areas

Very likely

Very likely Reduced diurnal temperaturerange over most land areas

Very likely

Likely, over many areas Increase of heat index8 over landareas

Very likely, over most areas

Likely, over many NorthernHemisphere mid- to high latitudeland areas

More intense precipitationeventsb

Very likely, over many areas

Likely, in a few areas Increased summer continentaldrying and associated risk ofdrought

Likely, over most mid-latitudecontinental interiors (Lack of consistentprojections in other areas)

Not observed in the few analysesavailable

Increase in tropical cyclone peakwind intensitiesc

Likely, over some areas

Insufficient data for assessment Increase in tropical cyclone meanand peak precipitation intensitiesc

Likely, over some areas

Table 4: Estimates of confidence in observed and projected changes in extreme weather and climate events. The table depicts an assessment of

confidence in observed changes in extremes of weather and climate during the latter half of the 20th century (left column) and in projected

changes during the 21st century (right column)a. This assessment relies on observational and modelling studies, as well as physical plausibility of

future projections across all commonly used scenarios and is based on expert judgement (see Footnote 4). [Based upon Table 9.6]

a For more details see Chapter 2 (observations) and Chapters 9, 10 (projections).

b For other areas there are either insufficient data of conflicting analyses.

c Past and future changes in tropical cyclone location and frequency are uncertain.

8 Heat index: A combination of temperature and humidity that measures effects on human comfort

Source: IPCC Third Assessment Report

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The Big Picture

To our best understanding, human activity is havinga measurable impact on Earth’s climate system

These changes will persist for at least 100 years,even if we act nowChanges in climate will impact

disease geographyeconomic/social structures

Kyoto Protocol: small reduction in warming, butenormous symbolic importanceAdaptation & mitigation will involve both social andtechnological changes

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The Big Picture

To our best understanding, human activity is havinga measurable impact on Earth’s climate systemThese changes will persist for at least 100 years,even if we act now

Changes in climate will impactdisease geographyeconomic/social structures

Kyoto Protocol: small reduction in warming, butenormous symbolic importanceAdaptation & mitigation will involve both social andtechnological changes

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The Big Picture

To our best understanding, human activity is havinga measurable impact on Earth’s climate systemThese changes will persist for at least 100 years,even if we act nowChanges in climate will impact

disease geographyeconomic/social structures

Kyoto Protocol: small reduction in warming, butenormous symbolic importanceAdaptation & mitigation will involve both social andtechnological changes

The Science of Climate Change:The Global Picture – p. 24/24

The Big Picture

To our best understanding, human activity is havinga measurable impact on Earth’s climate systemThese changes will persist for at least 100 years,even if we act nowChanges in climate will impact

disease geography

economic/social structures

Kyoto Protocol: small reduction in warming, butenormous symbolic importanceAdaptation & mitigation will involve both social andtechnological changes

The Science of Climate Change:The Global Picture – p. 24/24

The Big Picture

To our best understanding, human activity is havinga measurable impact on Earth’s climate systemThese changes will persist for at least 100 years,even if we act nowChanges in climate will impact

disease geographyeconomic/social structures

Kyoto Protocol: small reduction in warming, butenormous symbolic importanceAdaptation & mitigation will involve both social andtechnological changes

The Science of Climate Change:The Global Picture – p. 24/24

The Big Picture

To our best understanding, human activity is havinga measurable impact on Earth’s climate systemThese changes will persist for at least 100 years,even if we act nowChanges in climate will impact

disease geographyeconomic/social structures

Kyoto Protocol: small reduction in warming, butenormous symbolic importance

Adaptation & mitigation will involve both social andtechnological changes

The Science of Climate Change:The Global Picture – p. 24/24

The Big Picture

To our best understanding, human activity is havinga measurable impact on Earth’s climate systemThese changes will persist for at least 100 years,even if we act nowChanges in climate will impact

disease geographyeconomic/social structures

Kyoto Protocol: small reduction in warming, butenormous symbolic importanceAdaptation & mitigation will involve both social andtechnological changes

The Science of Climate Change:The Global Picture – p. 24/24

The Big Picture

To our best understanding, human activity is havinga measurable impact on Earth’s climate systemThese changes will persist for at least 100 years,even if we act nowChanges in climate will impact

disease geographyeconomic/social structures

Kyoto Protocol: small reduction in warming, butenormous symbolic importanceAdaptation & mitigation will involve both social andtechnological changes

The Science of Climate Change:The Global Picture – p. 24/24