Demystifying global warming

Some basic observations for international students

JN Birchall

‘Global Warming Update’,

• The greenhouse effect• Making predictions … and some possible

surprises• What are the predictions?• Past trends in climate• Debates on the ‘climate change’ problem• Policy advice

Supplementary materials:• Exercise on observations of recent climate

change• Information sources and ideas

The greenhouse effect

More gas!

Concentrations of greenhouse gases are higher now than at any time for the past 500,000 years

381

‘Natural’ CO2 conc.

Making predictions

• How are predictions made?

• What are the sources of uncertainty?

• Can we trust climate models?

• What factors do models include?

• Are there major sources of uncertainty not accounted for?

Basis of climate change predictions

Socio-economic scenarios

Greenhouse gas emissions

Greenhouse gas concentrations

Predicted temperature change

Uncertainty

V. large

Large

Moderate

Moderate

CO2 in SRES scenarios (SRES, 2000)

IPCC 2001 http://www.grida.no/climate/ipcc_tar/wg1/figspm-5.htm

Activity: Explore the IPCC scenarios and discuss their relative likelihood and/or policies which would see them fulfilled

GCM structure

Climate Research Unit, UEA

One way to test a climate model: Comparing observed climate with modeled climate

IPCC (2001): Figure 8.2 lower left

Major change to predictions from

similar GHG scenarios

(1996 cf. 1990)

Some possible surprises….

• Methane hydrates (oceans 9500 Gt, permafrost 400 Gt)

• Carbon cycle: strength of ocean and terrestrial ‘sinks’

• Ocean circulation: the ‘thermohaline conveyor’

NASA Earth Observatory

http://earthobservatory.nasa.gov/Newsroom/NasaNews/2001/200112106303.html

Activity: If 10% of methane hydrates were released, how does this compare with anthropogenic sources?

Methane hydrates stored in oceans and permafrost

Woods Hole research Center (2004) http://www.whrc.org/carbon/missingc.htm

Will natural sinks persist?

Activity: Evaluate the impact of the decrease/loss of the oceanic and/or terrestrial carbon sink on global carbon flux

Temperature change following shutdown of the North Atlantic conveyor (Vellinga and Wood, 2002. Climatic Change 54: 251-267)

Likelihood of decline in MOC - from a survey of scientists in the RAPID programme

http://www.soc.soton.ac.uk/rapid/sci/pdf/ann_mtg_survey.pdf

Activity: To what extent should adaptation policy be formed by the possibility of North Atlantic conveyor shutdown?

What are the predictions?

• Range• Regional patterns

• Changing ideas• Seasonality

IPCC(2001) Fig 9.14

IPCC (2001) Fig 9.10d.Multimodel ensemble annual temperature change 2071-2100 - 1961-1990Shading - temp change, Blue lines - range oC, green - mean change/mean sd

IPCC (2001) Fig 9.11d.Multimodel ensemble annual precipitation % change 2071-2100 - 1961-1990Shading - mean change, red lines - range, green - mean change/mean sd

IPCC reports- evolving predictions of climate change

Year Global temp Sea level

rise oC rise cm

1990 3.0 (1.5-4.5) 65

1995 2.0 (1.0-3.5) 48 (13-94)

2001 1.4-5.8 9-88

No best guesses

Seasonality can be more important than net change - e.g. UK precipitation (UKCIP02) www.ukcip.org.uk

2020s 2050s 2080s

Past trends in climate• Is there a trend in

global climate change?

• How do current temperatures compare with those in the past?

Frost fair on the River Thames (1814)

How much has global temperature risen over the past 100 years?

20001994

1989

Timing of IPCC report preparation

Activity(s): Are current trends in climate consistent with predictions for the future? See file.

Global temperature reconstructions for last 1000 years: are we now outside the range of “natural” variability?

1st IPCC report (1990)Note: no T scaleNote: no T scale

“no”

3rd IPCC report (2001)

based partly on using multi-proxy palaeoclimate data - the “hockey-stick” curve

probably “yes”

Is the hockey stick still valid?Multiple “spaghetti curves” now published

• larger changes than original hockey stick

• still show the late C20th as the warmest period of the last millennium

• how critical is this anyway to the case for human-induced warming?

DEBATES• There is genuine broad (although not

100%) consensus in the climate science community on main issues

• Argument, scepticism and hypothesis testing are at the heart of good science

• Publication of research, review and quality control are essential in this process

Arguments of ‘climate sceptics’

• Trends. There is no significant trend in global temperature (e.g. urban heat island effect, geographic coverage of data)

• Attribution. Human activities are not responsible for observed trends

• Impacts. The negative impacts of predicted climate change are over-estimated; cost-benefit analysis does not support mitigation action

Trendse.g. Urban heat island

Sources:

http://antwrp.gsfc.nasa.gov/apod/ap040822.html

http://data.giss.nasa.gov/gistemp/2005/

Activity: Compare temperature records from urban and rural areas in the UK – is there a systematic difference and how big is it?

Attribution

Observed changes are:

• within natural variability

• due to other effects (e.g. solar variability)

IPCC (2001) Figure 4 from SPM. Model outputs using natural (solar, volcanic) and anthropogenic (GHGs, aerosols) climate forcing

Impacts scepticsThe costs of mitigating climate change are greater than the benefits gained from adapting to change

Best exemplified by Bjorn Lomborg in ‘the skeptical environmentalist’

Activities:

How accurate are estimates of costs and benefits likely to be?

Economic costing does not include costs to natural systems – does this matter?

Science, consensus and debate

Consensus Consensus ScepticScepticSupporterSupporter

Contrasting reading - Fact vs fiction? Is the distinction clear?

Activity: Take extracts from the above (or use www sites) and identify differences in style, language, use of documentation, nature of documentation

International policy – is scientific advice followed?

International policyScientific advice Pressure groups (±)Media and public opinion

International policy

Government delegates

Acceptance in national governments

Government policy .. and action

Activity: Follow one of the COP meetings linked to the UN Framework Convention on Climate Change www.unfccc.org

What are ‘desirable’ levels of future climate change?

Defined by:• Global temperature (+2oC?)• Global emissions (2.5 Gt C fossil fuels pa?)• Atmospheric concentration (450-550 ppm CO2?)• Timescale

e.g. UK RCEP (2002) Suggest 60% reduction on 1990 CO2 emissions by 2050 for UK

Compare with:– Kyoto target of c. 5.2% by 2008-2012 for Annex 1 countries– UK Government target of 20% by 2010 (and may hit 10%....)

Use the graph below from the RCEP Energy report as a starting point for debating questions such as:

Which parts of the world are the biggest contributors to climate change?

Should targets for reductions be based on current total contributions, per capita emissions or perhaps emissions per GDP?