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Evidence in Science and PolicyScientific evidence

Vicky Pope

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• Growing evidence of man-made climate change

• Importance of natural variability

• Practical information for decision making

• Dealing with complexity and uncertainty

Scientific evidence

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Growing evidence of man-made change

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Scientific evidence• The average temperature of the Earth is 15 ºC. Without the

blanket of greenhouse gases it would be –18 ºC.

• CO2 has risen by 107ppm (38%) from pre-industrial levels of 280ppm.

• Two thirds of the increase is in the last 50 years.

• CO2 is 30% higher than at any time over at least the last 800,000 years.

• Global temperatures have increased decade on decade since the mid 20th century, consistent with the basic physics.

• The water vapour feedback enhances the warming due to man-made greenhouse gases

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Evidence of temperature rise:Independent datasets

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Practical information for decision making

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Central estimate from UKCP models

Upper limit of "high++“ model

Probability forecasts of coastal flood risk allow for a balanced approach to decision making

Change in extreme sea level of 50 year storm

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─ Observations█ Model Individual projections from 2009─ ─ ─

Global average temperature forecast for the next decadeLikely that half the years from 2010 will be warmer than 1998

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The impact of a global temperature rise of 4 ºC

Change in temperature from pre-industrial climate

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Current City population • 3-10 million • 10-20 million

Meltingice

OceanAcidification

Rainforestloss

Reduced crops

Forestfire

Increased drought

Stronger tropical storms

Methane release

More heatwaves