what are the main drivers of climate change?...global average sea level change september arctic sea...

What are the main drivers of climate change?

Professor John Mitchell FRSMet Office Hadley Centre

Long term perspective:Atmospheric CO2 concentrations over the last 800,000 years

© Crown copyright Met Office

© Crown copyright Met Office

Drivers of climate since1750

Natural- the sun- volcanoes

Human- greenhouse gases

and aerosols

Natural internal variations in the ocean and atmosphere

How sensitive is the climate?

Professor Keith Shine FRSUniversity of Reading

• A fundamental characteristic of the climate system• If we suddenly doubled the amount of carbon dioxide in

the atmosphere, by how much would the Earth eventually warm?

IPCC AR5 concludes it is:“likely between 1.5oC and 4.5oC”

and“extremely unlikely it is less than 1oC and

very unlikely greater than 6oC”

What is the evidence that climate change is due to human activity?

Professor Corinne Le QuéréTyndall Centre

Observed decadal mean warming

C. Le Quéré, Tyndall°Centrefor Climate Change Research

University of East Anglia

Observed warming inconsistent with that expected from natural factors

C. Le Quéré, Tyndall°Centrefor Climate Change Research

University of East Anglia

Observed warming consistent with that expected from greenhouse gases

C. Le Quéré, Tyndall°Centrefor Climate Change Research

University of East Anglia

It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th

century

C. Le Quéré, Tyndall°Centrefor Climate Change Research

University of East Anglia

The state of the climate system

Professor Brian Hoskins FRSImperial College London

Globally averaged surface temperature 1850-2012IPCC 2013Relative to 1961-90 mean

A warming climateIPCC 2013

Surface temperaturechange 1901-2012

in ºC/decade

Global average sea level change September Arctic sea ice area

Sept 2012

Projections of globally averaged surface temperature change from 1986-2005

IPCC 2013

Projections of regional surface temperature change1986-2005 to 2081-2100 for high emission scenario (RCP8.5)

IPCC 2013

Temperature

Precipitation

CO2already 

emitted to the 

atmosphere

about half the

historical emissions

about 3 x historical emissions

Emissions compatible with different futures

C. Le Quéré, Tyndall°Centrefor Climate Change Research

University of East Anglia

Thinking probabilistically about future projections

Professor Tim Palmer FRSUniversity of Oxford

F = ma

E = hω

Comprehensive climate models are based on the primitive laws of physics e.g.

Are Climate Models “Fundamentally Flawed”?• Only if the basic laws of physics are!

Can climate models be improved?• Certainly! Ability to represent small-scale processes

accurately (e.g. associated with clouds) requires bigger computers

How do we deal with uncertainties in current climate models?

• Make multiple predictions varying uncertain aspects of the representation of small-scale processes. Means (IPCC AR5) predictions are inherently probabilistic.

Extreme events and climate change

Professor Stephen BelcherMet Office Hadley Centre

© Crown copyright Met Office

AR5 update on extreme events

© Crown copyright Met Office

Recent extreme summers

• Summer 2012

• Wettest Summer since 1912

• Wheat yields down 15% on 5-yr average

• Cost insurers £800 million

• Likely part of a natural ocean-atmosphere cycle

• Summer 2003

• Hottest summer in Europe since 1540

• 20,000+ deaths

• Very likely that human influence at least doubled the risk of a heat wave such as 2003

• Normal by 2040s and cool by 2080s