Detection, attribution, and future projections

Question 1

What policy makers (and the public) want to know

Answer 1

Has the climate really changed?
If it has, is the change due to human action?
Will there be significant change in the future?

Question 2

To measure climate change, a baseline is needed

Answer 2

Meteorological records (vs previous normal period)

Question 3

Once you start to change the climate it generates a set of effects in the earth system:

Answer 3

River gauge data (beginning of record?)
Glacial extent and mass balance (historical, photos, satellites)
Snow and ice extent (satellites- short baselines)
The biosphere (people, ecologists, satellites- few baselines)

Question 4

Can the observed temperature change be simulated?

Play around with known forcing factors of temperature change to see if it looks like reality:

Answer 4

GHGs (positive)
Volcanoes (negative) (ash clouds dimming)
Solar variability (variable)
Anthropogenic aerosols (largely negative but highly uncertain)

Question 5

Where could you get data on greenhouse gas concentrations come from?

Answer 5

Ice cores

Question 6

Where could you get data on solar output?

Answer 6

Looking at cosmogenic isotopes such as beryllium which are affected by solar output

Question 7

What is the aerosol thats most likely a positive forcing?

Answer 7

Black carbon/ soot landing on ice sheet and changing albedo

Question 8

Simulated annual global mean surface temperatures

Answer 8

Natural
- Sun and volcanoes
- Omits anthropogenic
Anthropogenic
- Human 
- Omits natural
All forcings
- Red doesn't change in all observations
- Key experiment : anthropogenic forcing becomes evident in past 30 yr
- Not possible to replicate observations unless anthropogenic GHGs added

Question 9

What is attribution?

Answer 9

Attribution of recent climate change is the effort to scientifically ascertain mechanisms responsible for recent climate changes on Earth

Question 10

Main points of attribution?

Answer 10

Total radiative forcing is positive- energy uptake by climate system.
Largest contribution is increase of CO2 since 1750.
Human influence detected in warming of atmosphere, ocean. Plus snow/ ice reduction and sea level rise.
Warming has become clear since about 1980- extremely likely human influence is dominant cause.

Question 11

Can the observed temperature change be simulated?

Known forcing factors?

Answer 11

GHGs (positive forcing)
Volcanoes (negative forcing)
Solar variability (variable)
Anthropogenic aerosols (largely negative but variable)

Question 12

What gives an indication of solar variability?

Answer 12

Volcanic eruptions
Historical
Ash in ice cores.