L17 Flashcards
What is internal variability?
- climate variability not forced by external agents
what are the two forms of externally forced responses
natural eg volcanic or solar
anthropogenic eg greenhouse gases or aerosols
- Why is detection of climate change described as a “signal to noise problem”?
- Detection of climate change is a “signal to noise problem” because the effects of various forcing agents need to be detected above a background of natural variability, which has fluctuations in climate on many timescales resembling noise. The climate change we are trying to detect is caused by forcings with fairly well known spatial and temporal patterns, so if the effects are significant they should be detectable above the noise.
Define detection
- Detection of climate change means demonstrating that the observed changes in climate are significantly different from what would be expected due to natural variability (i.e., the variability that would occur without anthropogenic radiative forcing).
Define attribution
- Attribution of climate change means accounting for how different forcing agents cause the climate change that has been detected.
what are the problem with attribution
limited data and imperfect models
- proofof cause and affect is impossible
- relies on rejecting alternatives
- incomplete knowledge means that new alternatives are still emerging
What are the three requirements for successful detection and attribution?
1 good data - sufficient to see what is natural variability
2 understanding of the natural variability
3 clear responses or signals or footprints of forced changes in the observations and models : (fingerprint is what we would expect to see happen if something changed)
what does correlation not indicate …..
causation
do climate models run with external forcings?
no
how can we use forcing response relationships to separate natural and anthropogenic influences
- we can only do this if spatial and temporal responses are known
How can natural variability of the climate system be determined?
Natural variability of the climate system can be determined from long term climate records, palaeoclimate records or from long-term climate simulations without any external forcings applied.
What are the difficulties associated with methods to determine natural variability?
The main difficulty associated with using climate records to determine natural variability is that some of the record may contain the signal that we are trying to detect. Palaeo-records are usually of low temporal resolution so do not contain the high frequency natural variability. Climate model variability may not be the same as real variability if the climate model is not very good.
- In the instrumental temperature record, which combination of modelled forcing-response patterns best explains the changes in stratospheric temperature?
- In the instrumental temperature record, the forcing-response patterns due to greenhouse gas emissions and volcanic eruptions best explain the changes in stratospheric temperature. The greenhouse gases cause a slow cooling of the stratosphere and the transient volcanic eruptions cause brief increases in temperature because of the radiative heating effect of the acidic aerosol.
- The temporal pattern of global mean surface temperature change between 1900 and the present day shows two dominant influences which emerge from attribution studies. What are these patterns?
- The two dominant influences which emerge from attribution studies of global mean surface temperature change between 1900 and the present day are greenhouse gas warming and aerosol cooling. The cooling reached a maximum in the 1970s and most likely accounts for the slightly cooler period. The sharper increase in T since the 1980s is likely caused by rising greenhouse gas concentrations and decreasing or steady (negative) aerosol forcing.
