When are GCMs useful? A climate model will produce a lot of output. This game presents a number of potential questions someone could ask of a climate model. When designing an experiment it is important to consider how suitable a climate model is for answering a given question. In your group, you have 9 cards, each illustrating a weather / climate related question. For each card you need to categorise the cards into three groups: GCMs are useful GCMs can be useful for providing information about this topic GCMs are not useful You have 8-10 minutes to discuss all the cards in your group, then we’ll share our ‘answers’ and discussion points as a whole class.

GCMs are useful

GCMs can be useful

GCMs are not useful

Relative sea level rise in Jakarta by 2100 https://alatpenterjemahjakarta.wordpress.com/2015/08/26/ Relative sea level rise is the local change you’d see sitting on the beach in Jakarta. Relative sea level rise not only depends on how much water there is in the oceans and the thermal expansion, it also depends on other factors such as local geology, is the land rising or falling? GCMs can give us part of the story but not enough to inform any local decisions alone. GCMs Can Be Useful

Population change between 2010 and 2085 http://www.earthtimes.org/green-blogs/green-living/film-review-mother-caring-way-population-dilemma-27-May-11/ GCMs tell us nothing about how population might change however population is a key factor in the various Shared Socioeconomic Pathways (SSPs) that are used when making future projections. GCMs Not Useful

Change in North American crop yield (2051-2060) https://en.wikipedia.org/wiki/Harvest Crop yields depend on many variables but temperature and precipitation are key. All else being equal (varieties grown, fertiliser & pesticide use, soil fertility etc.) the output from GCMs can be used to estimate changes to crop yields. GCM Can Be Useful

Precipitation in London on 3rd May 2076 https://commons.wikimedia.org/wiki/File:Oxford_Street_in_the_Rain_-_geograph.org.uk_-_336737.jpg When analysing GCM output you are able to look at a grid box in England for the 3rd May 2076 to see if it’s raining or sunny. However weather is a chaotic process and beyond a few weeks the models have no skill in specific details. This is a nice example of something the model will tell you, but you must ignore. However, by looking at the 30 yr mean rainfall in May for London, GCMs can be informative. GCM Not Useful

Gridded annual surface air temperature (2081-2090) https://en.wikipedia.org/wiki/Temperature GCMs will produce an absolute temperature for every grid box. Whilst we believe there is skill in these projections there may be bias and any specific grid box could be quite wrong as it could be influenced by small scale features and processes not represented by the GCM. However there is uncertainty and different models produce different results. There is value in both running the same model multiple times (from different starting conditions and/or perturbed physics) and from running multiple models. GCM Useful

Mean global temperature anomaly http://www.inference.phy.cam.ac.uk/sustainable/climate/AR5-Top-Figures.html We believe GCMs do have skill in projecting mean global surface temperature change. Anomalies reduce the impact of model bias and averaging over the whole world reduces the impact of variable distribution. However there is uncertainty and different models produce different results. There is value in both running the same model multiple times (from different starting conditions and/or perturbed physics) and from running multiple models. GCM Useful

Can the UK become a major wine producer? https://commons.wikimedia.org/wiki/File:Coddington_Vineyard_-_geograph.org.uk_-_285794.jpg Grapes are very sensitive to local climatic conditions. GCMs are able to suggest how key variables like temperature and precipitation are likely to change but significant local scale uncertainties will remain. GCM Can Be Useful

Will the frequency of typhoons change? https://en.wikipedia.org/wiki/Typhoon_Parma#/media/File:ParmaMelor_AMO_TMO_2009279_lrg.jpg We believe GCMs have skill in broad scale variables such as sea surface temperature and humidity and we know typhoons are influenced by these variables. As such GCM output can be useful in understanding how typhoons might change. GCM Can Be Useful

Was 2003 Paris heat wave due to human factors? https://www.flickr.com/photos/aigle_dore/5238554034 Can GCMs be used in attribution studies. Yes – run with anthropogenic emissions, run without – compare probabilities of events. Issues with extremes, null hypothesis, internal variability etc. GCMs can be useful