Climate Defense

Climate Defense is a Tower Defense game around the issue of climate change made in just 1 week. On the 1st January 2013, the Kyoto Protocol, mired in the bickering of nation states, ended. Yet climate change goes ever onwards, “We’re talking about a fight between human beings and physics. And physics is entirely uninterested in human timetables. Physics couldn’t care less if precipitous action raises gas prices, or damages the coal industry in swing states. It could care less whether putting a price on carbon slowed the pace of development in China, or made agribusiness less profitable. … It’s implacable. It takes the carbon dioxide we produce and translates it into heat, which means into melting ice and rising oceans and gathering storms.” (Bill McKibben)

In Climate Defense we give you two modes of play – one is where, as with most games, we’ve moulded the game-data to make the game enjoyable (and so you can win) to play.  In the other version the game-data is moulded to better reflect reality; a reality where year after year we pump out more and more CO2.  You can play both versions and because which world you’d rather live in.  Below is a much more detailed discussion of how we’ve moulded the game-data in the real(er) version of the game, if you’re interested.

The game is free to download for Android from Google Play or you can download the .apk file directly.  Also we’ll be discussing this game and our others on Facebook and Twitter, so why not join in?

Sources & About Climate Defense

One of the difficult things for this game was deciding the end conditions as what the changes in the PPM (parts-per-million) of CO2 will be and will mean for the average global temperatures if a difficult thing to predict because there are so many variables involved.  We started with a base level of 370 PPM of CO2 at 2000 (about 57 degrees adapted from here) and decided that the end-point of the game would be a six degree rise in temperatures to 63 degrees or the date of 2100, which ever came soonest (as 63 degrees seems to be the point at which civilisation collapses).  The game models 63 degrees as being a PPM of 950 (Figure 5 graph here). There is no simple linear relationship between PPM and temperature (as can be seen here and here) however for the constraints of development time to make it a game, we had to assume a more linear relationship than in nature.  In this we opted for +100PPM meaning +1 degree rise (which matches the rough 0.25 degree per 20 PPM seen here).

In terms of absorbing CO2, it seems that the natural world as is takes in about 0.01 ppm/year (much less than what we put out.) Yes there are other greenhouses gasses but none are a long-lived in the atmosphere nor as potent at trapping heat as CO2.  In regard to the the impacts the game gives you, we used this New Scientist article for the 1 to 5 degree results.

Tower Damage & Rate
A tower represents a group of natural carbon sinks (because we’ve not created any deliberate artificial ones yet!). The game assumes that each tower you build represents an amount of trees that will then absorb carbon from emissions of carbon dioxide, thus stopping it from ending up in the atmosphere and adding to the PPM of CO2 already there.

As you will see from the game, you’re just building (growing!) leavers, fruit and blossoms on a single tree.  This tree represents the role plant life plays in absorbing CO2. Basic towers represent the actions  of an older tree. These as the least efficient absorbers of CO2 having reached a steady state. Medium towers are middle-aged trees, these are average absorbers of CO2. Heavy towers are young trees, which are the best type of absorbers of CO2 as they grow they absorb lots. Note that this is a very simplified  view as different species grow better in different climates and impact on the amount of CO2 absorbed per year in different ways.

You can build 10 towers maximum in the game. If we assume there are 32 billion hectares of land that can be used to grow trees on, then in this game you are able to double that natural CO2 sink.  Each ‘tower’ represents 1945.6 billion trees (at 608 trees per hectare). This number of trees will absorb around 3891.2 billion Kilograms of Carbon from the atmosphere, or 3.891 million tonnes of CO2. This means each tower can  absorb a tenth of that, so 0.3891 million tonnes, or in terms of PPM, each tower can absorb about a 750th of a PPM per year so as each wave is 5 years then each tower can absorb 1/150th of a PPM.

Because we are mapping this to a Tower Defense game, we’re making it so that the trees (towers) only absorb CO2 when it is in range of them and that this absorption is at a set time/rate. To be fair to the trees, we’re boosting the absorption rate (‘damage’)  to show that they are doing more absorbing work overall.

If we assume it costs $4000 to plant a hectare of trees, then each tree costs $6.6 to plant. So a typical tower represents 1945.6 billion trees at a cost of 12840 $Billion to develop.  We’ve assumed that this can be made much more cost effective and scaled it down to 10000, 15000 or 20000 $Billion per tower.

The money situation is also reflected in the amount of money you get per enemy unit ‘killed’ i.e. absorbed. If we assume that per tonne of carbon the cost is $20 (a mid-point of the European carbon trading scheme price) and as the PPM that an enemy represents an addition of say 20PPM for all 10 enemy unit for that 5 years,  Which means that 1 PPM is 291,758,181 tonnes of carbon, therefore each unit stopped is about 2PPM so giving 11 $Billion of income.

Enemy Units (CO2)
In this game the enemy units you need to stop are clouds of CO2. Ok, so CO2 does not float around as a cloud, that is something we’ve kept from the Tower Defense genre for the sake of the game, however what is accurate is that if the CO2 emitted by human activity is not intercepted then it adds to the PPM of the atmosphere, so trapping heat. Each wave of the ‘real’ version of the game has 10 enemy units. Each enemy unit, if not stopped, represents a tenth of the additions to the PPM of the atmosphere in that 5 years the wave covers. We got this figure by measuring the difference between PPM of 2010 and 2011 and looking at the carbon emissions, it seems a rough calculation is that a change of 1 PPM comes from 291,758,181 metric tones of C02. So each enemy, if it gets past your defences, adds one tenth of that as PPM to the total. We’ve started the game in 2000 and taken it up to 2100 where the PPM can reach 950 and each level has that growth in PPM into the stats.

You can try to tackle the problems at the emissions end also.  For this you can lower the rate of emissions.  In terms of cost, one estimate suggested it would cost 4% of GDP to cut to 1990 levels, so applied to the world, is 2,798 $Billion (at current GDP).  Because in the game, the benefit stays with you and is not a per-year cost, we’ve lowered the PPM impact to better reflect this and you have three options to implement a cut based on spending 3000, 2000 or 1000 $Billion spend to lower emissions by lowering the ‘health’ of the clouds of pollution by 30,20 or 10%.

This game has other global actions you can do. These represent improving the efficiency of how we use energy, so cutting demand.  If we look at efficiency there are two upgrades in the game.  These are represented by 12% cut in ‘speed’ of the enemy units (transport efficiency) or ‘spawn rate’ (industrial efficiency) of units and is estimated to cost the whole 100 $Billion budget that was put aside to help developing countries adapt for either (figures taken from this report).

Other Sources
For Climate Defense we got our data from a number of sources the main ones being the US based; National Oceanic & Atmospheric AdministrationNational Aeronautics and Space AdministrationEnvironmental Protection Agency plus & New Scientist.

Thanks also to Ashley Gwinnell – our guest developer for the week!  Thanks also to all the scientists and others who contributed to the data we used to create the game.


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  1. May LaMotte

    I am clicking on every snapshot on the top of this widow, however, it’s not doing anything. Would it be possible to give directions about how to play the game?

    Thank you,

  2. Dave_G

    Why am I totally unsurprised to see this game perpetuating the ’cause’ – no doubt this comment will be deleted/edited as it doesn’t meet with the meme……

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