The UK Green Party yesterday published it’s Manifesto for the forthcoming European Elections. There were some statistics that show a lack of numeracy.

UK Labour Party’s target emissions reduction

The Labour government now proposes a target of reducing emissions by 80% by 2050, which works out at about 2.5% per annum. (Page 4 Col 2)

          Let us keep the maths simple. Let us take the base year as 2010 and set that at 100. This gives 40 years to achieve the target, which is 20. There are 2 ways of calculating this. – Beancounters will recognize the terminology.

1. Straight Line Method. Take the same reduction every year. The reduction is 2.5 each year. So if 2010 is 100, 2011 is 97.5, 2012 is 95 etc. After 40 years emissions will be 100-(2.5*40) = 0
2. Reducing Balance Method. Each year reduce the balance by 2.5% from the previous year. So if 2010 is 100, 2011 is 97.5, 2012 is 95.06, 2013 is 92.69 etc. After 40 years emissions will be 100*0.975⁴⁰ = 36.32.

By the straight line method, emissions will be reduced by 100% and by the straight line method they will be reduced by 63.68%. The correct answer, by the straight line method is 2% per year, by the reducing balance method 3.95%. Neither approximates to 2.5%

Green Party’s target emission reduction

Based on the latest scientific predictions, an industrialised country such as the UK needs to reduce emissions by 90% by 2030. And we need a commitment to annual targets now, rather than aspirations for the distant future. The Green Party has calculated that the UK needs to be making reductions of around 10% per annum from now on. (Page 4 Col 2 to Page 5 Col 1)

            Let us see if the Green Party’s calculations are correct. Taking 2010 as a base, 2030 is in 20 years time. Using the straight line method, a 10% reduction per annum reduction will give 100-(10*40) = -100. That is we will be taking as much greenhouses gases out of the atmosphere as we are pumping in today. Children of today can look

forward to a chilly retirement. Vote Green for a White future!

            Using the reducing balance method, a 10% reduction per annum will be 100*0.90²⁰ = 12.16. Strictly, to get a 90% fall would require a 10.86% reduction per annum, but 10% reduction would only miss the target by 2 years, so is a good enough approximation.

Conclusion

Of the two statements, there are 4 possible answers. Only one of these answers can be correct, so a 25% mark is possible, or an E grade. However, as the method of calculation is not stated, a much less generous marker, would give them an F.