It’s just a guestimate. They should really be asking:
annual gas consumption in m3 (0)
electricity in kWh +or- (-1500)
litres of petrol and diesel per year. (about 350l petrol for three people)
kms of flights (I too put 1 in but rarely fly because I detest flying)
kms of train (about 1500)
kms of bus/taxi (about1500)
m2 of property occupied
gms of meat/week
weight of recycling and disposal bins each week in kgs
polluting activities: skiing, swimming, mechanical sports,
Number of TVs, phones, computers, amplifiers, US made guitars, white goods, cameras… owned
decorating bills for the last ten years