Table:
|  |  | Year-ended 31 March 2019 | Year-ended 31 March 2018 | Year-ended 31 March 2017 |
| --- | --- | --- | --- | --- |
|  |  | tCO2e | tCO2e | tCO2e |
| Scope 1 | Combustion of natural gas and operation of owned vehicles | 220.9 | 320.0 | 251.8 |
| Scope 2 | Electricity consumption in offices | 4,487.2 | 4,457.3 | 4,681.9 |
| Scope 3 | Business travel (air and car) | 3,260.9 | 5,117.4 | 4,510.9 |
| Total |  | 7,969.0 | 9,894.7 | 9,444.6 |
| Intensity ratio |  |  |  |  |
| tCO2e per $M of billings |  | 10.5 | 12.9 | 14.9 |
Paragraphs:
Greenhouse gas emissions
In line with the Companies Act 2006, Sophos is required to measure and report on its Greenhouse Gas (“GHG”) emissions disclosures. These have been calculated for the year-ending 31 March 2019, in line with the Group’s financial year. The calculation of the disclosures has been performed in accordance with Greenhouse Gas Protocol Corporate Standard and using the UK government’s conversion factor guidance for the year reported.
The Group’s operations that primarily release GHG includes usage of electricity and gas of owned and leased offices, business travel and usage of vehicles. The Group keeps its data capture process under review, seeking to extend the availability of direct information wherever possible. Where direct information for certain sites is not available, estimates have been developed that enable reporting for them. These estimates are revised if new or improved data is obtained.
The Group will continue to build its GHG reporting capabilities. The Group’s chosen intensity ratio is ‘tonnes of CO2 equivalent per million US dollars of billings’ as it aligns with Sophos’ strategic growth ambitions.
Creating an environmentally friendly HQ
The Group commissioned a greening study of its global headquarters in Abingdon, Oxfordshire. The purpose of the study was to benchmark the current environmental, health and wellbeing performance of the building against current best practice and against direct and indirect competitors.
The findings of the study showed that the building performance was consistent with intermediate good practice and the building management was consistent with standard good practice. The study highlighted areas of future improvement. The findings and recommendations of this report will be a key driver for developing best practice in environmental sustainability to match the growth aspirations and objectives of the Company.
The Group is endeavouring to achieve the standards in environmental performance, health and wellbeing that is expected of a global technology organisation at the Group’s headquarters.
Question:
What was the change in the intensity ratio in 2019 from 2018?
Answer: 10.5-12.9 = -2.4