Environmental Performance Summary Below are some key environmental indicators, and are compiled based on the “ESG Reporting Guide” in Appendix 27 to the Listing Rules. Unless otherwise specified, the following data covers Tencent’s major office buildings and the main data centres in Mainland China. 1. Emissions 1.1 Office Buildings
Due to its business nature, the significant air emissions of the Group are GHG emissions, arising mainly from fuels and purchased electricity produced from fossil fuels.
The Group’s GHG inventory includes carbon dioxide, methane and nitrous oxide. GHG emissions data for the year ended 31 December 2019 is presented in carbon dioxide equivalent and is calculated based on the “2017 Baseline Emission Factors for Regional Power Grids in China for CDM and CCER Projects” issued by the Ministry of Ecology and Environment of China, and the “2006 IPCC Guidelines for National Greenhouse Gas Inventories” issued by the Intergovernmental Panel on Climate Change (IPCC)
Diesel is consumed by backup power generators.
Hazardous waste produced by the Group’s office buildings mainly includes waste toner cartridge and waste ink cartridge from printing equipment. Waste toner cartridge and waste ink cartridge are centralised and disposed of by printing suppliers. Such data covers all office buildings of the Group in Mainland China.
Non-hazardous waste produced by the Group’s office buildings mainly includes domestic waste and non-hazardous office waste. Domestic waste is disposed of by the property management companies and kitchen waste recycling vendors, and its data is not available, therefore estimation of domestic waste is made with reference to “Handbook on Domestic Discharge Coefficients for Towns in the First Nationwide Census on Contaminant Discharge” published by the State Council. Non-hazardous office waste is centralised for disposal by vendors; hence such data covers all office buildings of the Group in Mainland China.
Hazardous waste produced by the Group’s data centres mainly includes waste lead-acid accumulators. Waste lead-acid accumulators are disposed of by qualified waste recycling vendors.
Non-hazardous waste produced by the Group’s data centres mainly includes waste servers and waste hard drives. Waste servers and destroyed waste hard drives are centralised and recycled by waste recycling vendors. Such data covers all the Group’s data centres.
Table:
Indicators | For the year ended 31 December | 
 | 2019 | 2018
Total GHG emissions (Scopes 1 and 2) (tonnes) | 113,501.50 | 102,831.74
Direct GHG emissions (Scope 1) (tonnes) | 3,785.86 | 2,554.31
Including: Gasoline (tonnes) | 197.25 | 191.00
Diesel (tonnes) | 10.87 | 11.07
Natural gas (tonnes) | 3,577.74 | 2,352.24
Indirect GHG emissions (Scope 2) (tonnes) | 109,715.64 | 100,277.43
Including: Purchased electricity (tonnes) | 109,715.64 | 100,277.43
Total GHG emissions per employee (tonnes per employee) | 1.90 | 2.01
Total GHG emissions per floor area (tonnes per square metre) | 0.07 | 0.09
Hazardous waste (tonnes) | 2.40 | 2.51
Hazardous waste per employee (tonnes per employee) | 0.00004 | 0.00005
Non-hazardous waste (tonnes) | 5,227.11 | 4,566.52
Non-hazardous waste per employee (tonnes per employee) | 0.09 | 0.09


Question: What is the change between 2018 and 2019 hazardous waste(tonnes)?
Answer: -0.11
Calculation: 2.40-2.51