Other new members include telecommunications company BT, truck maker Scania and department store chain Selfridges.
Together, the companies aim to reduce nearly 2 billion metric tonnes of carbon dioxide by 2040, more than 5% of the current global total.
While group members are encouraged to eliminate as many emissions as possible, those that cannot be avoided must be fully offset over the next two decades. This means paying for measures to ensure that by then as many emissions are absorbed as companies continue to emit.
Scientists say the world must reach net zero emissions by 2050 if it is to meet the Paris climate agreement target of preventing temperatures from rising more than 1.5 degrees Celsius (2 , 7 Fahrenheit) by the end of the century compared to pre-industrial times.