What we do with our food scraps and other waste products has a significant impact on climate change. Why is that? 
When organic matter breaks down in an anaerobic environment (without air), as in a cow's stomach or a tightly compressed landfill, methane gas is produced. Methane is a much more potent greenhouse gas than carbon dioxide, so it has a big impact on the changes ocurring to the climate. 4.4 gigatons of carbon equivalent is created annually by food waste, amounting to about eight per cent of anthropogenic (human-caused) emissions. This is $1.8billion worth each year in New Zealand.
This is part of the reason Project Drawdown puts reducing food waste at number three – the third most important thing we can do, worldwide, to reduce global warming. Energy is squandered and emissions created at all stages of food wastage (at harvest, through rejection by wholesalers and brokers, through supermarket oversupply and through consumer wastage). Every year Kiwis send 122,547 tonnes of food to landfill.
What does this mean in our everyday lives? In most centres throughout Aotearoa New Zealand, there are organisations, big and small, operating to recover food waste from supermarkets and wholesalers and redistribute it. 0800Hungry is probably the largest and best known, and they call for support from volunteers and sponsors on their website.
In our own lives, we can learn a lot about how to avoid food waste from love food hate waste. They promote more careful planning, using more parts of vegetables and offer many ideas for using up scraps and leftovers. When we do have leftover food that is no longer safe to eat, composting and all its cousins (worm farms, keeping chickens, bokashi) eliminate the problem of methane emissions. Cafes, restaurants and buildings with large cafeterias can do a lot about climate change if they plan their purchasing and storage more carefully and find ways to dispose of food scraps other than into the landfill.
The other gain from reducing our food waste is that we become more resilient and the food we grow is able to feed more people. As climate change impacts on our ability to grow and distribute food, we need to create a system which can feed all of earth's growing population. Changing our habits around over-consumption and the 'throw-away culture' can contribute a lot to the equality of access to basic human needs.
Other biodegradable items (such as seemingly responsible plates, bowls, cups and so on used for takeaway coffees, food and doggy bags) contribute to this problem, as most of them end up in the landfill. Many (those lined with or made entirely from polylactic acid or PLA) are not able to be composted at home and, as there are very few composting plants that can deal with them, consumers have no choice but to throw them into the landfill.
The best alternative to plastic bags, cups, plates and cutlery is reusable. Follow this lovely tutorial about how to make an easy-to-carry reusable kit for your bag.