Which of these can be used to see
how climate has changed over time?

The ocean/water, land, weather and food.

Explanation:

The Atlantic, or Artic ocean has been melting at a faster rate quicker than before . The melted iceburgs which turn into water will flow into the oceans which will then increase the rise in hight of water in ocean and seas. Land will eventually be dried up because of the rise in temperature and the change in climate. There will be less food/crops, because we have used up most of the fresh water we had been using to grow crops for over many years. Scientists and others have considered turning the ocean's salty water into fresh water for the crops . But the process will take a while and will be a very expensive process.

digestion

it excretes wastes