Question: How can plant pollen that has been preserved in sediments at the bottom of lakes tell us about past climates? How can plant pollen that has been preserved in sediments at the bottom of lakes tell us about past climates? larger-sized pollen grains indicate a warmer climate in the past the absence of pollen in lake sediments indicates a warmer climate in the past because decomposition rates are higher in warmer climates pollen found in lake sediments is not useful as an indicator of past climates if a lot of pollen from plants that thrive in colder environments is found, that indicates a colder climate in the past