In a new synthesis review with Danny Sigman, published in the Oxford Research Encyclopedia of Climate Science, we entertain the possibility that changes in the ocean’s biological pump and alkalinity were the dominant driver of CO2 and global climate change during Pleistocene ice ages. We show that land-carbon changes effects were canceled by ocean carbonate compensation, and that ice sheet and temperature changes cancel each other. The effect of deep ocean carbon storage, in contrast, is amplified by carbonate compensation, yielding durable CO2 changes.