Background: Land and Living Systems

What We Know: Underlying Processes

Living things don’t just respond to the climate—they affect it as well. Plants consume carbon dioxide and produce oxygen through photosynthesis. Earthbound plants take carbon dioxide directly from the air; while in the ocean, drifting photosynthetic microorganisms called phytoplankton absorb carbon dioxide dissolved in water.

Scientists estimate that plants and phytoplankton together absorb around 60 billion tons of carbon every year, by far the strongest mechanism for carbon dioxide removal from the atmosphere. (This removal is almost exactly balanced by respiration in animals, which combines oxygen with hydrocarbons to produce carbon dioxide and water vapor.)

Increases in the level of carbon dioxide in the atmosphere could promote plant growth, and greater absorption of carbon. However, recent research has suggested that the negative effects of climate change on plants—from things like drought and heat stress—would overwhelm the benefits of additional carbon dioxide. 

This satellite image shows phytoplankton in the ocean waters off the southeastern United States. Phytoplankton, like terrestrial plants, consume carbon dioxide in the process of photosynthesis.

Evidences and Uncertainties

Many species live in very sensitive ecological niches, so even small changes in temperature or precipitation could drastically alter their ability to survive. Increases in ocean temperatures of as little as 1°C (2°F) over two or three days can cause corals—organisms particularly sensitive to long-term variations in climate—to lose their symbiotic algae, which are essential for their nutrition. When the algae die, corals are “bleached” and appear white. 

Because all species are linked in complex webs of predator, prey, and habitat, impacts on one species always affect others—and it’s extremely difficult to predict how those effects will manifest. Changing the life cycles of a key species in a food chain may well affect an entire ecosystem.

Additionally, the ability of many species to adapt to changing climate through migration is much different than it was in earlier centuries. Habitats and migration routes are now fragmented by housing, industry, roadways, and other development. Species also need time to make adaptations, but the rate of climate change appears to be increasing: Over the last 16,000 years, the rate of increase in global temperatures has been about 1°C for every 4,000 years—and yet, some predictions now suggest that we may see an additional increase of 4°C or more over the next 100 years.

Some species may actually be helped by warmer temperatures, of course—but this may not necessarily be good news. Increasing the populations of some species may have serious effects on human health.

Each of these pinwheel patterns centers on a small community of soybean farmers in eastern Bolivia. Roads and fields have subdivided the tropical dry forest.

For example, even small increases in global temperatures, especially if they’re accompanied by flooding, may drive an increase in the mosquito populations in tropical areas, leading to much greater transmission rates of diseases like malaria, dengue fever, and West Nile virus. And again, changing the balance of species affects the way entire ecosystems function, with unknown consequences.