(40) Climate Science

State of ignorance - climate change and the biosphere (Video)

The Scientist - Climate change and the biosphere


Effects of Climate Change on the Biosphere scientists

Scientists working in the field of climate change response say that they are already seeing the effects of climate change on living systems. These effects are documented on every continent, in every ocean, across ecosystems, and in every major group of organisms. We discuss the impacts of warming climate on the biosphere-­impacts that match the predictions made by climate change models. Scientists see the effects of climate change on individual organisms, on species of organisms, and on entire ecosystems. Although temperature increases thus far have been small, a large percentage of the species studied have shown some response to climate change.

Effects on organisms

Organisms are adapted to live in particular environmental conditions. Polar bears (Ursus maritimus) need to walk across sea ice to hunt; and corals need water that is warm, with just the right salinity. When conditions change, organisms need to change, or they may die out locally or even go extinct. Scientists who study the effects of global warming on the biosphere have discovered that the processes of evolution do not work fast enough for organisms to adapt to rapidly changing climate. At most, species may evolve a greater ability to disperse into new geographic locations. For example, two species of bush crickets in the United Kingdom evolved longer wings in their northern range boundary. The longer wings allowed the crickets to travel to new territory farther north. The most common response, then, that a species has to warmer temperatures is to move to a cooler location, either higher latitudes or higher elevations. The fossil record indicates that changing latitude or altitude was a common response of organisms to climate change in the past. Of course, this strategy does not always work because the environment in the direction the organisms move may turn out to be unsuitable. Land-based species could find their way to favorable conditions blocked by an impassable ocean or extended out of reach beyond the top of a mountain. The situation is now more complicated than it was in prior Earth history because people have altered the environment with farms, ranches, and cities that may be incompatible with the species’ needs.

A species also may respond to climate change by altering the timing of phases of its life cycle, so that it breeds earlier in the spring, for example. This does not necessarily help it better adapt to the new circumstances; it only reflects the way the species is evolutionarily programmed to respond to weather cues: to breed when the night-time low temperature rises above freezing for several days in a row, for example. The science of how climate influences the recurrence of annual events in the life cycles of plants and animals is called phenology. Some of the findings of phenology as they concern global warming are discussed below.

Freshwater Organisms

Increased temperatures have brought conflicting changes to the aquatic life in some lakes. For example, with a longer growing season and less ice cover, a lake may have more algal growth and therefore higher primary productivity. (Algae are a very diverse group of organisms they are not plants, but most algae photosynthesize.) However, the warm water may remain at the surface, so that there is less mixing of nutrients, which may cause a decrease in productivity.

Warming temperatures have changed the phenology of some freshwater species. In large lakes, the phytoplankton population explodes in the spring, after mixing brings nutrients from deep water to the surface, and when the springtime sunlight becomes strong enough to support photosynthesis. To take advantage of the abundant food, zooplankton populations mushroom just after the spring phytoplankton bloom begins. Now, with spring arriving earlier than in the past, the phytoplankton bloom occurs up to four weeks earlier, but the zooplankton bloom has not kept up. By the time the zooplankton emerges, the phytoplankton populations have already peaked, and the zooplankton starve. Because zooplankton is food for the small fish that serve as food for larger fish, a loss of zooplankton can cause a collapse of the local food web. However, in some lakes, zooplankton populations have increased, and fish populations have grown. Some species of fish, both wild and farmed, have also changed their spring life cycle patterns.

Warming temperatures in rivers have affected the abundance, distribution, and migration patterns of some fish species. In some rivers, warm water species are replacing cold water species. Migrations may take place up to six weeks earlier in some fish populations. Populations that experience such a large change in timing typically suffer higher mortality rates in fish and their spawn.

Marine Organisms

In marine organisms, variations in abundance, productivity, and phenology are strongly influenced by short-term climatic variations, such as the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). Separating these influences from those due to greenhouse warming is sometimes difficult. Nevertheless, scientists say that several effects are largely due to global warming. NASA estimates that global plankton productivity has decreased at least 6% to 9% in the past 25 years due to rising SST. Warmer temperatures are also causing marine plankton and fish to move toward the poles. One large, recent study found that North Atlantic species moved northward by 10° latitude in 40 years. While overfishing is the cause of the collapse of the once copious North Atlantic cod (Gadus sp.) population, warming temperatures may be working against the species’ recovery.

Recent declines in plankton numbers may be a factor in the poor survival rates of cod larvae. The warming of the air over the Antarctic Peninsula by 4.5°F (2.5°C) in the past 50 years has greatly affected life in the Southern Ocean. Krill (Euphausia superba), an extremely abundant type of zooplankton, form the base of the Southern Ocean food web and are the favorite food of some whales. Since 1976, warming temperatures have reduced the extent of sea ice, which has reduced the habitat required for the ice algae that are a favorite food of the krill. This has been one factor in the 80% decline of krill in the southwestern Atlantic, where they have been historically concentrated. The decrease in

krill numbers has opened up the seas for an increase in salps. These jellylike organisms are not a good source of food for fish and other organisms higher up the food web. As a result, populations of seabirds and seals are in decline.

Many marine plankton species have advanced the timing of their seasonal behavior. Just as in large lakes, when the zooplankton no longer emerge in time to take advantage of the phytoplankton bloom, the zooplankton population suffers. The loss of zooplankton for the food web has negatively affected populations of fish, seabirds, and marinemammals. The migrations of some species of marine animals are also changing; migrations have been found to occur one to two months earlier in warm years.

Nearshore organisms are also showing the effects of warming. In the Pacific, the species found in the intertidal, kelp forest, and offshore zooplankton communities are shifting their ranges due to warmer temperatures. Sea anemones, for example, are moving into California’s Monterey Bay, where the water was previously too cool. The richest ecosystems in the oceans, coral reefs, are being damaged by rising ocean temperatures.

Global Warming Dead Zone

Scientists at Oregon State University are blaming warming temperatures for a dead zone that has formed in coastal waters off the state. As of 2006, the dead zone was 1,234 square miles (1985 sq. km), about the size of Rhode Island. In that year, it made its first appearance in the coastal region of Washington State. The dead zone recurred in 2007 but was not as large or intense as the 2006 event.

A survey by scientists using a remotely operated underwater vehicle found rotting Dungeness crabs (Cancer magister) and sea worms, and a complete lack of fish in the area. “Thousands and thousands of dead crabs and molts were littering the ocean floor, many sea stars were dead, and the fish have either left the area or have died and been washed away,” Professor Jane Lubchenko, who was involved in the study, said in a 2006 press release from Oregon State University.

Oceanic dead zones are caused by extremely low levels of oxygen in a region’s waters. Without oxygen, most marine organisms suffocate. The Oregon dead zone is different from most dead zones, including the much larger one in the Gulf of Mexico. In the gulf, Mississippi River waters carry loads of excess nutrients from fertilizers, detergents, and runoff from feed lots into the water, causing an algae bloom. When these algae die, they are decomposed by bacteria and other organisms that use up all the water’s oxygen.

In the Oregon dead zone, warmer air has changed ocean circulation. In normal years, southerly winds push surface water toward the shore, which keeps deep, nutrient- rich, oxygen-­ poor waters down below. These southerly winds alternate with northerly winds that then push the surface water out to sea. This brings the nutrient-rich, oxygen-poor water to the surface and allows it to mix with the normal surface nutrient- poor, oxygen- rich waters, providing an ideal environment for phytoplankton to bloom (but not over bloom) and support a healthy food web and marine fishery. In dead zone years, all the winds come from the north, and the nutrient- rich, oxygen-poor waters rise to the surface. Plankton bloom and feed off the nutrients, but when they die, they are decomposed by bacteria that take in the oxygen that remains in the water. As a result, oxygen levels dip as low as 10 to 30 times below normal: In one location, they were near zero.

Although they are far from certain, scientists say that changes in the jet stream due to global warming are the likeliest explanation.

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