Big Ecosystem Shifts from Climate Change

Big Ecosystem Shifts from Climate Change

  12:47:00 AM    Science Lover

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By 2100, global climate change will modify plant communities covering almost half of Earth's land surface and will drive the conversion of nearly 40 percent of land-based ecosystems from one major ecological community type -- such as forest, grassland or tundra -- toward another, according to a new NASA and university computer modeling study.

Predicted percentage of ecological landscape
being driven toward changes in plant species
as a result of projected human-induced climate
change by 2100. (Credit: NASA/JPL-Caltech)

Researchers from NASA's Jet Propulsion Laboratory and the California Institute of Technology in Pasadena, Calif., investigated how Earth's plant life is likely to react over the next three centuries as Earth's climate changes in response to rising levels of human-produced greenhouse gases. Study results are published in the journal Climatic Change.

The model projections paint a portrait of increasing ecological change and stress in Earth's biosphere, with many plant and animal species facing increasing competition for survival, as well as significant species turnover, as some species invade areas occupied by other species. Most of Earth's land that is not covered by ice or desert is projected to undergo at least a 30 percent change in plant cover -- changes that will require humans and animals to adapt and often relocate.

In addition to altering plant communities, the study predicts climate change will disrupt the ecological balance between interdependent and often endangered plant and animal species, reduce biodiversity and adversely affect Earth's water, energy, carbon and other element cycles.

"For more than 25 years, scientists have warned of the dangers of human-induced climate change," said Jon Bergengren, a scientist who led the study while a postdoctoral scholar at Caltech. "Our study introduces a new view of climate change, exploring the ecological implications of a few degrees of global warming. While warnings of melting glaciers, rising sea levels and other environmental changes are illustrative and important, ultimately, it's the ecological consequences that matter most."

When faced with climate change, plant species often must "migrate" over multiple generations, as they can only survive, compete and reproduce within the range of climates to which they are evolutionarily and physiologically adapted. While Earth's plants and animals have evolved to migrate in response to seasonal environmental changes and to even larger transitions, such as the end of the last ice age, they often are not equipped to keep up with the rapidity of modern climate changes that are currently taking place. Human activities, such as agriculture and urbanization, are increasingly destroying Earth's natural habitats, and frequently block plants and animals from successfully migrating.

To study the sensitivity of Earth's ecological systems to climate change, the scientists used a computer model that predicts the type of plant community that is uniquely adapted to any climate on Earth. This model was used to simulate the future state of Earth's natural vegetation in harmony with climate projections from 10 different global climate simulations. These simulations are based on the intermediate greenhouse gas scenario in the United Nations' Intergovernmental Panel on Climate Change Fourth Assessment Report. That scenario assumes greenhouse gas levels will double by 2100 and then level off. The U.N. report's climate simulations predict a warmer and wetter Earth, with global temperature increases of 3.6 to 7.2 degrees Fahrenheit (2 to 4 degrees Celsius) by 2100, about the same warming that occurred following the Last Glacial Maximum almost 20,000 years ago, except about 100 times faster. Under the scenario, some regions become wetter because of enhanced evaporation, while others become drier due to changes in atmospheric circulation.

The researchers found a shift of biomes, or major ecological community types, toward Earth's poles -- most dramatically in temperate grasslands and boreal forests -- and toward higher elevations. Ecologically sensitive "hotspots" -- areas projected to undergo the greatest degree of species turnover -- that were identified by the study include regions in the Himalayas and the Tibetan Plateau, eastern equatorial Africa, Madagascar, the Mediterranean region, southern South America, and North America's Great Lakes and Great Plains areas. The largest areas of ecological sensitivity and biome changes predicted for this century are, not surprisingly, found in areas with the most dramatic climate change: in the Northern Hemisphere high latitudes, particularly along the northern and southern boundaries of boreal forests.

"Our study developed a simple, consistent and quantitative way to characterize the impacts of climate change on ecosystems, while assessing and comparing the implications of climate model projections," said JPL co-author Duane Waliser. "This new tool enables scientists to explore and understand interrelationships between Earth's ecosystems and climate and to identify regions projected to have the greatest degree of ecological sensitivity."

"In this study, we have developed and applied two new ecological sensitivity metrics -- analogs of climate sensitivity -- to investigate the potential degree of plant community changes over the next three centuries," said Bergengren. "The surprising degree of ecological sensitivity of Earth's ecosystems predicted by our research highlights the global imperative to accelerate progress toward preserving biodiversity by stabilizing Earth's climate."

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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Are Plants Around the World Really Dying? A new study reveals that plant growth across the globe has decreased in the past 10 years, despite the observed increasing trend of the prior two decades. How can this be?

Are Plants Around the World Really Dying? A new study reveals that plant growth across the globe has decreased in the past 10 years, despite the observed increasing trend of the prior two decades. How can this be?

  11:04:00 PM    Science Lover

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According to a new study published in Science, global plant growth has decreased in the past decade, reversing trends observed over the past 20 years. The authors of the study, Maosheng Zhao and Steven Running, found a significant reduction in the global terrestrial net primary production (NPP), a measure of global plant growth that is calculated by a measure of estimated photosynthesis activity. Ultimately, the study reveals that plant productivity is decreasing, which means plants are taking less carbon dioxide out of the atmosphere as biomass, and there is, therefore, more CO2 in the air to reinforce current warming trends.

 Gary Windust/Flickr

The Methods

By analyzing digital photographs of the earth in the visible and near-infrared spectrum accumulated from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite, along with global meteorological data, Zhao and Running were able to take daily measurements of plant productivity for every square mile of the earth, which amounts to about 68,350,830 square miles daily. They used equations based on solar radiation, day length, temperatures, water-stress levels, and drought to infer photosynthesis activity within each area of the earth. Though Zhao and Running found that the high temperatures of the past decade resulted in longer growing seasons in the northern hemisphere and recorded an increase in plant growth there, the droughts caused by globally rising temperatures in the southern hemisphere resulted in a decrease in growth, which overwhelmed the increase in the northern hemisphere. The end result: an estimated 1 percent decrease in global plant productivity over the past decade. The authors' findings are only made more significant by the fact that in the 20 years before the beginning of their study, global plant productivity was still increasing despite the global warming trends and corresponding droughts that have continued to the current day.

The Conclusion 

Currently, terrestrial plants absorb 4.5 percent of fossil-fuel emissions every year, and, Running says, "if our biospheric uptake decreases, the carbon-dioxide concentration in the atmosphere will increase even faster than it already is." Though further decreases of global plant productivity are not inevitable, if the observed trend continues, it will hold enormous significance for future food security, our ability to turn to biofuel as an alternative energy source and the strength of terrestrial carbon sinks. As for further ecosystem disturbances, we can expect more accelerated wildfires, like those we are seeing in Russia, as well as large-scale insect epidemics, like those observed in the western U.S., which kill enormous numbers of trees, Running says.

The Implications 

Aside from a continuation of global monitoring of plant productivity, there seems to be little that scientists and individuals can do to reverse the trend. "Studies of global irrigation patterns show that we are irrigating dry areas to capacity," Running says, "and the amount of land we are able to irrigate might even go down in the next decade because we are running out of water with which to irrigate; rivers are currently being drained to capacity." The researchers do not expect massive food shortages or famines in the near future, but the study does indicate that biofuels, such as ethanol or biodiesel, could be a more risky alternative to fossil fuels than previously thought, given the downward trend in available biomass.

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