The world’s climate is already changing. Extreme weather events (floods, droughts, and heatwaves) are increasing as global temperatures rise. While we are starting to learn how these changes will affect people and individual species, we don’t yet know how ecosystems are likely to change.
Research published in Nature, using 14 years of NASA satellite data, shows eastern Australia’s drylands are among the most sensitive ecosystems to these extreme events, alongside tropical rainforests and mountains. Central Australia’s desert ecosystems are also vulnerable, but for different reasons.
As the world warms, this information can help us manage ecosystems and to anticipate irreversible changes or ecological collapse.
Tipping Points
Ecological theory tells us that as ecosystems become unhealthy, they approach critical thresholds (also referred to as tipping points). The more unhealthy they become, the quicker they respond to disturbances.
Ecosystems that cross a critical threshold are transformed into new states, often with losses in biodiversity, exotic species invasions, and sudden forest die-off events. For example, over the past 10 years, ecosystems in the western US have experienced large-scale tree deaths and native, black grama grasslands have been transformed to the exotic, South African Lehmann lovegrass.
Farms and crops can be thought of as agricultural ecosystems, and they are highly sensitive to variations in climate. This means they are very challenging to manage for sustainable livestock and crop production under such intensifying conditions of sudden good and bad periods.
As humans we show weakened resistance when we are sick, and we become more susceptible to external conditions. Similarly, slower than normal ecosystem responses to external changes may also be indicative of an unhealthy ecosystem.
Both of these measures, fast and slow, are early warning signs for ecosystem collapse.
Seeing Ecosystems from Space
But how do we know if an ecosystem is going to collapse? Space offers a unique vantage point. The new research uses data from NASA’s Moderate Resolution Imaging Spectroradiometer (or MODIS) satellites. The satellites, orbiting roughly 900 km above Earth’s surface, measure things like snow and ice, vegetation, and the oceans and atmosphere.
The satellites measure ecosystem “greenness”, which indicates how much an ecosystem is growing. This is not too different from a farmer visually interpreting cues of plant health based on colour, except that satellites can have the capability to analyse colour in parts of the spectrum beyond our sensing capabilities.
The researchers developed a “Vegetation Sensitivity Index”, which showed how ecosystems responded to changes in climate. They particularly looked at changes in temperature, cloud cover, and rainfall.
