Accelerated Shifts in Terrestrial Life Zones Under Rapid Climate Change

Rapid climate change is impacting biodiversity, ecosystem function and human well-being. Though the magnitude and trajectory of climate change are becoming clearer, understanding of how these changes reshape terrestrial life zones — distinct biogeographic units characterized by bio-temperature, precipitation and aridity representing broad-scale ecosystem types — has been limited.

To address this gap, a new journal article published in Global Change Biology by Blake Alexander Simmons and coauthors uses high-resolution historical climatologies and climate projections to determine the global distribution of historical (1901-1920), contemporary (1979-2013) and future (2061-2080) life zones. Comparing the historical and contemporary distributions shows that changes from one life zone to another during the 20th century impacted 27 million km2 (18.3 percent of land), with consequences for social and ecological systems. Such changes took place in all biomes, most notably in boreal forests, temperate coniferous forests and tropical coniferous forests.

Additionally, comparing the contemporary and future life zone distributions shows the pace of life zone changes is accelerating rapidly in the 21st century. By 2070, such changes will impact an additional 62 million km2 (42.6 percent of land) under ‘business-as-usual’ (RCP8.5) emissions scenarios. Accelerated rates of change were observed in hundreds of eco-regions across all biomes except tropical coniferous forests. And while only 30 eco-regions (3.5 percent) had over half of their areas change to a different life zone during the 20th century, by 2070 this number is projected to climb to 111 eco-regions (13.1 percent) under RCP4.5 and 281 eco-regions (33.2 percent) under RCP8.5.

The research team identified weak correlations between life zone change and threatened vertebrate richness, levels of vertebrate endemism, cropland extent and human population densities within ec0-regions, illustrating the ubiquitous risks of life zone changes to diverse social-ecological systems. The authors say the accelerated pace of life zone changes will increasingly challenge adaptive conservation and sustainable development strategies that incorrectly assume current ecological patterns and livelihood provisioning systems will persist.

Main findings:

• Projected changes are unequally distributed across the globe, in patterns that depart from existing models of univariate climate change.
  • Such changes are most extensive in boreal and subtropical zones and in regions with fewer croplands and lower population densities, though many densely populated areas that have not experienced such changes historically are also projected to experience substantial life zone changes.
• Stable life zones at the peripheries of life zone space are still projected to experience large increases in temperature and fluctuations in precipitation, which may stress the tolerances of some organisms and people living in these already harsh climates.
• Human activities can radically alter ecosystem characteristics through degradative processes or through nutrient supplementation to either reduce or increase ecosystem adaptation potential, respectively.
• The results indicate all biomes have experienced life zone transitions during the 20th century to some degree.
  • Weighted by biome area, boreal forests, temperate coniferous forests and tropical coniferous forests experienced the largest changes in life zone distributions during this period.
  • The analysis indicated high variability among eco-regions in historical life zone changes, which are projected to be exacerbated over the next 50 years.
• Overall, unstable life zones raise concerns for people due to the disruption of environmental conditions that currently support human livelihoods.

Importantly, the projected rate of future life zone change is much faster than the past, including in most eco-regions and within all biomes on Earth. This study’s high-resolution data provide the basis for temporal and spatial discrimination in the allocation of climate-adaptive conservation and sustainable development strategies. As the authors explain, policies and practices that are mismatched with life zone changes are likely to misallocate their limited resources and fail to meet biodiversity conservation and sustainable development goals, especially in regions where the pace of change is greatest and the climatological thresholds for failure are already near.