When the climate changes, species can either track their climatic optimum by moving in space—or respond adaptively adjusting to new climatic conditions. Climate change, however, often happens faster than species are able respond, leaving them with an unpaid "climatic debt".
To verify the existence of such debt, French researchers studied temporal shifts in climatic conditions and occupancy trends for 4,000 of the most common vascular plant species in Europe over the last 65 years.
Using more than 100 million GBIF-mediated species occurrences combined with six bioclimatic variables on temperature and precipitation, the authors calculated annual species climatic indices (SCI) for each species and variable and estimated species occupancy trends.
While negative correlation between SCI and occupancy trends—indicating a climatic debt—was not significant at the continental level, the two coldest biogeographic regions (boreal and alpine) showed an increase in temperature associated with negative occupancy trends over time, suggesting insufficient range shifts, i.e., climatic dept.
Surprisingly, the opposite pattern was present in the warmest Mediterranean region, as the occupancy of species experiencing temperature increases throughout their range tended to increase, suggesting a climate "bonus".